Pulse generators based on air-insulated linear-transformer-driver stages

A linear transformer driver (LTD) generator capable of delivering up to 0.9 MA current pulses with 160 ns rise time has been assembled and commissioned at University of California San Diego. The machine is an upgrade of the LTD-III pulser from Sandia National Laboratories, consisting of 40 capacitors and 20 spark gap switches, arranged in a 20-brick configuration. The driver was modified with the addition of a new trigger system, active premagnetization of the inductive cores, a vacuum chamber with multiple diagnostic ports, and a vacuum power feed to couple the driver to plasma loads. The new machine is called compact experimental system for Z-pinch and ablation research (CESZAR). The driver has a maximum bipolar charge voltage of AE100 kV, but for reliability and testing, and to reduce the risk of damage to components, the machine was operated at AE60 kV, producing 550 kA peak currents with a rise time of 170 ns on a 3.5 nH short circuit. While the peak current is scaled down due to the reduced charge voltage, the pulse shape and circuit parameters are close to the results of the cavity and power feed models but suggest a slightly higher inductance than predicted. The machine was then used to drive wire array Z-pinch and gas puff Z-pinch experiments as initial dynamic plasma loads. The evolution of the wire array Z pinch is consistent with the general knowledge of this kind of experiment, featuring wire ablation and stagnation of the precursor plasma on axis. The gas puff Z pinches were configured as a single, hollow argon gas shell, in preparation for more structured gas puff targets such as multispecies, multishell implosions. The implosion dynamics agree generally with 1D magnetohydrodynamics simulation results, but large zippering and magneto-Rayleigh-Taylor instabilities are observed. The CESZAR load region was designed to accommodate many load types to be driven by the machine, which makes it a versatile platform for studying Z-pinch plasmas. The completion of the CESZAR driver allows plasma experiments on energy coupling from LTD machines to plasma loads, instability mitigation techniques and magnetic field distributions in Z pinches, and interface dynamics in multispecies implosions.

Section: Introductionmentioning

confidence: 99%

MA-class linear transformer driver for Z -pinch research

Conti

Valenzuela

Fadeev

et al. 2020

“…One avenue for the development of LTD generators is the use of atmospheric pressure air as insulation for the LTD stages and the working medium of the switches [15][16][17]. This requires increasing the length of the surface between the high-voltage and low-voltage electrodes of the switch, and for this, the planar geometry of the switch is used [16][17][18][19]. The interelectrode gap of the planar switch is divided into a series of connected small gaps using ball electrodes, and parallel rows of these ball electrodes allow for multichannel switching.…”

Section: Introductionmentioning

confidence: 99%

Multichannel switching in a multigap gas switch at atmospheric pressure

Zherlitsyn

Kumpyak

2020

The multichannel switching mode of a controlled multigap switch is studied. The switch is designed for capacitive energy storage, with a charging voltage of up to 100 kV and an energy output time of about 100 ns. The interval between the high-voltage and low-voltage electrodes of this switch is divided into seven series-connected gaps using ball electrodes, and six parallel rows of these ball electrodes allow for multichannel switching. An optical system based on collimators and photodiodes was used to determine the number of channels in the switch gaps. Statistics on the number of channels were collected and the probability of ignition of parallel spark channels was calculated for each of the switch gaps under different operating conditions. We show that both the electrical isolation between the channels and the rate of rise of the triggering pulse significantly affect the number of parallel ignited channels and their distribution over consecutive gaps. At a high triggering voltage pulse rise rate (∼800 kV=μs), a larger number of spark channels are ignited in the switch with electrical isolation between the channels and the characteristics of this switch are better. At a low triggering voltage pulse rise rate (less than 250 kV μs), better characteristics are realized in the switch without electrical isolation between the channels.

“…The prime power source of such a machine may consist of a system of linear transformer drivers (LTDs) [7][8][9][10][11][12][13][14][15][16][17][18] fast Marx generators (FMGs) [7,9,[19][20][21][22] or impedance-matched Marx generators (IMGs) [18,23,24]. The pulsed power community has been developing LTD technology for 20 years on various single-cavity experiments [16,[25][26][27][28][29][30][31][32][33][34][35][36][37], multicavity (single "module") experiments [14,27,32,35,[38][39][40][41][42][43][44] and a few multimodule experiments [11,14]. The work presented here describes the design and performance of the first two meter...…”

Section: Introductionmentioning

confidence: 99%

100 GW linear transformer driver cavity: Design, simulations, and performance

Douglass¹,

Hutsel²,

Leckbee³

et al. 2018

Herein we present details of the design, simulation, and performance of a 100-GW linear transformer driver (LTD) cavity at Sandia National Laboratories. The cavity consists of 20 "bricks." Each brick is comprised of two 80 nF, 100 kV capacitors connected electrically in series with a custom, 200 kV, threeelectrode, field-distortion gas switch. The brick capacitors are bipolar charged to AE100 kV for a total switch voltage of 200 kV. Typical brick circuit parameters are 40 nF capacitance (two 80 nF capacitors in series) and 160 nH inductance. The switch electrodes are fabricated from a WCu alloy and are operated with breathable air. Over the course of 6,556 shots the cavity generated a peak electrical current and power of 1.03 MA (AE1.8%) and 106 GW (AE3.1%). Experimental results are consistent (to within uncertainties) with circuit simulations for normal operation, and expected failure modes including prefire and latefire events. New features of this development that are reported here in detail include: (1) 100 ns, 1 MA, 100-GW output from a 2.2 m diameter LTD into a 0.1 Ω load, (2) high-impedance solid charging resistors that are optimized for this application, and (3) evaluation of maintenance-free trigger circuits using capacitive coupling and inductive isolation.