Abstract
The building block of the linear transformer driver pulser, known as a brick, can be thought of as the smallest, independent unit from which the entire pulser is built. In a ``standard'' brick configuration, two capacitors and a spark-gap switch are connected in series and are oil insulated. Such a brick could be assembled, for example, from two 80-nF, 100-kV capacitors and a 200-kV spark-gap switch. A single brick in this configuration is capable of generating a current pulse with up to 50 kA of peak current and a rise time on the order of 100 ns, after the capacitors have been discharged at a combined output voltage of 200 kV (twice the bipolar charge voltage). By contrast, in a ``dry'' brick configuration, the two capacitors are placed in parallel and a multigap, multichannel ``ball'' switch follows them in series. The dry brick is epoxy insulated, and its slightly different configuration allows it to have a peak output current of up to 100 kA, after being discharged at a total output voltage of 100 kV (equal to the unipolar charge voltage). In this paper, we present how these two different brick topologies, either oil insulated (standard) or epoxy insulated (dry), affect a pulser's output parameters, where the pulser has been constructed by connecting the outputs of $N$ bricks together in parallel. We find that in many cases, the use of a dry brick configuration results in more current being delivered to the load. We also find that if the time to peak current is not a critical parameter for the experiment, then the lower charging voltage across the switch and the absence of insulating oil make the dry brick an excellent alternative to the standard brick, especially for smaller research laboratories with limited maintenance staff.
Highlights
The linear transformer driver (LTD) was first introduced in 1997 [1] as an alternative to the Arkad’ev-Marx generator. In this first LTD, one low-inductance capacitor and one multichannel, multigap switch were connected to form a unit, and two such units were connected in parallel to directly drive a discharge circuit without additional cables or long transmission lines
In modern LTDs, the single unit, called a brick, is comprised of two capacitors and a spark-gap switch connected in series, and many bricks are connected in parallel inside the single LTD cavity [2,3,4,5,6,7,8,9,10,11]
This brick topology is not unique though; around the same time, a different brick configuration was introduced [12,13,14], with two capacitors connected in parallel followed by a low-inductance, multigap, multichannel ball switch [12]
Summary
The linear transformer driver (LTD) was first introduced in 1997 [1] as an alternative to the Arkad’ev-Marx generator. This can be the case for a large pulser (a pulser with a large N), as long as the TL and the load have a combined inductance that is very small (an example is a parallel plate TL terminated with a strip-line load) In this case of Lextra ≪ Lpulser, a pulser comprised of dry bricks is more suitable for higher current applications: using the same number of bricks, it provides a higher output current, or alternatively, to achieve the same output current, the dry-brick pulser requires less bricks total (and does this without the use of insulating oil). If having a short tpeak is important, the standard-brick pulser will outperform the dry-brick pulser Up to this point, all of our discussion was based on the matched load solution, which is an important case that allows one to maximize the pulser’s output current while keeping the voltage and current reversals below the operational limits of the capacitors. Though the circuit simulations performed here are very elementary and can be done with any circuit simulation program, we prefer to use SCREAMER as it allows one to readily implement the many pulsed-power models available in SCREAMER (e.g., the Martin spark-gap switch model, a gas puff load model, etc.) at any point in the future
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