—Interim Director Schenkel returns to full-time research
Cameron Geddes Appointed as ATAP Division Director
Following an international search, Berkeley Lab has appointed Cameron Geddes, an award-winning scientist who is internationally known for his work on laser-plasma accelerators, to serve as Director of the Accelerator Technology & Applied Physics (ATAP) Division.
Cameron joined ATAP’s Berkeley Lab Laser Accelerator (BELLA) Center in 2000 as a University of California, Berkeley graduate student and a Hertz Fellow. He earned his Ph.D. in physics in 2005 and became a research scientist in the Center. Progressive responsibilities culminated in his appointment as BELLA Center’s Deputy Director for Experiments in January 2019.
“Cameron is an outstanding choice, and I am excited for the opportunity to work with him to continue advancing ATAP’s research portfolio across a broad front of accelerator and fusion science,” said Natalie Roe, the Associate Laboratory Director for the Physical Sciences Area. “I would also like to thank Thomas Schenkel for his excellent leadership as Interim ATAP Division Director for the past two years.”
“I am honored to be named to this position,” says Cameron. “ATAP has leading capabilities that work together for the benefit of everything we do. We have a unique combination of expertise in lasers, plasma science, beam physics, photon sources, controls and sources, as well as supporting methods such as advanced computation and magnetics. We also have deep connections to user needs in both high-energy physics and broad applications, including photon science. This is what allows us to create new capabilities. The kBELLA initiative is an example, and has the potential to realize a transformative combination of high average and high peak power lasers.”
At the BELLA Center, Cameron most recently led the creation of a quasi-monoenergetic gamma-ray source that can bring new capabilities to nuclear security applications (as well as medical and industrial imaging) based on compact laser-plasma accelerators. He oversaw the experimental portfolio within the BELLA Center, which develops plasma accelerators to extend the energy frontier of future high-energy physics experiments and for photon sources and applications. It includes two projects: the petawatt second beamline for high-energy physics and a high-intensity, tight-focus beamline for ion acceleration, oriented toward fusion energy sciences. It also supports user experiments under the LaserNetUS program that open the Division’s capabilities to international users in areas ranging from hydrodynamics to advanced imaging.
“Cameron provided outstanding leadership to our wide array of experimental activities,” says Eric Esarey, Director of the BELLA Center. “In addition to his keen scientific insight, he brought positive energy and created an atmosphere of enthusiasm and inclusion within the BELLA Center.”
Recognition for Cameron’s work included the U.S. Particle Accelerator School Prize, the American Physical Society Division of Plasma Physics (APS-DPP) John Dawson Award for Excellence in Plasma Physics Research, and Fellowship in the APS. His graduate work was recognized with the APS-DPP’s Marshall N. Rosenbluth Outstanding Doctoral Thesis Award, as well as the Hertz Foundation Dissertation Prize.
In addition to these laboratory endeavors, Cameron is well known for work on the steering committees that build the future of team science. These efforts gather diverse voices together into community consensus, expressed in reports that guide agency decisions. Presently he is a co-convener of the Advanced Accelerators topic in the “Snowmass” meeting—a high-energy physics community study, held every several years, that provides key input to the strategic direction of US investment in high-energy physics.
Cameron was a contributor to 2019’s multi-agency Basic Research Needs Workshop on Compact Accelerators for Security and Medicine, which gave rise to a crosscutting Office of Accelerator R&D and Production within DOE’s Office of Science. His publications are cited by others in multiple chapters of the workshop report.
Other related efforts include the DOE Fusion Energy Sciences Committee’s Subcommittee on Long-Range Planning; the APS-DPP Community Planning for Fusion Energy Sciences; and the Brightest Light Initiative, which defined a path forward for ultra-intense lasers in the US. He was also a chapter lead for the National Academies’ recent Decadal Assessment of Plasma Science.
Toward new horizons throughout ATAP
Cameron started his career at Berkeley Lab as an undergraduate, performing high-energy physics detector work under James Siegrist, who at the time was in Berkeley Lab’s Physics Division. Since then, Cameron’s career has ranged through both magnetic and inertial confinement fusion and plasma physics, many experimental aspects of laser-plasma accelerators and their applications, laser science and computer modeling, all of which gives him a special appreciation of the breadth and mutually reinforcing character of ATAP’s research portfolio. “The breadth of our expertise is one of the key reasons why I’m at Berkeley Lab,” he says. “I see ATAP, with these interlinked capabilities, as being crucial to US leadership in major scientific areas.”
ATAP will play an important role in addressing grand challenges for science society in the coming decade and beyond. The division continues to advance the frontiers of fundamental science ranging from particle physics, to high energy density science, to photon sources and new laser technology. From these cutting edge techniques, we develop new capabilities ranging across security, medicine, and society. “The Division is well positioned to help address the challenges of carbon cycle and clean energy, ” Geddes says.
The quest for abundant fusion energy through magnetic fusion will require high-field magnets and advanced computation methods that the Division develops, and there is renewed interest in the inertial fusion energy alternative, which is historically an area of Division expertise. At the same time our light sources are critical for clean-energy research including development of solar materials and advanced batteries, while our compact particle sources can bring capabilities to the field for carbon cycle analysis and clean industry. ATAP is also a leader in modeling on the eve of the opportunities that exascale computing will open, and in applying the promising new technologies of artificial intelligence, machine learning, and feedback controls. “Across all these areas, ATAP research creates tools that enable discovery science and new capabilities for society, ” he adds.
The human element
Cameron has a long history of commitment to developing both the quality and the diversity of ATAP’s workforce. “I see IDEA [the Labwide commitment to inclusiveness, diversity, equity, and accountability] as integral to both our workplace climate and our scientific leadership,” he said, adding, “It’s critical that we bring the best people to the Lab from all backgrounds, break down barriers, and create a culture in which they can thrive. That benefits both our progress and our engagement with the communities that we serve.”
He helped organize the recently established Pride Committee in APS-DPP, which envisions a scientific community that is open, welcoming, and supportive of all scientists within the gender and sexual-orientation minority communities, and has championed these issues as part of Berkeley Lab’s Lambda Alliance, an employee resource group for sexual-orientation and gender minority (SGM) members of our workplace.
