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The Cryogenic Current Comparator (CCC) extends the measurement range of traditional non-destructive current monitors used in accelerator beamlines down to a few nano-amperes of direct beam current. This is achieved by a cryogenic environment of liquid helium around the beamline, in which the beam’s magnetic field is measured with a Superconducting Quantum Interference Device (SQUID), which is itself enclosed in a superconducting shielding structure. For this purpose, a versatile UHV-beamline cryostat was designed for the CCCs at FAIR and is currently in production. It is built for long-term autonomous operation with a closed helium re-liquefaction cycle and with good access to all inner components. The design is supported by simulations of the cryostat’s mechanical eigenmodes to minimize the excitation by vibrations in an accelerator environment. A prototype at GSI has demonstrated the self-contained cryogenic operation in combination with a 15 l/day re-liquefier. The cryostat will be used in CRYRING to compare the FAIR-CCC-X with newly developed CCC-types for 150 mm beamlines. Both which will supply a nA current reading during commissioning and for the experiments., Proceedings of the 8th International Beam Instrumentation Conference, IBIC2019, Malmö, Sweden

A Cryogenic Current Comparator (CCC) is a non-destructive, metrological-traceable charged particle beam intensity measurement system for the nano-ampere range. Using superconducting shielding and coils, low temperature Superconducting Quantum Interference Devices (SQUIDs) and highly permeable flux-concentrators, the CCC can operate in the frequency range from DC to several kHz or hundreds of kHz depending on the requirement of the application. Also, the white noise level can be optimized down to 2 pA/sqrt(Hz) at 2.16 K. This work compares three different Pb- and Nb-based CCC-sensors developed at the Institute of Solid State Physics and Leibniz Institute of Photonic Technology at Jena, Germany: CERN-Nb-CCC, optimized for applica-tion at CERN Antiproton Decelerator (AD) in 2015 with a free inner diameter of 185 mm; GSI-Pb-CCC, designed for GSI-Darmstadt with a free inner diameter of 145 mm, 1996 completed, 2014 upgraded; GSI-Nb-CCC-XD, de-signed for the GSI/FAIR-project with a free inner diame-ter of 250 mm, 2017 completed. The results of noise, small-signal, slew-rate, and drift measurements done 2015 and 2018 in the Cryo-Detector Lab at the University of Jena are presented here.

For more than 20 years Cryogenic Current Comparators (CCC) are used to measure the current of charged particle beams with low intensity (nA-range). The device was first established at GSI in Darmstadt and was improved over the past two decades by the cooperation of institutes in Jena, GSI and CERN. The improved versions differ in material parameters and electronics to increase the resolution and in dimensions in order to meet the requirements of the respective application. The device allows non-destructive measurements of the charged particle beam current. The azimuthal magnetic field which is generated by the beam current is detected by low temperature Superconducting Quantum Interference Device (SQUID) current sensors. A complex shaped superconductor cooled down to 4.2 K is used as magnetic shielding and a high permeability core serves as flux concentrator. Three versions of the CCC shall be presented in this work: (1) GSI-Pb-CCC which was running at GSI Darmstadt in a transfer line, (2) CERN-Nb-CCC currently installed in the Antiproton Decelerator at CERN and (3) GSI-Nb-CCC-XD which will be operating in the CRYRING at GSI 2019. Noise, signal and drift measurements were performed in the Cryo-Detector Lab at the University of Jena., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

A Cryogenic Current Comparator (CCC) is an extremely sensitive DC-Beam Transformer based on superconducting SQUID technology. Recently, a CCC without a toroidal core and with an axially oriented magnetic shielding has been developed at the Institute of Photonic Technologies (IPHT) Jena/Germany. It represents a compact and lightweight alternative to the ’classical’ CCC, which was originally developed at PTB Braunschweig and is successfully in operation in accelerators at GSI and CERN. Excellent low-frequency noise performance was demonstrated with a prototype of this new CCC-type. Current measurements and further tests are ongoing, first results are presented together with simulation calculations for the magnetic shielding. The construction from lead as well as simplified manufacturing results in drastically reduced costs compared to formerly used Nb-CCCs. Reduced weight also puts less constraints on the cryostat. Based on highly sensitive SQUIDs, the new prototype device shows a current sensitivity of about 6 pA/Hz1/2 in the white noise region. The measured and calculated shielding factor is ~135 dB. These values, together with a significant cost reduction - resulting also from a compact cryostat design - opens up the way for widespread use of CCCs in modern accelerator facilities., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The non-destructive and highly sensitive measurement of a charged particle beam is of utmost importance for modern particle accelerator facilities. A Cryogenic Current Comparator (CCC) can be used to measure beam currents in the nA-range. Therein, charged particles passing through a superconducting toroid induce screening currents at the surface of the toroid, which are measured via SQUIDs. Classical CCC beam monitors make use of a high magnetic permeability core as a flux-concentrator for the pickup coil. The core increases the pickup inductance and thus coupling to the beam, but unfortunately also raises low-frequency noise and thermal drift. In the new concept from the Leibniz Institute of Photonic Technology the Coreless Cryogenic Current Comparator (4C) completely omits this core and instead uses highly sensitive SQUIDs featuring sub-micron cross-type Josephson tunnel junctions. Combined with a new shielding geometry a compact and comparably lightweight design has been developed, which exhibits a current sensitivity of about 6 pA/sqrt(Hz) in the white noise region and a measured shielding factor of about 134 dB*.

The storage of low current beams as well as the long extraction times from the synchrotrons at FAIR require non-destructive beam intensity monitoring with a current resolution of nanoampere. To fulfill this requirement, the concept of the Cryogenic Current Comparator (CCC), based on the low temperature SQUID, is used to obtain an extremely sensitive beam current transformer. During the last years, CCCs have been installed to do measurements of the spill structure in the extraction line of GSI SIS18 and for current monitoring in the CERN Antiproton Decelerator. From these experiences lessons can be learned to facilitate further developments. The goal of the ongoing research is to improve the robustness of the CCC towards external influences, such as vibrations, stray fields and He-pressure variations, as well as to develop a cost-efficient concept for the superconducting shield and the cryostat., Proceedings of the 7\textsuperscript{th} Int. Beam Instrumentation Conf., IBIC2018, Shanghai, China

Triggered by the need for current measurement in the nA range for slow extracted beams and for the beams in the storage rings at FAIR and CERN, the idea of the CCC as a current transformer has been revitalized during the last ten years. Compared to the first prototype, developed at GSI in the 90s, the second generation of CCCs is based on the possibility of detailed simulation of superconducting magnetic shielding properties, new nano-crystalline materials for the magnetic ring-cores, and on superior commercially available SQUID systems. In 2014, nA resolution measurements at 2 kHz bandwidth demonstrated the possibility of spill analysis at slow extracted beams from GSI SIS18. In the following year, the first stand-alone CCC system, including a cryostat with separate He liquefier, started operation in the CERN AD. Although the existing systems show an outstanding current resolution, their cost efficiency and robustness, as well as noise and vibration sensitivity can still be improved, which is subject of ongoing research. In this contribution recent results of our CCC tests are shown and future developments are discussed., Proceedings of the 6th Int. Beam Instrumentation Conf., IBIC2017, Grand Rapids, MI, USA