Laser-based electron acceleration to GeV in free space

Abstract

Iii this paper, the free-electron scattering by continuous or pulsed laser beams has been investigated in details. It is found that when Q E eE/(rrtwc) 100 an electron can be captured and violently accelerated to GeV energy under PrI)eI conditions. From the quantum viewpoint, we can explain this effect on the basis of non-linear and stimulated Compton scatterings. This phenom'ion provided us with a new far-field laser acceleration mechanism,whose practical feasibility and application possibility are also discussed.Keywords: free electron scattering, intense lasers, non-linear Compton scattering . IntroductionEver since the emergence of the first accelerator in England, the accelerator beam energy has been increased about one magnitude every ten years [1]. And at the same time, the building expenses and complexity rises drastically. But higher and higher energies are needed in particle physics. To solve the above dilemma, people begin to investigate new acceleration mechanism long ago, among which the laser acceleration is the most attractive one. Compared with the 2OMV/m acceleration gradient provided by present linear accelerators, the 1O7MV/m electric field gradient of the laser fields have made the laser acceleration a very promising way to increase the particle energy and decrease the accelerator size. But laser acceleration has its own problems. For instance, most of previous acceleration mechanisms have medium involved, such as gas[2}, plasma{3] etc., in order to slow down the phase speed of the laser fields. To overcome the problem of various non-stabilities inherent in the plasmas/matter interaction, we resort to the far-field free electron accelerations in vacuum. In this research area, there is a long-standing question that is whether an electron can get net energy gain from the laser beam in free space. According to the so-called Lawson-Wooclworth theorem arid previous research[4], the electron can obtain no energy gain through the whole interaction. But this conclusion is only confined to low-intensity laser fields since they either use the Born approximation(i.e. 1 / 'y2 is neglected in theoretical processing), or under-evaluate the interpose effect of different plane wave modes. To give a more exact answer to the above question, we devise a realistic laser beam satisfying Maxwell's equations and then inject the electron upon it to see how the electron ener' changes before and after the interaction. The results are very interesting and significant. For stationary laser beams, as Q < 0. 1 , there is no energy transfer between the electron arid the laser beam. As Q increases from 0. 1 to more than 10, the electron begins to obtain more and more net energies, which is of MeV magnitude when Q ''lO. The most surprising and meaningful results are that as Q ', 100 , the electron can be captured and accelerated to GeV energy. To pulsed laser beanis, we can have similar results when Q . ; 100. The underlying physical mechanism of such high net energy exchange has been discussed in Section 3.5. Here we have in...