PFI

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PFI

• Fast Ignition with Protons /Carbon /Heavy Ions
  Produced by UHI Lasers

• Objectives of the field
• Deliver Proton/Ions beam of matched energy
  distributionand Intensity to reach Ignition of a
  pellet compressed bymoderate primary driver
  energy
• Transport and focus beam energy into the fuel to
  the required density
• Develop a system that works under real ICF
  conditions and is technically compatible with
  requirements of a power plant

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PFI- Candidates

• Protons / Ions from TNSA (Maxwellian distr.)
• Mono-energetic Ions (target chemistry, pulse
  shape)
• Ions from BOA, RPD Mechanisms
• Ions driven by SPLA

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PFI - Status

• Objectives of the field
• Deliver Proton/Ions beam of matched energy
  distributionand Intensity to reach Ignition of a
  pellet compressed bymoderate primary driver
  energy
• Transport and focus beam energy into the fuel to
  the required density
• Develop a system that works under real ICF
  conditions and is technically compatible with
  requirements of a power plant

• TNSA
• Protons up to 60 MeV
• Sufficient to reach hot spot, dependent on laser
  intensity
• Exponential Spectrum
• Problem with source distance, might be
  beneficial with respect to change in stopping
  power
• High conversion efficiency
• 12 observed (would be 24 ), needs confirmation
• Source size, ion depletion, distance must match
• Excellent beam quality

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PFI Status

• BOA /RPD
• High energy ions expected (HI-FI possible)
• mono-energetic distribution
• needs confirmation, long source distance possible
• needs circularly polarized light and ultra thin
  foils
• number of available ions, source hydro stability
• Beam quality

• SPLA
• High particle numbers
• Hydro tolerance
• no need for a high gradient rear surface
• Low energy
• enough to reach hot spot
• Beam quality

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PFI Status

• Objectives of the field
• Deliver Proton/Ions beam of matched energy
  distributionand Intensity to reach Ignition of a
  pellet compressed bymoderate primary driver
  energy
• Transport and focus beam energy into the fuel to
  the required density
• Develop a system that works under real ICF
  conditions and is technically compatible with
  requirements of a power plant

Source to fuel distance critical (dispersion,
focus ability, source size) TNSA has
demonstrated 50 µm (15 required) Beam qualilty
allows for smaller spots (space charge) Electron
sheath shape crucial Lower divergence for Carbon/
HI Ion stopping in ICF plasmas is not known to
required detail Ion transport in transport region
might cause instabilities
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PFI Status

• Objectives of the field
• Deliver Proton/Ions beam of matched energy
  distributionand Intensity to reach Ignition of a
  pellet compressed bymoderate primary driver
  energy
• Transport and focus beam energy into the fuel to
  the required density
• Develop a system that works under real ICF
  conditions and is technically compatible with
  requirements of a power plant

Cone guided PFI might be beneficial Relaxed laser
focusing/ pointing requirements cone can act as
heat shield in direct drive reactor
scenarios cone can protect ion source (hydro
tolerance to drive pulse)
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Proton fast ignition - target stability
Shield to protect ion source
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Recent and short term experiments

• BOA at LANL
• Focusing experiments at SNL
• large focal spot ion acceleration at RAL
• conversion efficiency of 8 at RAL
• cone targets at LANL
• Experiments on SPLA at LULI

Ion acceleration with 10 ps lasers overlap of
multiple beams focusing including sheath
compensation improvement of conversion efficiency
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1 D curved foil
Z-100 TW 40J, lt1ps, gt1019 W/cm2
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Flat-top Cone Target Enhances Proton Beam Energy
and Efficiency
Flat-foil (slab)
15 mm x 2mm x 15 µm
LA-UR-08-3173
K. A. Flippo, E. d'Humières, S. A. Gaillard, J.
Rassuchine, et al. Phys. Plasmas 15, 056709
(2008)
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The laser-ion beam conversion efficiency is
determined by the rates of loss mechanisms versus
ion acceleration.
Ion Generation

• Efficiency enhanced by minimizing the target
  thickness
• Thickness limited by breakout of shock from laser
  prepulse
• Data from Key et al. (shown), Fuchs et al., IFSA
  2005
• Efficiency enhanced
  by
  increasing mass ratio of
  matrix
  / accelerated ions
  (minimize
  loss to matrix ions)
• Efficiency enhanced
  by
  minimizing collisional
  losses
• Work is needed to
  understand design
  tradeoffs.

