Prof Peter Norreys FInstP;

Abstract:

Recent progress in the physics of fast ignition of fusion targets is reviewed here. Fundamental studies on hot electron energy transport show that the scheme looks promising if the heating pulse can be guided close enough to a compressed core. The idea of using cone-guided compression was first demonstrated experimentally under a Japan-UK collaboration. The use of the gold cone was extremely successful and showed a 10³ neutron increase out of CD target implosion with a 300 J/0.5 ps enforced heating laser pulse. The heated temperature was close to 1 keV. In order to increase the temperature to 10keV, a 10kJPW^-1 laser system is necessary. Osaka University has started constructing such a laser system.

Abstract:

Vulcan is established as a world leading user facility for studies of ultra-high intensity laser interactions with matter. The Petawatt(PW) Upgrade project will deliver an order of magnitude increase in laser power to target, delivering interaction intensities of 10 21 Wcm -2. Before commencing operation to users a commissioning study was carried out. The objectives of this investigation were: To perform radiological surveys of the facility in anticipated target configurations and to install additional shielding for high-Z interactions as required To measure the target irradiance and the X-ray spot size To investigate the effects of electromagnetic noise on the chamber and target area equipment To determine the level of debris produced from the target and to devise a suitable operating scheme to protect chamber optics from damage Installation of an optical probe Contrast measurement of the laser pulses This report will review the experimental and radiological data obtained from the thirteen solid target interaction shots fired during the commissioning run in the newly constructed PW interaction facility 1) where doses of 45 mSv @ 1m were obtained. Commissioning of the PW laser and compressor chain is reported in separate articles, as is the commissioning of the large aperture gratings at high laser fluences 2).

Abstract:

The transport of intense relativistic electron beams in solid density plasma was analyzed. Ponderomotive kinetics modeling code (MPK) for the average relativistic laser-plasma interaction for laser absorption in under-dense or below critical density plasma was proposed. The focused peak intensity of the Petawatt laser system was measured as high as 3.1020W / cm 2. It was found that there was significant lateral electron transport, but of low energy electrons, into the solid.

Abstract:

Experimental measurements of electron transport and isochoric heating in 100 J, 1 ps laser irradiation of solid Al targets are presented. Modeling with a hybrid PIC code is compared with the data and good agreement is obtained using a heuristic model for the electron injection. The relevance for fast ignition is discussed.

Abstract:

The Vulcan laser at the Rutherford Appleton Laboratory in England has been used to show, for the first time, that picosecond laser generated non-thermal K-alpha radiation can be used effectively as a backlighter for radiographic imaging of an implosion. This novel method of x-ray radiography features high temporal resolution, high signal to noise ratio and monochromatic imaging. We present here the Ti K-alpha backlit images of a series of six-beam driven spherical implosions of thin-walled 500 micron Cu doped CD shells. These images, separated by ∼ 0.5ns intervals, capture various states of implosion in and around a stagnation time observed to be ∼ 3.25 ns. Images of imploding coned Cu doped CD shells used in fast ignition research are additionally presented. These images, taken near the previously determined stagnation time, show an imploded core collapsed around an attached gold laser entry cone. These radiographic results were linked to a study of fast electron transport within imploded Cu doped coned CD shells as a result of interaction with a high intensity, short pulse laser. The radiographic results, then, served as a verification of a smooth and uniform implosion and provided an empirical determination of stagnation time, both prerequisites for the electron transport diagnosis.