1. Operation of the RF System for heavy ion accelerators in RIKEN RI Beam Factory K. Suda, N. Sakamoto, K. Yamada, H. Okuno, Y. Higurashi, O. Kamigaito, M. Kase RIKEN Nishina Center for Accelerator-Based Science 1ARW2013

2. Contents RIKEN Radioactive-Isotope Beam Factory New injector RILAC2 Operating experience of the RF system of RILAC2 Reliability at present Summary ARW20132

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4. 4 RILAC2 RILAC 15 pnA (Dec. 2012) 15 pnA (Dec. 2012)

5. Acceleration of U and Xe ARW20135 0.68 MeV/u 345MeV/u 1f = 18. 25 MHz Cascade of cyclotrons with an new injector RILAC2 RF of RILAC2 and fRC are fixed frequency systems Intense beams are injected to the cyclotron RRC without charge stripping (U 35+, Xe 20+).

6. Acceleration of U and Xe ARW20136 0.68 MeV/u 345MeV/u 1f = 18. 25 MHz Cascade of cyclotrons with an new injector RILAC2 RF of RILAC2 and fRC are fixed frequency systems Intense beams are injected to the cyclotron RRC without charge stripping (U 35+, Xe 20+).

7. New injector RILAC2 ARW20137

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11. ARW201311 Cooling water: Supplied from co-generation system T. Fujinawa

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13. Circuit diagram of amplifier for DTL Tetrode based amplifier directly connected to the cavity. Power output 40 kW (max.) ARW201313

14. Operating experience of the RF system of RILAC2 ARW201314

15. Problems of RILAC2 RF system Problems occurred during high power tests, or beam commissioning. Cavity (DTL) - Discharges from pickup electrode - Discharge at drift tube by an intense beam of > 30 euA due to vacuum reduction caused by beam loss at drift tubes fast recovery within a few seconds Plate power supply - malfunction of crowbar (RFQ, DTL) - failure of a cooling fan (DTL) Amplifier - Water leak from upper floor ARW201315

16. DTL: Discharges from pickup electrode Field emission at high gap voltage of cavity (> 150 kV) once in a few min. High voltage signal (>50 V) caused damage of detector diode; pickup voltage decreased (Voltage regulation cannot be applied). ARW201316 Pickup (pole-type :4 mm diameter) High voltages observed from pickup +38 V

17. DTL: Discharges from pickup electrode Field emission at high gap voltage of cavity (> 150 kV) once in a few min. High voltage signal (>50 V) caused damage of detector diode; pickup voltage decreased (Voltage regulation cannot be applied). Pickups were exchanged to well developed capacity-divided type. ARW201317 Pickup (capacity-divided) O. Kamigaito et al., Rev. Sci. Instrum. 76, 013306 (2005) Block electrons emitted from cavityto protect ceramic e

18. RFQ: Failure of crowbar ignitron Failed to operate plate PS due to malfunction of crowbar ignitron. Withstand voltage of Ignitron decreased to 14 kV (need > 25 kV). Thermostat was broken; failed to keep ignitron 50 C with heaters. Broken Ignitron was never used; exchanged to a new one. ARW201318 Ignitron 7703EHV/NL35391 National Electronics 50 kV, 100 kA (peak) (for emergency short-circuiting to protect power supply). Heaters Thermostat Plate PS for RFQ final amp Denki Kogyo (Japan) DC 12 kV, 7A Final Amplifier Plate cable RFQ

19. DTL3: Malfunction of crowbar circuit ARW201319 Plate power supply for tetrode based amplifier of DTL. Crowbar fires at plate current of 5.5 A in 3 min by some noise (rated 8A). Noise protection was done in control circuit to avoid malfunction. Y. Touch and K. Hoshika (Sumitomo Heavy Industries) Noise protection: Plate, grid, screen, filament power supplymade by JEMA ELEC in Belgium. Plate 10 kV, 8 A(max)

20. Ceiling fan on plate power supply Short lifetime (one broken in 2.5 years). Thermal interlock don’t sense a broken fan. We notice it when electric leak occurs (main breaker turned off). Started to test a longer-life fan (only one at this moment). ARW201320 AC 230 V, 72 W, 15 m 3 /min, $175 Ball bearing 70 W, 20 m 3 /min, $74 254 mm OriginalNow Testing Thermal switch is too far from the motor Ebm-papst (Germany) W4S250-CA02-01 Orion Fans (United States) OA254AN-22-1TB Expected life 60,000 hours (= 6.8 years)

21. Water leak from upper floor Flow sensor was broken at an ion source on the upper floor. ARW2013 Flow sensor IFW510 (SMC, Japan) Ion source (not for RILAC2) Water tray Leak from diaphragm Cracks

22. Water leak from upper floor Flow sensor was broken at an ion source on the upper floor. Leaked water fell down through cracks in the floor and conducted to DTL3. The amplifier got wet through the air hole (Amp. was not in operation). ARW201322 Flow sensor IFW510 (SMC, Japan) Ion source (not for RILAC2) Cracks Water tray Leak from diaphragm

23. Cracks Water tray Leak from diaphragm Water leak from upper floor Flow sensor was broken at an ion source on the upper floor. Leaked water fell down through cracks in the floor and conducted to DTL3. The amplifier got wet through the air hole (Amp. was not in operation). ARW201323 Flow sensor IFW510 (SMC, Japan) Ion source (not for RILAC2) Roof DTL3Cavity FinalAmplifier Air hole Leak from diaphragm

24. Reliability at present ARW201324

25. Reliability ( 238 U, 2012 Nov. – Dec.) ARW201325 Beam service 80.3 % Standby 5.4 % Trouble 7.4 % Tuning 2.5 % RF 3.3 % Accelerator group think that down time due to RF should be < 1% to achieve 90 % of reliability. Reliability 85.7 % Scheduled period (876 h)

26. Reliability ( 238 U, 2012 Nov. – Dec.) ARW201326 Beam service 80.3 % RILAC2 0.5 h 0.05 % RRC 13.7 h 1.6 % SRC 9.3 h 1.1 % Standby 5.4 % Trouble 7.4 % Tuning 2.5 % fRC 2.7 h 0.3% IRC 2.9 h 0.3 % RF 3.3 % RILAC2 cleared the condition of < 1 %. Reliability 85.7 % Scheduled period (876 h)

27. Summary Major initial problems of RILAC2-RF system was solved by the end of beam commissioning. Reliability of RILAC2-RF was higher than 99.95% during the recent beam service period. Reliability of all the RF systems (3.3%) is close to the requirement we set (1%). Further improvement is required. 27ARW2013

28. U 35+ U 65+ ５-stage diff. pumping; 22 pumps He recirculating vol.; 300 m 3 /day Large beam aperture; >Φ10 mm 8 order pres. reduction; 7 kPa⇒10 -5 Pa Charge exchange here He gas; 7 kPa＊50 cm ⇒ 0.7 mg/cm 2 RIKEN Recirculating He-Gas Charge-State Stripper H. Imao et al. ARW201328

29. Damaged ceramic of DTL pickup Ceramic was damaged by electrons from cavity (protection required). Large discharge due to charge up of ceramic. ARW201329 No Protection against electrons e Damaged Ceramic +38 V