The linear-transformer-driver (LTD) is a recently developed pulsed-power technology that shows great promise for a number of applications. These include a Z-pinch-driven fission-fusion-hybrid reactor that is being developed by the Chinese Academy of Engineering Physics. In support of the reactor development effort, we are planning to build an LTD-based accelerator that is optimized for driving wire-array Z-pinch loads. The accelerator comprises six modules in parallel, each of which has eight series 0.8-MA LTD cavities in a voltage-adder configuration. Vacuum transmission lines are used from the interior of the adder to the central vacuum chamber where the load is placed. Thus the traditional stack-flashover problem is eliminated. The machine is 3.2 m tall and 12 m in outer diameter including supports. A prototype cavity was built and tested for more than 6000 shots intermittently at a repetition rate of 0.1 Hz. A novel trigger, in which only one input trigger pulse is needed by utilizing an internal trigger brick, was developed and successfully verified in these shots. A full circuit modeling was conducted for the accelerator. The simulation result shows that a current pulse rising to 5.2 MA in 91 ns (10%-90%) can be delivered to the wire-array load, which is 1.5 cm in height, 1.2 cm in initial radius, and 1 mg in mass. The maximum implosion velocity of the load is 32 cm=μs when compressed to 0.1 of the initial radius. The maximum kinetic energy is 78 kJ, which is 11.7% of the electric energy stored in the capacitors. This accelerator is supposed to enable a radiation energy efficiency of 20%-30%, providing a high efficient facility for research on the fast Z pinch and technologies for repetition-rate-operated accelerators.

An electrode configuration with microhollow array dielectric and anode was developed to obtain parallel vacuum arc discharge. Compared with the conventional electrodes, more than 10 parallel microhollow discharges were ignited for the new configuration, which increased the discharge area significantly and made the cathode eroded more uniformly. The vacuum discharge channel number could be increased effectively by decreasing the distances between holes or increasing the arc current. Experimental results revealed that plasmas ejected from the adjacent hollow and the relatively high arc voltage were two key factors leading to the parallel discharge. The characteristics of plasmas in the microhollow were investigated as well. The spectral line intensity and electron density of plasmas in microhollow increased obviously with the decease of the microhollow diameter.

This paper presents the design and tests of a repetitive 800 kA fast linear transformer driver (LTD) stage aimed for the Zpinch driven fusion-fission hybrid reactor (Z-FFR).The LTD stage consists of 34 parallel basic resistor R, inductor L, and capacitor C (RLC) circuits each made up of two 100 kV/40 nF capacitors, a multi-stage gas switch and Metglas magnetic cores. The stage can deliver about 800 kA current pulse with rise time of 100 ns into the matched liquid resistive load at a repetitive frequency 0.1 Hz. A novel method to trigger the stage via a continuous internal trigger bus composed by a single cable has been proposed and demonstrated. The experimental results show that the new trigger method is feasible and reliable. A 140 kV, 25 ns rising time trigger pulse, and a 5.2 kA, 30 μs width pre-magnetization current pulse which can operate at a repetition rate 0.1 Hz were used in this stage to insure the LTD stage generating a 80 kV/800 kA current pulse every 10 s. A multi-stage gas switch that has a lifetime in excess of 10,000 shots and a jitter less than 3 ns one sigma agrees well with the demand of Z-FFR. The electrical behavior of the stage can be predicted from a simple RLC circuit, which can simplify the design of various LTD-based accelerators.

Radiation uniformity is important for Z-pinch dynamic hohlraum driven fusion. In order to understand the radiation uniformity of Z-pinch dynamic hohlraum, the code MULTI-2D with a new developed magnetic field package is employed to investigate the related physical processes on Julong-I facility with drive current about 7–8 MA. Numerical simulations suggest that Z-pinch dynamic hohlraum with radiation temperature more than 100 eV can be created on Julong-I facility. Although some X-rays can escape out of the hohlraum from Z-pinch plasma and electrodes, the radiation field near the foam center is quite uniform after a transition time. For the load parameters used in this paper, the transition time for the thermal wave transports from r = 1 mm to r = 0 mm is about 2.0 ns. Implosion of a testing pellet driven by cylindrical dynamic hohlraum shows that symmetrical implosion is hard to achieve due to the relatively slow propagation speed of thermal wave and the compression of cylindrical shock in the foam. With the help of quasi-spherical implosion, the hohlraum radiation uniformity and corresponding pellet implosion symmetry can be significantly improved thanks to the shape modulation of thermal wave front and shock wave front.

This paper reports some important properties of a dynamic hohlraum radiation source intended to study the high-temperature opacity of medium- Z atoms. The time-resolved axial radiation power in two x-ray diodes gives the time-evolution of an equivalent black-body temperature that peaks at ∼260 eV at stagnation. Time-gated framing pinhole images show that the source comprises an intense high-temperature core that lasts for ∼2 ns preceded by a 10-ns-long lower-temperature implosion phase that emits mostly softer x rays. Combining pinhole images with soft x-ray power gives a time-resolved brightness radiation temperature that reaches 130 eV. Thus, the lower-temperature source could ionize an opacity sample, then the intense high-temperature radiation pulse could measure its opacity. Likewise, the time-integrated spectrum measured with a spherically bent crystal spectrometer is compatible with multiple blackbodies with different temperatures, from 176 to 185 eV. These characterizations suggest that this dynamic hohlraum can be used for high-temperature opacity measurements.