Laser Fusion Energy

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Title page
Laser Fusion Energy John Sethian Naval
Research Laboratory plus the over 60 members in
the High Average Power Laser Program June 11,
2004
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We are developing the science technology for a
practical fusion energy source based on Lasers,
Direct Drive Targets, and Solid Wall chambers
Modular lowers cost of development AND
improvements Separable parts Laser and target
factory separate from reaction chamber Inherent
engineering attributes spherical targets,
passive chamber Made substantial technical
advances since program started lt 5 years ago
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GUIDING PRINCIPLE
The fastest, most cost effective, least
risky approach to develop fusion
energy Develop the key science and
technologies together, using the end goal of a
practical power source as a guide
YB
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The High Average Power Laser (HAPL) ProgramAn
integrated program to develop the science and
technology forLaser Fusion Energy

• Government Labs
• NRL
• LLNL
• SNL
• LANL
• ORNL
• PPPL
• Universities
• UCSD
• Wisconsin
• Georgia Tech
• UCLA
• U Rochester, LLE
• PPPL
• UC Santa Barbara
• UNC
• DELFT
• Industry
• General Atomics

6 Government labs, 9 Universities, 14 Industries
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The Path to develop Laser Fusion Energy

• Basic Science and Technology
• Krypton fluoride laser
• Diode pumped solid state laser
• Target fabrication injection
• Final optics
• Chambers materials/design

• Target Design Physics
• 2D/3D simulations
• 1-30 kJ laser-target expts

Phase I 1999- 2005

• Develop Full Scale Components
• Power plant laser beam line
• Target fab/injection facility
• Materials evaluations
• Power Plant design

• Ignition Physics Validation
• MJ target implosions
• Calibrated 3D simulations

Phase II 2006 - 2014
Engineering Test Facility ? Full size laser 2-3
MJ, 60 laser lines ? Optimize targets for high
yield ? Optimize chamber materials and
components. ? ? 300-700 MW net electricity

Phase III Engineering Test Facility operating ?
2020
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TARGET DESIGNS

• We need gains gt100 for IFE because of modest
  7-10 laser efficiency
• We need robust designs that are resistant to the
  effects of target and laser imperfections
• We need target designs that can meet the needs
  for IFE
• Target fabrication,
• Target injection
• Emission spectra (what hits the wall)
• Cost,
• Safety (waste disposal)
• Recent advances in designs have greatly increased
  our confidence that the above can be achieved.

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Current high gain target designs use a DT Foam
Ablator
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Current target designs have gains ? 160 (2-D).
Include prepulse spike for adiabat control /
imprint reduction"Zoom" laser to maximize
absorption
NRL FAST Code High resolution 2D calculations,
account for both laser and target non-uniformity
2.5 MJ laser Gain 160
Zoom points
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NRL FAST codes have been benchmarked with
experiments
FAST simulation
Mass variation (mg/cm3)
Time (ns)
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The design has sufficient flexibility to optimize
the target physics along with the IFE
requirements
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The HAPL Program is developing two types of Lasers
DPSSL (Mercury-LLNL)
KrF Laser (Electra-NRL)

• Both lasers have potential for meeting IFE
  requirements
• Needed technologies are being developed and
  demonstrated on large (but subscale) systems.
• Technologies developed must scale to MJ systems
  (cost, durability, efficiency)

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Key Components of an electron-beam pumped KrF
Laser(? 248 nm)
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Demonstrated High Transmission Hibachi by
eliminating anode and patterning the electron beam
AFTER
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Electra has produced ? 680 J/shot in100 shot, 1
Hz bursts
5 Hz run, foil broke
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Electra has run at 5 Hz for 1895 shots continuous
with no change in output(run limited by
foil/cathode)
Laser Output (a.u.) ? 80 J/pulse
Single sided (one e-beam) pumping No patterning
of e-beam
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Phase I goals are in sight with Electra--the
main outstanding issue is foil durability

• Demonstrated 1.2 beam non-uniformity (not yet
  rep-rated)
• Demonstrated rep rate laser 400 - 700 J/pulse _at_
  1 Hz and 5 Hz
• Laser results predict KrF intrinsic efficiency gt
  12
• Developed high transmission hibachi (gt 80 e-beam
  into gas)
• Demonstrated solid state switch, will be basis
  for durable, efficient (85), cost effective
  pulsed power system
• Based on above, predict gt 7 wall plug efficiency
  for IFE systems
• What's Left HIBACHI FOIL LIFETIME
• Deflecting laser gas smoothing e-beam looks
  promising

