Thick film YBCO current concentrator for non-invasive sensing of charged particle beams

Full text: The principle of the High-Temperature-Superconducting cryogenic current comparator (HTS-CCC), coupled with an HTS SQUID detector, is here applied to the non-invasive sensing of charged-particle beams . When an ion or electron beam is passed along the axis of a superconducting tube, the Meissner effect causes a shielding current to flow in the opposite direction, along the inside surface of the tube. This screening current, which is independent of the trajectory and of the finite width of the beam, returns along the outside surface of the tube, where in principle its magnetic field can be coupled to a detector. The return current is concentrated in a specially-structured HTS thick-film bridge adjacent to a planar gradiometer SQUID. We have experimentally verified both the principle, and the expected sensitivity, of the technique with simple rectangular bridge geometries. We now plan more complex bridge geometries to enhance the sensitivity. For example, if the bridge is S-shaped, we calculate that the beam current resolution for optimum device parameters may be as small as 10 pA/(rtHz). Two thick-film HTS current concentrators designed along these lines are being constructed. As well as providing for continuous non-invasive monitoring of low-intensity beam currents, the above sensitivity together with a typical SQUID response time of ∼1 microsecond should, under appropriate conditions, allow the charged particles, irrespective of their radial distribution, to be individually resolved without interrupting the beam. Applications in ion-beam implantation systems and in mass spectrometry can be envisaged. Recent simulations and experimental measurements of the flux concentration ratio, linearity and sensitivity of such a prototype HTS-CCC operating at 77K are presented