Prof Peter Norreys FInstP;

Abstract:

Experimental results showing hot electron penetration into Cu wires using Kα fluorescence imaging are presented. A 500 J, 1 ps laser was focused at f/3 into hollow aluminum cones joined at their tip to Cu wires of diameters from 10 to 40 μm. Comparison of the axially diminishing absolute intensity of Cu Kα with modeling shows that the penetration of the electrons is consistent with one dimensional Ohmic potential limited transport. The laser coupling efficiency to electron energy within the wire is shown to be proportional to the cross sectional area of the wire, reaching 15% for 40 μm wires. Further, we find the hot electron temperature within the wire to be about 750 keV. The relevance of these data to cone coupled fast ignition is discussed. © 2009 American Institute of Physics.

Abstract:

Guided transport of a relativistic electron beam in solid is achieved experimentally by exploiting the strong magnetic fields created at the interface of two metals of different electrical resistivities. This is of substantial relevance to the Fast Ignitor approach to fusion energy production, since it allows the electron deposition to be spatially tailored-thus adding substantial design flexibility and preventing inefficiencies due to electron beam spreading. In the experiment, optical transition radiation and thermal emission from the target rear surface provide a clear signature of the electron confinement within a high resistivity tin layer sandwiched transversely between two low resistivity aluminum slabs. The experimental data are found to agree well with numerical simulations. © 2009 The American Physical Society.

Abstract:

The production of highly energetic beams of both electrons and ions is a major part of the experimental programme at the Central Laser Facility (CLF), STFC Rutherford Appleton Laboratory. Every year sees a significant number of experiments done in both areas. This has been complemented by theoretical studies that have been carried out at the CLF and UK universities. In a recent consultation on plans to build a 10 PW upgrade to the VULCAN facility, laser-driven particle acceleration formed a very significant part of the science case that emerged from this consultation. In this talk, I will review the experimental progress that has been made in particle acceleration, and I will also examine what theoretical investigations suggest the future of this field will be. Experimental studies of laser-driven ion acceleration of the CLF using both the VULCAN and ASTRA systems have looked at a number of aspects including focussing and control of the ion beam, manipulation of the energy spectrum, energy scaling with laser and target parameters, and direct use of the proton beam in both isochoric heating of secondary targets and proton radiography. Recently there has been great interest in a number of theoretical studies which indicate that it should be possible to explore radiation-pressure driven ion acceleration for intensities above 1021 Wcm-2, which will be accessible with the ASTRA-GEMINI system. This very exciting prospect will also be discussed. Electron acceleration in laser wakefields is also a well established part of the CLF programme. Experimental studies of laser-driven electron acceleration using the ASTRA laser have explored electron acceleration in both supersonic gas jets and gas-filled capillaries. This has led to the production of electron bunches with up to 1 GeV energy and a few percent energy spread. The influence of tuneable parameters such as the evolution of the plasma channel inside a capillary or the position of the laser focus with respect to the gas jet is actively being investigated. These efforts are backed up by a matching numerical campaign. Recent experiments have also shown that electron bunches trapped on a downward density ramp can have a very small absolute energy spread, and the potential consequences of these results will also be discussed. © 2011 Optical Society of America.