A 4-MA linear transformer driver for X-ray generation

We have designed, assembled, and tested a 4-MA, 60-ns fast linear transformer driver (LTD), which is the first operating generator featuring multiple LTD modules connected in parallel. The LTD-based accelerator comprises six modules in parallel, each of which has ten-stage cavities stacked in series. The six LTD modules are connected to a water tank of diameter 6 m via a 3-m-long impedance-matched deionized water-insulated coaxial transmission line. In the water tank, the electrical pulses are transmitted down by six horizontal tri-plate transmission lines. A 2.1-m-diameter two-level vacuum insulator stack is utilized to separate the deionized water region from the vacuum region. In the vacuum, the currents are further transported downstream by a two-level magnetically insulated transmission-line and then converged through four post-hole convolutes. Plasma radiation loads or bremsstrahlung electron beam diodes serve as loads that are expected to generate intense soft X rays or warm X rays. The machine is 3.2 m in height and 22 m in outer diameter, including support systems such as a high-voltage charge supply, magnetic core reset system, trigger system, and support platform for inner stalk installation and maintenance. A total of 1440 individual ±100-kV multi-gap spark switches and 2880 individual 100-kV capacitors are employed in the accelerator. A total of 12 fiber-optic laser-controlled trigger generators combining photoconductive and traditional gas spark switch technologies are used to realize the synchronous discharge of the more than 1000 gas switches. At an LTD charge voltage of ±85 kV, the accelerator stores an initial energy of about 300 kJ and is expected to deliver a current of 3–5 MA into various loads. To date, the LTD facility has shot into a thick-walled aluminum liner load and a reflex triode load. With a thick-walled aluminum liner of inductance 1.81 nH, a current with peak up to 4.1 MA and rise time (10%–90%) of about 60 ns has been achieved. The current transport efficiency from the insulator stack to the liner load approaches 100% during peak times. The LTD accelerator has been used to drive reflex triode loads generating warm X rays with high energy fluence and large radiation area. It has been demonstrated that this LTD is a promising and high-efficiency prime pulsed power source suitable for use in constructing the next generation of large-scale accelerators with currents of tens of megaamperes.