1. Preparation procedure and RF processining of cERL-ML power coupler at KEK Hiroshi Sakai, Takaaki Furuya, Masato Sato, Kenji Shinoe, Kensei Umemori, Kazuhiro Enami(KEK), Masaru Sawamura (JAEA), Enrico Cenni (Sokendai) 1 TTC CR mini-workshop 2014 @Saclay. (2014.Nov.12-Nov.14) RF power Warm window 80K 5K bellows vacuum Cold window N2 gas cooling cavity Basic design of input power coupler for cERL Main linac(ML) Cu plate:10um Cu plate:30um Cu plate:150um Variable (±5mm) Cold window moved by rod TRISTAN type coaxial disk ceramic window was used Basic parameters of cERL-ML input power coupler frequency : CW, 1.3GHz Accelerating gradient : Max 20MV/m (First) input power ： max 20kW, standing wave (Δf=50Hz) loaded Q(Q L ) ： (1-4) * 10 7 (variable coupling) Points (modified from STF-BL coupler for CW) Impedance from 50Ω to 60Ω (reduce inner heating) 99.7% purity of two ceramic window are used Main-Linac(ML) Cryomodule Input couplers Cryostat Tuner HOM absorber 9-cell cavity Preparation procedure of input coupler Fabrication & surface treatment Assembly for test stand (TS) High power RF processing @TS Assembly for cryomodule High power test @ cryomodule Processing for beam operation Compact ERL (cERL) @KEK Commisoning in 2013 7 pages

2. Fabrication & surface treatment & assembly for test stand 2 (Toshiba TETD) Cold window Warm window Inner conductor (choke) Disk Window HA997 TiN coating metalize Small hole for ultra pure water rinse Cold outer conductor bellows (copper plate inside) Bottom 10um top 50um (copper plate outside) Bottom 10um top 30um warm inner conductor bellows Brazing (mainly Au) Dried by ion gun(0.1um filter) & check particle at class 4 Assembly in class 4 Leak check & Baking 24 hours (150deg) U-tight seal keep one day dry all components at class 4 ultra pure water (18MOhm) rinsing at class 4 (outside HPR(5MPa), ceramic not HPR 2*5min dip&flow )

3. Aim Processing coupler before assembly: SW 20kW -> TW 80kW (1/2 duty) 1.3GHz CW 300kW klystron used  Try TW 100kW to get margin for CW arc sensor using fiber was tested for cryomodule power fast ITL < 10 us Coupler test stand for cERL-ML cryomodule in out Warm window （ UP) Cold window （ Up) Cold window （ down) Warm window （ down) Doorknob Coupling wave guide Arc sensor of cold window of both sides 1.3GHz 300kW CW klystron Coupling changing mechanics N2 gas into inner conductor to forced cooling Arc sensor of warm window CCG2 (cold) CCG1 (warm both) Setup Arc sensor signal processing fiber out Dummy load Pin =105kW Pin =75-76kW processed Pulse 2Hz 50ms CW 43kW 50kW 4hours Final Results 105kW (pulse, 27 hours) & 43kW(CW) was fed  satisfy our requirements 1h

4. Module assembly of input coupler for cERL main linac 4 Connection of input coupler warm window in clean boose Leak check (no leak) & keep test stand in vacuum in clean room & cleaned outside by ion gun Doorknob, inner rod, arc sensor, thermal sensor & RF cable were equipped Cavities & others were applied HPR & dried in class 4 Cold window cleaned by ion gun again (class 4) Connection of cold window to cavities with jig (class4) Prepare string assembly Ar purged & cleaned outside of cavities by ion gun Baking warm window (24h) Align input port before connecting level

5. Coupler aging of each cavities of cyromodule & power test After assembly, first we start aging at room temperature, 8 hours (short from TS) was needed for processing again in cryomodule. After finish processing, we did not meet the electron activity under warm and 2K condition. Aging up to 15kW with CW detune condition @ 2K. Thanks to the processing of room temperature, aging time is much small (< less then 10min). No significant temperature rise was observed. Finally in high power test, power fed into 4.5kW with on resonance with QL=1.5*10^7 Vacuum level is less than 1*10^-6 Pa. During beam operation, no ITL by coupler 5 Pin (kW) Vacuum of coupler (Pa) Aging history after module assembly (at room temperature) Aging history (at 2K condition) detune Pin (kW) Vacuum of coupler (Pa) Under processing to 25kW SW 1Hz 200ms 20Hz 100us 10Hz 2ms 5Hz 10ms pulseCW 15kW 25kW Coupler works well in cryomodule Bellows 5K side 8.1K -> 11.8K Bellows 80K side 88.8K -> 116.3K Cold window 89.1K -> 96.7K inner conductor 278.1K -> 316.3K Max  T=38K Warm window 288.2K -> 295.0K N2 gas cooling 60l/min Input Nb flange 4.1K -> 5.1K Temperature rise during 15kW CW(SW) power feeding 5K anchor 6.9K -> 9.9K (5Hz 10ms)

6. Normal coupler processing before beam operation (after warming up & cooling down) 6 Coupler processing up to CW 8kW after cooling down to 2K (detune SW) Coupler processing to CW 8kW after warming up on room temperature (detune SW) Warm window Cold window Warm vacuumCavity vacuum After warming up to room temperature, many vacuum works were observed under processing to 8kW especially on ML2 cav warm section. After cooling down to 2K, vacuum works much reduced on same condition. At cavity section, we did not see the vacuum work only coupler processing with detuning condition. Warm vac (ML2) Warm vac (ML1) Cav vac (ML2) Cav vac (ML1) 8kW (ML1) 8kW (ML2) Warm vac (ML2) Warm vac (ML1) Cav vac (ML2) Cav vac (ML1) 8kW (ML2) 8kW (ML1)

7. Normal cavity processing before beam operation 7 Cavity processing up to 11MV (3kW) after coupler processing & 2k cooling. We saw many vacuum work on cavity side from 5MV to 8MV. Once processing finished, no vacuum work was observed up to 11MV.. We did not see the vacuum work on warm side on resonance. Cavity processing ( ML2 cavity processing to 11MV (3kW) Warm vac (ML2) Warm vac (ML1) Cav vac (ML2) Cav vac (ML1) ML1 cavity processing to 11MV (3kW)

8. Suggestion and questions ? We need cold window to clean assembly ? Processing at room temperature is needed ? What type of monitor is needed for window? Arc sensor ? Electron probe ? Especially for cold window ? Before assembly, how treatment is critical for keeping clean assembly. For example, only ultra pure water rinse? Ultra Sonic ? High pressure rinse is needed ? 8