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Vacuum RF R&D in UK

Vacuum RF R&D in UK. U.K Cavity Development Consortium. Arash Zarrebini MuCool RF Workshop – 8 th July 2009. Button Test Results: 2007 – 2008. – LBNL TiN_Cu2. No Button 40 MV/m no field 16 MV/m @ 2.8 T. D. Huang – MUTAC 08. Performance is considerably improved by using

stephanie-gutierrez
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Vacuum RF R&D in UK

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  1. Vacuum RF R&D in UK U.K Cavity Development Consortium Arash Zarrebini MuCool RF Workshop – 8th July 2009

  2. Button Test Results: 2007 – 2008 –LBNL TiN_Cu2 No Button 40 MV/m no field 16 MV/m @ 2.8 T D. Huang – MUTAC 08 • Performance is considerably improved by using • stronger material and better coatings Why not use a single material and evaluate the manufacturing procedure instead ?

  3. EXPERIMENT (Button Test) New Design • 2 Individual Parts MuCool • Single part Cap Holder

  4. Experimental Procedure Cap Material Selection Surface Characterisation Surface is characterised by: • Interferometer (Physical) • XPS(Chemical) Cap Forming Surface Characterisation Holder Forming Cap Surface Treatment Surface Characterisation Final Cap Surface Characterisation High Power Testing

  5. A Typical Surface After Mechanical Polishing of OFHC Copper Up to 1500 Angsrom Evidence of re-crystallisation due to plastic strain and /or local temperature increases Lower Slab shaped cells with sharp boundaries Deeper still More defuse boundaries Virgin Copper Matthew Stable - 2008

  6. Interferometr Results Mechanical polish and chemical etch remove deep scratches while EP reduces the average roughness Matthew Stable - 2008

  7. Experimental Setup and EP results

  8. XPS Results Matthew Stable - 2008

  9. Effects of Impurities on Band Structure R. Seviour, 2008 DFT simulations of Cu surface with P impurity

  10. Dependence of SEY on Material’s Band Structure R. Seviour, 2008

  11. Simulation (Objectives) Investigate the relations between Surface defects and RF breakdown Examine the effects of Surface features on field profile Track free electrons in RF cavities Investigate various phenomena such as secondary electron emission, Heat and stress deposition on RF surface due to particle impact

  12. Model Setup On-Axis Defect Off-Axis Defect Model 1 805 MHz cavity with no defect (top view) Models 2 & 3 805 MHz cavity with a single defect (bottom view) 700 μm 600 μm

  13. Electric Field Profile (Model 1 ) 803.45 MHz Maximum E Field at the Centre of Cavity The colour bar is a good representation of the field. However, it needs to be scaled in order to represent the actual field values

  14. Electric Field Profile (Model 2 – off axis ) 803.46 MHz Maximum E Field at the Tip of the Asperity The overall Field profile is similar to model1, as the Asperity enhances the field locally. This is due to the small defect size compared to the actual RF cavity

  15. Comsol in built tracker Model 2 – Particles emitted from a distance of 0.00071m away from the RF surface (tip of the Asperity) The local field enhancement due to the presence of Asperity, clearly effects the behaviour of the electron emitted from the tip of the Asperity

  16. Particle Tracking Procedure Extract E & B Field Parameters at particle’s position (primary & new) Obtain Cavity’s Field Profile in Comsol Obtain new particle position using 4th & 5th order Runge Kutta Integration Define a new set of coordinates for each particles Stage 1 Contact with wall ? Stage 3 No Measure the number of SEs and their Orientation Does Particle go through the Surface ? Stage 2 Yes No Measure the amount of energy deposited on the Impact surface Investigate surface deformation and heating Yes Dead Particle

  17. So where we are? • New batch of 20 buttons manufactured (spotted problems with the first batch) • EP and Scanning of batch 1 underway (access to XPS machine at Liverpool has been granted ) • High power RF test (date depending on MTA timetable) • Validating stage 1 results • Identifying the requirements for stage 2 and 3

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