1 / 28

Electron transport in the shock ignition regime Tony Bell University of Oxford

Electron transport in the shock ignition regime Tony Bell University of Oxford Rutherford Appleton Laboratory. Acknowledgements: Guy Schurtz, Xavier Ribeyre et al (CELIA, Bordeaux) Robert Kingham, Alex Robinson, Mark Sherlock (Imperial/RAL) Michail Tzoufras (Oxford/RAL). Key papers:

doris
Download Presentation

Electron transport in the shock ignition regime Tony Bell University of Oxford

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Electron transport in the shock ignition regime Tony Bell University of Oxford Rutherford Appleton Laboratory • Acknowledgements: • Guy Schurtz, Xavier Ribeyre et al (CELIA, Bordeaux) • Robert Kingham, Alex Robinson, Mark Sherlock (Imperial/RAL) • Michail Tzoufras (Oxford/RAL) • Key papers: • Betti et al PRL 98 155001 (2007) • Theobald et al Phys Plasmas15 056306 (2008) • Ribeyre et al PPCF (in press)

  2. Shock ignition • Compress target on low isentrope • Final laser spike launches ignition shock Figures from: Betti et al (2008) JPhys conf series 112 022024 Pressure (Gbar)

  3. Starting point: work at CELIA on off-axis drive Does electron transport increase symmetry? Benefits of going to higher laser intensity (‘fast shock ignition’) Ribeyre et al PPCF 51 015013 (2009)

  4. Fast electrons produced by ignition pulse Fast electron range Can heat with 100keV electrons without excessive preheat Pressure in core: 800 (T/5keV) (ne/5x1025cm-3) Gbar Pressure at critical: 0.32 (T/10keV) (ne/1022cm-3) Gbar need strong shock convergence high T at critical Gitomer et al Phys Fluids 29 2679 (1986) Il2=1016 Wcm-2mm2: T~10-30keV Il2=1017 Wcm-2mm2: T~10-100keV Beg et al 1997: Thot = 100 (Il2/1017 Wcm-2)1/3 keV Betti et al PRL 98 155001 (2007): Ignition shock pressure ~ 1Gbar Laser spike: ~ 6x1015Wcm-2, 47kJ, 540TW, 100-300psec, 3w 10% 100keV electrons from instabilities - beneficial

  5. Explore shock ignition driven by high energy electrons using KALOS electron transport code

  6. Non-local electron transport mfp of 10keV electron at critical density ~ 80 mm (llaser =0.33mm) transport is non-local • Features of non-local transport: • Reduced heat flow for scalelengths < 30 x mfp (‘flux limiter’) • Increased heat flow at base of heat front • Heat flow at angle to sT • Magnetic field where sn x sT = 0

  7. Nishiguchi et al (1992) Extra heat flow at base of heat front Reduced heat flow L < 30 mfp Bell et al (1981) Heat flow at angle to -sT Non-local mag feld deflected heat flow Epperlein et al (1988) Kingham & Bell (2002)

  8. Other ‘non-(non-local)’ effects Resistive electric field inhibition sn x sT source of magnetic field Guerin et al PPCF 41 285 (1999) Borghesi et al (1998) with collisions without collisions

  9. Electron transport model requirements • Kinetic: non-Maxwellian, anisotropic • Energy range: 100 eV – 100 keV • Density range: less than critical – more than solid • Collisional to collisionless • Magnetic field • Implicit on electron plasma frequency timescale • Unified treatment of thermal (0.1-30keV) with hot (10-1000keV) electrons

  10. Kinetic a Laser-plasma o Simulation KALOS code PPCF 48 R37 (2006) Expand velocity distn in spherical harmonics f(x,y,v,q,f,t) = S fnm(x,y,v,t) Pn|m|(cosq) eimf velocity coordinates in 3D • Any degree of anisotropy by expanding to any order • Without collisions operates as efficient Vlasov code • Collisions and B easily included • E calculated implicitly • Equations simple – efficient despite small explicit timestep

  11. collisions magnetic field advection electric field

  12. KALOS as a pure Vlasov code ExB drift & rotation 20 grid-points in magnitude of momentum Spherical harmonics up to 10th order No collisions

