1. Cryogenic Current Comparator for FAIR Transfer lines
Febin Kurian
GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt and Helmholtz Institute Jena
Febin Kurian, GSI Darmstadt

2. Contents Introduction to Beam Current Measurements
9/16/2018
Contents
Introduction to Beam Current Measurements
Beam Intensity Measurements with Cryogenic Current Comparator (CCC) at FAIR
CCC Working Principle, SQUID and Electronics
Superconducting Magnetic shield
Upgrade of GSI CCC and Beam Measurements
Status and Conclusion
Febin Kurian, GSI Darmstadt
Febin, GSI

3. Beam Current Measurements
9/16/2018
Beam Current Measurements
160 nA 16
Particles per second
Nuclear Charge Z
Working ranges of the spill-intensity monitors
used for the slow extraction GSI
(SCL: space charge limit)
Standard Beam current measurement techniques
Current Transformers
Measurement of beam’s magnetic field
No dependence on beam energy
Detection threshold ~1µA
Faraday cups
Measurement of beam’s electric charges
Destructive techniques
For low energy only
Detection down to 10pA
Particle detectors (Scint., IC, SEM)
Detection of particles energy loss in matter
Used for lower currents at higher energies
Plastic Scintillators, Ionization chamber, SEM etc...
N-DCCT (Novel DC Current Transformer)
The N-DCCT is a DC beam current transformer, based on GMR magnetic sensor technology. It is designated to measure the high intensity beam currents circulating in the FAIR synchrotron SIS100.
Important working conditions and parameters:
max. circulating current~ 2 A peak bunch current~ 150 Bunch revolution frequency  MHz in. bunch width~ 25 ns FWHMaimed system bandwidth~ 10 MHzaimed resolution≤ 1 mA BW
Motivation: The well-known “magnetic-modulator” or “flux gate” principle up to now used in the designs of DCCTs shows disturbed performance at highest beam currents, due to interactions between signal and modulation frequencies, electronic slew rate limitations, common-mode EMI, etc.
During R&D on the GMR sensors, the utilization of a magneto-optic sensor principle, as well as a GMI oscillator for DCCT systems also were investigated.
Non destructive device is preferred,
Beam is not influenced, allowing for online measurement of high intensity beams
Ref. P. Forck, Lectures on Beam Instrumentation and Diagnostics
Febin Kurian, GSI Darmstadt
Febin, GSI

4. Cryogenic Current Comparator for FAIR
SIS
FRS
ESR
SIS 100/300
HESR
Super
NESR CR
RESR
CBM
HADES
FLAIR
CRYRING
Foreseen installation locations:
Slow extraction from SIS18/100/300
Super Fragment Separator
In front of beam dumps
Collector Ring (CR)
In CryRing
Along with high intensity beams,
Slowly extracted beams also have to be transported
to experiments up to long extraction times
For these beam lines,
Min. beam intensity of 104 pps (with spill time 1 sec.)
Max. intensity of 1012 pps
=> Beam current of 160 nA (protons) - 4.5µA (U28+)
CCC realizes non-destructive online monitoring of slowly extracted beams (very low (nA) mean beam current).
Febin Kurian, GSI Darmstadt

5. Working Principle - CCC (1/2)
9/16/2018
Working Principle - CCC (1/2)
Principle
Measure the beam’s magnetic field
Ceramic gap to prevent shielding by mirror currents
Magnetic alloy toroid – Flux concentrator
Enhance the field coupling to the pick up coil
Superconducting pick up coil
Detects the magnetic field of the beam
Superconducting Quantum Interference Device (SQUID), a high sensitivity magnetic flux sensor
Efficient magnetic shield to screen any magnetic noise field components
Febin Kurian, GSI Darmstadt
Febin, GSI

6. Working Principle- CCC (2/2)
He gas exhaust
beam
DC SQUID
Temperature /Pressure Readout
GM refrigerator
Thermal insulation + Radiation shield
SQUID control +
Readout
50cm
Amplifier
Oscilloscope & FFT
LHe Dewar
Febin Kurian, GSI Darmstadt

7. SQUID - Principle SQUID – Superconducting QUantum Interference Device
Josephson Junction
Two superconductors separated by a thin insulating layer allows tunneling of electrons proportional to the phase difference of the wave functions in the absence of a voltage
Flux quantization
Even in the presence of a steadily increased magnetic field, the magnetic flux associated with a superconducting ring is quantized by the elementary flux quantum
ɸ0 = h/2.e = 2.06x10-15 T.m2
DC SQUID
Two identical Josephson junctions form a superconducting ring. For a magnetic field applied to the ring, the voltage across the junction oscillates with a period of one flux quantum.
Figure courtesy: hyperphysics webpage(
Febin Kurian, GSI Darmstadt

8. Current Measurement Using SQUID(2/2)
FLL mode of operation
The output signal of the SQUID is linearized by flux locked loop mode of operation, fed to an amplification stage and read out in terms of equivalent current.
Typical schematic connection scheme of CCC
Febin Kurian, GSI Darmstadt

