Dual-10 terawatt system for 0.2 GeV-class LPAs and injection control
Multiple synchronized laser pulses each with 10-terawatt class peak power at ~40 femtosecond duration are provided by the Godzilla and Chihuahua Ti:Sapphire CPA systems for laser-controlled electron injection and guiding experiments. The two final amplifiers each generate 1-joule-class pulses at a 10 Hz repetition rate. These can be split and compressed using three separately adjustable grating-based optical pulse compressors, and part can also be delivered uncompressed for heating. The beams are focused onto gas jet plasma targets for LPA experiments.
The laser is equipped with sophisticated diagnostics and controls. Control systems safely operate and continuously monitor its important parameters from a centrally located control room. A magnetic electron spectrometer using phosphor screens and multiple CCD cameras allows high repetition rate analysis. Optical diagnostics monitor the energy, spectrum, and other parameters of the transmitted laser to infer its coupling to the LPA. Gas jet targets offer an open geometry and hence plasma density is monitored on-line via interferometry using a frequency. Terahertz emission from the plasma interaction region is detected for electron bunch characterization purposes. On-line neutron and gamma ray monitoring is also available inside the experimental cave.
The first production of high quality electron beams (few percent energy spread and few mrad divergence at ~ 90 MeV) in an LPA was demonstrated here in 2004 using a laser-preformed plasma channel. Recent experiments control trapping of electrons in the LPA to improve beam quality. Plasma density gradients (downramps) were used to control wake phase velocity and trigger trapping in 2008. Colliding laser pulses can form a beat wave, and this effect has recently been used to generate very low energy spreads. Continued work on laser guiding has increased the bunch energy achieved with 10 terawatt lasers to 250 MeV. Activation experiments and betatron radiation observation using these beams are also proceed in parallel on this beamline.