Standard EP recipe at KEK T. Saeki KEK Hot topics session SRF – 29 July 2011, Chicago

EP facility at STF/KEK EP bed 9-cell cavity Automatic Operation Console 2 nd floor 1 st floor EP solution reservoir tank New EP facility at KEK was constructed in 2008, instead of old Nomura EP facility, which was closed in the summer of 2009.

We had been keeping the KEK recipe established by Kenji SAITO in TRISTAN age. Current density = 50 mA/cm2 The KEK recipe by Kenji SAITO from TRISTAN age. Current density = 50 mA/cm2 Slide from Nagoya Univ. by K. Saito

Difference between Jlab and KEK November 2009 JLabKEK EP Acid Tank270L (Tank Capacity) 230L (EP acid volume) 2000L (Tank capacity) 1000L (EP acid volume) EP Acid Flow Rate 5 ～ 10L/min. Over flow pipes 15mmφ 10 ～ 20L/min. Over flow pipes 25mmφ EP and Water Rinsing Atmosphere Nitrogen During EP: 12L/min. During Rinsing: 13 ～ 20L/min. Air EP Acid Temp.16 ~ 26 0 C EP acid (Return pipe) 21 ～ 34 0 C Outside cavity 17 ～ 32 0 C EP acid (Center of Cell) 28 ～ 50 0 C Outside cavity EP Voltage and Current14 – 17 V Current density = 20 – 30 mA/cm2 19 ～ 21V Current density = 50 mA/cm2 Related to nice results of JLab? => Now, EP current density (Final EP) = 30 – 40 mA/cm2 at KEK Yield rate for ILC threshold of VT (35 MV/m): 50% for recent 6 MHI cavities (1 bad cavity with only 1st VT).

EP2 (finial 20um) Recipe at KEK Flow rate of EP electrolyte ： 15L/min. Current density ： mA/cm2 (Current ~200A), Voltage=15-22 V Cavity rotation speed ： 1rpm Cooling: Air cooling (Outer surface of cavity<35 0 C) After EP voltage turned off (V=0). EP electrolyte rinse with cavity rotation: 3rpm. 20min. Draining of EP electrolyte Vertical position: 5min. Horizontal position: 2min. Vertical position: 2min. (Purging with N2 gas ） UPW filling and draining (rinse) UPW+PW(flow rate : L/min) with vibrator Water should reach the top of cavity for 20min. Additional PW running rinse reaching top of cavity (20L/min) with vibrator Sub-total, 60min. PW Filling 10min. Draining 3min. Repeat for 30min. Total 90min. Disassembly of setup and low pressure UPW rinse Flange and HOM cap/antenna, beam-pipes: Brushing with 2% FM-20 detergent Detergent rinse of cavity with 2% FM-20 at 50 0 C (60 min.) Disassembly and low pressure UPW rinse and HPR

EP1(bulk 100um) recipe at KEK Flow rate of EP electrolyte ： 15L/min. Current density ： mA/cm2, Voltage=18-22 V Cavity rotation ： 1rpm Cooling ： Air cooling After V=0 EP electrolyte rinse with cavity rotation: 3rpm. 20min. Draining of EP electrolyte Vertical position 5min. Horizontal position 2min. Vertical position 2min. (Purging with N2 gas) UPW Filling 10min. Draining 3min. Repeat for 60min. Disassembly and low pressure UPW rinse Detergent rinse 2%FM-20 at 50 0 C for 60min. Disassembly of setup and HPR Setting HPR

EP parameters at KEK (June 2010 – July 2011) Final EP (~20 um) for 9-cell cavities Current density = 30 – 40 mA/cm2 T of acid inside cavity = 23 – 31 0 C Voltage = 15 – 22 V Nb concentration (g/L)

EP parameters at KEK (June 2010 – July 2011) Bulk EP (~100 um) for 9-cell cavities Current density = 45 – 50 mA/cm2 T of acid inside cavity = 30 – 40 0 C Voltage = 18 – 22 V Nb concentration (g/L)

Experiment by Saclay

Nb sample anode Moving shaft Aluminum plate covered by Teflon tape EP acid Bolt to connect shaft and Al plate Bolt to connect Nb sample and Al plate EP with Nb sample in laboratory Labo-EP setup at KEK Aluminum cathode

Reduction Reactions at the Cathode Reduction of H + : 2 H e - → H 2 (Predominant) Reduction of SO 4 2- : SO H + + 6e - → S + 4H 2 O Does a cathodic overpotential lead to an increased sulfur generation? → Two Niobium samples electro-polished at 5V and 20V for a similar heavy removal with (HF-H 2 SO 4 -H 2 O) Mixture Sample A, 20 Volts: 9.18g removed 51 hours EP Sample B, 5 Volts: 9.11g removed 115 hours EP = Theoretical way to reduce Sulfur Contamination (investigation ongoing) TEST OF LOW VOLTAGE EP (5V) AT SACLAY TO REDUCE SULFUR CONTAMINATION Experiment at Saclay Slide by F. Eozenou

TEST OF LOW VOLTAGE EP (5V) TO REDUCE SULFUR CONTAMINATION SULFUR FOUND IN THE EP MIXTURE (200mL) AFTER TREATMENTS OF SAMPLES A AND B. SULFUR EXTRACTED WITH CHLOROFORM: SampleA (20 V)B (5V) 1 st Rinse 4.5mg mg 2 d Rinse mg mg Experiment at Saclay Slide by F. Eozenou

Backup slides if we have time

Rinse Effect to Remove Sulfur precipitation/contamination U.P.W. ultrasoni c rinse Ethanol rinse (vibration) Ethanol ultrasonic rinse Detergent FM % Detergent FM % Detergent FM % Detergent FM % Cleani ng Result × △○△△○○ Before rinse After rinse Many white dots are sulfur contamination Ethanol ultrasonic rinseFM-550 (>10%) rinse Sulfur removed U.P.W. ultrasonic rinse Teflon texture 10

Results of rinse effect tests Test of FM-20 (LION detergent) and 10% H 2 O 2 Test of Ethanol and FM-550 (LION detergent) U.P.W. ultrasoni c rinse Ethanol vibration rinse Ethanol ultrasonic rinse Detergent FM % Detergent FM % Detergent FM % Detergent FM % Cleani ng Result × △ ○ △△ ○○ Detergent FM-20 2 % Detergent FM-20 5 % Detergent FM % 10% H 2 O 2 Cleanin g Result ○○○ ×or △ 11

JLab Nb sample with artificial pits BCP (30um) EP (30um) EP (60um)EP (90um) As received Pit3 EP (120um) After BCP(30um)+EP(120um), still the edge of pit is sharp! Large steps at grain-boundaries after BCP. 40 um 9

Nb sample anode Moving shaft Aluminum plate covered by Teflon tape EP acid Bolt to connect shaft and Al plate Bolt to connect Nb sample and Al plate EP with Nb sample in laboratory Labo-EP setup at KEK Aluminum cathode