Investigations of fast electron transport in intense laser-solid interactions

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Quinn, Mark N. and McKenna, Paul (2011) Investigations of fast electron transport in intense laser-solid interactions. PhD thesis, University Of Strathclyde.

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Abstract

This thesis reports on experimental investigations of relativistic (`fast') electron transport in solid density plasma. Intense laser pulses, >1019W=cm2, interacting with solid targets generate a front surface plasma from which a mega-ampere relativistic electron beam is created. The transport of this fast electron beam through the target is occluded from direct measurement. Novel diagnostic methods involving proton emission are developed to investigate the effects of magnetic pinching, filamentation and reuxing on fast electron transport.Results of the effect of self-generated kilo-tesla magnetic fields on fast electron transport in solid aluminium targets are reported. For target thickness of 25 um to 1.4 mm, the maximum energies of protons are measured to infer changes in the fast-electron density and therefore the divergence of the fast-electron beam. If the electron transport was purely ballistic, a much faster decrease in the maximum proton energy with increasing target thickness would be expected. This implies that some degree of `global' magnetic pinching is occurring, particularly in the case of thick (> 400 um) targets. Numerical simulations show that the magnetic pinching effect is significantly reduced in thin targets where enhanced electron reuxing can disrupt the magnetic field growth.Results of the influence of beam scattering and material resistivity on electron beam filamentation are reported. This phenomena is diagnosed in solids targets ranging from 50 - 1200 um in thickness using proton beam uniformity measurements. Electron and proton beam uniformity are correlated using a 3D analytical model. In targets of similar initial resistivity, it is found that increasing the target Z (and therefore scattering) produces no measurable effect on electron beam filamentation. Simulations suggest that target resistivity in the low temperature regime and self-induced magnetic pinching are significant influences on beam filamentation in sold targets.Results of an investigation of fast electron refluxing within solid targets are reported. Refluxing occurs when the fast electrons are reflected by the sheath potentials formed at the front and rear surfaces. The number of times the fast electrons reflux through a Cu fluorescence layer is controlled by varying the thickness of a second layer comprised of plastic (CH). Enhancements in the K x-ray yield and source size are measured as the thickness of the CH layer is decreased. Comparison with analytical and numerical modelling confirms that significant refluxing occurs. This work highlights the importance of considering this phenomenon when deriving information on fast electron transport in thin solid density targets.

  • Item type:Thesis(PhD)
    ID code:66540
    Dates:
    Date
    Event
    2011
    Published
    Subjects:Science > Physics
    Department:Faculty of Science > Physics
    Depositing user: Pure Administrator
    Date deposited:10 Jan 2019 16:35
    Last modified:21 Dec 2024 01:29
    URI:https://strathprints.strath.ac.uk/id/eprint/66540
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