Cameron’s plans to further our workplace progress include recruitment from and retention of under-represented groups, mentoring and training, and engaging IDEA experts (as he says, “most of us are not IDEA experts, but all of us are responsible for it — that’s the ‘A’ in IDEA”) from both within and outside the Lab, and also through our influence in the scientific community.
BELLA Center staff scientist Jeroen van Tilborg, who has led several of the Center’s initiatives, including a compact free-electron laser (FEL) based on a laser-plasma accelerator, will fill Geddes’s former position as the Center’s Deputy Director for Experiments.
Thomas Schenkel, who has served ATAP as Interim Director since January 2019, will resume full-time duties as head of ATAP’s Fusion Science and Ion Beam Technology Program. He is excited to pursue new opportunities in that diverse and highly collaborative program on themes of qubits, beams and fusion, including his work in the hardware foundations of approaches to quantum information science applications with spins and color centers.
“I leave the Division in good hands,” said Schenkel. “Cameron is impressive in both breadth and depth as a physicist, and also has interpersonal skills that will lead us to further success.”
“What we do all across ATAP is important to meeting the nation’s scientific needs,” said Cameron. “I’m excited to work with our talented staff, and our partners at other labs and universities, to build next-generation technologies and applications.”
—Tony Gonsalves, Kei Nakamura to support van Tilborg as Associate Deputy Directors for Experiments
Jeroen van Tilborg Appointed as BELLA Deputy Director for Experiments
Staff scientist Jeroen van Tilborg has been appointed Deputy Director for Experiments in the Berkeley Lab Laser Accelerator (BELLA) Center.
He succeeds Cameron Geddes, who is now Director of the Accelerator Technology & Applied Physics Division.
Jeroen’s new position comes after his service as the BELLA Center’s Associate Deputy Director for Experiments, coordinating operation and enhancement of the Center’s ever diversifying and expanding facilities. He led experiments on the BELLA hundred-terawatt laser and participated in experiments on all other BELLA laser facilities, including the BELLA petawatt laser. He has mentored students and early career staff members, including postdoctoral scholar Sam Barber, who was recently promoted to Research Scientist.
“Jeroen is an outstanding scientist with superb organizational skills,” says Eric Esarey, Director of the BELLA Center. “His broad base of knowledge in lasers, beams, and plasma physics makes him ideally suited to oversee the wide range of experimental activities within the Center.”
In his own research, Jeroen was awarded a US Department of Energy Early Career Research Program (ECRP) grant, funded through the Office of Basic Energy Science — an extremely competitive program (about 15% of applicants are funded). He also received a grant from the Gordon and Betty Moore Foundation and has been simultaneously heading these efforts, successfully building a new hundred-terawatt laser and accelerator facility. This facility combines state-of-art capabilities to manipulate and diagnose all aspects of a laser-plasma accelerator (LPA): the laser pulses, the plasma target, the electron beam production, transport, and phase-space manipulation, and finally the photon source and its characterization. His push to combine stabilization and precision control concepts for the laser-plasma interaction represents an integrated approach to enabling high-profile applications of LPAs.
“My goal is to make sure that everyone’s talent is utilized in the best way, continuing the cross-team collaboration, always with a focus on science.”
Jeroen is also a leader in the community-planning processes that build and summarize consensus for scientific program directions. In the ongoing “Snowmass” particle physics community planning exercise, he serves as co-coordinator of Near-Term Applications in the Advanced Accelerator Concepts topical group, and is the liaison between the Advanced Accelerator Concepts and the Community Engagement frontiers. In the American Physical Society’s Division of Plasma Physics community-planning process, he contributed to the Disruptive Technologies topical group.
Jeroen’s research interests include ultra-intense laser physics, laser-plasma accelerators, nonlinear optics, AMOS (atomic, molecular, and optical sciences), undulator and FEL physics, high harmonic generation, high-energy physics, plasma diagnostics, ultrafast phenomena, advanced electron beam transport, and novel radiation sources. The unifying theme of his work has been, as he puts it, “to measure changes that happen very quickly — picoseconds, femtoseconds — that you can study with very fast pulses from high-powered lasers.”
Jeroen is co-author of 47 publications in the refereed literature and lead author of another 15, including two Physical Review Letters, on topics covering nonlinear optics, plasma diagnostics, X-ray phenomena, molecular dynamics, and accelerator physics.
Jeroen’s association with BELLA Center — then known as the Laser Optics and Accelerator Systems Integrated Studies (LOASIS) Program — began with an internship when he was in a bachelor’s/master’s degree program at the Technical University of Eindhoven. Two years later, in 2001, LOASIS leaders Wim Leemans and Eric Esarey suggested that he do his PhD research at LOASIS. There followed a transatlantic program of academic work at Eindhoven and experimental work at Berkeley Lab, culminating in a PhD, cum laude, in applied physics in 2006. The American Physical Society Division Physics of Beams recognized his work through the 2007 Outstanding Doctoral Thesis Research in Beam Physics Award.
After earning his doctorate, Jeroen spent three years as a postdoctoral scientist in Berkeley Lab’s Chemical Sciences Division, performing science based on soft-x-ray beams. This enriching phase and beam-user perspective allowed him to understand and appreciate the quality that the science community expects from advanced particle and light sources. He then joined BELLA Center in 2009.
“The people as well as the projects at the BELLA Center are really diverse,” Jeroen says. “My goal is to make sure that everyone’s talent is utilized in the best way, continuing the cross-team collaboration, always with a focus on science. I’m really excited to be selected to lead these efforts.”
Anthony Gonsalves, Kei Nakamura Appointed as BELLA Center Associate Deputy Directors for Experiments
BELLA Center scientists Anthony Gonsalves and Kei Nakamura have been appointed as Associate Deputy Center Directors for Experiments. They will support Jeroen van Tilborg in his role as Deputy Center Director for Experiments.
Tony Gonsalves is a Staff Scientist leading the laser-plasma accelerator experiments in the BELLA Center, including next-generation injection techniques and high-efficiency staging. Tony received his PhD from the University of Oxford in 2006, where he developed plasma based laser waveguides and used them to enhance short wavelength lasing and, working with the BELLA Center’s researchers and lasers, to achieve the first GeV electron beams from a laser-plasma accelerator. Tony then joined the BELLA Center in 2006 as a postdoctoral scholar.
