Progress In Kinetic Inductance Thermometers For X-Ray Calorimeters

Conventional X-ray microcalorimeters have so far used ion-implanted resistors for thermometers. Recently, however, several new methods for sensing small temperature changes have been suggested that are non-dissipative. Such devices may have intrinsically better energy resolution by eliminating the Johnson noise present in resistive devices. We are investigating the use of kinetic inductance thermometers for X-ray microcalorimeters. This technique exploits the strong temperature dependence of magnetic penetration depth of thin superconducting films. Our prototype system, designed for operation at 1.5 K, uses films of aluminum and tin. Once the expected temperature sensitivity and alpha particle detection have been demonstrated, we expect to replace the aluminum with titanium or another material with a suitable critical temperature and operate the device at 0.3 K. At this temperature the energy resolution from thermal noise should be sufficiently good to allow X-ray detection.