LANL, Los Alamos, New Mexico
LBNL, Berkeley, California
SAIC, Los Alamos, New Mexico
Funding: National Nuclear Security Administration of the US Department of Energy
The Dual-Axis Radiographic Hydrodynamic Test Facility (DARHT) at Los Alamos National Laboratory (LANL) consists of two linear induction accelerators oriented at right angles to each other. The DARHT First Axis has been successfully operated since 1999 and produces a 60 ns pulse with beam energy of 20 MeV and beam current of 1.9 kA. The DARHT Second Axis was successfully commissioned in May 2008 and produces a 1600 ns pulse with beam energy of 17.5 MeV and beam current of 2.1 kA. The Second Axis Injector uses a 16.5 cm diameter thermionic cathode with a 10 A/cm2 required current density to emit electrons into the accelerator. During the early Second Axis commissioning activities in 2006, deficiencies in the DARHT Second Axis Injector were found that prevented the injector cathode from meeting the required 10 A/cm2 current density. A comprehensive campaign was initiated to solve the injector cathode performance issues. This paper describes the deficiencies found and the solutions used to enable the DARHT Second Axis Injector to meet its requirements.
LLNL, Livermore, California
LBNL, Berkeley, California
Funding: Work performed under the auspices of US Department of Energy by LLNL under Contract DE- AC52-07NA27344 and by LBNL under Contract DE-AC03-76SF00098.
The Virtual National Laboratory for Heavy-Ion Fusion is developing a physics design for NDCX-II, an experiment to study warm dense matter heated by ions near the Bragg-peak energy. Present plans call for using about thirty induction cells to accelerate 30 nC of Li+ ions to more than 3 MeV, followed by neutralized drift-compression. To heat targets to useful temperatures, the beam must be compressed to a sub-millimeter radius and a duration of about 1 ns. An interactive 1-D particle-in-cell simulation with an electrostatic field solver, acceleation-gap fringe fields, and a library of realizable analytic waveforms has been used for developing NDCX-II acceleration schedules. Multidimensional source-to-final-focus simulations with the particle-in-cell code Warp have validated this 1-D model and have been used both to design transverse focusing and to compensate for injection non-uniformities and 3-D effects. Results from this work are presented, and ongoing work to replace the analytic waveforms with output from circuit models is discussed.
LBNL, Berkeley, California
LLNL, Livermore, California
PPPL, Princeton, New Jersey
Voss Scientific, Albuquerque, New Mexico
The Heavy-Ion Fusion Sciences Virtual National Laboratory is pursuing an approach to target heating experiments in the warm dense matter regime, using space-charge-dominated ion beams that are simultaneously longitudinally bunched and transversely focused. Longitudinal beam compression by large factors has been demonstrated in the Neutralized Drift Compression Experiment (NDCX) with controlled ramps and forced neutralization. Using an injected 30 mA K+ ion beam with initial kinetic energy 0.3 MeV, axial compression leading to ~100X current amplification and simultaneous radial focusing to a few mm have led to encouraging energy deposition approaching the intensities required for eV-range target heating experiments. We discuss the status of several improvements to NDCX to reach the necessary higher beam intensities, including:
- greater axial compression via a longer velocity ramp;
- beam steering dipoles to mitigate aberrations in the bunching module;
- time-dependent focusing elements to correct considerable chromatic aberrations; and
- plasma injection improvements to establish a plasma density always greater than the beam density, expected to be >1013 cm-3.