During his 15-year career at the Lab, Tony has developed a number of novel plasma targets and diagnostics and used them for precision control of laser-plasma acceleration. He led the experiments producing record energies from laser-plasma accelerators, including the current world record of 8 GeV achieved using the BELLA petawatt laser. His current focus is on integration of novel high-power laser guiding concepts, giving ATAP an excellent shot at continuing to hold the world record for the energy output of LPAs.
His strong technical and leadership contribution to past projects has positioned him to be science lead on the BELLA Second Beamline, a facility upgrade adding a second high-power laser beamline to the BELLA petawatt laser, thus significantly enhancing the precision, control, and complexity of LPA regimes that can be accessed.
Kei Nakamura is an Applied Physicist and is currently leading the high-field laser experiments in the BELLA Center. He joined the Center in 2003 as an intern, then returned as a PhD student in 2004, completing his PhD from the University of Tokyo in 2008 with a Young Scientist Award from the Particle Accelerator Society of Japan. Following his PhD, he joined Berkeley Lab as a postdoctoral scholar, and was promoted to the rank of Applied Physicist in 2012.
Over his career, Kei has developed a very broad range of expertise, including laser-plasma acceleration, high-field laser-matter interactions, high-power laser operation and diagnostics, and broadband charged-particle transport and detectors.
Kei’s managerial expertise in leading high-profile visitor-based experimental campaigns has enabled him to become science lead on BELLA IP2, a project adding a new intensity-boosted laser delivery system to the BELLA petawatt laser that will support highly-nonlinear laser-matter interaction studies and laser-solid ion acceleration.
Innovative Plasma Mirror to Help Measure Record-Setting Electron Beams
— BELLA Center, UC-Berkeley, Ohio State team develops new diagnostic technique
Glenn Roberts, Jr., Berkeley Lab Strategic Communications
Physicists at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) are figuring out new ways to accelerate electrons to record-high energies over record-short distances with a technique that uses laser pulses and exotic matter known as a plasma. But measuring the properties of the high-energy electron beams produced in laser-plasma acceleration experiments has proven challenging, as the high-intensity laser must be diverted without disrupting the electron beam.
Now, a new, compact system has been successfully demonstrated at the Berkeley Lab Laser Accelerator (BELLA) Center to provide simultaneous high-resolution measurements of multiple electron-beam properties.
The new system uses ultrathin liquid-crystal films, developed by Prof. Douglass Schumacher and his team at Ohio State University, to redirect the laser while allowing the electron beam to pass through, largely unaffected. The laser forms a plasma that reflects the bulk of its laser light.
While each laser pulse destroys the liquid-crystal film, similar to a bubble machine, the liquid-crystal film is replenished by a rotating disc and wiper device after each laser shot. The films formed by this device are just tens of nanometers (billionths of meters) in thickness, about a factor of 1,000 thinner than those in other replenishable plasma mirror systems that use VHS cassette tape, for example. This reduction in thickness serves to preserve the electron beam’s properties.
The deflection of laser light away from the electron beam is essential for producing a precise diagnostic of the electron beam, noted Jeroen van Tilborg, a BELLA Center staff scientist, and it is also crucial for multistage laser-plasma acceleration experiments, in which the laser pulses are refreshed at each stage to provide an additional “kick” of acceleration for the electron beam until it reaches its required acceleration.
The liquid-crystal plasma mirror (LCPM) also enables the use of a gas-filled, 6-centimeter-long strong focusing device for the electron beam, known as an active plasma lens.
This lens allows a compact alternative to a large diagnostic tool called a magnetic spectrometer device, which has bulky magnets that weigh more than a ton and are coupled to a large power supply.
“We were able to replace this with dipole (two-pole) magnets about the size of a sandwich,” said Sam Barber, a research scientist at the BELLA Center in Berkeley Lab’s Accelerator Technology and Applied Physics (ATAP) Division. “Laser plasma accelerators can produce high-energy electrons in compact footprints, but there is still much that can be done to shrink some of the components, including electron beam diagnostics.”
He added, “This is a huge reduction in the scale. We are combining a petawatt (high-power) laser with ultrathin LCPMs and active plasma lenses – all novel technologies that have just recently been developed. We combined all three of them and we got a nice result. We are making big steps forward. There is a whole slew of new applications that this could be used for.”
Barber was the lead author of a study detailing the performance and setup of the new diagnostic tool, published in the journal Applied Physics Letters. Other BELLA Center researchers participated in the study, too, along with researchers from UC Berkeley and Ohio State University.
The development of high energy and high quality electron beams based on laser-plasma acceleration at the BELLA Center is funded primarily by the DOE Office of High Energy Physics and by an Early Career Research Program grant from the Office of Basic Energy Sciences, as well as by LaserNetUS, the recently formed network of high-power laser facilities that is funded by the DOE Office of Fusion Energy Sciences.
Carl Schroeder, a Berkeley Lab senior scientist who is deputy director of the BELLA Center, said that besides its compactness, the new diagnostic technique can collect several electron-beam properties at once, including the detailed energy distribution of the electron beam and the beam’s emittance, on a single-shot basis. Emittance is a critical property of an electron beam that dictates how tightly the beam can be focused. A low emittance means the beam can be focused down to a very small spot, crucial for most accelerator applications like colliders and free-electron lasers.
“Typically, these are multishot diagnostics,” he said, which average the measurements of several beam pulses but don’t measure on a pulse-by-pulse basis – as does the new technique.
In the demonstrated setup, a laser is focused into a gas cell, where it creates and interacts with a plasma, generating and accelerating an electron beam. After passing through this cell, the combined laser beam and electron beam arrive at the LCPM, at which point the laser is deflected while the electron beam is transmitted – with negligible disruption.
The electron beam then passes through the active plasma lens. The lens is used to focus the electron beam into a sequence of small magnets. The magnetic field disperses the electrons according to energy – much like the way light is dispersed by color when passing through a prism.
The dispersed electron beam then passes through a special crystal that produces light as the electron passes through. High-resolution images of the crystal’s light signature enable a precise, sub-percent-resolution mapping of the energy of the electron beam, and simultaneous emittance measurements.
The measurements can ultimately help researchers to troubleshoot, tune, and improve the performance of laser-plasma acceleration experiments, and the setup could potentially be relevant for future collider applications and compact X-ray free-electron lasers, researchers noted, which could have a wide array of applications.
