E.G. Cook

Status of the dual axis radiographic hydrodynamics test (DARHT) facility

The Dual-Axis Radiographic Hydrodynamics Test (DARHT) facility will employ two perpendicular electron Linear Induction Accelerators to produce intense, bremsstrahlung x-ray pulses for flash radiography. We intend to produce measurements containing three-dimensional information with sub-millimeter spatial resolution of the interior features of very dense, explosively-driven objects. The facility will be completed in two phases with the first phase having become operational in July 1999 utilizing a single-pulse, 20-MeV, 2-kA, 60-ns accelerator, a high-resolution electro-optical x-ray imaging system, and other hydrodynamics testing systems. We will briefly describe this machine. The first electron beams will be generated in the second phase of DARHT this year. The second DARHT accelerator consists of a 18.4-MeV, 2-kA, 2-microsecond pulse-width accelerator. Four short electron micropulses of variable pulse-width and spacing will be chopped out of the original, long accelerator pulse for producing time-resolved x-ray images. The second phase also features an extended, high-resolution electro-optical x-ray system with a framing speed of about 2-MHz. We will discuss this accelerator by summarizing the overall design of the long-pulse injector and accelerator. We will also discuss the fast kicker used to separate the long-pulse beam into short bursts suitable for radiography.

Solid-state kicker pulser for DARHT-2

To replace a hard tube design, a solid-state kicker pulser for the Dual-Axis Radiographic Hydrodynamic Test facility (DARHT-2) has been designed and tested. This kicker modulator uses multiple solid-state modules stacked in an inductive-adder configuration where the energy is switched into each section of the adder by a parallel array of MOSFETs. The modulator features very fast rise and fall times, pulse width agility and a high pulse-repetition rate in burst mode. The modulator can drive a 50 /spl Omega/ load with voltages up to 20 kV and can be easily configured for either positive or negative polarity. The presentation includes test and operational data.

Plasma Cathode for a Short-Pulse Dielectric Wall Accelerator

The Beam Research Program at Lawrence Livermore National Laboratory is continuing development of the dielectric wall accelerator (DWA), a type of accelerator which uses stacked pulse-forming lines (PFLs) to apply an accelerating field directly to the beam through a nonconducting vacuum boundary. Here, we report operation of a DWA as an electron diode using a surface flashover plasma cathode. Peak perveances in excess of 6 times 10-6A/V3/2 were measured, with current extraction and pulse train format depending on flashover source timing and PFL switching speed.

Modeling of an inductive adder kicker pulser for a proton radiography system

An all solid-state kicker pulser for a proton radiography system has been designed. Multiple solid-state modulators stacked in an inductive-adder configuration are utilized in this kicker pulser design. Each modulator is composed of multiple metal-oxide-semiconductor field-effect transistors (MOSFETs) which quickly switch the energy storage capacitors across a magnetic induction core. Metglas is used as the core material to minimize loss. Voltage from each modulator is inductively added by a voltage-summing stalk. A circuit model of a prototype inductive adder kicker pulser modulator has been developed to predict the performance of the pulser modulator. The modeling results are compared with experimental data.

Design and testing of a fast, 50 kV solid-state kicker pulser

The ability to extract particle beam bunches from a ring accelerator in arbitrary order can greatly extend an accelerators capabilities and applications. A prototype solid-state kicker pulser capable of generating asynchronous bursts of 50 kV pulses has been designed and tested into a 50 /spl Omega/ load. The pulser features fast rise and fall times and is capable of generating an arbitrary pattern of pulses with a maximum burst frequency exceeding 5 MHz. If required, the pulse-width of each pulse in the burst is independently adjustable. This kicker modulator uses multiple solid-state modules stacked in an inductive-adder configuration where the energy is switched into each section of the adder by a parallel array of MOSFETs. Test data, capabilities, and limitations of the prototype pulser are described.

Solid-state modulated kicker pulser

A solid-state high voltage pulse generator for highspeed beam kicker applications has been designed and tested at Lawrence Livermore National Laboratory. This kicker pulser uses multiple stages stacked in an inductive-adder configuration where the energy is switched from each stage of the adder by a parallel array of MOSFETs. Features include pulse width, format and amplitude agility all at a high pulse-repetition rate. The modulator can drive a 50%o load at voltages up to 18 kV with +/-10% amplitude modulation at several MHz burst frequency. Rise and fall times are on the order of 10 ns, and the pulser can easily be configured for either positive or negative polarity. The presentation will include test and operational data collected from both the ETA II accelerator kicker and resistive dummy loads.