9. Superconducting Magnetic shield
9/16/2018
Superconducting Magnetic shield
beam
Important component in defining the current sensitivity of the CCC
Needs to attenuate unavoidable magnetic noise components (e.g.: Earth’s magnetic field (~50µT), bipolar and quadrupole magnets in the beam line)
Meissner effect ensures that all magnetic field components have to pass through the meander shaped plates before detected by the pick up coil
Meander shape of the shield plates causes strong attenuation for all magnetic field components except the azimuthal magnetic field which has information about the beam.
The larger is the effective meander path- the stronger is the field attenuation
Caution... Nothing is drawn to scale here!!!
Febin Kurian, GSI Darmstadt
Febin, GSI

10. Field Attenuation by S.C. Magnetic Shield
Known external magnetic field applied through
“Helmholtz coil” and measure the field inside
the shield by
SQUID sensor
Given the inductance L and the area A of the
ring core at low temperature, the Magnetic flux
can be calculated from the SQUID as,
𝐵= 𝐿.𝐼 𝐴 B
Attenuation factor,
A=20 log(Bout/Bin)
For an applied transverse magnetic field Attenuation factor AT =148dB
For a Longitudinal Magnetic field,
Attenuation factor AL =176dB
The magnetic field measured inside the shield geometry using
the SQUID across externally applied known magnetic field
To put this into perspective,
Earth’s magnetic field of ~40µT will attenuate to 30 fT due to the magnetic shield geometry.
Febin Kurian, GSI Darmstadt

11. 10 nA signal measured by the existing CCC at GSI
Re-Commission of GSI CCC
Goal : Use the existing CCC as a prototype for the new CCC system
GSI CCC consists of :
DC SQUID (UJ111) and SQUID controller developed at University of Jena
Superconducting magnetic shield made of Lead (10 meander plates)
Ring core- Vitrovac 6025-F
10 nA signal measured by the existing CCC at GSI
Time (1 S/div)
Current (10 nA/div) 10 20 30 40
-20
-10
Current sensitivity of the SQUID- 175nA/ɸ0
Noise limited current sensitivity at low frequency range (<100Hz) – 70 pA/√Hz
For the production of multiple CCC system, several SQUID and electronics were investigated.
Next step: Install the newly selected sensor unit and measure beam current
Febin Kurian, GSI Darmstadt

12. CCC Installation in GSI
The CCC is installed in the high energy transport section of the Synchrotron SIS18, HTP which is used as the beam diagnostic test bench.
CCC
Febin Kurian, GSI Darmstadt

13. Measurement of Beam current using CCC (1/4)
Goal : Measure the beam current with the newly installed SQUID sensor and Electronics
New SQUID (from Supracon™) and SQUID electronics (from Magnicon™) were introduced into CCC.
Noise spectrum of the CCC installed in the extraction line of SIS18
The SQUID output signal of A 50 nA test pulse
(2s) applied to the calibration winding of CCC
Febin Kurian, GSI Darmstadt

14. Measurement of Beam current using CCC (2/4)
Plot of an 8 nA current signals produced by unbunched beam of 600 MeV particles of Ni26+ extracted from the synchrotron, SIS18 with an extraction time of 500mS.
DC Current Transformer signal from the synchrotron shows the full cycle of the beam operation
2&3. The differential output signals of the extracted current beam by CCC
Current measured by a Secondary Electron Monitor 1
2&3 4
Febin Kurian, GSI Darmstadt

15. Measurement of Beam current using CCC (3/4)
Full spill of a measured ion current extracted
from SIS18 with an extraction time of 500 ms
The average beam current is 8 nA
Zoomed in view of the spill structure
of the extracted beam
Febin Kurian, GSI Darmstadt

16. Measurement of Beam current using CCC (4/4)
Plot of a 3.5 nA current signals which are produced by bunched beam of 109 particles of Ni26+ at an energy of 600 MeV extracted from SIS18. The beam is extracted with an extraction time of 1 second.
Febin Kurian, GSI Darmstadt

17. Status and Conclusions
The CCC system at GSI has been recommissioned for prototype development of an improved CCC unit for FAIR
CCC has been upgraded with novel SQUID unit and first beam tests at GSI were very successful.
Sensitivity is found to be much higher than the previous installations- could accurately measure beam current below 1 nA
Parallel measurement of the beam current using a Secondary Electron Emission Monitor matches perfect the CCC signal.
A lot more to explore from the beam time measurement results...
Febin Kurian, GSI Darmstadt

18. Summary What a Cryogenic Current Comparator offer
Non intercepting technique
High Resolution (<100pA /√Hz )
Measurement of the absolute value of current
Exact calibration by using an additional wire loop
Measurement is independent of ion energy and the trajectories in the beam
Useful investigations of the beam structures
Useful calibration tool for other techniques
Febin Kurian, GSI

19. Acknowledgements Acknowledgements
Helmholtz Institute, Jena for the support in this project.
Part of this PhD work was supported by DITANET, a Marie Curie Initial Training Network and also Frankfurt Institute Advanced of Studies (FIAS)
Each and everyone in the LOBI group at GSI, all put their own share of contribution into this work in one way or the other...
Our collaborations:
W. Vodel, R. Geithner, R. Neubert, HIJ, Jena & Friedrich-Schiller University, Jena
R. v. Hahn, MPI-Kernphysik, Heidelberg
A. Peters, HIT, Heidelberg
Febin Kurian, GSI Darmstadt