“You want to be able to rapidly characterize these beams and use that as feedback for optimization,” Barber said. “This is useful for the characterization and control of electron-beam properties.”
Three Questions For… Marlene Turner
Welcome to 3Q4, in which we put three questions to someone from our staff to help get to know the people behind the science. In this issue, we meet Marlene Turner, a BELLA Center postdoctoral researcher.
With interests rooted in both particle physics and accelerator science and technology, Marlene is a postdoctoral scholar with ATAP’s Berkeley Lab Laser Accelerator Center (BELLA). A native of Austria, she earned a master’s degree in engineering physics and applied physics at the Technical University of Graz.
Her relationship with CERN began with summer internships and eventually became a PhD program. Her interests turned toward accelerator science and technology, and for her doctoral studies, she worked on AWAKE, their proton-driven plasma wake acceleration experiment.
Marlene won a student-poster prize at the 2016 North American Particle Accelerator Conference, and was also chosen to represent her US Particle Accelerator School class with a talk about their class project — a concept for a light source based on a compact storage ring with a laser-plasma accelerator injector.
In 2019 she was selected for the Laser-Plasma Accelerator Workshop’s John Dawson Thesis Prize, which honors the best doctoral dissertations in their field, as well as the Viktor-Hess Thesis Prize of the Austrian Physical Society.
“The key ingredients are passion and the motivation to do something. I believe that if you have that, there’s nothing that can stop you.”
How did you get interested in accelerator physics?
I started out at CERN doing data analysis for one of the detector collaborations, but I was always more oriented toward the technical side and became more interested in the accelerator itself. I used to work in conventional accelerators, designing and building beamlines. but for a PhD you want something that’s research oriented and new, so I was attracted toward their plasma wakefield concepts.
After I finished my PhD, a second segment of our experimental work began, and I really enjoyed the work and was well integrated into the team, so I stayed on for a bit more than a year after graduation because I didn’t want to leave the experiment while it was running.
At CERN, instead of big laser systems, we used proton bunches to excite the plasma wakefields. I thought it would be good to have a postdoc that was similar but not the same, so I could make use of the experience but broaden my horizons. So I decided to come to BELLA, where we do similar physics but in a different way.
My interests include both particle physics and accelerator technology, and working on the BELLA petawatt laser and the staging experiments, I feel that I’m really in the mainstream of the long-term goals of BELLA. It’s no secret why I wanted to come here, and for me it’s really the perfect match, staying true to what I wanted to have a career in, and also pushing myself to learn about lasers as well as particle accelerators.
How do you do team science when it’s so hard to get the team together during the pandemic?
Of course, we went virtual, like everybody. Since June, with the Lab’s phased re-opening I’ve had the possibility to go back to the Lab, but it’s a lot different when you can have the whole team together rather than being almost alone. We’ve had to learn how to work effectively together without physically being together. That involves a lot of Zoom, headphones, and cameras to make the people who can’t be at the Lab feel they’re there.
It isn’t what I would have ever chosen, but I must say I am learning a lot because I have the opportunity to do everything, under the guidance of the experts who otherwise would have done it themselves.
It’s a challenge to overcome, but as scientists, all our work is overcoming challenges, isn’t it? A career path in science involves building things that we don’t know how to build, and being flexible when we encounter obstacles. Our challenges with COVID and with accelerator physics really draw on the same qualities.
A lot of the things we’re trying to do in advanced accelerators, nobody knows if they can be done, but that’s our job, right? — to try, and to seek. Once we show that it can be done, making it work every time is another important job, but to me, pushing forward to that first demonstration is the beauty of what we do.
What inspired you to go into science, and what advice would you give?
I grew up in a very technical family, where we always fixed things ourselves, always built things. My dad bought broken cars and we used to repair them together. One of my favorite things that we did together was building “killer robots.” It may not be necessary, but it’s a background that inspired me to do technical work, and gave me the confidence that I can do it. I even wanted to be a car mechanic, but I was also very good at school, and my father insisted that I go to university.
I didn’t really have anybody who pushed me into accelerator physics, but accelerators are just a big toy to play with! We build them, we use them, we improve them… I saw accelerator people, how they work, how exciting it is when things finally work, and I said, “Yeah, I want to do the same.”
I really like seeing more women getting into the field. It’s important to have more diversity, to be more open, to be more inclusive. All my career, I haven’t exactly been surrounded by a lot of women, let’s say it like that. There’s still work to do, and I’d like to see more of it, to really see it become normal, but I’m happy to see that at least the acknowledgment that it needs to be done is there now.
I think it’s very good that here at the Lab, these things are acknowledged and discussed. Being here, I feel like I fit in, and it’s a very good opportunity to make things better.
I definitely had people in my life who supported me in the choices that I made, and when you feel you can’t do something, that’s what you go back to. The key ingredients are passion and the motivation to do something. I believe that if you have that, there’s nothing that can stop you.
AAC Seminar Series is a Virtual Success
When the 2020 Advanced Accelerator Concepts Workshop, which was being put together by the Berkeley Lab Laser Accelerator Center, had to be cancelled due to the pandemic, its organizers set up the virtual Advanced Accelerator Concepts Seminar Series.
The Seminar Series consisted of nine half-day sessions on Wednesday mornings, November 18 through February 3, with holiday breaks. The first session gave an introduction to the format, followed by deep-dive tutorials, and attracted 390 participants. After that, a topical session was devoted to each of the eight AAC eight working groups.
Several sessions were shared on Twitter and LinkedIn by Axel Huebl of ATAP’s Accelerator Modeling Program as well.
There were a lot of excellent talks, and I’d like to thank the organizers and the Working Group leaders. I think everyone did a great job — and all the participants,” said general chair Eric Esarey. “Hopefully for the next AAC we can all get together in person.”
Videos of the oral sessions, as well as posters, are available at aacseminarseries.lbl.gov.
Laser-Plasma Microsource Enables Bi-Modal Imaging
An international team, including ATAP scientists Tobias Ostermayr of the Berkeley Lab Laser Accelerator Center and Axel Huebl of the Accelerator Modeling Program, has made the first proof-of-principle demonstration of bi-modal radiographic imaging for biological and technological objects with a laser-driven microsource of x rays and protons. The results were announced December 2 in the journal Nature Communications.
