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.
Review of the Experimental Results with a Cryogenic Current Comparator
A new type of beam transformer, using the principle of a Cryogenic Current Comparator, was built to measure extracted ion beams from the SIS, the heavy ion synchroton at GSI. A current resolution of 0.1-0.3 nA/ p Hz, depending on the frequency range, could be achieved which allows to measure ion beams with intensities greater than 10 9 particles per second with high accuracy. Numerous investigations were carried out to study the zero drift of the system which shows a strong exponential slope with two different time constants. Furthermore the microphonic sensistivity of the system was studied by taking noise spectra of the detector output signal. Additional measurements were made with a vibration sensor to separate the horizontal and vertical components of the mechanical influences from the disturbing electrical interferences. The recent results including the first tests with ion beams will be presented in this paper. 1 THE DETECTOR SYSTEM 1.1 The Measuring Principle A non-destructive method was sought for measuring the intensity of extracted ion beams from the GSI synchroton in the region above 10 9 particles per second (pps). Beam transformers of the fluxgate type can measure in a nondestructive manner and with a bandwidth from dc to several kHz, but their resolution only reaches one A. Therefore a much more sensitive measuring principle was chosen – a Cryogenic Current Comparator (CCC), first developed by Harvey (National Standards Laboratory, Sydney, Australia) for precise dc current ratios in 1972 [1]. To compare two currents with high precision he used a superconducting meander shaped flux transducer. Only the azimutal magnetic field component, which is proportional to the current in the wires, will then be sensed by the pick-up coil – all other field components are strongly suppressed. The very small magnetic flux coupled into the coil were detected by an RFSQUID. A further device for beam intensity measurements using the CCC-principle achieved a current resolution of about 10 nA, but the stability was inadequate due to the installed RF-SQUIDs and other technical difficulties [2]. Figure 1: Cryostat with detector system built in the beam line of the beam diagnostics test facility (Photo: Achim Zschau, GSI) 1.2 The Construction of the Detector Some new techniques were used in our concept [3] to solve the problems that occured in the PTB-device [2]. The main components of the detector (see fig. 1) are the superconducting flux transducer made of lead tubes and plates isolated by Teflon foil; the attenuation of all non-azimutal magnetic field components was designed and calculated to realize a level of 10 , a superconducting flux coupling coil as the antenna for the ion beam, consisting of a superconducting niobium toroid with a VITROVAC 6025-F core (VAC GmbH, Hanau, Germany), a coupled d.c. SQUID system made by the FriedrichSchiller-University of Jena as the extremely high sensitive magnetic flux sensor (noise limited sensitivity: 4 10 6 0= p Hz) with a modulation frequency of 125 kHz and a measuring bandwidth of nearly 10 kHz, a special LHe-bath-cryostat with a ”warm hole” of Ø 100 mm for the passing ion beam; the outer heat shield consist of a superinsulated copper vessel cooled down to 35 K by a refrigerator . 2 THE PERFORMANCE OF THE CCC 2.1 The Current Resolution After testing and assembling of all parts of the detector measurements concerning the current resolution and the noise limitations were started with. To simulate the ion beam a simple wire loop (one winding) around the flux transducer was installed. Using a calibrated picoampere current source (KEITHLEY 261) the current sensitivity was measured. Fig. 2 shows the output of the SQUID electronics as a function of the calibration current. The current sensitivity of the detector system was determined to 177.3 nA/ 0 the linearity error is smaller than 0.5 %; 1 0 corresponds to an output signal of 2.5 V in the most sensitive range of the SQUID system. During the measurements the refrigerator was switched off to avoid microphonic effects (see below). To determine the current resolution of 0,0 0,2 0,4 0,6 0,8 1,0 S Q U ID -O u tp u t [V ]
Solitary Orbital Paget Disease: A Case Report
Purpose: To describe the clinical findings in a patient who had developed painless supraorbital prominence. Methods: Clinical and histopathological findings of the case are reviewed and presented. Results: The patient had an isolated histologically confirmed Paget disease of the orbit. Local excision of the lesion was performed. Conclusion: Paget disease can present not only as a diffuse process but also as a painless, solitary lesion of the orbit.