Heavy Ion Fusion Sciences Virtual National Laboratory Warp simulations illustrate the novel acceleration strategy Design Studies for NDCX-II W. M. Sharp, A. Friedman, D. P. Grote, S. M. Lund – LLNL B. G. Logan, J. W. Kwan, A. Faltens, J. Y. Jung, E. P. Lee, W. L. Waldron - LBNL Project Overview The Heavy Ion Fusion Science Virtual National Laboratory is building NDCX-II, an induction-accelerator facility for studying ion-heated warm dense matter and aspects of ion-driven targets for inertial-fusion energy. The goal is to produce Li + ion beam with a 1- ns pulse length, MeV energy, 40-nC charge per pulse, and pulse repetition once per minute. The accelerator re-uses induction cells and Blumlein voltage sources from the decommissioned Advanced Test Accelerator (ATA) at LLNL. Among other changes, the original dc solenoid magnets are replaced with new 2-3 T pulsed solenoids. The machine will have twelve or more cells, a neutralized drift compression line, and an 8-T final focusing solenoid, followed by a target chamber. The total length of the machine will be about 12 m. NDCX-II project construction at LBNL began in July 2009 and will be complete before March NDCX-II design with 12 active induction cells p NDCX-II will enable studies of warm dense matter and key physics for ion direct drive LITHIUM ION BEAM BUNCH Final beam energy~ MeV Final spot diameter ~ 1 mm Final bunch length ~ 1 cm or ~ 1 ns Total charge delivered ~ 40 nC Exiting beam available for measurement TARGET  m foil or foam 30 J/cm 2 isochoric heating would bring aluminum to ~ 1 eV Added cells will substantially increase beam kinetic energy How induction cells work An induction cell works like a transformer, with the beam as a “single-turn” secondary Changing flux in the ferrite core induces an electric field E z along the axis The applied voltage waveform determines the rate of flux change in the core and hence E z (t) 11.0” oil vacuum high-voltage feed insulator beam Ferrite torroid (70 ns, 250 kV) 5.5” aperture 1.5 – 3 T pulsed solenoid 5-mm copper sleeve Volt-seconds of ferrite cores are reduced by return flux of solenoids eddy currents, mainly in end plates, dissipate energy and induce noise new 5-mm flux-channeling copper shells and thinner end plates address these issues schematic of an NDCX-II cell Design Principles ion source ~ 500 ns target foil injector custom waveforms for rapid compression neutralized drift compression and final focus > 1.2 MV, 40 nC Equalize beam energy after injection Compress longitudinally before main acceleration using custom waveforms to impose a nearly linear variation with z in the beam mean velocity Compress until the gap transit time is near the 70-ns duration of the ATA Blumleins Apply 250-kV flat-topped pulses with ATA Blumleins, letting the beam length “bounce” Apply steering corrections once every fourth cell Apply the “exit tilt” needed for drift compression in final tilt cells. Neutralize beam space charge during final compression with a sufficiently dense plasma Focus radially with 8-T solenoid from NDCX-I flat waveforms for acceleration ramped waveforms for velocity tilt Warp studies show that the design tolerates anticipated errors in waveform timing and solenoid alignment nominal offsetnominal jitter “ramps” from modified ATA cells “correction” to reduce energy ^variation “custom” to impose velocity tilt for ^initial compression “flat-top” ATA pulses Simulations use experimentally measured waveforms for accurate modeling of the NDCX-II design oil-filled ATA transmission lines ATA Blumlein voltage sources long-pulse voltage sources Li + ion injector neutralized drift compression line with plasma sources Final-focus solenoid and NDCX-I target chamber ATA induction cells with pulsed 2.5-T solenoids