Numerical and Experimental Studies of Wakefield Accelerators

Abstract: This thesis is based on work done by the author on the development of laser wakefield accelerators.Wakefield acceleration in plasmas is a promising technique to provide the next generation of accelerating structures and particle beams. Plasmas can sustain electric fields that are many orders of magnitude stronger than those possible in conventional accelerators. Other benefits of wakefield accelerators are that electron beams produced inside the plasma can be generated with high peak current and ultra-low emittance.These strongly accelerating structures can reduce the size of particle accelerators, making them more available, for example in hospitals, or to increase the energy in particle colliders.In wakefield acceleration, a driver is used to excite a plasma wave.The acceleration of charged particles takes place in a plasma wave excited by, and co-propagating with, the driver. The driver can be a laser pulse or a bunch of charged particles.However, many technical challenges remain to be solved before a reliable particle source can be realized based on this technology.This thesis describes numerical studies performed using particle-in-cell simulations and experimental work using high-intensity laser pulses, with the aim of improving our knowledge on wakefield accelerators. The work presented here focuses on three different topics: trapping mechanisms, achieving higher electron energies and improvement of the betatron X-rays generated.In particular, trapping in a density down-ramp, ionization induced trapping, and trapping by colliding pulses have been investigated numerically and experimentally.A novel guidance technique for high-intensity laser pulses is suggested, the merging of two laser wakefields is experimentally demonstrated and suggested as a possible means of staging wakefield accelerators, and the possibility of carrying out a beam-driven plasma wakefield experiment is investigated through simulations. An improved X-ray source based on laser wakefield acceleration and enhancement of the betatron oscillations through direct laser acceleration is investigated and two applications are demonstrated.