Systems Analysis for Modular versus Multi-beam HIF Drivers*
Wayne Meier – LLNL
Grant Logan – LBNL
15th International Symposium on
Heavy Ion Inertial Fusion
June 7-11, 2004
Princeton, NJ
The Heavy Ion Fusion Virtual National Laboratory
* This work performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore and Lawrence Berkeley National Laboratories under contracts No. W-7405-Eng-48 and DE-AC03-76SF00098.
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Outline
• Introduction / Motivation for modular drivers• R&D advances needed• Design trades for all-solenoid modules
– Number of modules– Ion mass
• Solenoid/quadrupole hybrid options– Optimal transition energy
• Potential improvements for multi-beam, quad-focus accelerator
• Future work
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Modular drivers have potential advantages but also present some new challenges
• Primary motivation is to address development cost issue with conventional multi-beam linacs
• Modularity is proven approach for lasers• Disadvantage for HI accelerator is need for
induction cores for each beam– Circumvented by reducing number of beams,
using lower mass ions (higher current per beam), and double pulsing each module on each shot
• Solenoid magnets are best for large currents, especially at low ion energy
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Solid state lasers have taken advantage of modular development
The Beamlet laser was a single-beam, scientific prototype of the 192-beam National Ignition Facility (NIF).
Beamlet NIF
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• Single-beam solenoid accelerator, tens of accelerators for driver
• Hybrids: Solenoids at front end feeding single-beam quad section, tens of accelerators
• Solenoids feeding multi-beam quad section, tens of accelerators
• All quads (multi-beam), tens of accelerators
• A systems code is being developed for consistent comparisons
We are considering a range of options for modular HI drivers
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Key developments required for this approach
• Large aperture source/injectors (~30 cm radius)• Double pulsing• Neutralized drift compression to pulse duration
required by target (10’s of ns)• Larger spot size target (~5 mm radius)• Plasma channel (assisted pinch) or compensated
neutralized ballistic focusing (See talks by Simon Yu and Ed Lee)
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Hybrid target allows larger spot size beams ~ 5 mm radius
Beams
Capsule
Hohlraum
Shineshield
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Example design point parameters illustrate the features of the modular design
• Total driver energy = 6.7 MJ• Number of modules = 24 (12 per side)• Double pulsing (48 total beam pulses)• Energy per pulse = 140 kJ• Ion = Neon+1 (A = 20)• Final ion energy = 200 MeV• Core radial build = 0.62 m• Acceleration gradient = 0.28 – 2.4 MV/m• Accelerator length = 125 m• Accelerator efficiency = 33%
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Example beam parameters for this case
• Initial/final ion energy = 0.9 MeV / 200 MeV• Charge per pulse = 0.70 mC• Initial pulse duration = 20 s• Pre-accel bunch compression = 8x 2.5 s• Beam current into accelerator = 280 A• Pulse length = 7.2 m = constant• Line charge density = 97 C/m• Final pulse duration = 0.17 s• Beam current at exit of accelerator = 4.1 kA
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Magnetic pulse compression, especially at higher ion energy is cost effective
Pulse compression factor
Cos
t, $
/mC
ost,
$/m
Cos
t, $
/m
Pulse compression factor Pulse compression factor
Magnetic comp50 MeV
100 MeV 150 MeV
Switching
Total
at 100 MeV
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Magnet bore is held constant; occupancy decreases due to increasing gap with higher accel gradient
Ion energy, MeV
Beam radius
Pipe radiusWinding radius
Occupancy fraction
Solenoid spacing
Meters
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Optimal initial pulse duration is ~ 20 s
Ed = 6.7 MJ24 modules
Injector
Accelerator
Total
Tot
al c
ost,
$B
Initial pulse duration, s
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A small number of modules would be best, but target requires ~24 for drive symmetry and pulse shaping
0
0.5
1
1.5
2
2.5
3
0 20 40 60 80
Number of modules
To
tal
cost
, $B
Ed = 6.7 MJNe+ (A = 20)Tf = 200 MeV
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Driver cost increases with increasing ion mass -A = 20 (Neon) is our base case
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
0 20 40 60 80 100
Ion mass, amu
To
tal c
ost
, $B
Ed = 6.7 MJ24 ModulesTf = 10A MeV
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A transition to quad focusing at ~120 MeV has a slight benefit for single beam modules
Ion energy for transition to quads, MeV
Tot
al c
ost,
$B
Injector
Solenoids
Quads
Total
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If beams could be split at transition, quads become attractive at lower ion energy
Ion energy for transition to quads, MeV
Tot
al c
ost,
$B
Injector
Solenoids
Quads
Total4 beams per module in quad section
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Neutralized drift compression and relaxed focusing requirements also benefit multi-beam, quad-focus drivers
Cdriver T1o T2o Tmpo Nbgi 0o ao Eo Ao Bwo Bdco Lfo o
50 100 150 200 2500
500
1000
1500
2000
Number of beams
1 acceleratorNe+1
Tf = 200 MeV
3.2 MJ/pulseDouble pulsing (6.4 MJ total)
Total
Front end (Injector + ESQ)
Electrostatic quads up to ~ 6 MeV
Magnetic quads for remainder
Totalcost, $B
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Neutralized drift compression/focusing + hybrid targets may reduce costs by ~50 % for both conventional multiple-beam quadrupole and modular solenoid driver options for IFE
2500
3000
“Robust Point Design”
Multiple-beam quad linac driver Modular solenoid linac driver
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Findings are promising for modular drivers
• Modular drivers are a potentially attractive option with:
– Low mass ions (< 40 amu)
– 10’s of modules (not 100’s)
– Neutralized drift compression
– Relaxed target spot size requirements
• All-solenoid modules or solenoid-to-quad hybrid modules are comparable in cost
• If feasible, beam splitting at transition to quads would be beneficial
• Neutralized drift compression and larger spot size targets also benefit standard multi-beam, quad-focus linacs
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More systems modeling work is needed
• Improve injector model – dominates in some cases• Beam focusing models (including pulse shaping)
are needed for new schemes• Determine target gain scaling with beam spot size• Compare high-current modular drivers using large
spot size targets to low-current multi-beam linacs using smaller spot size targets
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