Transition-edge Sensor Calorimeters Research Articles

The Phonon-Mediated TES Cosmic Ray Detector for Focal Plane of ATHENA X-Ray Telescope

The current projects of future X-rays space telescopes foresee high resolving power transition edge sensor (TES) micro-calorimeters arrays as focal plane instrument. In order to full exploit their sensitivity in the space environment, they need an anticoincidence detector to reject the background due to cosmic charged particles. High-energy protons (> 150 MeV) and other charged particle may release in the X-ray calorimeter, the same energy of the X-rays sources under observation. We report the description of the last prototype based on TES calorimeter where a 1-cm2 silicon chip is used as both substrate and absorber. The readout is made of 96 iridium/gold TESs uniformly distributed on its surface and parallel wired. In this paper, we will describe the design, with the preliminary phonon dynamics simulation, the fabrication, of first demonstration model for the ATHENA space telescope project.

Soft x-ray measurement of the toroidal pinch experiment RX reversed field pinch plasma using transition edge sensor calorimeter

A superconductive transition edge sensor (TES) calorimeter is for the first time applied for the diagnostics of the reversed field pinch plasma produced in the toroidal pinch experiment RX (TPE-RX), and the instrumental system is fully described. The first result from the soft x-ray spectroscopy in 0.2–3keV with an energy resolution ∼50eV are also presented. The TES calorimeter is made of a thin bilayer film of titanium and gold with a transition temperature of 151mK and its best energy resolution at our laboratory is 6.4eV, while it was significantly degraded by about a factor of eight during the plasma operation. The TES microcalorimeter was installed in a portable adiabatic demagnetization refrigerator (ADR), which is originally designed for a rocket experiment. The detector box is carefully designed to shield the strong magnetic field produced by the ADR and TPE-RX. The ADR was directly connected to TPE-RX with a vacuum duct in the sideway configuration, and cooled down to 125mK stabilized with an accuracy of 10μK rms using an improved proportional, integral, and derivative (PID) control method. Thin aluminized Toray Lumirror or Parylene-N films were used for the IR to UV blocking filters of the incident x-ray window to allow soft x-rays coming into the detector with good efficiency. TPE-RX was operated with the plasma current of Ip=220kA, and the wave forms of the TES output for every plasma shot lasting ∼80ms were obtained with a digital oscilloscope. The wave forms were analyzed with the optimal filtering method, and x-ray signals were extracted. A total of 3472 counts of x-ray signals were detected for 210 plasma shots during the flat-top phase of t=35–70ms. Combined with the data measured with a lithium drifted silicon detector in the 1.3–8keV range, spectral features are investigated using a spectral fitting package XSPEC. The obtained spectrum is well explained by thermal plasma emission, although an impurity iron-L line emissions at variously ionized states are dominant around 0.7–1.2keV. At least three different temperature components ranging T=350–900eV are required to account for the spectral shape, while the average temperature is consistent with the ruby laser Thomson scattering measurement.

Characterization and reduction of noise in Mo/Au transition edge sensors

We measured noise in a variety of Mo/Au transition-edge sensor (TES) X-ray calorimeters. We investigated the relationship between the noise, bias, and the superconducting phase transition in the TESs. Our square TES calorimeters have achieved very good energy resolutions (2.4eV at 1.5keV) but their resolutions have been limited by broadband white excess noise generated by the TES when it is biased in the phase transition. We have recently fabricated Mo/Cu TESs with interdigitated normal metal bars deposited on top of the bilayer. The new TES calorimeters have demonstrated little or no excess noise in the phase transition. These results point the way to development of TES calorimeters with higher energy resolution.

High-current resolution broad-band SQUID amplifier suitable for TES calorimeter

A superconducting quantum interference device (SQUID) amplifier has been developed as a current detector with both high-current resolution and broad bandwidth for a transition edge sensor calorimeter. The amplifier is a two stage SQUID (TSS) that consists of an input-SQUID with a 38-turn input coil and a 100-serial SQUID array (100-SSA) output, and has been integrated on a 3 /spl times/ 3 mm Si chip using Nb thin film fabrication technology. It is designed to increase the amplifier gain and maintain matching with the parameters of the calorimeter. To avoid flux trapping in the SSA, the washer coil of the dc-SQUIDs in the SSA was made with a narrow line width of 17.5 /spl mu/m. We experimentally confirmed that the designed output voltage was achieved using a one-layer p-metal magnetic shield tube in the earth's magnetic field. The performance of the shielded TSS amplifier was evaluated in liquid helium. The TSS amplifier had a gain of 10 kV/A and an impedance of 0.07 /spl Omega/ at 100 kHz. When a flux locked loop circuit was used to drive the amplifier, a current resolution of 1 pA//spl radic/Hz and a rise time of 1 /spl mu/s were achieved.

First results from Mo/Au transition-edge sensor X-ray calorimeters

Superconducting bilayers made of thin films of molybdenum and gold show promise as robust transition-edge sensor (TES) thermometers for calorimeters. We present our first X-ray results from experiments with Mo/Au TES calorimeters on silicon-nitride membranes. These results include analysis of the signal pulse shape and noise as functions of the bias point, which is varied through changing the bias voltage for operation at different places within the superconducting transition and changing the heat sink temperature relative to the transition temperature. Ultimately, we determined that the performance of our devices is limited by the slew rate of the SQUID amplifier used to measure the change in current, which restricts the choice of bias. The amplifier must be replaced before further device characterization and optimization can proceed.