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Los Alamos “Ranchero” Magnetic Flux Compression Generators (FCGs) have been used to power imploding liner loads. The fundamental FCG design is based on a cylindrical detonation system that expands the armature simultaneously into a coaxial generator volume and has been shown to generate currents as high as 76 MA. Analysis of the 76 MA test results revealed a weakness in the design at the output glide plane. To prevent premature shorting at the output current slot of the generator, the armature/glide plane interface was originally designed to lag the leading edge of the armature. However, 2D-MHD calculations reveal that at very high currents a magnetically driven aneurism develops in this lagging section which reduces the performance of the generator. A new model Ranchero is being developed to correct this weakness and provide enhanced performance. In the new model, the output glide plane is eliminated and the armature is extended along the FCG axis, with its radius increasing along a curve until it reaches the current output slot. A cylindrical detonation system of the type required for earlier designs continues to be used, and the high explosive (HE) in the extended section is detonated by the last point of the cylindrical detonator. The stator of the FCG is contoured, allowing the contact point of the armature to zipper from the input to the output end in the last few μs of flux compression. In addition, the new model Ranchero is intended to use PBX 9501 (9501) for the HE and also remove the smoothing layer, which has been part of all Ranchero HE systems to date. Both of these factors lead to increased performance. 9501 is more energetic than the PBXN 110 used in Ranchero generators to date, and both calculations and experiments have shown that the smoothing layer is not needed when the detonator point spacing is 18 mm. Tests of original model Rancheros using PBXN 110 castable HE, with an imbedded smoothing layer, demonstrated an armature expansion velocity of 3.1 mm/μs. Further tests show that removal of the smoothing layer increases the speed to 3.3 mm/μs, and replacement of the cast PBXN 110 with 9501 without a smoother gives a velocity of 3.8 mm/μs. Designs, concerns, and experimental results facilitating the new model Ranchero are presented. In addition, performance estimates are given for the initial imploding liner tests to be conducted, and further computational details are presented in a companion paper given by C. L. Rousculp and others at this conference.

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.

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.

When completed, the DARHT-II linear induction accelerator (LIA) will produce a 2 kA, 18 MeV electron beam with more than 1500 ns current/energy “flat-top.” In initial tests DARHT-II has already accelerated beams with current pulse lengths from 500 ns to 1200 ns full-width at half maximum (FWHM) with more than 1.2 kA peak current and 12.5 MeV peak energy. Experiments will soon begin with a ∼ 1600 ns flat-top pulse, but with reduced current and energy. These pulse lengths are all significantly longer than any other multi-MeV LIA, and they define a novel regime for high-current beam dynamics, especially with regard to beam stability. Although the initial tests demonstrated the robustness of the DARHT-II LIA to BBU, the < 1200 ns FWHM pulse lengths were too short to test the predicted protection against ion-hose instability. The present experiments are designed to resolve these and other beam-dynamics issues with a ∼ 1600 ns pulse length beam.

When completed, the DARHT-II linear induction accelerator (LIA) will produce a 2-kA, 18-MeV electron beam with more than 1500-ns current/energy "flat-top." In initial tests DARHT-II has already accelerated beams with current pulse lengths from 500-ns to 1200-ns full- width at half maximum (FWHM) with more than 1.2- kA, 12.5-MeV peak current and energy. New experiments are planned with a ~1600-ns pulse length but with reduced current and energy. These pulse lengths are all significantly longer than any other multi-MeV LIA, and they define a novel regime for high-current beam dynamics, especially with regard to beam stability. Although the initial tests demonstrated absence of BBU, the pulse length was too short to determine whether ion- hose instability would be present toward the end of a pulse longer than 1500-ns. The 1600-ns pulse experiments are designed to resolve these and other beam-dynamics issues with a long-pulse beam.

The dual axis radiographic hydrotest facility (DARHT) at Los Alamos National Laboratory produces flash radiographs of hydrodynamic experiments using two linear induction accelerators situated on orthogonal axes. The first axis accelerator is operational and has produced radiographs of hydrodynamic experiments. The second axis accelerator, which is in the commissioning stage, will generate an 18-MeV, 2-kA, 2-/spl mu/s electron beam. These parameters are reduced during the initial phase of commissioning to /spl ges/12-MeV, /spl ges/1-kA, and /spl ges/350-ns. These reduced parameters allow lower voltages and fewer components than what will be necessary for the final machine. This paper presents experimental results of commissioning the second axis DARHT accelerator, including an overview of the pulsed power system plus electrical performance data from the 3-MV injector Marx generator and the 200-kV, 2-/spl mu/s induction accelerator cells. Beam transport data will also be presented.

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.