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Cryogenic Current Comparator for FAIR Transfer lines

Cryogenic Current Comparator for FAIR Transfer lines. Febin Kurian GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt and Helmholtz Institute Jena. Contents. Introduction to Beam Current Measurements Beam Intensity Measurements with Cryogenic Current Comparator (CCC) at FAIR

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Cryogenic Current Comparator for FAIR Transfer lines

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

  2. 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

  3. Beam Current Measurements 160 nA 16 • 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... Nuclear Charge Z Particles per second Working ranges of the spill-intensity monitors used for the slow extraction GSI (SCL: space charge limit) 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

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

  6. Working Principle- CCC (2/2) He gas exhaust Temperature /Pressure Readout Amplifier Thermal insulation + Radiation shield Oscilloscope & FFT LHe Dewar DC SQUID SQUID control + Readout beam GM refrigerator 50cm 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(http://hyperphysics.phy-astr.gsu.edu/hbase/solids/squid.html) 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 stageand read out in terms of equivalent current. Typical schematic connection scheme of CCC Febin Kurian, GSI Darmstadt

  9. Superconducting Magnetic shield 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 beam Caution... Nothing is drawn to scale here!!! Febin Kurian, GSI Darmstadt

  10. Field Attenuation by S.C. Magnetic Shield 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, Known external magnetic field applied through “Helmholtz coil” and measure the field inside the shield by SQUID sensor 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. 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 • Current sensitivity of the SQUID- 175nA/ɸ0 • Noise limited current sensitivity at low frequency range (<100Hz) – 70 pA/√Hz 40 30 20 10 Current (10 nA/div) 0 -10 -20 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 Time (1 S/div) 10 nA signal measured by the existing CCC at GSI 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. 1 2&3 4 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 4. Current measured by a Secondary Electron Monitor 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 hasbeenrecommissionedfor prototype developmentof an improved CCC unitfor FAIR CCC hasbeenupgradedwithnovel SQUID unitandfirst beam tests at GSI wereverysuccessful. Sensitivityisfoundtobemuchhigherthantheprevious installations- couldaccuratelymeasure beam currentbelow 1 nA Parallel measurementofthe beam currentusing a SecondaryElectron Emission Monitor matchesperfectthe CCC signal. A lotmoretoexplorefromthe beam time measurementresults... Febin Kurian, GSI Darmstadt

  18. 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 Summary 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

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