A multichannel superconducting tunnel junction detector for high-resolution X-ray spectroscopy of magnesium diboride films

Abstract

We have built a high-resolution soft x-ray spectrometer using a 3 3 array of superconducting Nb-Al-AlOx-Al-Nb tunnel junctions. The detector is cooled to 0.1 K by a two-stage adiabatic demagnetization refrigerator while being held at the end of a 40-cm-long detector snout that can be inserted into an experimental chamber. The 0.6 mm 0.6 mm array has an energy resolution of 10-15 eV FWHM for x-ray energies below 1 keV and total count rate capabilities above 100 000 counts/s. We demonstrate the capabilities of the instrument in a study of anisotropy in-axis oriented MgB films by near edge x-ray absorption spectroscopy. The absorption fine structure at the B K-edge differs for excitation with x-rays polarized along the-axis and in the-plane of the MgB film. We discuss the implications of the anisotropy for the density of states in MgB at the Fermi surface.

The BeEST Experiment: Searching for Beyond Standard Model Neutrinos using $^7$Be Decay in STJs

“…The BeEST confronts these challenges using high-rate STJ radiation detectors and is the first instance of adapting them to search for BSM physics in nuclear decay. STJs are high-rate quantum sensors that were originally developed for high-resolution X-ray spectroscopy [14][15][16] and have been used for many years in astronomy 16 and at synchrotron facilities 17 . STJs are a type of Josephson junction that consists of two superconducting electrodes separated by a thin insulating tunneling barrier.…”

“…Since we implanted 100× less beam in the second implantation, the (138 µm) 2 STJs were used, which gave the best combination of statistics and resolution. For energy calibration of the Phase-II data, the STJs were simultaneously exposed to 3.49965 (15) eV photons from a pulsed Nd:YVO 4 laser triggered at a rate of 100 Hz. We adjusted the laser intensity such that multi-photon absorption provides a comb of peaks over the energy range of interest from 20 -120 eV in the (138 µm) 2 STJ.…”

Passive Spectroscopic Diagnostics for Magnetically-confined Fusion Plasmas

“…Cryogenic x-ray detector arrays, such as the microcalorimeter [181][182][183] , transition-edgesensor (TES) microcalorimeter [184][185][186] , and superconducting tunnel junction (STJ) detector 187 , are…”

Cryogenic X-ray detectors for synchrotron science

“…STJs are the cryogenic detector technology that has been used most extensively in synchrotron-based research so far because of their comparably high count-rate capabilities of over 10000 counts s À1 pixel À1 (Fig. 9) Friedrich et al, 2003). The maximum count rate is determined by the time that the excited excess charges remain in the junction area, either until they diffuse into the leads or until they recombine back into the superconducting ground state.…”