Researchers at Los Alamos National Laboratory (LANL) are developing a new solid-state high-voltage Marx modulator for the generation of pulsed power. The initial application of the LANL modulator is to provide power to a magnetron that requires a 46-kV, 160-A, 5-mus rectangular pulse. This modulator technology is also being developed for other applications, including portable millimeter wave sources, a beam energy corrector for induction accelerators, and space-based power systems. The LANL solid-state modulator has several benefits, including wave shape control, switch protection, efficiency, and compactness. The present paper describes this source technology and its design.

SABRE (Sandia Accelerator and Beam Research Experiment) is a 10-MV, 250-kA, 40-ns linear induction accelerator. It was designed to be used in positive polarity output. Positive polarity accelerators are important for application to Sandia's ICF (Inertial Confinement Fusion) and LMF (Laboratory Microfusion Facility) program efforts. SABRE was built to allow a more detailed study of pulsed power issues associated, with positive polarity output machines, MITL (Magnetically Insulated Transmission Line) voltage adder efficiency, extraction ion diode development, and ion beam transport and focusing. The SABRE design allows the system to operate in either positive polarity output for ion extraction applications or negative polarity output for more conventional electron beam loads. Details of the design of SABRE and the results of initial machine performance in negative polarity operation are presented in this paper.

HELIA is a four stage, 4-MV, 250-kA, 30-ns accelerator used to study the design concepts for Hermes III. The accelerator consists of eight pulse forming lines (PFLs) that deliver 1-MV, 125-kA pulses to four linear induction cavities. The cavities are in series. and the voltage addition is accomplished in a coaxial self magnetically insulated transmission line (MITL). A positive polarity experiment has been performed on Hermes Ill that shows efficient current transport through the system. HELIA has been reconfigured for positive polarity operation, and initial experimental results show operation consistent with Hermes Ill results. These experiments are aimed at obtaining a more complete understanding of the system performance in positive polarity and to investigate the interactions of the cavities, adder MITL, and extensions in this configuration. Initial results and details of these tests are presented in this paper.

Measurements are made of surface doses necessary to initiate an anode plasma by electron bombardment of Ta, Ti, and C anodes for coaxial geometries characteristic of high-power electron-beam diodes. Measured lower and upper bounds of doses necessary to form an anode plasma are 54±7–139±16 J/g in Ta, 214±23–294±71 J/g in Ti, and 316±33–494±52 J/g in C. Within these bounds, probable values for the threshold are given under specific assumptions. The measurements are consistent with a thermal desorption model for plasma formation.

Significantly improved spatial uniformity of bremsstrahlung radiation, relative to a planar-anode diode, is obtained on the 3-MV, 150-kA HELIA accelerator when a Bθ lens diode is used to actively control the high-power electron beam at the exit of a coaxial, magnetically insulated transmission line. The advantage of this diode over other diodes which only passively control the beam is that better radiation uniformity for less beam loss is possible. Measurements taken on HELIA are shown to agree with theoretical expectations.

The impedance of a diode having an annular cathode and indented anode that terminates a coaxial MITL (magnetically insulated transmission line) is measured and compared with a semiempirical model developed from calculations made using the magic code. The measurements were made on the 16-Ω electron accelerator HELIA (high-energy linear induction accelerator) operating at 3 MV. The model agrees with the measurements within the 10% measuring error and shows that the diode operates in either a load- or line-dominated regime depending on AK (anode-cathode) gap spacing. In the load-dominated regime, which corresponds to small AK gaps, the diode impedance is controlled by an effective anode-cathode gap, and the flow is approximately axial. In the line-dominated regime, which corresponds to large AK gaps, the impedance is independent of the AK gap and corresponds to the impedance associated with the minimum current solution of the MITL, with the flow becoming more radial as the AK gap is increased.

The relation ∝ IV2.65 is widely used to estimate the on-axis radiation-dose rate for flash X-ray sources, as a function of diode current, I, and voltage, V, 1 m downstream of an optimized bremsstrahlung target. This relation is valid only for pencil beams. In this paper, we show that for diodes having beams with finite spatial and angular extent, this relation can still be used if the power 2.65 is modified. Using particle-in-cell and radiation-transport codes, this modification is evaluated for a diode proposed for the 20-MeV HERMES III accelerator that is currently under construction. Predictions of the calculational model are compared with measurements obtained from experiments on the existing 3-MeV HELIA accelerator and are found to be in good agreement. These results are characteristic of finite-area coaxial diodes in general and show the trend of the deviation from 2.65 for such sources.

Use of an indented anode in a cylindrical-cathode, planar anode diode placed at the exit of a coaxial magnetically insulated transmission line on the helia accelerator results in improved radiation uniformity. Measurements of the uniformity made on the accelerator at 3 MV, 150 kA are compared and shown to agree with theoretical calculations. The advantage of this scheme over that of the planar anode is that the diode impedance, pinch angle, and radial impact position at the anode can be partially decoupled.

A new, large-area, high-uniformity, flash x-ray source that efficiently couples electrical energy to photon energy has been successfully constructed and tested on the 1-MV, 2-MA electron accelerator SPEED (short pulse experimental electron device). The source employs 18 individual blade diodes arranged in the configuration of a frustum. Each blade was magnetically isolated on the real-cathode side of an anode foil, but not on the virtual-cathode side. The operation of the diode was heavily diagnosed using 24 Rogowski coils, a vacuum voltage monitor, p-i-n diode detectors, an 80-element TLD array, and a fast-framing x-ray pinhole carnera. The individual blade diodes were found to exhibit line pinching, end-to-end pinching, and minimal electron reflexing through the Ta anode foil, with a radiation yield that agreed with Monte Carlo simulations. The end-to-end pinch location could be controlled by tapering the anode–cathode gap. The impedance depended on only the smallest spacing, and was independent of pinch location.

MABE is a multistage, electron beam linear accelerator. The accelerator has been operated in single beam (60 kA, 7 Mev) and multiple beam configurations. This paper deals with the multiple beam configuration in which typically nine Ɉ 25 kA injected beams are transported through three accelerating gaps. Experimental results from the machine are discussed, including problems encountered and proposed solutions to those problems.