E.O. Abeyta

Long-pulse beam stability experiments on the DARHT-II linear induction accelerator

When completed, the DARHT-II linear induction accelerator (LIA) will produce a 2-kA, 17-MeV electron beam in a 1600-ns flat-top pulse. In initial tests, DARHT-II accelerated beams with current pulse lengths from 500 to 1200 ns full-width at half-maximum (FWHM) with more than 1.2-kA, 12.5-MeV peak current and energy. Experiments have now been done with a /spl sim/1600-ns pulse length. These pulse lengths are all significantly longer than any other multimegaelectronvolt LIA, and they define a novel regime for high-current beam dynamics, especially with regard to beam stability. Although the initial tests demonstrated insignificant beam-breakup instability (BBU), the pulse length was too short to determine whether ion-hose instability would be present toward the end of a long, 1600-ns pulse. The 1600-ns pulse experiments reported here resolved these issues for the long-pulse DARHT-II LIA.

First beam at DARHT-II

The second axis of the Dual Axis Radiographic HydroTest (DARHT) facility will provide up to four short (< 150 ns) radiation pulses for flash radiography of high-explosive driven implosion experiments. To accomplish this the DARHT-II linear induction accelerator (LIA) will produce a 2-kA electron beam with 18-MeV kinetic energy, constant to within /spl plusmn/ 0.5% for 2-/spl mu/s. A fast kicker will cleave four short pulses out of the 2-/spl mu/s flattop, with the bulk of the beam diverted into a dump. The short pulses will then be transported to the final-focus magnet, and focused onto a tantalum target for conversion to bremsstrahlung pulses for radiography. DARHT-II is a collaborative effort between the Los Alamos, Lawrence Livermore, and Lawrence Berkeley National Laboratories of the University of California.

Commissioning the darht-II scaled accelerator

When completed, the DARHT-II accelerator will produce a 2-kA, 17-MeV beam in a 1600-ns pulse. After exiting the accelerator, the long pulse will be sliced into four short pulses by a kicker and quadrupole septum and then transported for several meters to a tantalum target for conversion to bremsstrahlung for radiography. In order to provide early tests of the kicker, septum, transport, and multi-pulse converter target we assembled a short accelerator from the first available refurbished cells, which are now capable of operating of operating at over 200 kV. This scaled accelerator was operated at ~8 MeV and ~1 kA, which provides a beam with approximately the same beam dynamics in the downstream transport as the final 17-MeV, 2-kA beam.

Commissioning the DARHT-II scaled accelerator downstream transport

The DARHT-II accelerator will produce a 2-kA, 17-MeV beam in a 1600-ns pulse when completed mid-2007. After exiting the accelerator, the pulse is sliced into four short pulses by a kicker and quadrupole septum and then transported for several meters to a tantalum target for conversion to X-rays for radiography. We describe tests of the kicker, septum, transport, and multi-pulse converter target using a short accelerator assembled from the first available refurbished cells. This scaled accelerator was operated at ~8 MeV and ~1 kA, providing a beam with approximately the same v/gamma as the final 18-MeV, 2-kA beam, and therefore the same beam dynamics in the downstream transport. The results of beam measurements made during the commissioning of this scaled accelerator downstream transport are described.

DARHT-II Long-Pulse Electron Beam

Summary form only given. The second axis of the dual-axis radiographic hydrotest (DARHT) facility will provide four radiographic images within ~1.6 microseconds. This will be accomplished by slicing four short pulses out of a ~1.6-microsecond long electron beam produced by the DARHT-II linear induction accelerator and directing them onto a bremsstrahlung converter target. Commissioning of the full 17-MeV configuration the DARHT-II accelerator will begin in spring of 2007 following tests of a new high-perveance (2 kA at 2.5 MV) diode. We will present the results of diode performance measurements as well as initial measurements of the fully accelerated electron beam parameters.