Conceptual design of a ${10}^{13}$-W pulsed-power accelerator for megajoule-class dynamic-material-physics experiments

We have developed a conceptual design of a next-generation pulsed-power accelerator that is optimized for megajoule-class dynamic-material-physics experiments. Sufficient electrical energy is delivered by the accelerator to a physics load to achieve—within centimeter-scale samples—material pressures as high as 1 TPa. The accelerator design is based on an architecture that is founded on three concepts: single-stage electrical-pulse compression, impedance matching, and transit-time-isolated drive circuits. The prime power source of the accelerator consists of 600 independent impedance-matched Marx generators. Each Marx comprises eight 5.8-GW bricks connected electrically in series, and generates a 100-ns 46-GW electrical-power pulse. A 450-ns-long water-insulated coaxial-transmission-line impedance transformer transports the power generated by each Marx to a system of twelve 2.5-m-radius water-insulated conical transmission lines. The conical lines are connected electrically in parallel at a 66-cm radius by a water-insulated 45-post sextuple-post-hole convolute. The convolute sums the electrical currents at the outputs of the conical lines, and delivers the combined current to a single solid-dielectric-insulated radial transmission line. The radial line in turn transmits the combined current to the load. Since much of the accelerator is water insulated, we refer to it as Neptune. Neptune is 40 m in diameter, stores 4.8 MJ of electrical energy in its Marx capacitors, and generates 28 TW of peak electrical power. Since the Marxes are transit-time isolated from each other for 900 ns, they can be triggered at different times to construct–over an interval as long as $1\mu \mathrm{s}$–the specific load-current time history required for a given experiment. Neptune delivers 1 MJ and 20 MA in a 380-ns current pulse to an $18\text{−}\mathrm{m}\mathrm{\Omega }$ load; hence Neptune is a megajoule-class 20-MA arbitrary waveform generator. Neptune will allow the international scientific community to conduct dynamic equation-of-state, phase-transition, mechanical-property, and other material-physics experiments with a wide variety of drive-pressure time histories.

Figure 1

Cross-sectional view of two modules of the ZR pulsed-power accelerator.

Figure 2

Conceptual design of Neptune. Since the design includes no MITLs, it has negligible current loss and enables use (on shots conducted with a hazardous material) of a passive containment system, one that is always closed.

Figure 3

Cross-sectional view of a three-dimensional model of Neptune. Each Marx tower includes six Marx generators.

Figure 4

Cross-sectional view of Neptune’s six-level conical-transmission-line system and post-hole convolute.

Figure 5

Circuit model of the Neptune accelerator. The quantities $L_M$, $C_M$, and $R_M$ are the series inductance, capacitance, and resistance, respectively, of a single Marx generator; $Z_{\mathrm{in}}$ and $Z_{\mathrm{out}}$ are the input and output impedances, respectively, of a single water-insulated coaxial-transmission-line impedance transformer; $Z_{\text{conical}}$ is the impedance of the system of twelve parallel water-insulated conical transmission lines; $L_{\mathrm{con}}$ is the inductance of the water-insulated post-hole convolute; $L_{\text{radial}}$ is the initial inductance of the solid-dielectric-insulated radial transmission line; $Z_{\mathrm{load}}$ is the load impedance (which in this article is assumed to be constant); and $R_{\text{radial}}$ is a resistive circuit element that models the time-dependent energy loss to the two radial-transmission-line electrodes.

Figure 6

(a) Circuit model of an impedance-matched Marx generator. (b) Equivalent circuit of such a Marx, when each brick of the circuit is triggered at time ${\tau }_b$ after the brick immediately upstream is triggered. The quantity ${\tau }_b$ is the one-way transit time of the transmission-line segment that connects two adjacent bricks.

Figure 7

Simulated load-current time history for a Neptune shot conducted with a single Marx generator. The peak current is 55 kA.

Figure 8

Simulated load-current time history for a Neptune shot conducted with 600 Marx generators. The Marxes are triggered as required to achieve a 380-ns linear current ramp. The peak current is 20 MA.

Figure 9

Simulated load-current time history for a Neptune shot conducted with 600 Marx generators. The Marxes are triggered as required to achieve a 300-ns linear current ramp followed by a top that is flat to $\pm 0.5\%$ for 150 ns. The peak current is 15.7 MA.

Figure 10

Idealized version of the Neptune-circuit model illustrated by Fig. 5. The circuit presented here assumes all the Neptune Marx generators are triggered simultaneously.