  13. 20 grid-points in magnitude of momentum Spherical harmonics up to 10th order No collisions ExB drift & rotation py 0 px 0

  14. ExB drift & rotation After nearly one rotation py 0 px 0

  15. KALOS as a Fokker-Planck code Reproduce Spitzer conductivity • Tests: • Collisions • Advection • Electric field Uses an approximate electron-electron collision term

  16. Comparison with Spitzer conductivity • Spitzer applies in limit of: • long scalelength • small temperature variation • steady state (long times) Epperlein & Haines Phys Fluids 29 1029 (1986) KALOS time-dependent calculation for dT proportional to sin(kx) x x x x x

  17. Simulations to test effect of varying hot electron temperature Parameters relevant to possible expts (not fusion targets)

  18. Initial conditions at start of ‘ignition pulse’ Cylindrical target n=3x1023cm-3 n=1022cm-3 density n=5x1021cm-3 100 micron T=3keV temperature T=150eV Polar drive, absorbed intensity = 8x1016 cos2q Wcm-2 Absorption at n = 1022 cm-3 Constant for 32psec Thot=100keV

  19. Electron pressure (Mbar) 800 t = 0 psec 0

  20. Electron pressure (Mbar) Pmax=640Mbar at edge of high density symmetric pressure 800 t = 32 psec coronal heating lower pressure at absorption surface central preheat (but not for fusion rR) 0

  21. Reduced intensity: initial conditions Cylindrical target n=3x1023cm-3 n=1022cm-3 density n=5x1021cm-3 100 micron T=3keV temperature T=150eV Polar drive Iabsorbed = 8x1015 cos2q Wcm-2 Absorption at critical: n = 1022 cm-3 Constant for 28psec Thot=10keV

  22. Electron pressure (Mbar) 400 t = 28 psec 0 Polar drive Iabsorbed = 8x1015 cos2q Wcm-2 Thot=10keV

  23. Electron pressure (Mbar) Pressure lower by only 50% Less symmetric 400 t = 28 psec Less energy into corona Less energy into core: Stronger shock 0 Lack of symmetry compensated for by hydro? (Ribeyre et al) Polar drive Iabsorbed = 8x1015 cos2q Wcm-2 Thot=10keV

  24. Further reduce intensity & larger scalelength Cylindrical target n=3x1023cm-3 larger scalelength density n=1022cm-3 n=5x1021cm-3 100 micron T=1keV temperature T=50eV Polar drive Iabsorbed = 1.5x1015 cos2q Wcm-2 Absorption at n = 1022 cm-3 Constant for 32psec Thot=3keV

  25. Electron pressure (Mbar) Large pressure asymmetry Max pressure occurs at critical 80 t = 32 psec 0 Much lower pressure in core Polar drive Iabsorbed = 1.5x1015 cos2q Wcm-2 Thot=3keV

  26. More details of calculation at intermediate intensity Iabsorbed = 8x1015 cos2q Wcm-2, Thot=10keV, t=28psec Magnetic field Electron density Electron pressure 0.5 to 30x1022cm-3 up to 330 Mbar -0.16 to 0.85 MG Qtheta |QSpitzer| Qradial up to 41x1015 Wcm-2 -6.7x1015 to .3x1015 Wcm-2 -2.5x1015to 4.5x1015Wcm-2

  27. Planar target Iabsorbed = 8x1015 cos2q Wcm-2, Thot=10keV, t=28psec 300mm Electron density Electron pressure 5x1021cm-3 240 Mbar 120 Mbar (T=250eV) 75mm 3x1023cm-3 Heat flow into target 3x1015 Wcm-2 5x1015 Wcm-2 Heat flow along surface Magnetic field 3x107 Vm-1 480 kG Electric field along surface

  28. Conclusions Energetic electrons are useful: Deposit energy at high density - giving high pressure Spread energy around target allowing uneven irradiation Preheat not a problem Crucial parameter: electron range compared with ablation scalelength & target radius Prospect of integrated simulation of transport expts relevant to shock ignition

More Related