K.H. Kuit

SQUID Developments for the Gravitational Wave Antenna MiniGRAIL

We designed two different sensor SQUIDs for the readout of the resonant mass gravitational wave detector MiniGRAIL. Both designs have integrated input inductors in the order of 1.5 muH and are planned for operation in the mK temperature range. Cooling fins were added to the shunt resistors. The fabricated SQUIDs show a behavior that differs from standard DC-SQUIDs. We were able to operate a design with a parallel configuration of washers at reasonable sensitivities. The flux noise saturated to a value of 0.84 muPhi0/radicHz below a temperature of 200 mK. The equivalent noise referred to the current through the input coil is 155 fA/radicHz and the energy resolution yields 62 h.

Preparing for science run 1 of MiniGRAIL

We report on the eighth cryogenic run of MiniGRAIL, which is planned to be the first science run. Three new capacitive transducers were mounted on the sphere, all coupled to superconducting transformers and a double-stage SQUID amplifier. All SQUID modules had a noise level between 1 and 2 μΦ0 Hz−1/2 at 4 K in separate test runs. The detector was upgraded with a complete data acquisition and data storage system, and a data analysis program for millisecond burst signals was written using a matched filter. Two cosmic-ray detectors were built and installed on the roof above MiniGRAIL as a veto for cosmic rays. A test run was done, but failed because of bad electrical isolation of the transducer electrode at low temperatures. A new cool-down is currently going on. With an already obtained sphere temperature of 65 mK and a SQUID noise of 100, the expected sensitivity should be 4 × 10−22 Hz−1/2.

Hybrid magnetometers based on a doped silicon-on-insulator Hall device and a YBa2Cu3O7−δ flux concentrator

We are developing a hybrid magnetometer based on a doped Si Hall device and a high Tc superconducting flux concentrator. An overview of the present status of the various aspects of research is given. This includes a theoretical derivation of the expected device properties and an optimal design of the concentrator which shows that in theory a sensitivity of 23 V T−1 can be obtained at T = 77 K with an As doped Si Hall device. Moreover, the sensitivity is enhanced by a factor of 10–25, depending on the desired dynamic range, by the concentrator. Implantation of As in Si and pulsed laser deposition of YBa2Cu3O7−δ on Si are the two main challenging production steps which will be discussed in more detail.