Charles H. Mielke

A simple machine for isentropic compression experiments (ICE)

A single-turn magnet pulsed power system, at the Los Alamos National Laboratory (LANL) National High Magnetic Field Laboratory (NHMFL), was originally designed to measure actinide samples in extremes of high magnetic field (to 300 Tesla) [1, 2]. A simple modification to the system has converted it to a fast turnaround, inexpensive, magnetic system for Isentropic Compression Experiments (ICE). For the design and predictions of performance of the NHMFL-ICE experiment a circuit code simulation was chosen to model all aspects of the experiment, electrical and physical. This paper describes the potential performance of the system, recent experiments, and plans for a portable system. The 2.2 is rise time of the system allows sample thicknesses up to ~5 mm. With the present design the maximum stresses are ~50GPa (0.5 Mbar) at the maximum bank voltage of 60 kV.

Reversal of the Upper Critical Field Anisotropy and Spin-Locked Superconductivity in K2Cr3As3

Recently, superconductivity in K2Cr3As3 (Tc =6.1 K) was discovered. The crystalline lattice contains an array of weakly coupled, double well [(Cr3As3)2-]∞ linkages stretched along the c axis, suggesting the possibility of quasi-one-dimensional superconductivity. Moderately anisotropic upper critical field was revealed in single crystals, with very large initial slopes, dH∥c2 /dT=12 T/K along the Cr chains and dHperpendicularc2 /dT =7 T/K perpendicular to the chains. Given the ambiguity of conclusions based on the extrapolations of Hc2(T) measured near Tc to low temperatures, we performed high-field measurements of Hc2(T) on K2Cr3As3 single crystals in pulsed magnetic fields which enabled us to reveal the full anisotropic Hc2(T) curves from Tc down to 600 mK.