Laser-plasma accelerator group

Abstract:

The generation of GeV-scale electron beams in the plasma channel formed in a gas-filled capillary discharge waveguide is investigated. Electron beams with energies above 900 MeV and with root-mean-square divergence of 3.5 mrad are observed for plasma densities of 2.15 × 1018 cm-3 and a peak input laser power of only 55 TW. The variation of the electron energy with the plasma density is measured and found to exhibit a maximum at plasma densities for which the dephasing length approximately matches the length of the plasma channel. Injection and acceleration of electrons at the relatively low plasma density of 3.2 × 1017 cm-3 is observed. The energy spectra of the generated electron beams are shown to exhibit good shot-to-shot reproducibility, with the observed variations attributable to the measured shot-to-shot jitter of the laser parameters. Two methods for correcting for the effects on the measured energy spectrum of off-axis electron beam propagation are investigated. © 2012 American Institute of Physics.

Abstract:

We present an outline of experiments being conducted at Oxford University on multiple-pulse, resonantly-enhanced laser plasma wakefield acceleration. This method of laser plasma acceleration uses trains of optimally spaced low energy short pulses to drive plasma oscillations and may enable laser plasma accelerators to be driven by compact and efficient fibre laser sources operating at high repetition rates. © 2012 American Institute of Physics.

Abstract:

We use coherent optical transition radiation (COTR) to measure the transverse profile of laser-accelerated electron bunches. The retrieved electron beam profiles are compared to scintillator-based beam profile measurements. © 2012 American Institute of Physics.

Abstract:

Inclusive-jet cross sections have been measured in the reaction ep→e+jet+X for photon virtuality Q 2<1 GeV 2 and γp centre-of-mass energies in the region 14217 GeV and -1< jet<2.5. In addition, measurements of double-differential inclusive-jet cross sections are presented as functions of ETjet in different regions of jet. Next-to-leading-order QCD calculations give a good description of the measurements, except for jets with low ETjet and high jet. The influence of non-perturbative effects not related to hadronisation was studied. Measurements of the ratios of cross sections using different jet algorithms are also presented; the measured ratios are well described by calculations including up to O(αs2) terms. Values of α s(M Z) were extracted from the measurements and the energy-scale dependence of the coupling was determined. The value of α s(M Z) extracted from the measurements based on the k T jet algorithm is αs(MZ)=0.1206-0.0022+0.0023(exp.)-0.0035+0.0042(th.); the results from the anti-k T and SIScone algorithms are compatible with this value and have a similar precision. © 2012 Elsevier B.V.