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Key Components of a DPPSL Laser
Goals (both amplifiers) 100 J at 1w 10 Hz
10 efficiency _at_ 1053 nm 3 ns 5x
diffraction-limited
2 gas-cooled amplifier heads
Crystals
Output
Lens Duct
Diode (pump) arrays
Front-end
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The LLNL program has accomplished four major
steps towards developing the DPPSL laser for IFE
Amp Head
Laser Beam
Pump
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With a single amplifier, Mercury has produced up
to 34 J single shot, and 114 W average power at
5 Hz..
Average Power
Energetics
Model
Data
What's left Efficiency (351 nm) Cost Beam
quality Durability
Second amplifier being activated to allow 100 J
operation
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Final Optic ProgressGrazing Incidence Aluminum
Mirror meets IFE requirements for reflectivity
(gt99 _at_ 85?) damage threshold ( 5 J/cm2)
Concept
Results
100,000 shots at 5 J/cm2 No discernable change
to the surface Surface finally showed change at
11 J/cm2 _at_ 78,500 shots, may be due to initial
surface imperfections
What's left Large scale testing Evaluate
resistance to x-rays Fabrication
Mark Tillack UCSD
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Target Fabrication Progress ? Foam shells by
batch production ? Cryo layers grown over foam
are ultra smooth ? Chemical plant analysis gtgt
direct drive targets lt 0.16 ea
Produced very smooth (? 0.6 ?m RMS) DT ice layers
over foam
Batch produced foam shells
Targets 0.16 each from chemical process plant
methodology
Cumulative RMS S L-mode (256-n), T 19 ?K
X-Ray picture of mass produced foam shell 4 mm
dia, 400 ? wall
D. Goodin et al General Atomics
J. Hoffer D. Geller LANL
What's left Overcoating
What's left Target that meets all specs
Mass Production
D. Schroen J. Streit Schafer Corp
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Target Injector / Tracking Progress? Light gas
gun injector in rep-rate operation? Achieved
required 400 m/sec? Demonstrated separable
sabot? Target placement accuracy /-10 mm (need
?5 x better)
Target Injection and Tracking system
R..Petzoldt, B. Vermillion, D. Goodin et
al General Atomics
Whats left Better placement
Target Tracking
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We have established a "chamber operating" window
that simultaneously meets the requirements for
efficiency, wall survival (gt 1000's shots), and
target injection
First wall is tungsten armor bonded to low
activation steel
154 MJ target No gas 6.5 m radius
Tungsten stays below melting point (3410 ?C)

Temperature (?C)

• Whats left Long Term Wall Survival
• Thermomechanical Fatigue
• Helium retention
• Bonding W to Steel base

UCSD Wisconsin LLNL
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Thermo-mechanical fatigueUse an array of
facilities to expose FW materialsto expected
target emissions
BIG ISSUE...DOES OBSERVED ROUGHENING LEAD TO MASS
LOSS?
X-rays XAPPER Latkowski (LLNL) Z
confirmation Tanaka (SNL) Ions RHEPP
Renk (SNL) Laser Dragonfire
Najmabadi (UCSD)
Experiments Spectra Surface temperature TEM
sub-surface cracks Modeling Predict Surface
temperature Sub surface cracks Stress
modeling to get evolution of fatigue
Blanchard (Wisc)
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Helium Retention Experiments show may be not be
a problem at IFE Conditions
Proton spectra for single crystal tungsten
implanted at 850?C and flash annealed to 2000?C
(or 2500 ?C) in 1, 10, and 1000 cycles to reach
a total dose of 1019 He/m2.
Whats left Prototypical anneal cycle
Snead (ORNL) UNC
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Bond strength we are using the Oak Ridge IR
processing facility to study the long term
integrity of the Tungsten-Steel bond
Romanoski (ORNL)
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We are developing advanced, micro- engineered
tungsten in case we have a problem
The concept small feature size Features less
than He migration distance (? 20-50 nm )
Small size allows tungsten to "breathe" under
cyclic thermal stress The Issues Does it
work? Thermal conductivity High integrity
bond/structure The approaches Tungsten foam on
ODS Sharafat (UCLA) Williams (Ultramet,
Inc) Vacuum Plasma Sprayed Tungsten O'Dell
(Plasma Processing, Inc) Raffray (UCSD)
Ultramet foam
UCLA modeling
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The Path to develop Laser Fusion Energy

• Basic Science and Technology
• Krypton fluoride laser
• Diode pumped solid state laser
• Target fabrication injection
• Final optics
• Chambers materials/design

