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.
A Cryogenic Current Comparator for the Low-Energy Antiproton Facilities at CERN
Several laboratories have shown the potential of using Superconducting QUantum Interference Device (SQUID) magnetometers together with superconductor magnetic shields to measure beam current intensities in the submicro-Ampere regime. CERN, in collaboration with GSI, Jena university and Helmholtz Institute Jena, is currently working on developing an improved version of such a current monitor for the Antiproton Decelerator (AD) and Extra Low ENergy Antiproton (ELENA) rings at CERN, aiming for better current resolution and overall system availability. This contribution will present the current design, including theoretical estimation of the current resolution; stability limits of SQUID systems and adaptation of the coupling circuit to the AD beam parameters; the analysis of thermal and mechanical cryostat modes. LOW-INTENSITY BEAMS CURRENT MEASUREMENT Low-intensity charged particle beams present a considerable challenge for existing beam current diagnostics [1], this is particularly significant for coasting beams with average current below 1μA which is the minimum resolution of DC Current Transformers. Other monitors, such as AC Current Transformers or Schottky monitors are able to measure low-intensity beam currents, but neither can simultaneously provide an absolute measurement, with a high current and time resolution, which is at the same time independent of the beam profile, trajectory and energy. At CERN’s low-energy antiproton decelerators, the AD and the ELENA (currently under construction) rings, circulate both bunched and coasting beams of antiprotons with average currents ranging from 300 nA to 12μA [2]. Having a current measurement with the above mentioned characteristics would benefit the machine operation and optimization. To meet these requirements, a low-temperature SQUIDbased Cryogenic Current Comparator (CCC) is currently under development. Similar devices have already been developed for electrical metrology [3], and later for beam current measurements in particle accelerator [4]. The current, a collaboration between CERN, GSI, Jena University and Helmholtz Institute Jena aims to make this a fully operational device, with a prototype foreseen to be tested in the AD machine at CERN in 2015. ∗Funded by the European Unions Seventh Framework Programme for research, technological development and demonstration under grant agreement no 289485. The main design specifications for the monitor are: beam current resolution < 10 nA; and measurement bandwidth > 1 kHz. Overview of the Functioning Principle of the CCC The CCC (see Fig. 1) works by measuring the magnetic field induced by the particle beam current. This field is concentrated in a high-permeability ferromagnetic pickup core, from which it is coupled into a Superconducting QUantum Interference Device (SQUID). These are highly sensitive magnetic flux sensors that permit sensing the weak fields created by the beam. A superconducting magnetic shield structure around the pickup-core, as described in [4, 5], renders the coupled magnetic field nearly independent of the beam position and makes the system practically immune to external magnetic field perturbations. Figure 1: Schematic of the CCC. CCC MONITOR DIMENSIONING The AD CCC will in a first phase use a superconducting shield and pickup core developed by Jena University and Helmholtz Institute Jena. This core has a single turn inductance LP = 104μH, while the SQUID device 1 has the following parameters, input coil self-inductanceLi = 1μH and mutual inductance Mi = 3.3φ0/μA 2. Coupling Circuit and esolution The circuit such as the one depicted in Fig. 2 will be used to couple the beam current signal into the SQUID. The transfer function of this circuit, defined as the change 1Manufactured by Magnicon GmbH. φ0 = 2.0678×10−15 Wb is the magnetic flux quantum which is the unit commonly used for magnetic flux when dealing with SQUID systems. R WEPF04 Proceedings of IBIC2014, Monterey, CA, USA ISBN 978-3-95450-141-0 530 Co py rig ht © 20 14 CC -B Y3. 0 an d by th er es pe ct iv ea ut ho rs Beam Charge Monitors in the flux coupled to the SQUID per unit change in beam current SIB = ΦS(t)/IB(t), excluding the RC-shunt, is given by: SIB = [ MiMPMf (LP + L1)(L2 + Li)−M f ]
Judicial politics in Britain: Patrolling the boundaries
This study considers judicial policy‐making in Great Britain by noting the peculiarly British institutional restraints on judicial action of parliamentary sovereignty, the resulting subordination of all courts to the legislative branch and the absence of a codified charter of rights or constitution. Though there is no judicial power to annul legislative or executive actions, British courts and judges still play a small, but significant, role in policy‐making through the common law and, in particular, through judicial review of adminstrative actions. A written bill of rights would likely draw courts further into the the political arena and politicise the appointment of judges.