AXIAL CRYOGENIC CURRENT COMPARATOR (CCC) FOR FAIR
L. Crescimbeni1,2,D.M., Haider1, A. Reiter1, M. Schwickert1, T. Sieber1, F. Schmidl2
V. Tympel1,3, M. Schmelz4, R. Stolz4, V. Zakosarenko4,5, and T. Stoehlker1,3GSI, Darmstadt; 2FSU Jena; 3Helmholtz Institute Jena; 4Leibniz IPHT, Jena; 5Supracon AG, Jena

1

# IBIC 2023, International Beam Instrumentation Conference, Saskatoon, Canadal.crescimbeni@gsi.de• The Cryogenic Current Comparator (CCC) provides a calibrated nonThe FAIR prototype CCC-eXtendeddestructive measurement of beam current with a resolution of 10 nA or better.
Dimensions (GSI-CCC-xD)• A first prototype of the detector, FAIR-Nb-CCC-xD with axial geometry, has beentested on the beamline at the storage ring CRYRING@ESR confirming its current
resolution in the order of 10 nA, even if some limitations has been found out
250 mm

65 kg

CCC installation
on CRYRING@ESR
beamline

Deuterium beam in CRYRING@ESR
Time [s]Axial Lead Coreless CCC

A new CCC version is under development in collaboration with IPHT
Jena to solve the issues found out with the FAIR-Nb-CCC-xD, inparticular the low slew rate and the low magnetic shieldingThe new CCC will have an axial geometry and it will lack the highmagnetic permeability coreThis CCC will be equipped with a two parallel squid system, toincrease the bandwidth and the resolutionOne of the squid will be more sensible but with lower bandwidth, theAxial CCC:
other one will have a lower sensitivity but higher bandwidth
Up left : SchematicThe new CCC will reach a 10 MHz bandwidth,Up right: Side view andallowing to reach an higher slew rate without
dimensions
decreasing the detector resolution
Right: Axial CCC front view
The lack of the core will reduce the low frequency
noise due to magnetic field trapped in the core
The axial shielding allows to strongly increase theshielding,up
toanestimate
theoreticalvalueof200 dB
Electric

Characteristics of the two squids.
High: Squid CN4, higher sensitivity
Low: Squid CN2, lower sensitivity circuit scheme

Test in GSI beam-line cryostat

First Axial CCC Prototype Construction•First prototype built in collaboration with IPHT Jena•First step: Magnetic shielding, meanders structure, 10 layers– First layer: 1 mm thick Pb sheet, placed inside a fiberglass cylinder (250 mminner radius) that provide structural integrity, wielded to upper and lower cap,
carved out of 1.5 mm thick Pb sheet– 9 inner layers: made out of 0.25 mm thick Pb-Sl sheet, interlaced by a layer ofthin electric-insulation•Pick-up Coil: 2 coils of 0.25 mm thick Pb-Sl sheet are windedaround a structure of XPS foam
– The XPS foam is not magnetic and is used to fill up thevolume of the pick-up coil and provide structural integrity•Squid Box: The squid are connected with small PB strip to thepick-up coil
– The squid are enclosed in a Pb box that shields themfrom external magnetic field•Outer layer: The CCC is then completed by a 320 mm inner
radius fiberglass cylinder, to provide integrity and avoid
deformation during handling, enclosed by a last layer of 1mm
thick Pb sheet that connect the upper and the lower cap.
First inner meander layer, the•The wielding is performed with Pb-Sn material (ensure junction
insulation will be added onthe outside of the lead sheet superconductivity) and the insulation is held in place by cryoglue

The test in GSI has shown huge issues of the Axial Coreless
CCC:• The noise is too high, the squid can not be set in a proper
working point SQUID V/ɸ Characteristics in FSU Jena

Cryostat scheme,
The CCC is
Installed over the
beam tube

CCC
Beam Tube
SQUID V/ɸ Characteristics inGSI
is noisy, the squid working
point is not stable, it will not
be possible to use it for thedata acquisition

XPS foam structure duringcostruction, the foam piece areheld together with cryoglue

Test in FSU Jena Laboratory
The axial coreless CCC has been tested in Jena FSU
laboratory. In this controlled environment we were able to test
mainly three features of the CCC:
CURRENT RESOLUTION:
Minimum 10 nA
Lower than the one of the
FAIR-Nb-CCC-xD, due tothe lack of the core,especially because:-Lower coupling with thebeam field-Higher noise floor (Morethan 10 times higher than
100 µT
the FAIR-Nb-CCC-xD)
Field on

FSU Wide Neckcryostat, CCC during
Example of external field effect on FAIRinstallation
Nb-CCC-xD-MAGNETIC SCREENING FACTOR:
FAIR-Nb-CCC-xD Screening factor 75 dB: 100 μT → 10 nA squid
Field OFFsignal
AXIAL CORELESS CCC (Estimated 200 dB) 1 mT → <0.1 nA squid
signal (too low to see it, much lower than noise floor)-SLEW RATE: Axial Coreless CCC: Slew Rate 4 μA/μS → FAIR-Nb-CCC-xD: Slew Rate 0.16 μA/μS
The results found out for the magnetic screening factor and the slew rate are very positive, with strong
improves for both. The main issues of the device seems the noise floor, that is much higher than theone of the FAIR-Nb-CCC-xD. What is left to do is to test the CCC in the GSI beamline cryostat•The noise floor in GSI cryostat (≈ 1 μA) is much higher than in FSU lab, and around 50-100 times higher
than the noise floor of FAIR-Nb-CCC-xD•The Axial coreless CCC can not be used in GSI cryostat, the noise is too high and the squid will never
be able to work
•But the shield efficiency has been confirmed and the cascade squid system has strongly increased theslew rate, so the axial geometry is effectively a strong improve.

NEXT STEPS•At the end of 2023 the FAIR-nB-CCC-xD will be definitively tested in thetransfer lines at GSI, to perform the last test of the radial prototype inexactly the same condition in which it will be used in FAIR
•Even if the test in GSI has shown that the axial coreless CCC will not workin the accelerator environment it has confirmed the validity of the axial
geometry for the magnetic shielding and of the cascade squid system toimprove the slew-rate of the system•This has suggested a new version of the CCC detector with axial
geometry, based on the CCC Sm (Smart & Small) series¹, a double coreaxial CCC
•This new version will be tested in the GSI cryostat in the first months of2024•This test will be followed by a beam-line test at the end of the first half of2024, as a final test of axial CCCs in the accelerator environment¹V. Tympel, et al., Creation of the first high-inductance sensor of the CCC-Sm series. IBIC’22, Krakow, Poland, Sept. 2022,
doi:10.18429/JACoW-IBIC2022-WEP30

Work supported by the BMBF under contract No 05P21SJRB1.