G. Doucas

The Oxford Free Electron Laser Project

It is proposed to use the Oxford 10 MV Van de Graaff accelerator as an electron beam source for a free electron laser (FEL) operating in the far infra red (FIR). The configuration and layout of the Van de Graaff make it very suitable for conversion, with a potentially high efficiency for electron beam recovery. Using a 2 m long wiggler of 34 mm period, the FEL would operate in the 60-300 /spl mu/m wavelength band, with extension down to 30 /spl mu/m on the 3rd harmonic. When constructed, the FEL will support a programme of FEL research and development, concentrating at first on investigations of behaviour in the moderately high-gain regime (/spl equiv/ 100% per pass) and mechanisms for lasing on higher harmonics. It will also be the basis for a national UK user facility in the FIR.

Investigation of the role of plasma channels as waveguides for laser-wakefield accelerators

The role of plasma channels as waveguides for laser-wakefield accelerators is discussed in terms of the results of experiments performed with the Astra-Gemini laser, numerical simulations using the code WAKE, and the theory of self-focusing and self-guiding of intense laser beams. It is found that at a given electron density, electron beams can be accelerated using lower laser powers in a waveguide structure than in a gas-jet or cell. The transition between relativistically self-guided and channel-assisted guiding is seen in the simulations and in the behaviour of the production of electron beams. We also show that by improving the quality of the driving laser beam the threshold laser energy required to produce electron beams can be reduced by a factor of almost 2. The use of an aperture allows the production of a quasi-monoenergetic electron beam of energy 520u2009MeV with an input laser power of only 30u2009TW.

Light concentrators for the Sudbury Neutrino Observatory

Abstract There is an important and growing class of elementary particle detectors which are characterized by a large sensitive volume (thousands of tonnes), very low radioactive backgrounds, and rely on the emission of light for particle detection. Water Cherenkov detectors come into this category; they have a large mass of water as the sensitive medium. Particles are detected when they interact with the water and produce Cherenkov light, so detection efficiency relies on having a huge light sensitive area at the periphery of the detector. The most cost-effective way of achieving this is by placing light concentrators on large photomultiplier tubes (PMTs). This paper describes the work carried out on light concentrators for the PMTs in the Sudbury Neutrino Observatory, a 1000 tonne heavy water Cherenkov detector. We discuss the advantages of using light concentrators, summarize the optical theory of non-imaging light concentration, and describe in detail the development and manufacture of the concentrators themselves.

Study of near-GeV acceleration of electrons in a non-linear plasma wave driven by a self-guided laser pulse

Electrons are accelerated up to 0.8u2009GeV in a self-injecting laser wakefield accelerator driven at a plasma density of 5.5 × 1018u2009cm−3 by a 10u2009J, 55u2009fs, 800u2009nm laser pulse in the blow-out regime. The electron beam stability is correlated with the laser focal spot pointing stability and depends on the target alignment. Variations of the laser pulse energy, focal spot size and energy within the full width at half maximum have little effect on the electron beam profile (stability) but impact the electron energy (stability). The peak electron energy is higher than expected for the initial vacuum intensity. This is evidence for intensity amplification which also explains the observation of polyenergetic beamlets.

A prototype RICH detector using multi-anode photo multiplier tubes and hybrid photo-diodes☆

The performance of a prototype Ring Imaging Cherenkov Detector is studied using a charged particle beam. The detector performance, using CF4 and air as radiators, is described. Cherenkov angle precision and photoelectron yield using hybrid photo-diodes and multi-anode PMTs agree with simulations and are assessed in terms of the requirements of the LHCb experiment.

Proposed addition of superconducting linac modules to the Daresbury tandem

Abstract It is proposed that nine split loop lead plated superconducting resonators be added as a post accelerator to the Daresbury 20 MV tandem. The refrigeration system will allow the addition of at least a further twelve resonators at a later stage which should enable beams with mass 200 to be accelerated to almost 5 MeV per nucleon.

Conversion of the Oxford Van de Graaff into an electron accelerator

Abstract The Oxford Van de Graaff accelerator has been converted from a heavy ion machine into a single-ended accelerator for electrons. The purpose of the conv

The Oxford free electron laser project

Abstract It is proposed to use the Oxford 10 MV Van de Graaff accelerator as an electron beam source for a free electron laser (FEL) operating in the far infra red (FIR). The configuration and layout of the Van de Graaff make it very suitable for conversion, with a potentially high efficiency for electron beam recovery. Using a 2 m long wiggler of 34 mm period, the FEL would operate in the 60−300 μm wavelength band, with extension down to 30 μm on the 3rd harmonic. When constructed, the FEL will support a programme of FEL research and development, concentrating at first on investigations of behaviour in the moderately high-gain regime (∼ 100% per pass) and mechanisms for lasing on higher harmonics. It will also be the basis for a national UK user facility in the FIR.