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PIC Simulation of Fast Ignition Targets with OSIRIS

PIC Simulation of Fast Ignition Targets with OSIRIS. J. Tonge, M. Tzoufras, J. Fahlen, B. J. Winjum, F. S. Tsung, W. B. Mori, UCLA C. Ren, Rochester M. Marti, R. Fonseca, L. O. Silva, IST. How much laser energy can we get into the Core?.

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PIC Simulation of Fast Ignition Targets with OSIRIS

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  1. PIC Simulation of Fast Ignition Targets with OSIRIS J. Tonge, M. Tzoufras, J. Fahlen, B. J. Winjum, F. S. Tsung, W. B. Mori, UCLA C. Ren, Rochester M. Marti, R. Fonseca, L. O. Silva, IST

  2. How much laser energy can we get into the Core? • What are the characteristics, energy spectrum and spread, of the fast electrons generated by the laser plasma interaction? • How are fast electrons be transported through plasma to the Core? • How do the fast electrons interact with the Core? • How do these effect each other?

  3. Code Development and Scientific Discovery in Parallel • Scientific Discovery is incremental • New code developments yields new scientific results • New scientific results guide code development priorities

  4. Overview • Recent Code Improvements • Simulation Results • Absorbing core • Target density profile • Future Code improvements

  5. Simulation Technology • Load balancing: • Static real 4x speed up of simulations vs no load balancing. • Reduced numeric heating: • Quadratic spline current deposition and field interpolation scheme + current smoothing. • Core: • Add particle drag to core. This adds current termination at core. Not an attempt at first principles implementation.

  6. Improved Energy Conservation Allows lower temperature and higher density Dx/lD=10.6 (100 nc 1.3 kev) Quadratic Spline + 3 pass Smoother Dx/lD=6.7 (40nc 1.3 kev) Quadratic Spline + 4,1 pass Smoother Dx/lD=2.8 (40 nc 7.6 kev) Quadratic Spline + 4,1 pass Smoother Dx/lD=2.8 (40nc 7.6 kev) Area Weighting + 4,1 pass Smoother

  7. Resistive Core Target • Target radius 51 mm diameter • Linear slope to max density (100 nc) at 16 mm • Resistive Core • 6.4mm diameter • Drag ( g-1) on electrons within core. • No drag on particles with Energy less than ~12Te or greater than 10MeV. 100nc 16m 3m 25.5m laser 100m

  8. Compressed Target Data Courtesy R. Betti, Rochester

  9. PIC Simulation Target and Setup • Isolated target with vacuum region between target and boundary • Resistive Core. • Peak Target Density(nt) = 100nc • 1256012560 grids • xmax=0.5 c/p • quadratic spline & current smoothing • 2.6 108 particles and 7.4104 steps • 71 hours on 128 cpu’s (on Dawson) • Initial Te= 1.3 keV, Ti=1 keV • 1m Laser • I=1020-21 w/cm2 • spot size (FWHM) 7.5 m (scaled) • 1 ps long, p-polarized.

  10. Density: Standard Targetwith Resistive Core

  11. Magnetic Field Laser and current filamention component

  12. Net Electron Power Into Core

  13. Core Heating • 1 kJ Laser • 4% efficiency • 40 Joules into core with 3.2 mm radius • Core Density ~ 1026 cm-3 • Would heat core to 12 kev

  14. Average Electron Energy (g)

  15. Shallow Density Gradient Target • Vacuum region between target and boundary • Target core Density(nt) = 100nc • Surrounding plasma with linear density gradient • 1203212032 grids • (x=0.5 c/p ) • quadratic spline & current smoothing • 2.4 108 particles and 6104 steps • Initial Te=1.3 keV, Ti=1 keV • 1-laser, • I=1020-21 w/cm2 • spot size (FWHM) 7.5  • 1 ps long, p-polarized

  16. Density:Shallow Gradient Target

  17. Interaction Region 397 fsLaser and current filamention B field n = 100 nc Te = 1.3 keV Shallow gradient target 4.5 nc/m n = 100 nc Te = 1.3 keV Steep gradient target 10.5 nc/m

  18. Interaction Region 397 fsLaser and current filamention B field n = 100 nc Te = 1.3 keV n = 40 nc Te = 7.4 keV n = 40 nc Te = 1.3 keV n= 40 nc targets have 4.2 nc/m density gradient n= 100 nc target has 10.5 nc/m density gradient

  19. Simulation Technology • Load balancing: • dynamic - may provide additional 1.5x to 2x speed improvement. • Boundary conditions: • Better isolation of boundaries using perfectly matched (PML) boundary conditions (Vay). • Core: • Add position dependent 2-particle collisions. (Takizuka, Nanbu)

  20. Absorbing (PML) Boundaries

  21. Collisions (IST) Collision of same species • Sort particle buffer by collision cells • Calculate particle statistics for each collision cell • Pair the particles randomly • For each pair: • calculate the number of collisions within the current collision cycle • calculate a sample of the deflection angle • deflect the momentum of the collision partners according to this deflection angle. This corresponds to a rotation of the respective momentum in the center of mass reference frame of the pair Even number Odd number Pic Cell Collision Cell Same number Different number Collision of different species

  22. Summary • Improved current deposition scheme, core and load balancing. • Simulations show a few percent of Laser power is deposited in core. • Filament size and length changes in Laser particle interaction region due to change in target profile. • New simulation technology: Improved Boundary conditions, Load balancing, Collisional core.

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