Understand Condensed Matter at Extreme Conditions: by Integrating Dynamic and Static Compression Methods
Yogendra M. Gupta
Department of Physics and Institute for Shock Physics, Washington State University
The combination of shock wave and static pressure experiments has been used for more than 50 years to gain insight into the response of condensed matter at extreme conditions. While both these approaches result in large compression of matter, there are significant differences between the states of matter achieved using these two methods: uniaxial strain versus nearly hydrostatic compression; large temperature rise versus isothermal compression; and very short time response versus very long time response. Depending on the magnitude of peak stresses achieved in shock compression experiments, one or more of these differences may play a significant role in comparing the two sets of results. At high stresses (well above a Mbar), the temperature rise under shock compression leads to thermodynamic states that are quite different from the isothermal compression under static pressure loading. At lower stresses (below a Mbar), deformation and kinetic issues can result in significant differences in matter compressed statically and using shock waves.
This talk will give an overview of shock wave compression issues along with representative examples of some recent achievements. Some new developments will be indicated with a particular emphasis on ramp wave loading resulting in quasi-isentropic compression. Ramp wave loading experiments have two important benefits: to provide thermodynamic states that are closer to isothermal compression, and to span large regions of thermodynamic space that are not accessible by either shock wave or static pressure experiments. Thus, dynamic compression experiments, due to recent advances in pulsed power technology and lasers, are now very versatile. However, to achieve good accuracy in the results and to gain detailed insight into the material response will require careful and systematic wave propagation analysis; a small price to pay for very significant payoff.
With increased versatility of dynamic compression experiments, there is an ever-increasing impetus to combine dynamic and static compression methods to better understand matter at extreme conditions. Static compression experiments have some inherent benefits: separation of compression, deformation and temperature. Perhaps, the most significant benefit of static pressure experiments is that they are more amenable to “microscopic” examination using a diverse array of methods available at national and international facilities like CHESS, APS, ALS, and LCLS.
Advances in dynamic compression drivers, DAC capabilities, and national facilities for improved probing of matter point to an exciting future for understanding condensed matter at extreme conditions. In my opinion, two challenges are paramount: how to achieve constructive synergy between national and international facilities; and how to ensure that the whole is greater than the sum of the parts. Finally, deep scientific understanding will require that theory and experiment be integrated in an effective and meaningful manner.