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Theory

• Recent theoretical insights
• Two beam, shaped ignition at only 6-7 kJ
  compatible with HIPER (Temporal, Atzeni,
  Honrubia, POP 2008)
• BOA, RPD mechanism predicted
• Improved simulation capabilities lead to better
  understanding of the acceleration mechanism
• Code predictions to be experimentally tested

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Simulations Show Geometry and Plasma Conditions
Affect the Sheath formation and Proton Energy but
Electron Temperature Remains About the Same
1-µm scale-lengthpreplasma (shown)
Bottom Line Best Case78 absorption26 MeV
2nc preplasma
Bottom Line Absorption up butproton energydown
to 18 MeV
Simulations by Emmanuel d'Humières, UNR currently
at CHPT Ecole Polytechnique
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Expansion modeling and PIC-simulations 2/2

• Construct transfer function, that maps positions
  of proton to their respective momenta
• Solve equations of motion of proton flow
• Charged Particle Transfer (CPT) Code by H. Ruhl,
  M. Schollmeier
• Trident shot 18500
• top left experiment RCF
• CPT fitted to experiment
• - top right RCF image
• - bottom left envelope
• - bottom right transverse emittance

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The laser-breakout afterburner a path to high
efficiency high energy ion beam.
C-based

• Requirements
• Ultra-high laser contrast, 1021 W/cm2
• Ultra-thin targets (e.g., 30 nm C)
• 1D 2D Simulations using VPIC code
• Start with solid density C, including
  
  cases with H contaminants
• Mechanism
• Laser penetration across target
• Electron heating
• Electron energy ? ion energy via kinetic Buneman
  instability.
• Initial Results
• 35 (1D, 15 in 2D) of all ions accelerated to
  0.3 GeV ? 7, 4 conversion efficiency.
• C-ion acceleration is immune to surface proton
  contamination!

This concept is the new focus of LANL research in
ion-beam generation
Simulations by Brian Albright X-1-PTA LANL
Yin et al., Laser and Part. Beams 24, P. 291
(2006) Phys. Plasmas 14, 056706 (2007)
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3D VPIC simulation of the RPA mechanism has
beenperformed to examine higher-dimensional
effects

• Our largest simulation to date on ion
  acceleration (run on Roadrunner base system)
• Physical domain 25x25x20 µm w/ solid target
  density 14x109 cells, 21 x 109 particles,
• 4096 processors
• Contrasting with sim. size at the time of the
  proposal
• 0.5x109 cells, 2.2x109 particles, 510 processors
• 3D visualization using EnSight server-of-servers
  mode enables viewing, analysis of very large
  (multiple-TB) data sets.

Circular polarization, 30nm C and I01021 W/cm2
312 fs pulse
Simulations by Lin Yin X-1-PTA LANL
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LASNEX Simulation Shows Two Carbon Beams (480
MeV) with 7.2 kJ Yields a Gain of 6.5
35.5 kJ absorbed laser energy, peak fuel density
is ?DT 150 g/cc.
14.2 ns pulse (foot P t3.5 pulse) that peaks
at 270 eV,
Simulations by Brian Albright X-1-PTA LANL
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Questions

• 10 ps ion acceleration and instabilities of the
  laser in preplasma
• overlap of multiple beams
• source stability, ion depletion
• conversion efficiency
• higher Z ions (still Maxwellian)
• stopping in degenerate plasma

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Proton Fast ignition - target stability (1)
Target under consideration
1-D 3-T code DEIRA
High yield target 4.4 mg fuel mass, yield 500 MJ
2.7 mm
Be
2.5 mm
DT ice
2.25 mm
Driving X-ray pulse
DT gas
t1 2.0 ns, T1 90 eV t2 24.0 ns, T2
95 eV t3 26.0 ns, T3 110 eV t4 32.0
ns, T4 110 eV t5 34.5 ns, T5 130
eV t6 39.0 ns, T6 145 eV t7 44.0 ns,
T7 240 eV t8 46.0 ns, T8 240 eV
Tx
Driving pulse for optimum compression without
ignition
Absorbed X-ray energy Ecaps ? 1 MJ Implosion
velocity vim 2.40?107 cm/s Maximum
compression ??r?m 3.53 g/cm2 at tm
47.76 ns, RDT 0.180 mm,
rDT 180 260 g/cm3,
TDT 0.80 0.38 keV
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Proton fast ignition - target stability (2)
Problems 1) Proton production target rear
surface has to remain cold 2) A vacuum gap
for acceleration is required 3) distance
between proton target and capsule should be small
Proton target is closely attached to the target
or hohlraum therefore subject to the soft-x-rays
driving the capsule
A shield is required to protect the production
target
Requirements for the shield as thin as
possible to avoid energy loss/straggling
thick enough to protect the target
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Proton fast ignition - target stability (3)
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Proton fast ignition - target stability (4)
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Proton fast ignition - target stability (5)
Conclusion a 50 µm shield is displaced by 280
µm at the time of ignition (maximum
compression) the shield is heated up to 2-3 eV
at the time of ignition temperature of the
production target closely coupled to the shield
(a problem ? Evaporation of proton layers) a
second (thin) shield could further reduce the
thermal load on the target
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