Breakdown Performance Statistics of a Nanoparticle Composite System

Summary form only given. Nanoparticle composites offer promise for construction of high voltage pulse-forming systems since they allow the combination of tunable dielectric constant and high dielectric strength. To estimate the expected lifetime of insulation subjected to high electric fields in actual use conditions it was necessary to determine the probability of failure as a function of electric field. This Weibull probability function is presented for a nanoparticle composite with a dielectric constant of 10. The implication of this result for the use of this material in actual use conditions is discussed.

Three turn secondary for the prototype SLAC solid state induction modulator

The Next Linear Collider accelerator proposal at SLAC requires a high efficiency, highly reliable, and low cost pulsed power modulator to drive the X band klystrons. The present NLC envisions a solid state induction modulator design to drive up to 8 klystrons to 500 kV for 3(S) at 120 PPS with one modulator (>1000 megawatt pulse, 500 kW average). A prototype modulator is under construction, which will power 4 each 5045 SLAC klystron to greater than 380 kV for 3(S) (>600 megawatt pulse, >300 kW ave.). The prototype induction modulator utilizes a three-turn secondary to produce the 500 kV pulse. The design, installation and testing of the three turn secondary and its effect on rise time and fault conditions is discussed. The design and implementation of a snubber to improve the arcing condition are covered.

Pulsed-power systems for the Dual-Axis Radiographic Hydrodynamics Test (DARHT) facility

The Dual-Axis Radiographic Hydrodynamics Test (DARHT) facility will employ two perpendicular electron linear induction accelerators to produce intense, bremsstrahlung X-ray pulses for flash radiography. The first DARHT accelerator became operational in July 1999 producing a single electron beam pulse at 20 MeV, 2 kA, and 60 ns pulse. The second DARHT accelerator consists of a 18.4 MeV, 2 kA, 2 microsecond pulse-width accelerator. Four short electron micropulses of variable pulse-width and spacing will be chopped out of the original, long accelerator pulse for producing time-resolved X-ray images. The first electron beam in this machine will be produced this year. We discuss the pulsed power systems associated with this machine. These include an injector driven by a Marx consisting of 88 type-E PFN stages driving a matched load at 3.2 MV with a 500 ns risetime, 2 microsecond e-beam pulse. The Metglas-filled induction cells making up the accelerator are described. Each induction cell is driven by a cell-driver that contains 4, 7-section E-network PFNs in a Marx configuration with a 20 /spl Omega/ impedance that delivers flattop of greater than 2 microseconds into a resistive load of 5 /spl Omega/ for a total drive current of 10 kA at 200 kV. The principal element of the electron beam transport system is the fast deflector, or kicker, used to generate four micropulses from the primary beam. The kicker modulator generates bi-polar 18 kV pulses of arbitrary pulse width and spacing using solid-state circuitry that is described. Component test data from the injector, accelerator, and kicker system is discussed.

The LLNL z-pinch ion probe experiment (ZIPX)

Dense Plasma Focus (DPF) Z-pinches are copious sources of radiation including neutrons, x-rays, and MeV level electron and ion beams. Energetic protons and deuterons up to 10 MeV have been observed from ~cm long pinches indicating average acceleration gradients up to 1 GV/m. Corresponding electron beams with lower particle energy are also emitted. These beams contribute significantly to the neutron and x-ray output of the device. However, the mechanisms behind these gradients are not completely understood and hence a true predictive capability required for optimization or application is not currently available. At LLNL we are assembling a DPF experiment with a unique 4 MV ion probe beam designed to measure these gradients directly and to examine the possibility of using the DPF as a high-gradient acceleration stage. These unique data along with fully kinetic simulation of the DPF z-pinch will form an integrated simulation and experimental approach to understanding the DPF. In this poster we will review the design, construction, and initial operations of a 4 kJ modular DPF. We will also discuss how the probe beam will be used to measure the acceleration gradients in the plasma.