Cryogenic Current Comparators for Larger Beamlines
The new version of a cryogenic current comparator with eXtended dimensions (CCC-XD) for the beam monitoring of charged particles, which is currently in the optimization cycle, is presented herein. The CCC-XD is designed for a nondestructive, highly sensitive monitoring of a few nA beam intensities for 150-mm beamline diameters at the Facility for Antiproton and Ion Research at GSI (Helmholtz Center of Heavy Ion Research). The new CCC comprises a combined superconducting pickup loop, a magnetic shield, and a ferrite core with superconducting quantum interference device based readout. Compared to the previous CCC currently running at CERN, the niobium shield exhibits enlarged geometric dimensions, which results in a more effective suppression of magnetic stray fields from the beamline environment. First results of laboratory measurements as well as simulations of the electrical behavior are presented in this paper. The CCC-XD system—in combination with a newly developed cryostat—will be ready for testing in the beamline of CRYRING at GSI in 2018.
SQUID BASED CRYOGENIC CURRENT COMPARATOR FOR MEASURING LOW-INTENSITY ANTIPROTON BEAMS
In the low-energy Antiproton Decelerator (AD) and the Extra Low ENergy Antiproton (ELENA) rings at CERN, an absolute measurement of the beam intensity is essential to commission and troubleshoot the diﬀerent accelerator systems, to measure the operational eﬃciency, and to provide calibration information for the diﬀerent experiments using the antiproton (p) beam. Both the AD and ELENA are synchrotron decelerators, operating with both bunched and debunched - Direct Current (DC) - beams. The beam currents can be smaller than 100 nA, and the total number of circulating particles is of the order of 10^7. Non-intercepting measurements of low-intensity charged particle beams are particularly challenging due to the low amplitude of the induced electromagnetic ﬁelds. This is even more diﬃcult for DC beams. The most common diagnostics that are able to measure DC beams are the DC Current Transformers (DCCTs), but these present considerable limitations when used to measure low-intensity beams, since these are limited in current resolution to 1 µA. In the AD a longitudinal-Schottky (Schottky) monitor is currently used for intensity measurements but this presents several limitations, including accuracy errors above 10 %. Several laboratories have shown in the past the potential of Superconducting QUantum Interference Device (SQUID)-based Cryogenic Current Comparator (CCC), using Low-Temperature Superconductors (LTS) technology, to measure beam current intensities of slowly varying beams in the nano-ampere range. However, previous CCC beam monitors suﬀered from a strong susceptibility to mechanical vibrations, and ElectroMagnetic Interference (EMI) perturbations, and also presented limited availability which limited their operational use. Additionally, these were never able to cope with short bunched beams in a synchrotron accelerator. In the present work a CCC system was developed for the AD machine. This monitor was optimised in terms of its current resolution, ability to cope with short bunched beams and overall system stability. Also, a dedicated cryostat was designed and fabricated to house the CCC, and to be installed in the AD beam line, aiming at decoupling external mechanical vibrations from the monitor, and to have a reduced heat in-leak, allowing for a standalone operation with an external liquid helium reliqueﬁer. The new monitor was characterized in laboratory and diﬀerent measurements are presented. Measurements with real beam were also performed in the AD, and the resolution and accuracy of beam current and beam intensity measurements were assessed. Optimal beam current resolutions of 2.5 nA, and beam intensity resolutions of 1.2 × 10^4 charges (at the highest beam energy) were obtained. However, the limiting factor in the obtained absolute measurement accuracy was the observed drift of the zero beam baseline, which could amount to 25 nA. These are the ﬁrst CCC beam current and intensity measurements ever performed in a synchrotron machine with both coasting and short bunched beams. Future improvements could be obtained by studying the origin and eﬀect of the external perturbations causing the observed drift, leading to the implementation of mitigation and compensation techniques.
Superconductivity: Fundamentals and Applications
Introduction.1 Fundamental Properties of Superconductors.1.1 The Vanishing of the Electrical Resistance.1.2 Ideal Diamagnetism, Flux Lines, and Flux Quantization.1.3 Flux Quantization in a Superconducting Ring.1.4 Superconductivity: A Macroscopic Quantum Phenomenon.1.5 Quantum Interference.2 Superconducting Elements, Alloys, and Compounds.2.1 Conventional and Unconventional Superconductors.2.2 Superconducting Elements.2.3 Superconducting Alloys and Metallic Compounds.2.4 Fullerides.2.5 Chevrel Phases and Boron Carbides.2.6 Heavy-Fermion Superconductors.2.7 Natural and Artificial Layered Superconductors.2.8 The Superconducting Oxides.2.9 Organic Superconductors.2.10 Superconductivity Due to the Field Effect.3 Cooper Pairing.3.1 Conventional Superconductivity.3.2 Unconventional Superconductivity.4 Thermodynamics and Thermal Properties of the Superconducting State.4.1 General Aspects of Thermodynamics.4.2 Specific Heat.4.3 Thermal Conductivity.4.4 Ginzburg-Landau Theory.4.5 Characteristic Lengths of Ginzburg-Landau Theory.4.6 Type-I Superconductors in a Magnetic Field.4.7 Type-II Superconductors in a Magnetic Field.4.8 Fluctuations Above the Transition Temperature.4.9 States Outside Thermodynamic Equilibrium.5 Critical Currents in Type-I and Type-II Superconductors.5.1 Limit of the Supercurrent Due to Pair Breaking.5.2 Type-I Superconductors.5.3 Type-II Superconductors.6 Josephson Junctions and Their Properties.6.1 Current Transport Across Interfaces in a Superconductor.6.2 The RCSJ Model.6.3 Josephson Junctions Under Microwave Irradiation.6.4 Vortices in Long Josephson Junctions.6.5 Quantum Properties of Superconducting Tunnel Junctions.7 Applications of Superconductivity.7.1 Superconducting Magnetic Coils.7.2 Superconducting Permanent Magnets.7.3 Applications of Superconducting Magnets.7.4 Superconductors for Power Transmission: Cables, Transformers, and Current-Limiting Devices.7.5 Superconducting Resonators and Filters.7.6 Superconducting Detectors.7.7 Superconductors in Microelectronics.Monographs and Collections.Outlook.Subject Index.