Ostermayr is lead author of the paper and (together with co-corresponding author Joerg Schreiber of Ludwig-Maximilians-Universität München and Max-Planck-Institut für Quantenoptik) originated the idea. Huebl performed particle-in-cell simulations in support of the study. The experiments were performed with the Texas Petawatt Laser at the University of Texas at Austin.
Synchronized single-sourcing of multiple modalities
Conventional radiography machines produce only a single kind of radiation, such as protons, electrons, or x-rays. Using more than one kind of radiation source gives complementary sets of information about the specimen, but in order to take advantage of this, significant post-processing is usually needed because the sources and image acquisitions were separate in space and/or time.
Laser-driven plasmas can simultaneously emit multiple forms of radiation, including x-rays and protons, and they produce it in short bursts, which is also desirable for, say, “freezing” motion. This study demonstrated, for the first time ever, how such a laser-driven source can be used to make images of biological and technological samples.
The team achieved intrinsic nanosecond-scale synchronization of these two powerful and important imaging techniques (compared to seconds or minutes in conventional machines), and the two radiation sources overlapped on a scale of a few micrometers. These attributes, combined with the exquisitely small source size enabled by laser plasma techniques, gave sharper and more detailed insights into materials and samples than could be expected from either source alone—a unique capability of laser plasmas.
In the near future, the researchers hope to extend multimodal imaging capabilities and applications to include electrons and neutrons, and to image dynamic events.
To learn more…
T.M. Ostermayr et al., “Laser-driven x-ray and proton micro-source and application to simultaneous single-shot bi-modal radiographic imaging,” Nature Communications 11, 6174 (02 December 2020).
“A new laser-driven X-ray and proton micro-source,” Attoworld, 3 December 2020.
—Lasers at Berkeley Lab’s BELLA Center are part of network across the U.S. and Canada
LaserNetUS Receives $18M DOE Continuation Funding
In 2018, the U.S. Department of Energy established LaserNetUS, a network of facilities operating ultrapowerful lasers. Organized and funded through DOE’s Office of Fusion Energy Sciences (FES), the new network was created to provide vastly improved access to unique lasers for researchers, and to help restore the U.S.’s once-dominant position in high-intensity laser research. Now, new DOE funding totaling $18 million, including $1 million for user support, will be distributed among 10 partner institutions and will continue and expand LaserNetUS operations for three years.
“The LaserNetUS initiative is a shining example of a scientific community coming together to advance the frontiers of research, provide students and scientists with broad access to unique facilities and enabling technologies, and foster collaboration among researchers and networks from around the world,” said James Van Dam, DOE associate director of science for Fusion Energy Sciences. “We are very excited to work with all of these outstanding institutions as partners in this initiative.”
The initiative includes a node at Berkeley Lab, home of the BELLA Center in the Accelerator Technology and Applied Physics Division, with the BELLA petawatt and 100-terawatt-class lasers. According to Lawrence Berkeley National Laboratory (Berkeley Lab) principal investigator Thomas Schenkel, “Opening our door to users from LaserNetUS has been a great experience, and we are looking forward to working with a growing user community in this next phase.”
LaserNetUS includes the most powerful lasers in the U.S. and Canada, some of which have powers approaching or exceeding a petawatt. Petawatt lasers generate light with at least 1 million billion watts of power, or nearly 100 times the combined output of all the world’s power plants, but compressed to the briefest of bursts. These lasers fire off ultrafast pulses of light shorter than one-tenth of a trillionth of a second.
All facilities in LaserNetUS operate high-intensity lasers, which have a broad range of applications in basic research, advanced manufacturing, and medicine. They can recreate some of the most extreme conditions in the universe, such as those found in supernova explosions and near black holes. They can generate particle beams for high-energy physics research or intense X-ray pulses to probe matter as it evolves on ultrafast time scales. They are being used to develop new technology, such as techniques to generate intense neutron bursts to evaluate aging aircraft components or implement advanced laser-based welding.
Several LaserNetUS facilities also operate high-energy, longer-pulse lasers that can produce exotic and extreme states of matter, like those in planetary interiors or many-times-compressed materials. They can also be used to study laser-plasma interactions that are important to fusion-energy programs.
In its first year of user operations, LaserNetUS awarded time for 49 user experiments to researchers from 25 different institutions. Over 200 scientists, including more than 100 students and postdoctoral researchers, have participated in experiments so far.
The institutions hosting LaserNetUS facilities are Colorado State University, Berkeley Lab, Lawrence Livermore National Laboratory, SLAC National Laboratory, Ohio State University, University of Michigan, University of Nebraska-Lincoln, University of Rochester, and University of Texas at Austin in the U.S., and Institut National de la Recherche Scientifique in Canada. All proposals are peer-reviewed by an independent external panel of national and international experts.
The U.S. has been a pioneer in high-intensity laser technology, and was home to the research that was recognized by the 2018 Nobel Prize in Physics. The network and future upgrades to LaserNetUS facilities will provide new opportunities for U.S. and international scientists in discovery science and in the development of new technologies.
Lindau Honors for BELLA Postdoc Lieselotte Obst-Huebl
Lieselotte (“Lotti”) Obst-Huebl, a postdoctoral researcher in ATAP’s BELLA Center, recently had the honor of making an alumni presentation at the Lindau Nobel Laureates Meetings.
The annual Lindau meeting is intended to foster the exchange among scientists of different generations, cultures, and disciplines. Typically 30-40 Nobel Laureates convene in Lindau, Germany to meet the next generation of leading scientists: 600 undergraduates, PhD students, and postdocs from all over the world. Normally this would be an in-person event, but in the year of the COVID-19 pandemic, Lindau alumni and this year’s new speakers were asked to submit abstracts for an online meeting. Obst-Huebl was one of 24 selected to give a presentation.
Obst-Huebl gave a 10-minute talk on June 30 about laser-plasma particle acceleration. The talk was followed by an hourlong virtual poster presentation in the Scientific Exchange session.
Powering through time zone differences
An in-person session would have been at 10:30 a.m. Central European Time, but Obst-Huebl was on the west coast of the US. “I gave the talk at 1:30 in the morning,” she recalls.
She found it rewarding despite the hour, as “The range of people at the meeting was really broad: scientists, politicians, economists, international relations, and obviously some Nobel laureates as well,” she says.
It was a demonstration of the communication skills of the up-and-coming scientists as they presented their work at a comprehensive level for a broader audience, she says. “Everybody tried hard to do that, and it was pretty great.”
