Nov. 28, 2003RF System Overview, K. Akai1 RF System Overview Contents: ◆ High beam current and measures ◆ Construction ◆ Damping ring RF system ◆ Crab cavity ◆ Impedance-related issues K. Akai Nov. 28, 2003 SuperKEKB mini workshop, KEK

Nov. 28, 2003RF System Overview, K. Akai2 High beam current and measures Strong longitudinal instability due to a large detuning, even with ARES and/or SCC. Growth rate = (0.3 ms) -1 –Reduce the growth rate to (1.6ms) -1 by modifying the ARES. –Improve the -1 mode damper to increase gain. –The -2 mode also needs to be cured. Large HOM power in each cavity –Improve HOM dampers –Reduce loss factor (ex. Large beam pipe radius in SCC section) Large RF power to beam (4 times as high as KEKB) –Change to 1 ARES/1 klystron configuration –Double the number of RF stations

Nov. 28, 2003RF System Overview, K. Akai3 Modify the ARES in LER Modify the A- and C- cavity (S-cavity is not changed) –So that the total stored energy is increased. –To reduce the growth rate by reducing the detuning frequency. –To reduce the load to the C-cavity damper. –For example, exsistingmodified Energy ratio1:91:15 Detuning (kHz)6545 Growth time (ms) C-damper power (kW)4126 Details will be given by Kageyama’s talk.

Nov. 28, 2003RF System Overview, K. Akai4 Feedback with comb filter for the -1 mode Successfully operating in KEKB. Much higher gain ( 〜 30dB) required for Super-B. The -2 mode filter will be added.

Nov. 28, 2003RF System Overview, K. Akai5 ARES HOM power T. Kageyama

Nov. 28, 2003RF System Overview, K. Akai6 SCC HOM power and beam pipe Present HOM dampers in KEKB have been operated up to 10 kW/cavity. Beam pipe diameter150 mm (present)220 mm (enlarged) Loss factor for 3mm bunch (Furuya) 2.46 V/pC1.69 V/pC HOM power for 4.1A, 5000 bunches 83 kW/cavity57 kW/cavity Influence to other groups No changeReplace chambers Large bore magnets Develop gate valves

Nov. 28, 2003RF System Overview, K. Akai7 SCC HOM damper The beam pipe diameter should be changed to 220 mm to reduce the loss factor. The present HOM damper will be bench tested to see its power limit. The point is effective cooling, surface temperature, and outgassing. If SBP side damper works at 20kW, the present dampers may be used for Super-KEKB. If not, modification or new design of dampers is necessary.

Nov. 28, 2003RF System Overview, K. Akai8 RF parameters

Nov. 28, 2003RF System Overview, K. Akai9 Other R&D’s Input coupler –surface treatment, cooling, protection Control and feedback –much higher gain needed for the comb filter damper –digital system Beam tests –ARES (modified cavity) –Crab –SCC for positron beam?

Nov. 28, 2003RF System Overview, K. Akai10 Construction Before 2008 –Construct 14 units of RF system To change to 1 ARES/1 klystron configuration –2 RF stations for Crab crossing After 2008 –Construct 18 units of RF system –Fabricate 10 more ARES’s –Fabricate 4 SCC’s –Construct RF system for Crab cavities

Nov. 28, 2003RF System Overview, K. Akai11 Schedule

Nov. 28, 2003RF System Overview, K. Akai12 New buildings to be constructed Building for Power Supply (hight=5m) Control roomSchedule D4455 m 2 (35m×13m) 170 m 〜 06 D5-- D7273 m 2 (21m×13m) 100 m 〜 06 D8304 m 2 (16m×13m+12m×8m) 〜 06 D1081 m 2 (9m×9m) 50 m 2 〜 2009 D11-- Total1113 m m 2

Nov. 28, 2003RF System Overview, K. Akai13 Cost estimation Total cost = Oku-yen, including –32 klystrons –15 power supplies –Evaporative cooling system for klystron collector –32 High-power and Low-level systems –20 existing ARES’s to be modified –10 new ARES’s for LER –4 additional SCC’s for HER –RF system for Crab cavities –R&D and Beam tests Cost for related infrastructures such as buildings, electricity, cooling system are not included.

Nov. 28, 2003RF System Overview, K. Akai14 RF system for Damping Ring Base plan assumed –Same RF frequency as KEKB –Use ARES (full set) Construction –Fabricate a klystron and an ARES cavity. –An existing power supply (B- type) will be moved. –High-power and low-level system: partly new, partly reused. –Total cost is about 2.4 Oku-en. (Building is not included.) RF-related parameters Bunch charge2.5nC Number of bunches4(2x2) Circumference131.3m Beam current23mA Energy loss/turn0.073MV RF frequency508.9MHz RF voltage0.261MV Wall dissipation42kW Beam power1.7kW Number of cavity1

Nov. 28, 2003RF System Overview, K. Akai15 Crab Cavity Currently being developed –Squashed cell + Coaxial pipe –All parasitic modes are damped. New design for 10A beam –Squashed cell + Waveguides –Lower frequency mode needs tuning and feedback.

Nov. 28, 2003RF System Overview, K. Akai16 Coupling impedance of new crab cavity Zx Z// Zy

Nov. 28, 2003RF System Overview, K. Akai17 Impedance and loss factor Crabbing mode –R/Q = 41.4Ω, Q = (Type-I cavity: R/Q = 47.2) If NC, Vkick = 0.35 kW If SC, Vkick = 1.4MV Highest impedance of parasitic modes and loss factor The impedance is reduced by a factor 8 〜 10 compared to Type-I. The loss factor is reduced by half.

Nov. 28, 2003RF System Overview, K. Akai18 Crab experiment in For the crab crossing experiment in KEKB, beam instability is OK with present crab cavity.

Nov. 28, 2003RF System Overview, K. Akai19 Crab cavity in SuperKEKB Type-II has advantages for Super-KEKB, especially in LER. Type-I may be used in HER, if HOM absorber is OK with 50kW.

Nov. 28, 2003RF System Overview, K. Akai20 Impedance-related issues (Suetsugu, Shibata, Stanic, Kageyama, Akai) Loss factor of LER

Nov. 28, 2003RF System Overview, K. Akai21 Loss factor and Number of RF units Required number of RF units is expressed as: k others is loss factor except cavities, and P bo is beam power by each unit. 28 unit

Nov. 28, 2003RF System Overview, K. Akai22 Instabilities due to RF cavities Longitudinal Transverse