Andreev reflection from a B-A interface in superfluid3He

Superfluid3He-B has an isotropic energy gap. However, when a magnetic field is applied this gap becomes distorted and at a critical field a transition to the A-phase occurs. In the B-phase a quasiparticle entering a region of increasing field may find that it carries too little energy to continue and is Andreev reflected back along its trajectory. We use a miniature superconducting solenoid to generate a field in a small region. We direct a beam from a Quasiparticle Black Body Radiator into the bore of the solenoid. The Andreev-reflected quasiparticle flux increases the temperature within the radiator. From this we can calculate the maximum gap within the solenoid.