Since coming to LBNL a year ago, Obst-Huebl has worked on a wide spectrum of BELLA Center activities, including high-energy electron acceleration using the 20-cm plasma capillary; a LaserNetUS project with Ohio State University researchers on plasma mirrors with liquid-crystal film targets; and a radiobiology experimental campaign that accelerated protons from tape targets and transported the beam to cell samples. “It was quite nice—it gave me an opportunity to learn the whole experimental system at one of the most interesting laser-particle acceleration set-ups there is in the world,” she notes, adding, “It’s a nice area here as well.”
To explore further…
• Visit the Lindau Nobel Laureates Meeting website.
• Read an interview with Obst-Huebl while she was earning her PhD at Helmholtz-Zentrum Dresden-Rossendorf, before she came to LBNL, that was featured on the Women in Research blog.
• Berkeley Lab postdocs who wish to begin the application process for the 2021 program are reminded that the deadline is close of business (5 p.m. Pacific time) Friday, August 14. The Lab’s online form is available on our Google Drive, as are the criteria from the Lindau website. For now, just fill out the form, which will be submitted to the national laboratories office in the University of California Office of the President. Recommendation letters are not needed at this stage.
September Slam On Schedule for ATAP’s Amorim
Accelerator Modeling Program postdoc Lígia Diana Pinto de Almeida (Diana) Amorim competed in the final round of the third annual Berkeley Lab Research Slam.
In this popular event, styled after poetry and storytelling “slams,” early-career scientists hone their communication and outreach skills as they compete to tell compelling stories about their work in 3 minutes or less. A $3000 grand prize awaited the winner.
The Slam (virtual this time) was live-streamed September 17. If you couldn’t join live, you can catch the full event at slam.lbl.gov to learn more about what some of the brightest young minds through the Lab are doing. A standalone version of Diana’s talk is available on YouTube.
Meanwhile, you can learn more about Diana in this 2019 article on the LBNL Postdoc Association website (which features a recorded video of a Slam-like event at Brookhaven); this August 2020 article in the LBNL newsletter Elements; and her LinkedIn page.
She also gave a talk on “Plasma based Technology for Future Particle Colliders” September 13 at the Virtual Visit on Modern Physics, an event hosted by Birla Vishvakarma Mahavidyalaya Engineering College under the auspices of the IEEE Nuclear and Plasma Sciences Society.
Lining Up for Laser Plasma Acceleration
On March 31, 2020, Physics Review Letters published a paper by Palastro and colleagues from the University of Rochester, where a dephasingless laser-wakefield accelerator (DLWFA) was proposed. This proposed design for plasma accelerators would use line-focused laser pulses to overcome the problem of particles outrunning the acceleration region. To highlight this work, the American Physical Society asked Jeroen van Tilborg of ATAP Division’s Berkeley Lab Laser Accelerator (BELLA) Center to write a Viewpoint perspective, reproduced here, in their online magazine Physics. The DLWFA presents a clever way of shaping the spatial and temporal laser energy delivery onto a plasma, aimed at realizing a compact (room-size) high-energy electron accelerator. This goal is very much in-line with research in BELLA Center, where, over recent years, key community milestones on laser-plasma acceleration were demonstrated. This Viewpoint article and Palastro et al., Physical Review Letters 124, 134802 (31 March 2020), will help in appreciation of the various approaches being employed to pursue the same objectives: the compact production of multi-GeV electron beams and the development of novel “table-top” radiation sources.
One way to accelerate particles is to fire an intense laser pulse into a plasma, creating a density wake whose electric field pushes charged particles like electrons to high speeds . The accelerating gradient from such a plasma wakefield is much higher than can be achieved in conventional radio-frequency-based technology. However, a central difficulty with employing laser wakefield accelerators (LWFAs) is that the electrons eventually outrun the accelerating region of the laser-driven wakefield. Because of this dephasing, a single stage of wakefield acceleration is typically limited to a few tens of centimeters in length, and it is forced to operate at a low density, which constrains the accelerating gradient.
Several ideas have been proposed to deal with this dephasing limit. A new idea from John Palastro and colleagues from the University of Rochester, New York, uses special optical components to focus the laser into points along a line, thus extending the wake region so electrons are accelerated for longer and at a higher gradient . This method faces some hurdles, such as increasing the laser power above what’s currently available, but it has the potential to accelerate electrons to TeV energies over just a few meters.
The high gradients offered by laser wakefield acceleration open the path for tabletop accelerators at universities, hospitals, and smaller R&D labs, with applications such as x-ray bio-imaging, active nuclear interrogation, and medical treatments. LWFA also enables progress towards future TeV-scale particle colliders that promise to extend our understanding of the basic structure of the Universe . In the past 20 years, the LWFA community has evolved from small-scale proof-of-principle demonstrations to milestones in the production of beams with high current, low emittance, and narrow (percent-level) energy spread. Precision control of the laser-plasma interaction with multiple lasers or density profile shaping is a central thrust in ongoing research. Efforts are also underway to increase the number of laser shots from a few per second to more than a thousand per second, which will benefit stabilizing feedback procedures and applications that require high flux.
The maximum achievable electron energy for LWFA is determined by the accelerating field strength and the length of acceleration Lacc, both of which are limited by laser and plasma physics . The field strength scales with the plasma density as Ez∼n1∕2. At currently used densities (1016–1019 cm−3), the field strength can exceed 10–100 GV/m, which is about a thousand times the acceleration in traditional radio frequency cavities used at places like CERN. Ez also depends on the laser, whose intensity is determined by the laser energy, wavelength, pulse duration, and spot size.
The effective accelerator length depends on the laser as well. Specifically, the acceleration is limited to the region over which the laser remains focused. In vacuum, this focus region is characterized by the Rayleigh length zR, which is calculated with the laser wavelength and spot size. For most setups, the Rayleigh length is in the millimeter to centimeter range, but researchers can extend the focusing region by adding light-guiding structures, as was demonstrated in a recent LWFA experiment that achieved 8-GeV acceleration energies with a 20-cm-long waveguide . However, guiding structures are not without challenges, including the need for precise alignment and transverse mode control to avoid damage from the high-power laser pulses.
