In this article we present the design and test results of the most powerful, fast linear transformer driver (LTD) stage developed to date. This 1-MA LTD stage consists of 40 parallel RLC (resistor R, inductor L, and capacitor C) circuits called ''bricks'' that are triggered simultaneously; it is able to deliver $1 MA current pulse with a rise time of $100 ns into the $0:1-Ohm matched load. The electrical behavior of the stage can be predicted by using a simple RLC circuit, thus simplifying the designing of various LTD-based accelerators. Five 1-MA LTD stages assembled in series into a module have been successfully tested with both resistive and vacuum electron-beam diode loads.
The linear transformer driver (LTD) technological approach can result in relatively compact devices that can deliver fast, high current, and high-voltage pulses straight out of the LTD cavity without any complicated pulse forming and pulse compression network. Through multistage inductively insulated voltage adders, the output pulse, increased in voltage amplitude, can be applied directly to the load. In this paper, we present the design and first test results of an LTD cavity that generates such a type of output pulse by including within its circular array a number of third harmonic bricks in addition to the main bricks. A voltage adder made out of a square pulse cavity linear array will produce the same shape output pulses provided that the timing of each cavity is synchronized with the propagation of the electromagnetic pulse.
The load inductance, Ld, can be several times smaller than that of the pulsed power generator, L0, limiting the energy transfer efficiency. We define a relatively simple circuit modification, which improves the generator-to-load coupling, multiplying the load current in the case of interest, where L0⪢Ld. The suggested circuit modification operates similarly to an N:1 transformer and it can be designed to operate in vacuum with pulsed-power loads at high currents (many megaamperes). The current multiplier requires an additional volume having high self inductance, L, connected through convolutes to the generator and load. In its simplest configuration, N=2, a single convolute is required. The presented analysis shows that the efficiency of the proposed current multiplication scheme can theoretically exceed the values for a typical direct load-to-generator circuit. The modified hardware allows an increase of the load current by the factor of Id∕Ig=NL∕(L+Ld), where Ig represents the generator current and L can be easily made much greater than Ld either with or without the use of magnetic cores. The only uncertainties of this approach are potential convolute losses and the slight increase in load current rise time. Preliminary experimental tests were performed with a scaled down configuration which demonstrated current gain of 1.7 in the frequency range of interest and showed good agreement between analytically predicted and measured currents. The benefit of the scheme is also illustrated by simple circuit simulations for two types of potential applications requiring high power densities in vacuum: isentropic compression studies with Ld=constant loads, and imploding z-pinch research with dynamic [Ld(t)] loads. The proposed device is applicable for improving the characteristics of existing and future pulse power facilities.
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