Dry-ice (CO 2 -snow) Cleaning - Motivation - Cleaning mechanism, - PowerPoint PPT Presentation

Dry-ice (CO 2 -snow) Cleaning - Motivation - Cleaning mechanism, technique & apparatus - Nb cavity results - Copper rf gun cleaning - Summary, open topics + next steps Detlef Reschke, Arne Brinkmann IWLC-2010, Oct. 21st, 2010

Motivation for dry-ice cleaning > High cleaning potential for removal of particles + field emission by dry- ice cleaning proven on samples => publications by Univ. Wuppertal (e.g. SRF Workshops, …) > Additional cleaning option: no replacement of high pressure water rinse ! > advantages of dry-ice cleaning: - Effective removal of particulate and film contamination - Dry cleaning process => horizontal cleaning option of Nb cavities => final cleaning just before string assembly => all applications unsuitable for water e.g. application to Cu gun cavity => no drying procedure necessary Detlef Reschke, Arne Brinkmann | IWLC-2010 | Oct. 21, 2010 | Page 2

Effect of DIC on a flake-like emitter (courtesy Univ. Wuppertal) emitter HPR HPR+DIC emitter of ~ 20 µm size destroyed by DIC remnants emitting at higher E on ! E on (MV/m) 54.3 62.8   67.4 35.4 EDX: no foreign element detected   51.2 38.0 (probably oxide of Nb) S  (m 2 ) 10 -17 10 -13 2 8.3 S  (m 2 ) 1.2 10 -15 2.4 10 -13 Detlef Reschke, Arne Brinkmann | IWLC-2010 | Oct. 21, 2010 | Page 3

Motivation for dry-ice cleaning > High cleaning potential for removal of particles + field emission by dry- ice cleaning proven on samples => publications by Univ. Wuppertal (e.g. SRF Workshops, …) > Additional cleaning option: no replacement of high pressure water rinse ! > advantages of dry-ice cleaning: - Effective removal of particulate and film contamination - Dry cleaning process => horizontal cleaning option of Nb cavities => final cleaning just before string assembly => all applications unsuitable for water e.g. application to Cu gun cavity => no drying procedure necessary Detlef Reschke, Arne Brinkmann | IWLC-2010 | Oct. 21, 2010 | Page 4

Cleaning mechanism > dry- ice “snow”: mechanical, thermal + chemical cleaning forces - thermo-mechanical: i) embrittling by shock-freezing ii) shearing forces by high momentum iii) drastic volume increase by sublimation - chemical: liquid CO 2 acts as solvent for hydrocarbons + silicone => embrittling, blasting, shearing, dissolving, washing > removal of particles down to < 100nm > local, dry, without residues > simple checks with air and surface particle counters possible Detlef Reschke, Arne Brinkmann | IWLC-2010 | Oct. 21, 2010 | Page 5

Cleaning technique > patent-registered nozzle design for CO 2 surrounded by nitrogen designed by Fraunhofer IPA, Stuttgart, Germany > spontaneous formation of snow/gas mixture by relaxation of liquid CO 2 - app. 40-45% snow at -78,9 C; ~50-55 bar > surrounding supersonic nitrogen gas (20 C; (12-18)bar) => accelerating + focussing of jet => (partially) avoidance of condensation of humidity Detlef Reschke, Arne Brinkmann | IWLC-2010 | Oct. 21, 2010 | Page 6

Apparatus: General > schematic of dry-ice cleaning set-up 1 2 3 5 1 valve 2 pressure reducer carbon dioxide 4 3 gas purifier nitrogen 4 chiller 5 filter 5 1 Detlef Reschke, Arne Brinkmann | IWLC-2010 | Oct. 21, 2010 | Page 7

Apparatus: key components + operation Detlef Reschke, Arne Brinkmann | IWLC-2010 | Oct. 21, 2010 | Page 8

Apparatus: key components + operation > system for horizontal cleaning of (1-3)-cell cavities in stable operation Detlef Reschke, Arne Brinkmann | IWLC-2010 | Oct. 21, 2010 | Page 9

Single cell Nb cavity results > Results with actual cleaning parameters: => 3 of 5 tests show no fieldemission up to 35 MV/m; 2 tests with moderate FE > Potential to remove HPR resistant field emitters ?? 1.00E+11 1DE10, test 4 at 1.8K (leak at 2K) first test after bake + HPR 1.00E+11 1DE11, Test 3: Q(E) at 2K test 2 after add. DIC with old parameters 1DE11, Test 4: Q(E) at 2K 1DE11, Test 5: Q(E) at 2K test 3 after add. DIC with improved parameters 1DE11, Test 7 at 1.8K (leak at 2K) Qo Qo 1.00E+10 1.00E+10 1.00E+09 1.00E+09 0 5 10 15 20 25 30 35 40 0 5 10 15 20 25 30 35 40 MV/m MV/m Detlef Reschke, Arne Brinkmann | IWLC-2010 | Oct. 21, 2010 | Page 10

Copper rf gun cavity cleaning > Task: cleaning of the copper rf gun cavity of the photo injector for FLASH and European XFEL > Goal: effective removal of particles => low dark current with no oxidation of Cu Photo injector area with rf gun cavity at FLASH Detlef Reschke, Arne Brinkmann | IWLC-2010 | Oct. 21, 2010 | Page 11

Copper rf gun cavity cleaning (ctd.) > new vertical cleaning stand with modified movable nozzle Detlef Reschke, Arne Brinkmann | IWLC-2010 | Oct. 21, 2010 | Page 12

Copper rf gun cavity cleaning: first result > three guns cleaned example: gun cavity 4.2 conditioning at PITZ => dark current during gun processing app. factor 20 reduced 5000 Gun 3.1 (standard cleaned) Cs2Te #58.1 (2006-05-08) Gun 3.2 (standard cleaned) 4000 Cs2Te #42.4 (2007-08-05) maximum dark current (  A) Gun 4.2 (CO 2 cleaned) Mo 2008-01-14: 60  s 3000 Mo 2008-02-06: 400  s Mo 2008-02-11: 700  s 2000 1000 0 1 2 3 4 5 6 7 rf power (MW) Detlef Reschke, Arne Brinkmann | IWLC-2010 | Oct. 21, 2010 | Page 13

Open topics + ideas > Further optimisation of cleaning parameters: reduced CO 2 -capillary size, cleaning speed => reduce consumption of CO 2 => reduce/avoid moisture condensation => avoid heating ?? > What is the “better” nozzle head: One movable nozzle vs. two fixed nozzles? (angle of nozzles?) > Heating of cavity or inert gas atmosphere ?? > Improved drive system of cavity Detlef Reschke, Arne Brinkmann | IWLC-2010 | Oct. 21, 2010 | Page 14

Summary + Outlook > In operation: - horizontal cleaning of (1-3) cell cavities => successful - cleaning of 1.3 GHz Cu gun cavity with movable nozzle => successful > Future: - Cleaning of REGAE (Relativistic Electron Gun for Atomic Explorations) - Regular cleaning of 1.3 GHz gun cavities for FLASH and European XFEL - Cleaning of water sensitive special parts > Options: - Extension to Nb nine-cell accelerator cavities ? - Cleaning of full accelerator modules ??? Detlef Reschke, Arne Brinkmann | IWLC-2010 | Oct. 21, 2010 | Page 15

Detlef Reschke, Arne Brinkmann | IWLC-2010 | Oct. 21, 2010 | Page 16