Electron Accelerator

Oscillograms showing (left to right): the RF filling of the
gun, the laser pulse and the electron pulse. Top: Signals with Cu
photo-cathode (the electron pulse is composed of the dark
current and the photo-current). Bottom: Signals with Cs2Te
photo-cathode (the dark current is now negligible compared to
the photo-current).

For more cool photos please see page

The electron accelerator is the ELYSE platform’s heart; without it would be just a place with no purpose.

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
General Layout
ELYSE accelerator setup
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.

H.F. of ELYSE accelerator
Interior of accelerator cavity

The photocathode

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.

Horizontal section through the vacuum chamber for the Cs2Te photo-cathode preparation

The characteristics

  • 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.