Towards a free-electron laser driven by a laser wakefield accelerator

The free-electron laser (FEL) is a powerful source of tuneable coherent radiation that currently demands kilometre-scale beam lines for high-energy vacuum ultraviolet (VUV) and X-ray output. Driving an FEL with a laser wakefield accelerator (LWFA) electron beam would radically reduce the size of such systems as well as delivering ultra-short duration radiation pulses. In this thesis, the production and optimal transport of high-quality electron beams in an LWFA and the feasibility of using such beams to drive a VUV FEL has been investigated. The ALPHA-X LWFA uses a 25 TW femtosecond laser pulse focused into a 2 mm gas jet to accelerate electrons. Using simulation codes [General Particle Tracer (GPT) and TRANSPORT], the initial ALPHA-X transport system has been analysed and an improved system using additional permanent magnet quadrupoles has been designed and installed. GPT has also been applied in analysis of the beam transport through a high resolution magnetic dipole electron spectrometer. It is shown that measurements of beam energy spreads of less than 1% imply a normalised transverse emittance of less than 1 μ mm mrad, showing that these beams are suitable for driving an FEL. Efficient electron beam transport through an undulator (100 periods, period = 15 mm) is demonstrated implying an estimated source diameter of 300 μm close to the centre of the undulator (in agreement with simulation). Undulator radiation have been generated using electron beams of energy 83-131 MeV. Output radiation spans the range 180-500 nm and the scaling of photon yield with electron charge provides tentative evidence of coherent emission - the radiation flux is up to ~3 times greater than the expected spontaneous emission flux. The maximum number of photons peaks at 8 x 10⁶ and, assuming a pulse duration of 100 fs, the maximum peak brilliance is 10¹⁸ photons/second/mm²/mrad²/0.1% bandwidth.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral-pg

Grantor dc:publisher.institution

University of Strathclyde

Year dc:date.issued

2014

Author dc:creator

• Anania, Maria Pia

DOI

10.48730/tg8j-m606

Identifier

T14083

Author Identifier

200766903

OAI identifier oai:identifier

oai:strathclyde:t435gd086