# Presentation: 381951

## 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.

## 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

## 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

## 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**

## 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

**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**

## 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*)

## Hybrid target allows larger spot size beams ~ 5 mm radius

**Beams**

**Capsule**

**Hohlraum**

**Shine**
**shield**

## 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%

## 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

## Magnetic pulse compression, especially at higher ion energy is cost effective

**Magnetic pulse compression, especially at higher ion energy is cost effective**

**Pulse compression factor**

**Cost, $/m**

**Cost, $/m**

**Cost, $/m**

**Pulse compression factor**

**Pulse compression factor**

**Magnetic comp**

**50 MeV**

**100 MeV**

**150 MeV**

**Switching**

**Total**

**at 100 MeV**

## Magnet bore is held constant; occupancy decreases due to increasing gap with higher accel gradient

**Magnet bore is held constant; occupancy decreases due to increasing gap with higher accel gradient**

**Ion energy, MeV**

- Beam radius

- Pipe radius

- Winding radius

- Occupancy fraction

- Solenoid spacing

-  **Meters**

## Optimal initial pulse duration is ~ 20 s

**Optimal initial pulse duration is ~ 20 ********s**

- Ed = 6.7 MJ
- 24 modules

**Injector**

**Accelerator**

**Total**

**Total**** cost, $B**

**Initial pulse duration, ********s  **

## 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

## Driver cost increases with increasing ion mass -A = 20 (Neon) is our base case

- Ed = 6.7 MJ
- 24 Modules
- Tf = 10A MeV

## A transition to quad focusing at ~120 MeV has a slight benefit for single beam modules

**A transition to quad focusing at ~120 MeV has a slight benefit for single beam modules**

**Ion energy for transition to quads, MeV**

**Total cost, $B**

**Injector**

**Solenoids**

**Quads**

**Total**

## If beams could be split at transition, quads become attractive at lower ion energy

**If beams could be split at transition, quads become attractive at lower ion energy**

**Ion energy for transition to quads, MeV**

**Total cost, $B**

**Injector**

**Solenoids**

**Quads**

**Total**

**4 beams per module in quad section**

## Neutralized drift compression and relaxed focusing requirements also benefit multi-beam, quad-focus drivers

**Number of beams**

- 1 accelerator
- Ne+1
- Tf = 200 MeV
- 3.2 MJ/pulse
- Double pulsing
- (6.4 MJ total)

- Total

- Front end
- (Injector + ESQ)

- Electrostatic quads up to ~ 6 MeV
- Magnetic quads for remainder

**Total**
**cost, $B**

## 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**

## 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

## 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