Laser linac colliding beam arrangement at high energies, a feasibility study

Abstract

I) IntroductionIn an earlier paper (l) a new principle in accelerating charged particles in the focus of a high power laser beam was discussed. It was demonstrated that field configurations in the focus of a laser beam enable single particles to be accelerated which travel along a so-called "acceleration channel" tuned to the particle velocity by a birefringent crystal outside the laser focus.In the following an attempt will be made to investigate whether or not a real particle accelerator based on this idea will be useful in high energy physics.This new acceleration principle will be examined in a colliding beam arrange ment wherein two laser linacs are brought to fire against each other. The point around which most interest centres is luminosity and how it will compare with that achieved with conventional storage rings at superhigh energies.The aim is to find out whether a laser colliding beam arrangement with luminosity equal to that of a storage ring will compare favourably with a storage ring with regard to cost.As laser accelerators are still at the stage of discussion, it is of course obvious that all these considerations will have to be of a tentative nature.The first step is to establish what kind of laser can be used. During this discussion it should however be borne in mind that the rapid expansion in the technology of high power lasers will only permit of a survey of laser types suited to the present purpose. Having defined the possibly usable types of laser, this paper will then be devoted to the investigation of particle beam optics, that is to a discussion for the first time ever of the a c c e l erating of a real beam with finite emittances by means of such an accelerator.Following this discussion a rough estimation of maximum luminosities for a colliding beam arrangement will be given. In the last section a possible physical layout of a 2 x 100 GeV colliding beam arrangement and the costs are discussed. The unsolved problems are collected over the course of the whole 2 paper and listed in the summary. II. Principle of Acceleration ChannelsAlthough described in an earlier paper in more detail (l), a survey of the basic idea will be given here. If an electromagnetic wave is used for the acceleration of charged particles, the following two points must be taken into consideration.(a) Both electric and magnetic fields act on the particle. In order to achieve a satisfying gain of energy, the magnetic field component along the particle trajectory should vanish. This demand can be fulfilled by the use of standing waves where the maxima of the electric and the magnetic field are separated by a quarter wave-length.(b) When the magnetic component of the electromagnetic field no longer exerts any influence on the particle trajectory, the rapidly changing sign of the electric field strength accelerates and decelerates the particle and the net energy gain can be neglected. Therefore the particle must travel through a field-free region in which the deceleration half-wave cannot reduce the particle energy. A si...