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Field emission issue and strategy to improve

Field emission issue and strategy to improve. H. Hayano. Field emission Issue in STF. Radiation level of Recent STF cavities in VT. Radiation monitor is placed at Top outside of VT cryostat end-plate, inside of radiation shield. 1 Sv =100rem For X-ray, 1rem=1rad=0.01Gy=0.01J/kg

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Field emission issue and strategy to improve

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  1. Field emission issue and strategy to improve H. Hayano

  2. Field emission Issue in STF

  3. Radiation level of Recent STF cavities in VT Radiation monitor is placed at Top outside of VT cryostat end-plate, inside of radiation shield. 1 Sv=100rem For X-ray, 1rem=1rad=0.01Gy=0.01J/kg Cf. KEK Radiation worker area: <20µSv/h KEK cavities in VT have strong radiation, every time.

  4. T-map & X-ray-map example in MHI-009 9-cell cavity Some correlation was observed on T-map and X-ray-map. We could not observe the source defect by Kyoto-camera. Not enough resolution? 1st VT of MHI-009

  5. Field emission by defect on iris, happened in KEK ERL 9-cell cavity ERL X-ray map: Total 82 PIN diode array rotates around cavity Electron trajectory calculation

  6. Top & bottom PIN-diodes on beam-pipe flange of 9-cell cavity X-ray signal intensity MHI cavity favors to emit radiation on top side ( input coupler port on top, VT power from bottom beam pipe end plate ).

  7. Stain problem in STF Fluorine concentration change in 2000 litter EP acid for 1 year Final concentration 37 g/l 20091007 MHI#7 33.5MV/m 20100209 MHI#8 37.8MV/m 20090610 MHI#7 16.5MV/m 20100127 ERL2cell#1 43.7MV/m 20100616 HIT#01 35.1MV/m Final concentration 26 g/l Stain problem Stain problem

  8. A lot of stains were found in MHI-006, However, field was limited by RF cable trouble at 20MV/m. (2009.06.04) MHI-007 cavity limited at 8~16MV/m, with stains in right figure.(2009.06.25)

  9. HIT-01 cavity without HOM reached 35MV/m, with stains below. Relation with field emission and stains is not clear !

  10. Field emitter scan on stain sample : JLAB-KEK collaboration

  11. For more systematic study of field emission and stain correlation, SEM-FES combination device is under development in KEK Scanning Electron Microscope – Field Emission Scanner Picture of SEM-FES movable table under developing Schematic view of SEM-FES

  12. EP’d surface analysis (monitoring) using button samples For understanding of Residuals after treatment, SEM-EDX, XPS, AES, SIMS are the tool of analysis. XPS analysis example Nb button samples: 8mm dia. O Nb-1cell-5-equator-2008/11/12 back holder Nb F C seal Al S Al Nb ~4g/l seal button sample Nb-1-CavityEP1-2009/5/07-equator O C Nb S Nb ~8g/l

  13. EP’d surface analysis (monitoring) using button samples SEM analysis example button sample on beam-pipe new EP acid aged EP acid (Nb = 7.9g/l ) (Our EDX could not analyze the white spot.)

  14. Monitoring dissolved metal in EP acid Final concentration 9.8 g/l Nb Final concentration 17m g/l Al

  15. How to suppress Field emission

  16. Jlab succeeded field emission reduction Strategy to reduce field emission, (1) Analyze Jlab process and learn fromthem STF will send people to Jlab with STF cavities fair comparison of radiation level, EP process, rinse, clean-room work (2) Identify the source location by upgrading T-map, X-ray-map, inspection camera (3) Q.C. of cavity handle ( clean room work ) Review of cavity handling work Training of people, establish procedure (3) EP process optimization and monitoring (4) rinsing optimization and monitoring (5) research on EP’d surface

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