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A Cryogenic Current Comparator for beam diagnostics in accelerators and storage rings

Volker Tympel

Collaborators:
Volker Tympel2, Ralf Neubert3, Jessica Golm3, Febin Kurian4, Thomas Sieber4, Marcus Schwickert4, David Haider4, Matthias Schmelz5, Ronny Stolz5, Vyacheslav Zakosarenko5,6, Herbert De Gersem7, Nicolas Marsic7, Wolfgang F.O. Müller7, Miguel Fernandes8, Jocelyn Tan8, Frank Schmidl3, Paul Seidel3 und Thomas Stöhlker1,2,4

1Institut für Optik und Quantenelektronik, Friedrich-Schiller-Universität Jena
2Helmholtz-Institut Jena
3Institut für Festkörperphysik, Friedrich-Schiller-Universität Jena
4GSI Helmholtzzentrum für Schwerionenforschung GmbH
5Leibniz-Institute of Photonic Technology (Leibniz IPHT), Jena
6Supracon AG, Jena
7TU Darmstadt
8CERN, Genf


Monitoring of ion beam intensities in particle accelerators without affecting the beam guiding elements, interrupting the beam current or influencing its profile is a major challenge in accelerator technology. A solution of this issue is the detection of the magnetic field generated by the moving charged particles. In a joint effort with the Institute of Solid State Physics at Friedrich Schiller University Jena, the Helmholtz Institute Jena and the beam diagnostics group at GSI a non-destructive beam monitoring system for particle beams in accelerators based on the Cryogenic Current Comparator (CCC) principle was recently developed [1]. The CCC consists of a high-performance, low-temperature DC superconducting quantum interference device system, a superconducting toroidal pick-up coil, and an extremely effective meander-shaped superconducting niobium shield. This device allows the measurement of continuous as well as pulsed beam currents in the nA range.


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Figure 1: Circuit diagram of the CCC

The resolution and the frequency response of the detector strongly depends on the toroidal pick-up coil and its embedded ferromagnetic core. Investigations of both the temperature and frequency dependence of the relative permeability and the noise contribution of several nanocrystalline ferromagnetic core materials were carried out to optimize the CCC with respect to an improved signal-to-noise ratio and extended transfer bandwidth [2]. The current noise of the CCC could be decreased by a factor of five compared to previous systems also tested at GSI and DESY Hamburg [3, 4]. This improvement results from the usage of iron-based nanocrystalline Nanoperm as core material for the pick-up coil. With this optimized CCC, a noise-limited current resolution of 1 nA should be achievable in the noise-prone environment of an accelerator.

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Figure 2: Response of the CCC to rectangular current pulses of 2 µA (a), 1 µA (b), 200 nA (c), 100 nA (d), 20 nA (e) and 10 nA (f) applied to a beam simulating wire along the beam axis. The inset shows the calibration current dependence of the magnetic flux coupled to the SQUID. It demonstrates the user-friendly calibration method and the linear transfer function over a wider dynamic range of the detector. A current sensitivity of 42 nA/Φ0 is calculated from the interpolation of these data.

For the international FAIR project at Darmstadt, the installation of several CCC detectors at the high-energy transport beam lines is planned. Here, maximum beam currents for slow extraction in the range between 10-4 and 10-2 mA are to be expected. Depending on the charge state and the extraction time particle numbers between 108 and 1013 will be detectable. In addition the installation of a CCC system at CRYRING and at AD @ CERN is planned for highly accurate absolute current measurements at low beam energies and small particle numbers for ions as well as for antiprotons. Here, it should be possible to detect down to 100 particles depending on the revolution frequency and the charge state.


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Figure 3: Engineer Ralf Neubert (formerly IFK) assembling the CCC-XD for the 150 mm beam tube diameter of the FAIR project (Photo: Jan-Peter Kasper/FSU)


References:

[1] A Cryogenic Current Comparator for FAIR with Improved Resolution

[2] Low temperature permeability and current noise of ferromagnetic pickup coils

[3] A Cryogenic Current Comparator for the Absolute Measurement of nA Beams

[4] Dark current measurements on a superconducting cavity using a cryogenic current comparator