A.A. Kim

100 ns current rise time LTD stage

LTD stages are designed to be used as a primary energy storage in high power pulsed generators. Previously the LTD stages with the current rise time of 1000 ns and 450 ns were reported. Present report describes the design and test results of the LTD stage that provides /spl sim/200 kA rising in 100 ns in the matched /spl sim/0.4 Ohm load.

1 MV ultra-fast LTD generator

Fast LTD technology looks promising for making the pulsed power generators for some applications more compact and less expensive because it does not need any pulse forming lines to produce nanosecond output pulses. In the report we present the 1 MV generator that is being produced to demonstrate the technology capability. The generator is designed to deliver a 1 MV, 125 kA, /spl sim/50 ns width at 80% of peak amplitude pulse to the /spl sim/8 Ohm vacuum diode. The stored energy of the generator is 14 kJ, the footprint /spl sim/ 2 m/sup 2/.

Multi gap switch for Marx generators

A new gas switch for Marx generators is presented that is designed for a /spl plusmn/100 kV charge voltage. The trigger electrode divides the switch into two parts (positive and negative), each with three intermediate electrodes. The charge voltage is evenly distributed between these electrodes with a corona discharge. This allows safe operation of the switch when filled with air at pressures of about 3 atm. This report presents the design of the switch, and test results on a test bed and in a Marx bank.

Prefire probability of the switch type Fast LTD

In this paper, we present the most recent test of the multigap gas switches which are one of the key elements of the fast LTD stages with oil insulation [1, 2]. Inside these switches, the charge voltage is distributed between the multiple gaps with the use of a corona discharge [3]. The evident advantages of this technique are low cost and extreme compactness of the voltage divider because it just consists of few needles that are soldered to the switch electrodes. At the same time, for proper operation of the switch, special features of the corona discharge have to be taken into account. These features include the nonlinear volt-ampere characteristics of the corona discharge that must be the same in each serial gap; the influence of UV radiation and free charged particles, that appear during the corona discharge, on the breakdown voltage of the gaps; and the variation of the shape of the needles that may burn during the switch operation thus limiting its life time. Each of these features (and probably some others that might be not as evident at this moment) may influence the voltage distribution between the gaps and therefore be a reason for the switch prefire. Below we present the design of the switch type Fast LTD, the breakdown voltage of the switch gaps, the volt-ampere characteristics of the corona discharge, and the statistics on the switch jitter and prefire probability.

Numerical Analysis of a Pulsed Compact LTD System for Electron Beam-Driven Radiography

This paper describes the configuration and operation of a seven-cavity linear transformer driver (LTD) system. This LTD system is configured to deliver ~1 MV and 125 kA into a critically damped load. A detailed transmission line model coupled to particle-in-cell simulations is used to assess the system electrical performance. The evolution of the electron power flow in negative polarity is simulated, and the impact of this flow on the operation of the system with a large-area hollow electron beam diode is examined. The simulation results are compared with available electrical measurements and with dose rate measurements where a flash X-ray pulse is produced by an annular electron beam diode. These comparisons suggest that the LTD system meets the design specifications and is a robust pulsed power architecture. Additionally, the positive polarity operation for the LTD system driving a rod-pinch diode load is modeled to further assess the utility of the LTD system

High Current Fast 100-NS LTD Driver Development in Sandia Laboratory

During the last few years Sandia is actively pursuing the development of new accelerators based on the novel technology of linear transformer driver (LTD). This effort is done in close collaboration with the High Current Electronic Institute (HCEI) in Tomsk, Russia, where the LTD idea was first conceived and developed. LTD based drivers are currently considered for many applications including future very high current Z-pinch drivers like ZX and IFE (Inertial Fusion Energy), medium current drivers with adjustable pulse length for ICE (Isentropic Compression Experiments), and finally relatively lower current accelerators for radiography and x-pinch. Currently we have in operation the following devices: One 500-kA, 100-kV LTD cavity, a 1-MV voltage adder composed of seven smaller LTD cavities for radiography, and one 1-MA, 100-kV cavity. The first two are in Sandia while the latter one is still in Tomsk. In addition a number of stackable 1-MA cavities are under construction to be utilized as building blocks for a 1-MA, 1-MV voltage adder module. This module will serve as a prototype for longer, higher voltage modules, a number of which, connected in parallel, could become the driver of an IFE fusion reactor or a high current Z-pinch driver (ZX). The IFE requirements are more demanding since the driver must operate in rep-rated mode with a frequency of 0.1 Hz. In this paper we mainly concentrate on the higher current LTDs: We briefly outline the principles of operation and architecture and present a first cut design of an IFE, LTD z-pinch driver.

0.75 MA, 400 ns rise time LTD stage

The LTD stage with following parameters was designed and tested: stored energy 14 kJ, output voltage 90 kV, current amplitude in secondary turn 0.75 MA, current rise time /spl sim/430 ns. The stage could be used as a base unit in generators driving PRS Z-pinch loads as well as in high current e-beam accelerators. As a storage elements the IK-100-0.17 capacitors are used, designed and produced by PKB of Electrohydraulics, Nikolaev, Ukraine. The multi channel, multi gap spark switches in air without of overpressure connect the capacitors to the stage circuit. The electrodes of the switch are made of a cylindrical spring, providing inductive insulation between the neighboring spark channels. A special scheme is developed for triggering the switch with large surface of the electrodes.

10 stage LTD for e-beam diode

Single stage of the driver stores 5.5 kJ at 90 kV charge. The capacitance of the stage is 1.36 /spl mu/F, the inductance of the discharge circuit including secondary turn is about 40 nH. The module of the LTD for high current e-beam diode contains 10 single stages connected in series. The report includes the design of the single stage and that of the 10-stage LTD module, the description of the high voltage synchronization system, as well as test results with e-beam diode.

High Current Linear Transformer Driver (LTD) Experiments

Sandia Laboratories are actively pursuing the development of new accelerators based on the novice technology of Linear Transformer Driver (LTD) [1,2,3]. LTD based drivers are considered for many applications including future very high current Z-pinch ICF (Inertial Confinement Fusion) drivers like ZX and Z-pinch IFE (Inertial Fusion Energy). The high current LTD driver experimental research is concentrated on two aspects; first to study the repetition rate capabilities, life time and jitter of the LTD cavities, and second to study how a number of cavities behave and add their energy, power and voltage output in a voltage adder configuration assembly.

Tests of 6-MV triggered switches on APPRM at SNL

The Advanced Pulsed Power Research Module (APPRM) was constructed at Sandia National Laboratories (SNL) to serve as a test bed for the development of pulsed power technologies and components that could be used in future generation high power facilities. This test bed is being used to develop, test, and certify switches for reliable 6 MV operations. Several switches have been designed and tested on APPRM. The first switch tested (in self break mode) was an evolved version of the Sandia designed HERMES III switch. It consists of a self breakdown (cascade) section where the discharge current flows in several parallel channels, and a trigger section where the current flows through a single spark channel. The second switch tested was an HCEI/Sandia Hybrid switch. The trigger section of the hybrid switch, designed at High Current Electronics Institute (HCEI) in Tomsk, Russia, includes six HCEI composite electrodes connected in parallel to a triggered gap via a 4-/spl mu/H series isolation inductor. The discharge current in the hybrid switch trigger section flows in several parallel channels eliminating the single channel flow as in the Sandia switch trigger section. The last switch tested is a HCEI switch design where the trigger and cascade sections are comprised of HCEI composite electrodes. The design of the switches and results of these tests are presented as well as the analysis and comparison of results.