Guiding structures also don’t alleviate the problem of dephasing. Dephasing occurs because the wakefield region travels behind the laser at a speed slower than the vacuum speed of light, so electrons accelerated to relativistic energies will eventually get ahead of it. As such, the wakefield speed places an upper limit on the acceleration length, which scales with density as n−3∕2. To increase this limit—and correspondingly increase the maximum electron energy—traditional setups use a low plasma density.
Recently, a group proposed a scheme to overcome this dephasing limit by obliquely intersecting two tilted-pulse-front lasers . The interference between the lasers would generate a wakefield region that travels at the speed of light in vacuum. However, this approach requires precision control of two lasers, with potential challenges from transverse wakefield asymmetries.
Palastro et al.  have a similar idea for speeding up the wakefield region that uses a single laser and special optics rather than interfering lasers. Specifically, their proposed method combines an echelon (a mirror with specially designed steps) and an axiparabola (a recently developed curved mirror) . As the team conceives it, a laser pulse would first strike the echelon, which divides the light into a number of concentric rings (Fig. 1). These rings would be separated in time, such that the outer rings arrive at the axiparabola ahead of the inner rings. The curved reflective surface of the axiparabola would focus the rings at successive points along a line. This spatiotemporal shaping of the laser pulse offers a way to generate a wakefield traveling at the vacuum speed of light, which would circumvent dephasing.
To see how this “dephasingless” LWFA compares to previous schemes, we can imagine the system is tuned so that each ring produces the same acceleration effect as a single laser pulse in the traditional nonguided LWFA. In other words, each ring generates a focal segment that is one Rayleigh-length long, and if there are N rings, the total acceleration length would be N times the Rayleigh length. In addition to increasing the acceleration length, dephasingless LWFA could operate at high plasma density, which means a higher accelerating gradient. The bottom line is that dephasingless LWFA could potentially reach higher electron energies than previous methods with the same acceleration length.
One potential hurdle to this proposal is the laser energy requirements. If each of the N rings is to produce a separate wakefield, then the single laser pulse would need roughly N times more energy than in a traditional LWFA of comparable laser intensity. For TeV-scale electron acceleration, the number of rings would need to be in the thousands, and the corresponding femtosecond-duration laser energy would be multiple kilojoules, which may pose a challenge in terms of the availability of laser systems and power consumption limitations (especially for kHz operation). There are other issues that may require further investigation, such as how well does the line-focus scale to large ring numbers, and how will the spatiotemporal laser evolution affect wakefield generation and laser-electron overlap. In addition, questions remain over the inverse accelerated charge scaling with plasma density .
Despite these uncertainties, Palastro et al. have provided a clever variation of staged acceleration, with independently timed laser “beamlets” driving acceleration without the need for intrastage optics or complex guiding structures. As such, dephasingless LWFA enables new opportunities in the choice of density and laser-plasma accelerator architecture. This could be of particular importance for leveraging future multipetawatt lasers to compactly create high-energy electron beams that can probe nonlinear quantum electrodynamics . Next on the dephasingless LWFA to-do list: performing detailed simulations of laser delivery and wakefield production at multi-GeV scale and testing the waters regarding practical limitations.
Their research was published in Physical Review Letters 124, 134802 (March 31, 2020).
E. Esarey et al., “Physics of laser-driven plasma-based electron accelerators,” Rev. Mod. Phys. 81, 1229 (2009).
J. P. Palastro et al., “Dephasingless laser wakefield acceleration,” Phys. Rev. Lett. 124, 134802 (2020).
W. P. Leemans and E. Esarey, “Laser-driven plasma-wave electron accelerators,” Phys. Today 62, No. 3, 44 (2009).
A. J. Gonsalves et al., “Petawatt laser guiding and electron beam acceleration to 8 GeV in a laser-heated capillary discharge waveguide,” , Phys. Rev. Lett. 122, 084801 (2019).
A. Debus et al., “Circumventing the dephasing and depletion limits of laser-wakefield acceleration,” Phys. Rev. X 9, 031044 (2019).
S. Smartsev et al., “Axiparabola: A long-focal-depth, high-resolution mirror for broadband high-intensity lasers,” Opt. Lett. 44, 3414 (2019).
W. Lu et al., “Generating multi-GeV electron bunches using single stage laser wakefield acceleration in a 3D nonlinear regime,” Phys. Rev. Special Topics: Accelerators and Beams 10, 061301 (2007).
A. Di Piazza et al., “Extremely high-intensity laser interactions with fundamental quantum systems,” Rev. Mod. Phys. 84, 1177 (2012).
About the Author
Jeroen van Tilborg is an experimental staff scientist at the BELLA Center at Lawrence Berkeley National Laboratory (LBNL), California. Jeroen moved to Berkeley in 2001 for a combined Ph.D. program from LBNL and the Eindhoven University of Technology, Netherlands. For his work on femtosecond bunch length measurements he received the outstanding thesis award from the APS Division of Physics of Beams. Following a postdoctoral appointment in LBNL’s chemistry division (studying molecular dynamics), he returned to the BELLA Center in 2009. In 2016 Jeroen received a five-year DOE Early Career Research Program grant, which is funding his current pursuit of laser-plasma accelerator applications towards novel radiation sources.
—Multiprong platform at the Berkeley Lab Laser Accelerator Center will produce X-ray images and chemical details
Laser, Biosciences Researchers Combine Efforts to Study Viruses in Droplets
Glenn Roberts, Jr., LBNL Strategic Communications
Laser and biology experts at Lawrence Berkeley National Laboratory (Berkeley Lab) are working together to develop a platform and experiments to study the structure and components of viruses like the one causing COVID-19, and to learn how viruses interact with their surrounding environment. The experiments could provide new insight on how to reduce the infectiousness of viruses.
The new platform will build upon Berkeley Lab’s world-leading R&D efforts in laser-based plasma acceleration, in which a laser pulse creates an exotic, superhot state of matter known as a plasma that in turn rapidly accelerates charged particles – electrons and ions. Berkeley Lab scientists last year bested their own world record in accelerating electrons to high energies in a 20-centimeter span.
In the new setup, the accelerated electrons will generate X-rays that will act as microscopic strobes to capture images of virus-laden droplets that are dripped into the path of the X-rays. At the same time, synchronized within quadrillionths of a second, a second laser beam will strike the droplets to capture another layer of data about the virus particles and their makeup, and about other matter in the droplets.
