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