Systems Analysis for Modular versus Multibeam HIF Drivers

1
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
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.
The Heavy Ion Fusion Virtual National Laboratory
2
Outline

• Introduction / Motivation for modular drivers
• RD 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

3
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

4
Solid state lasers have taken advantage of
modular development
Beamlet
NIF
The Beamlet laser was a single-beam, scientific
prototype of the 192-beam National Ignition
Facility (NIF).
5
We are considering a range of options for modular
HI drivers

• 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

6
Key developments required for this approach

• Large aperture source/injectors (30 cm radius)
• Double pulsing
• Neutralized drift compression to pulse duration
  required by target (10s 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)

7
Hybrid target allows larger spot size beams 5
mm radius
Hohlraum
Shine shield
Beams
Capsule
8
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 Neon1 (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

9
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 ms
• Pre-accel bunch compression 8x ? 2.5 ms
• Beam current into accelerator 280 A
• Pulse length 7.2 m constant
• Line charge density 97 mC/m
• Final pulse duration 0.17 ms
• Beam current at exit of accelerator 4.1 kA

10
Magnetic pulse compression, especially at higher
ion energy is cost effective
at 100 MeV
100 MeV
150 MeV
Total
Cost, /m
Cost, /m
Cost, /m
50 MeV
Magnetic comp
Switching
Pulse compression factor
Pulse compression factor
Pulse compression factor
11
Magnet bore is held constant occupancy decreases
due to increasing gap with higher accel gradient
Solenoid spacing
Occupancy fraction
Meters
Winding radius
Pipe radius
Beam radius
Ion energy, MeV
12
Optimal initial pulse duration is 20 ms
Ed 6.7 MJ 24 modules
Total
Total cost, B
Accelerator
Injector
Initial pulse duration, ms
13
A small number of modules would be best, but
target requires 24 for drive symmetry and pulse
shaping
Ed 6.7 MJ Ne (A 20) Tf 200 MeV
14
Driver cost increases with increasing ion mass
-A 20 (Neon) is our base case
Ed 6.7 MJ 24 Modules Tf 10?A MeV
15
A transition to quad focusing at 120 MeV has a
slight benefit for single beam modules
Total
Solenoids
Total cost, B
Injector
Quads
Ion energy for transition to quads, MeV
16
If beams could be split at transition, quads
become attractive at lower ion energy
4 beams per module in quad section
Total
Solenoids
Total cost, B
Injector
Quads
Ion energy for transition to quads, MeV
17
Neutralized drift compression and relaxed
focusing requirements also benefit multi-beam,
quad-focus drivers
1 accelerator Ne1 Tf 200 MeV 3.2
MJ/pulse Double pulsing (6.4 MJ total)
Total
Total cost, B
Front end (Injector ESQ)
Number of beams
Electrostatic quads up to 6 MeV Magnetic quads
for remainder
18
Neutralized drift compression/focusing hybrid
targets may reduce costs by 50 for both
conventional multiple-beam quadrupole and modular
solenoid driver options for IFE
Multiple-beam quad linac driver
Modular solenoid linac driver
3000
?Robust Point Design
2500
19
Findings are promising for modular drivers

• Modular drivers are a potentially attractive
  option with
• Low mass ions (lt 40 amu)
• 10s of modules (not 100s)
• 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

20
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