DEVELOPMENT OF ADVANCED INSTRUMENTATION FOR STATIC AND PULSED FIELDS

Abstract

The DC and pulsed magnets now available at the NHMFL provide routine access to high magnetic fields in cryogenic environments (down to even dilution refrigerator levels), that are world-record unique. This uniqueness comes with a price that reflects constraints of the magnets and the low temperatures, including limited volume and time at peak magnetic field, cryogenic power limits on electronics, and, particularly for pulsed magnets, increased noise. In effect, the instrumentation constraints are similar for NHMFL superconducting, resistive and pulsed magnets. An NHMFL experimentalist therefore has a simple goal: acquisition of all the information produced by a measurement in the shortest time permitted by information theory, with minimum sensitivity to noise and interference. To assist with this, we propose here to eliminate commercial general-purpose lock-in amplifiers, preamplifiers and digitizers and replace them with commercial-quality custom building blocks optimized for NHMFL measurements, that are faster, quieter, more versatile, and cheaper. We will use these new instruments to support users by improving present measurements as well as adding new capabilities, including specific heat for materials that suffer adiabatic effects in pulsed fields, and thermal conductivity in both dc and pulsed magnets based on 3rd harmonic methods. We will use these techniques to measures the thermal conductivity of high Tc superconductors at high field in the normal state, and to test the Weideman-Franz relationship between electronic thermal conductivity and electrical conductivity in the extreme high-field limit.