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.

The Heavy Ion Fusion Virtual National Laboratory 2 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

The Heavy Ion Fusion Virtual National Laboratory 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

The Heavy Ion Fusion Virtual National Laboratory 4 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

The Heavy Ion Fusion Virtual National Laboratory 5 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

The Heavy Ion Fusion Virtual National Laboratory 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 (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)

The Heavy Ion Fusion Virtual National Laboratory 7 Hybrid target allows larger spot size beams ~ 5 mm radius Beams Capsule Hohlraum Shine shield

The Heavy Ion Fusion Virtual National Laboratory 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 = 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%

The Heavy Ion Fusion Virtual National Laboratory 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  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

The Heavy Ion Fusion Virtual National Laboratory 10 Magnetic pulse compression, especially at higher ion energy is cost effective Pulse compression factor Cost, $/m Pulse compression factor Magnetic comp 50 MeV 100 MeV150 MeV Switching Total at 100 MeV

The Heavy Ion Fusion Virtual National Laboratory 11 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

The Heavy Ion Fusion Virtual National Laboratory 12 Optimal initial pulse duration is ~ 20  s E d = 6.7 MJ 24 modules Injector Accelerator Total Total cost, $B Initial pulse duration,  s

The Heavy Ion Fusion Virtual National Laboratory 13 A small number of modules would be best, but target requires ~24 for drive symmetry and pulse shaping E d = 6.7 MJ Ne + (A = 20) T f = 200 MeV

The Heavy Ion Fusion Virtual National Laboratory 14 Driver cost increases with increasing ion mass - A = 20 (Neon) is our base case E d = 6.7 MJ 24 Modules T f = 10  A MeV

The Heavy Ion Fusion Virtual National Laboratory 15 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

The Heavy Ion Fusion Virtual National Laboratory 16 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

The Heavy Ion Fusion Virtual National Laboratory 17 Neutralized drift compression and relaxed focusing requirements also benefit multi-beam, quad-focus drivers Number of beams 1 accelerator Ne +1 T f = 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

The Heavy Ion Fusion Virtual National Laboratory 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  “Robust Point Design” Multiple-beam quad linac driver Modular solenoid linac driver

The Heavy Ion Fusion Virtual National Laboratory 19 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

The Heavy Ion Fusion Virtual National Laboratory 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