Vitaly M. Alexeenko

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.

Super Fast 75 ns LTD Stage

Summary form only given. In the report, we present the new super fast LTD prototype which delivers a 75 ns FWHM voltage pulse into a -0.5-0.6 Ohm matched load at ~20 GW power. The stage is designed without of peaking capacitors, it includes 32 GA35436 (8 nF, 100 kV) storage capacitors, 16 spark gap switches and magnetic core with reduced thickness of the tape (50 mum) to reduce the current losses. This stage prototype was specifically designed with an hemispherical vessel to operate with compressed gas (SF6, SF6/dry air mixtures, and pure dry air) up to 6 ata pressure, as well as with transformer oil. Test results of the stage prototype will be given and compared with numerical simulation.

Lifetime of the HCEI spark gap switch for linear transformer drivers

Spark gap switches, storage capacitors, and ferromagnetic cores are the most important components of the Linear Transformer Driver (LTD) cavities. Depending on their output voltage and current, LTD-based accelerators may need several thousands switches, hence the switch lifetime is of crucial importance. Unlike the capacitors and the cores, the LTD switches are still in the developmental stage and are designed and built mainly by various laboratories; thus the lifetime of different switches may vary. In this paper we present recent results of the first full-scale experiments that were aimed to evaluate the life-time of the LTD switches developed by HCEI.

Square pulse LTD with 5 th harmonic bricks

Up to now, the Square Pulse LTDs consisting of only 1st and 3rd harmonic bricks were developed and tested [1]. At the same time, discussions with pulsed power scientists indicated that the Square Pulse LTDs with additional 5th harmonic bricks might be even more interesting for some applications. Such LTDs could produce output pulses with a faster rise time and most importantly a flatter and longer length pulse top. In the present report we describe the Square Pulse LTDs, including 5th harmonics, and analyze their benefits and possible drawbacks.

Square pulse LTD

The usual LTD architecture [1, 2] provides sine shaped output pulses that may not be suitable in flash radiography, high power microwave production, z-pinch drivers, and certain other applications. A more suitable driver output pulse would have a flat or inclined top (slightly rising or falling). In this paper, we present the design and first test results of an LTD cavity that generates this type of the output pulse by including within its circular array some number of the third harmonic bricks in addition to the standard bricks.