Isentropic compression experiments on the Sandia Z accelerator

Abstract

A long-standing goal of the equation of state (EOS) community has been the development of a loading capability for direct measurement of material properties along an isentrope. Previous efforts on smooth bore launchers have been somewhat successful, but quite difficult to accurately reproduce, had pressure limitations, or tended to be a series of small shocks as opposed to a smoothly increasing pressure load. A technique has recently been developed on the Sandia National Laboratories Z accelerator which makes use of the high current densities and magnetic fields available to produce nearly

High-pressure tailored compression: Controlled thermodynamic paths

“…We estimate the strain rate to average 3 − 5 × 10 4 s −1 for these shots by using hydrodynamic simulation results. These strain rates are similar to or are an order of magnitude lower than other quasi-isentropic compression techniques [17][18][19][20].At the presented˙ in metals, the sample is expected to be near local thermal equilibrium, since the thermal relaxation times for particle interactions are significantly faster: 10 −13 s (electron-phonon), 10 −12 s (phonon-phonon), and 10 −12 s (electron-electron) [29]. Specifically in Fig.…”

“…With these tools, they have simulated the physical conditions in the Earth's core and planetary interiors [1,2], probed a wide range of high pressure and temperature material properties [5][6][7][8][9][10], synthesized novel materials [11,12], and solved long standing physics problems such as the metallization of hydrogen [13]. These extreme conditions were achieved through three main techniques: static, shock and quasi-isentropic compressions [13][14][15][16][17][18][19][20][21][22][23][24]. Since the pioneering work by P. W. Bridgman [25], advances in diamond anvil cell technology have pushed the peak pressure by static compression from 200 kbars to more than 4 megabars [21,22].…”

“…Shock compression rapidly loads a sample at strain rates of˙ > ∼ 10 9 s −1 to a single state on the Hugoniot -a locus of shock compression states. Current quasi-isentropic compression techniques constrain samples to lie near an isentrope, with strains rates of around˙ ≈ 10 5 s −1 to˙ ≈ 10 8 s −1 [17][18][19][20].With these vastly different strain rates varying as much as 10 orders of magnitude, there is no a priori reason to assume that the high pressure and temperature data gathered with these differing techniques can be directly compared [1]. What is needed is a less constrained approach that can produce highly compressed states, as well as afford continuity between the thermodynamic paths and time scales.…”

“…Since the pioneering work by P. W. Bridgman [25], advances in diamond anvil cell technology have pushed the peak pressure by static compression from 200 kbars to more than 4 megabars [21,22]. Similarly, shock compression and quasi-isentropic compression techniques [13][14][15][16][17][18][19][20] can load samples to megabar pressures in a fraction of a nanosecond to microseconds.Future advances will likely push the peak pressure higher and extend the pressure loading time. However, these techniques will continue to be limited to a portion of the high pressure phase diagram by their characteristic loading rate and a single thermodynamic path.…”

Modeling Planetary Interiors in Laser Based Experiments Using Shockless Compression

“…Quasi-isentropic has been performed using pillow impactors on gas guns [12], temporal pulse shaping on z-pinch facilities [13], HE expanding across a vacuum gap [14] and a two component target on laser facilities [15,16]. In a similar fashion to the HE case, the laser target uses a plastic reservoir which is shocked with a high-powered laser and the plasma blow off from the ensuing blast wave crosses a vacuum gap and pressurizes the sample.…”