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Fast Electron Divergence

Fast Electron Divergence. Fast Ignition Workshop 2008. Thanks to : J.R.Davies, R.G.Evans, and R.Stephens. Current Status: Motivation. Divergence Angle has a massive impact on the Beam Energy required for Ignition E.g. Talks by Stoeckl (I4.060) and Honrubia (I5.078).

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Fast Electron Divergence

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  1. Fast Electron Divergence Fast Ignition Workshop 2008 Thanks to : J.R.Davies, R.G.Evans, and R.Stephens

  2. Current Status:Motivation • Divergence Angle has a massive impact on the Beam Energy required for Ignition • E.g. Talks by Stoeckl (I4.060) and Honrubia (I5.078).

  3. Current Status:Experiments • Fast electron flow divergent? • 1ps ; > 1019 Wcm-2 ; 1ωinteractions • e.g. Lancaster et al. (PRL), Stephens et al. (PRE) • Any evidence of collimation?

  4. Current Status:Experiments • What is the best diagnostic approach as regards fast electron divergence? • Can different mechanisms be distinguished? • K-alpha, XUV imaging, transverse optical probing.

  5. Current Status:Theory • What determines the initial fast electron divergence? • Beam Instabilities? • Curvature of Critical Surface? • Details of Absorption?

  6. Current Status:Theory • Is our current understanding of transport and magnetic collimation consistent with the experimental observation of divergent flows? • Bell & Kingham (PRL) • J.R.Davies (PRE and PPCF)

  7. Next Experiments? • 2ω or 3ω ? (HiPER) • Under conditions closer to FI (OMEGA-EP) ? • Better controlled and diagnosed versions of current experiments? • Novel Ideas?

  8. Theoretical Developments? • Absorption: • PIC simulations and analytic models. • Transport: • Magnetic collimation (Bell-Kingham) model, hybrid codes, VFP codes, hybrid-PIC codes, Filamentation models, Beam-Hollowing (Davies) model.

  9. Forward Look:Short-Intermediate Term • What can be achieved before the next FIW? • A better set of experimental results? • Better codes? • A better understanding of absorption and transport?

  10. Forward Look: Long Term Is electron divergence a fundamental problem that one must “live with” or can it (must it?) be controlled and mitigated?

  11. Strucured Collimator Concept • Enhance generation of collimating magnetic field by structuring the target resistivity, i.e. by using different Z materials. Electric Field E = -ηjf Published in Phys.Plasmas, 14, 083105

  12. Comparison Same laser conditions. Fast electron density profiles at 1ps. Homogeneous Al target Structured Collimator

  13. 3D simulation of slab confinement Al-Sn-Al target Pure Al target Sn Layer (~12.5 um wide) Al Al Laser x-y midplane plot of fast electron density

  14. Rear Surface Electron Density (linear scale) Al Slab Target Al-Sn-Al Target

  15. Simulation Experiment

  16. Sn (~10 um wide) Al Al 532 nm 700 nm Total signal is ~ twice the reference Total signal is ~ twice the reference slide courtesy of S.Kar

  17. Collimation of electron beam?(Experiment July 08) Typical FI experiment: Laser Intensity determinedby Implosion Conical collimator: Laser Intensity becomes Free parameter

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