• Target Design Physics
• 2D/3D simulations
• 1-30 kJ laser-target expts

Phase I 1999- 2005

• Develop Full Scale Components
• Power plant laser beam line
• Target fab/injection facility
• Materials evaluations
• Power Plant design

• Ignition Physics Validation
• MJ target implosions
• Calibrated 3D simulations

Phase II 2006 - 2014
Engineering Test Facility ? Full size laser 2-3
MJ, 60 laser lines ? Optimize targets for high
yield ? Optimize chamber materials and
components. ? ? 300-700 MW net electricity

Phase III Engineering Test Facility operating ?
2020
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The Engineering Test Facility (ETF) will have
four goals, including upgrade to generate net
electricity
1. Demo Laser full size performance 2.5 -
3 MJ _at_ 5 Hz
2. Optimize target performance
4. Produce Electricity Upgrade materials/optics
based on RD Chamber Cooling (200-2000
MWth) 300-700 MW net electricity to grid
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Our goal is to develop an attractive energy
source based on Laser Fusion Energy
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BACK-UPS
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Critical Issues that must be addressed to go to
Phase II
Target Design Verify a robust family of target
designs, using 2D and 3D modeling Benchmark with
experiments on Nike and Omega Lasers
(KrF) Durability of hibachi foil and amplifier
windows, efficiency in "real" system Lasers
(DPPSL) Cost of diodes, large crystals,
efficiency in "real" system, beam
smoothing? Chambers Long Term materials He
retention and thermo-mechanical fatigue Blanket
and underlying neutron resistant structure Final
Optics Bonding to substrate (ok if Al, needs
demo if SiC) Resistant to target emissions
(neutrons, x-rays, ions) Target
Fabrication Mass produced shells that meet all
IFE specs Mass cryo-layering technique Target
Injection Placement accuracy and
tracking Target survival in integrated scenario
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Advantages of KrF for laser fusion energy

• Short laser wavelength (248 nm) suppresses
  laser-plasma instability and increases
  hydrodynamic efficiency.
• Superb beam uniformity to minimize imprint of
  laser (lt 1.2 non-uniformity)
• Laser can be programmed to follow an imploding
  pellet (zooming)
• Scales to very large energies gt50 kJ amplifiers
• Gas media facilities needed repetition rates, and
  there is no durability issue (as there is with
  solid state laser media)
• Sufficient intrinsic efficiency 12-14 to allow
  6-7 wall-plug efficiency needed for IFE.

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Advanced Laser Gated and Pumped Thyristor should
lead to an efficient (gt 85), durable (gt 109),
economical system

• CONCEPT
• Flood entire switch with photons
• ultra fast switching times (lt 100 nsec)
• Continuous laser pumping reduces losses
• PROGRESS
• Demo prototype at required voltage (16 kV),
  rep-rate (5 Hz) and dI/dt (14 A/nsec/cm2)
• gt 1,000,000 shots

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Electra ? 10 intrinsic efficiency as an
oscillator...expect gt 12 as an amplifier
70
7
60
6
50
5
40
4
PE-beam (GW)
PLaser (GW)
Efficiency (9.8) PLaser (5.54 GW)/ PE-Beam
(56.4 GW)
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3
20
2
10
1
0
0
0
50
100
150
200
time (ns)
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Based on our research, an IFE-sized KrF system is
projected to have a wall plug efficiency of gt 7
Pulsed Power Advanced Switch 85 Hibachi
Structure No Anode, Pattern Beam 80 KrF Based
on Electra exp'ts 12 Optics Estimate 95 Ancill
aries Pumps, recirculator 95 Total 7.4
gt 6 is adequate for gains gt 100... ...and
latest designs have 2D gains 160
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Straightforward with KrF to "Zoom" laser beams.
This can boost laser absorption substantially
(30)
Decrease the laser focal spot to follow the
compressing target
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Recirculator to cool and quiet laser gas plus
cool hibachi foil is under evaluation
Blower
Heat Exchanger
Laser Cell
Static Pressure Contours varies by 14 Pa (10-4)
over laser cell
Homogenizers Turning Vanes
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The recirculating laser gas can be used to cool
the Hibachi
Gas Velocity
Rib
Rib
gas flow
Louvers
Modeling A.Banka J.Mansfield, Airflow
Sciences, Inc
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The louvers significantly lower the foil
temperature (1 Hz)
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At 5 Hz operation, the pressure foil reaches
400C with "monolithic cathode" Expect 20 higher
w/ strip cathode
150 Shots at 5 Hz