SQUID Developments for the Gravitational Wave Antenna MiniGRAIL

Abstract

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> 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 <formula formulatype="inline"><tex>$\mu{\rm H}$</tex></formula> 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 <formula formulatype="inline"> <tex>$\mu\Phi_{0}/\surd{\rm Hz}$</tex></formula> below a temperature of 200 mK. The equivalent noise referred to the current through the input coil is 155 <formula formulatype="inline"><tex>${\rm fA}/\surd{\rm Hz}$</tex></formula> and the energy resolution yields 62 <formula formulatype="inline"><tex>$\hbar$</tex> </formula>. </para>