“The idea is to learn about the virus and what’s around it,” said Thomas Schenkel, acting director of the Accelerator Technology and Applied Physics Division at Berkeley Lab who is part of the team planning the experiments. “How does it behave inside a droplet and what binds to it? How long is the virus viable in a droplet?”
The goal is to study the virus in certain biofluids, like saliva, and how it reacts to compounds mixed into the droplets. Biosciences experts at Berkeley Lab will prepare the samples and participate in the data analyses.
In this pilot study, researchers will use surrogate viruses that have similar properties to the SARS-CoV-2 virus that causes COVID-19 but are safe for laboratory workers to work with.
“These droplets aren’t just mini sacks of water, but a complex mixture of proteins and salt that affects viral stability,” said Antoine Snijders, a staff scientist and chair of the department of BioEngineering and BioMedical Sciences in Berkeley Lab’s Biological Systems and Engineering Division.
The droplets are intended to simulate the environment of the body’s respiratory system.
“What’s exciting about this study is that it will lead to a better understanding of the chemical characteristics of respiratory droplets and the virus contained within them,” Snijders added. “Once we understand the chemical characteristics, and the mechanism of viral inactivation within these droplets, we may be able to reduce efficiency of airborne disease transmission.”
The effort is supported by Berkeley Lab’s Laboratory Directed Research and Development (LDRD) program, through which the Lab directs funding to specific areas of research. Berkeley Lab, like the U.S. Department of Energy’s other national laboratories, is making COVID-19 research a priority.
The experiments will combine two techniques: X-ray imaging for structural information, and mass spectrometry to learn details about the chemical makeup of samples down to the level of individual proteins and molecules.
The secondary laser in the experiments will provide the spectroscopic information by charging up and breaking apart matter in the samples. Those bits and parts, such as individual protein components of a virus, can then be chemically measured and analyzed by a detector.
Conceivably, the setup could be used or modeled as a testing platform for coronavirus disease. Schenkel noted that with existing capabilities at the Berkeley Lab Laser Accelerator (BELLA) Center, it is possible to image and measure about five droplets every second. A proposed BELLA Center upgrade, called kBELLA, could drive that rate up to 1,000 droplets per second.
Eric Esarey, BELLA Center director, said an ultimate aim in developing laser plasma acceleration techniques is to reduce the size and cost of particle accelerators that could serve in a range of capacities for the medical, industrial, and research communities.
“In principle, this could be a compact, powerful, and low-cost device that could be put in lots of laboratories and lots of hospitals,” he said.
New types of X-ray sources based on laser-plasma accelerators are in active research in the BELLA Center, and they continue to be improved. These improvements are needed to provide high-resolution imaging of very small viruses in their environment.
While the BELLA Center is now offline due to shelter-in-place orders, Schenkel said that planning has started for the new experimental setup, with the goal of first experiments later this summer. A collaboration with biologists at the BELLA Center is ongoing, and there is already mass spectroscopy equipment that can be adapted for the new experiments.
Schenkel added that researchers can proceed with modifying a Berkeley Lab-developed computer code that models the laser and electron beams to optimize them for the new research.
“We are excited to use our tools to advance our understanding of COVID and contribute to future pandemic prevention,” Schenkel said.
“There are many analytical techniques that have originated from research with atom-smashers and particle beams years ago and that have since become workhorse tools in biomedical science.” Schenkel added, “When we discussed this new idea, there was a strong sense of urgency and excitement. This project is one example where we can immediately adapt our capabilities in response to the current crisis and advance our arsenal for the prevention of future pandemics. We want to show that this works so that we can establish it as a new capability for the community.”
Editor’s Note: These videos, released since the publication of the article, detail some of Berkeley Lab’s other coronavirus and COVID-19-related research.
Tong Zhou Among Berkeley Lab ECRP Winners
Tong Zhou, a research scientist in ATAP’s Berkeley Lab Laser Accelerator Center (BELLA), is among three Berkeley Lab employees selected by the U.S. Department of Energy’s Office of Science to receive significant funding for research through its Early Career Research Program (ECRP). In addition, three faculty scientists with joint appointments at Berkeley Lab and UC Berkeley will receive ECRP funding through their UC Berkeley affiliations.
Zhou’s research focuses on ultrafast laser technologies, including laser systems based on optical fibers and solid-state materials, and their applications — especially on high-repetition-rate laser-plasma accelerators.
His award is for research on a multi-kilohertz laser-plasma accelerator driven by a spectrally combined fiber laser. Laser-plasma accelerators (LPAs) could greatly reduce the size and cost of particle accelerators, and fiber lasers are very promising to drive future high-repetition-rate LPAs. However, the optical pulses produced by existing fiber lasers are too long. This research will address the gap between the limited pulse durations of existing fiber lasers and the LPA application needs, and will demonstrate a fiber-laser-based, high-repetition-rate LPA that will use machine learning to implement feedback control. Technologies developed in this research can enable many applications using high-repetition-rate electron beams, including those in science and medicine, and with further development can enable the path to future laser-driven particle colliders.
“The Department of Energy is proud to support funding that will sustain America’s scientific workforce, and create opportunities for our researchers to remain competitive on the world stage,” said DOE Under Secretary for Science Paul Dabbar. “By bolstering our commitment to the scientific community, we invest into our nation’s next generation of innovators.”
The program, now in its 11th year, is designed to bolster the nation’s scientific workforce by providing support to exceptional researchers during the crucial early career years, when many scientists do their most formative work. The three Berkeley Lab recipients are among 76 recipients selected this year, including 26 from DOE’s national laboratories.
The scientists are each expected to receive grants of up to $2.5 million over five years to cover salary and research expenses.
Zhou, who joined the ATAP career staff after an appointment as a postdoctoral researcher, is ATAP’s fourth awardee in this prestigious and competitive program. ATAP staff with ongoing ECRPs are Chad Mitchell (beam theory and modeling of intensity frontier particle beams in collaboration with the IOTA project at Fermilab), Qiang Du (scalable control of multidimensional coherent pulse addition for high average power ultrafast lasers), and Jeroen van Tilborg (demonstration of a free electron laser driven by electron bunches from laser-plasma-acceleration). Past recipients include Daniele Filippetto (HiRES, a high-repetition-rate beam source for ultrafast electron diffraction) and Tengming Shen (high-Tc superconductor to high-field magnets).