Spectacular progress has been made during the last 15 years in our understanding of laser based plasma acceleration processes. Among these processes, let us cite the non-linear propagation of UHI laser pulses in plasmas, non-linear wakefield excitation, relativistic self-focusing, or self-temporal compression. All these processes are strongly interdependent and a huge amount of work is still necessary on the fundamental side to provide the optimum conditions for an attractive and reliable electron accelerator who could reasonably compete with accelerators devoted to high energy physics or to the conception of an X-ray Free Electron Laser.
These achievements, mainly due to the accuracy of the experiments on high rep-rate 100 TW class lasers and to their essential coupling with numerical large scale PIC simulations, are impressive. Laser guiding in a plasma channel over a few centimeters has been shown to produce electrons accelerated in the GeV range . In the non-linear regime, the injection of the electrons in the accelerating field produces electron bunches shorter than the laser beam itself, with energies on the order of 100 MeV in a few mm long gas jet . These relativistic electron sources are now to a certain extent mono-energetic, ultra-short (few fs), stable and tunable.
The laser-plasma electron acceleration program on CILEX will grasp the opportunity of the APOLLON-10P laser to explore new acceleration domains. With the support of the satellite facilities, we expect, , improving the electron beam characteristics in term of energy, pulse duration and beam luminosity. A dedicated electron beam line will be developed to address the most significant bottlenecks. On this line, after a conception phase and tests on satellite facilities, diagnostics of the spatial and spectral beam profiles, of the emittance, pulse duration and charge will be implemented. After characterization of the beam, a specific electron beam line consisting in dipoles and quadrupoles will be constructed to transport the beam for specific applications as the injection in a secondary acceleration stage or in an undulator for beam diagnostics or for photon production.
The complementarity of the groups involved in CILEX (laser plasma physics - accelerator’s physics) together with the high availability of lasers with complementary performances (APOLLON-10P - satellites facilities) guaranty that outstanding results will be achieved in the highly competitive domain of the design of compact accelerators. Thanks to the high repetition rate of satellites facilities, a wide range of parameters will be explored, while extreme values will be ultimately tested with APOLLON-10P.
To explore the possibility to improve continuously the electron beam characteristics, two main scientific ways will be explored:
In the bubble/blow out regime, one laser beam is able to produce an electron beam with a quasi-mono energetic distribution and with a very high efficiency of the order of 10-20%. In some conditions, few nC, 30 GeV electrons beams, with large energy spread (tens of %) are expected. But other conditions, such as the cold injection scheme which uses two laser beams, will considerably improve the electron beam quality . It is expected that up to 50 pC, with a relative energy spread below the 1% level and peak energy of several tens of GeV could be produced with this new scheme. Interesting in itself, this single-stage approach is also required to test the validity of theoretical models and simulations.
The multi-stage laser plasma accelerator  will allow the study of the key issues related to the design of an accelerator scalable to very high energy . It will consist of an injector and two acceleration plasma stages. They will be tested in the linear and in the non-linear regime. The injector will be all-optical.
Coupling to an undulator
In addition to the preceding studies, the electron beam-lines generated by APOLLON-10P itself could be coupled to a magnetic wiggler if its measured characteristics are suitable . This set-up will first allow a precise diagnostic of the accelerated electrons, especially the emittance and could serve as a key element for the conception of compact X-rays lasers. External extra injection of harmonics – from gas or plasma mirror- to seed the signal and strongly shorten the wiggler length is also envisaged .
The program using Apollon10P has been sequenced in 4 stages of increasing difficulties.
Maj : 16/05/2012 (14)