Abstract: The device includes a first body (1) of superconducting material placed in the magnetic field to be measured, an arrangement (7) suitable for successively changing the temperature of this first body above and below its transition temperature, at a first frequency, so as to generate field variations in the vicinity of the body, and an arrangement for determining the field from these variations. The arrangement includes a second body (4) of superconducting material, placed in the vicinity of the first body (1), an optical fiber (8) suitable for changing the temperature of at least one portion of this second body, above and below its transition temperature, at a second frequency greater than the first frequency, in order to generate, in this second body, current variations proportional to the field variations. These current variations are then measured and the field is determined from these variations.

Abstract: This device for converting a very-low-amplitude steady voltage signal into an alternating voltage signal, of the type comprising a centre-tapped transformer (1) associated with a transistor (3,4) chopper (2), is characterised in that the transformer (1) and the transistors (3,4) are arranged in a housing (15) held at very low temperature and in which is arranged a material (20) for thermal insulation of the transistors (3,4) with respect to the rest of the housing so as to reduce temperature fluctuations and allow operation of these transistors by self-heating due to their drive current.

Abstract: Apparatus for electrically chopping a direct current signal by controlling the superconductivity state of resistance elements contained within a cryostat. The resistance elements are in a bridge arrangement and the control is provided by laser diodes also contained within the cryostat.