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Princinple of operation
The ELYSE platform of the Physical Chemistry Institute is centered on an electron accelerator that delivers electrons of 3 to 9 MeV in the form of pulses lasting 5 to 10 picoseconds with a charge of up to 7 nC. These electrons are generated using a femtosecond pulsed laser that extracts the electrons from a semiconductor, the photocathode, placed within a radio frequency cavity that accelerates them to the desired energy. For more details see ELYSE—A picosecond electron accelerator for pulse radiolysis research Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 539, 2005, 527-539; doi.org/10.1016/j.nima.2004.11.006
The great originality of ELYSE comes from the fact that the "pump-probe" experiments are carried out with an electron source synchronized with the photon source. The laser is the source of the ultra-short optical pulses that extract the electrons from the photocathode of the accelerator.
The accelerator has three ways, two of which are used. The pump-probe experiment is implanted on the direct way and the streak camera absorption spectroscopy experiment is located on the most bend way 2.
The photocathode used on ELYSE is a copper substrate on which Tellurium and Caesium Chromate are deposited. A deposit of Cs2Te is then formed whose quantum efficiency is close to 1% much higher than that of metal cathodes (= 0.0001%).
The lifetime of these photocathodes is about 1 to 2 years.
- pulse duration: < 10 ps at half height;
- charge per pulse: 1 nC to 7 nC;
- energy: 4 to 9 MeV;
- repetition frequency: 0.1 to 10 Hz;
- rms energy dispersion: 1% (100 keV to 9 MeV);
- beam diameter on target: 3 to 4 mm.