First application of a TES microcalorimeter to a thermonuclear fusion plasma experiment

We report the first application of a superconductive transition edge sensor (TES) microcalorimeter to a thermonuclear fusion plasma experiment in the toroidal pinch experiment RX (TPE-RX). The TES microcalorimeter was installed in a portable adiabatic demagnetization refrigerator (ADR), which is originally designed for a rocket experiment. The ADR was directly connected to TPE-RX with a vacuum duct, and thin Toray–Lumirror or parylene films were used for entrance windows to allow soft X-rays coming into the detector with good efficiency. The detector box was designed to shield the strong magnetic field produced by ADR and TPE-RX. A total of 3472 counts of X-ray signals were detected in 0.2–3.0 keV for 210 plasma shots during the flat-top phase (35–70 ms) after discarding pile-up events. Combining the data with that measured in the energy range of 1.3–8 keV using a SiLi detector, we examined a wide band X-ray spectrum of the plasma. The obtained spectrum is dominated by thermal plasma emission, although at least four different temperature components are required to account for the whole band spectral shape. Impurities in the deuterium plasma are also investigated.