The generation of warm dense matter using fast magnetic compression at 10 MA

Abstract

Knowing the properties of warm dense matter is crucial to understanding the formation and evolution of giant planets, including gaseous giants or mega-Earths. Generating warm dense matter in the laboratory has been limited to samples on the micron scale. Probing such small volumes raise major challenges in measuring the properties of warm dense matter using standard diagnostics. This work proposes a new method to produce warm dense matter samples on the centimeter scale using pulsed-power generators with current rise-times on the order of 100 ns. We numerically demonstrate that the early expansion phase of the sample, usually encountered in pulsed-power driven implosions, can be virtually eliminated by using a fast current switching scheme. To avoid mixing the plasma and warm dense matter states, the present strategy uses a low-Z gas puff z-pinch as a closing plasma switch. A cylindrical metallic sample is connected between the anode and the cathode of a pulsed-power generator. Using a fast valve, gas is injected cylindrically around the sample. The gas is pre-ionized just before the main current discharge. Since the sample is initially cold and its diameter is much smaller than the gas column, most of the current flows inside the gas during the first part of the discharge. During this phase, the gas is compressed as a z-pinch and converges radially until it reaches the sample. At this time, all the current carried by the gas z-pinch switches to the sample in 10 ns, rapidly heating and compressing it. The sample gets into a warm dense matter state while the strong azimuthal field generated by the z-pinch prevents the expansion of the sample. Numerical simulations show that this method can produce centimeter-size warm dense matter samples using a 10 MA linear transformer driver.