Superconducting thin film spiral coils as low-noise cryogenic actuators

Abstract We present results on actuator development for a cryogenic superconducting inertial sensor with a displacement sensitivity of a few <?CDATA ${\rm{fm}}/\sqrt{{\rm{Hz}}}$?> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi mathvariant="normal">fm</mml:mi> <mml:mo>/</mml:mo> <mml:msqrt> <mml:mrow> <mml:mi mathvariant="normal">Hz</mml:mi> </mml:mrow> </mml:msqrt> </mml:mrow> </mml:math> at 0.5 Hz. The first version will use niobium as sensor mechanics material. Niobium is sufficiently superconducting below 5 K allowing superconducting coils to form low-noise actuators as part of a force feedback sensing scheme. Future improvements include the use of silicon in combination with high temperature superconductors for even lower frequency fm/ <?CDATA ${\rm{fm}}/\sqrt{{\rm{Hz}}}$?> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi mathvariant="normal">fm</mml:mi> <mml:mo>/</mml:mo> <mml:msqrt> <mml:mrow> <mml:mi mathvariant="normal">Hz</mml:mi> </mml:mrow> </mml:msqrt> </mml:mrow> </mml:math> performance. This device will be the world’s most sensitive low-frequency inertial sensor. Here, we focus on its actuator, which ensures low-noise performance below 5 Hz by decreasing the mechanical loss and therefore thermal noise.