D Longuevergne IPN Orsay TTC topical CERN 89 November 2018 Experimental vs theoretical Magnetic sensitivity SPIRAL2 QWR F 0 88 MHz T 42K Sv 0006 n mG ID: 1035718
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1. How is trapped flux affected by the cavity geometryD. Longuevergne, IPN Orsay TTC topical, CERN, 8-9 November 2018
2. Experimental vs theoreticalMagnetic sensitivity SPIRAL2 QWR F0 = 88 MHz T = 4.2K Sv = 0.006 n/mG St = 0.05 n/mG Sthéo = 0.08 n/mG MYRRHA Spoke F0 = 352 MHz T = 2K Sv = 0.04 n/mG St = X Sthéo = 0.12 n/mGESS Spoke F0 = 352 MHz T = 2K Sv = 0.06 n/mG St = X Sthéo = 0.12 n/mGSSR1 Spoke F0 = 325 MHz T = 2K Sv = X St = 0.05 n/mG Sthéo = 0.11 n/mG Magnetic sensitivity is way less than theoretical value and depend on field direction!
3. In the literatureHow is flux trapped ? “Angular dependence of the magnetization of isotropic superconductors : which is the vortex direction ?”, S. Canda and L. Civale, Supercond. Sci. Technol. 12 (1999) 192–198.“Due to the geometrical constraint, the irreversible magnetization Mirr remains locked to the sample normal over a wide range of fields and orientations”.“Etude de la dissipation dans les supaconducteurs en régime haute fréquence”. Christophe Vallet, PhD thesis in 1994 done at CEA Saclay.
4. Geometrical effect How to apply corrections ?The calculation of the real sensitivity especially for complex geometries can’t be analytic!How to calculate magnetic sensitivity of a structure with simulation code :Evaluate the surface normal component and the additional resistanceThis gives the amount of trapped flux… but not the sensitivity!Trapped flux has to be subject to RF magnetic fieldEvaluate local power dissipations and integrate all over the geometry
5. TESLA 1.3 GHzANALYSISTheoretical :0.22 n/mG@2KTrapped flux regions RF surface currentsSensitive regions to magnetic fieldVertical fieldHorizontal field(beam axis)0.137 n/mG0.092 n/mGMAXMINAre there some data showing this difference of sensitivity on 1.3 GHz cavities ?
6. DSR (ESS) 352 MHzANALYSISTheoretical :0.11 n/mG@2KTrapped flux regions RF surface currentsSensitive regions to magnetic fieldVertical fieldHorizontal field(beam axis)MAXMIN0.057 n/mG0.055 n/mG
7. SSR1 (PIP-II) 325 MHzANALYSISTheoretical :0.11 n/mG@ 2KTrapped flux regions RF surface currentsSensitive regions to magnetic fieldVertical fieldHorizontal field(beam axis)0.046 n/mG0.064 n/mGMAXMIN
8. SSR (MYRRHA) 352 MHzANALYSISTheoretical :0.11 n/mG@ 2KTrapped flux regions RF surface currentsSensitive regions to magnetic fieldVertical fieldHorizontal field(beam axis)0.047 n/mG0.062 n/mGMAXMIN
9. QWR (Spiral2)ANALYSISTheoretical :0.08 n/mG@ 4.2KTrapped fluxRF surface currentsSensitive regions to magnetic fieldvertical fieldHorizontal field(beam axis)0.011 n/mG0.048 n/mGMAXMIN
10. Geometrical effect SUMMARYn/mGTransverse sensitivityBeam axis sensitivityVertical sensitivitySPIRAL2 QWR@ 4.2K@ 88 MHzCalculated0.0480.0480.011Measured0.05 (IPNO)0.006 (IPNO)Error (%)4 (-38)-45 (-93)MYRRHA SPOKE@ 2K@352 MHzCalculated0.0610.0620.047Measured0.043 (IPNO)Error (%)-8.5 (-64)ESS SPOKE@ 2K@352 MHzCalculated0.0570.0550.057Measured0.06 (IPNO)Error (%)9 (-50)PIP-II SSR1 @ 2K@ 325 MHzCalculated0.0460.0640.046Measured0.05 (FNAL)Error (%)-22 (-55)Theoretical0.08 n/mGTheoretical0.12 n/mGTheoretical0.12 n/mGTheoretical0.11 n/mGError : relative error between measurement and calculations(Error) : relative error between measurement and theoretical value
11. CONCLUSIONSystematic error from theoretical values : measured sensitivities are always a lot less! =>Sensitivity does not only depend on material!Considering only the normal component seems to be a good approximation:No systematic error between calculated and measured sensitivitiesExplains difference between theoretical and measured sensitivities on several geometriesExplains difference of sensitivity depending on the orientation of residual field (SPIRAL2)Trapping flux is not enough to explain magnetic sensitivity, it has to happen in a RF magentic field region
12. THANKS FOR YOUR ATTENTION
13. ELLIPTICALMAXMIN
14. SPIRAL2MAXMIN
15. MYRRHAMAXMIN
16. SSR1 (PIP-II)MAXMIN
17. ESSMAXMIN