Heavy Ion Fusion Sciences Virtual National Laboratory

Warp simulations illustrate the novel acceleration strategy

Design Studies for NDCX-II

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, 1.2 - 3 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 2012.

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

NDCX-II will enable studies of warm dense matter and key physics for ion direct drive

LITHIUM ION BEAM BUNCH

Final beam energy ~ 1.2 - 3 MeVFinal spot diameter ~ 1 mmFinal bunch length ~ 1 cm or ~ 1 nsTotal charge delivered ~ 40 nC

Exiting beam available for measurement

TARGET

m foil or foam

30 J/cm2 isochoric heating would bring aluminum to ~ 1 eV

Added cells will substantially increase beam kinetic energyAdded 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 Ez along the axis

• The applied voltage waveform determines the rate of flux change in the core and hence Ez(t)

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 foilinjector 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 waveformsfor acceleration

ramped waveforms for velocity tilt

Warp studies show that the design tolerates anticipated errors in waveform timing and solenoid alignment

Warp studies show that the design tolerates anticipated errors in waveform timing and solenoid alignment

nominal offset nominal 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