Isentropic compression studies at the Los Alamos National High Magnetic Field Laboratory

A single-turn magnet pulsed power system at the National High Magnetic Field Laboratory (NHMFL) at Los Alamos was originally designed to study actinide samples in extremes of high magnetic field (to 300 Tesla) [1, 2]. A simple modification to the single-turn magnet has converted it to a fast turnaround dynamic high pressure measurement system for Isentropic Compression Experiments (ICE). This paper details the work done including design, theory, modeling and results. The NHMFL system has the advantage of a relatively long-duration current with a ~2.3-μs rise time, which allows for large sample dimensions, i.e., up to 5 mm thickness, see II.D. The maximum stress is ~50GPa (0.5 Mbar) at the maximum bank voltage (60 kV); higher stresses may be obtained with modifications to the load design. For the design and predictions of performance of the NHMFL-ICE experiment it is important to have good numerical models. A novel SPICE code simulation was chosen to model all aspects of the experiment, electrical and physical. To this end, accurate dynamic load models were developed to simulate the compression and expansion of the dynamic load at high pressures using shock physics principles. In this study feasibility of adapting the existing NHMFL capacitor bank for ICE experiments up to 100 GPa is demonstrated. The adaptation saved the expense of building a dedicated capacitor bank yet this new system produces high quality ICE data with a rapid turnaround and very low cost per experiment. A series of proof-of-principle experiments [3] demonstrated the feasibility of the NHMFL-ICE technique; some of the results will be shown here to illustrate the effectiveness of the new technique.