nov. 28, 2003rf system overview, k. akai1 rf system overview contents: ◆ high beam current and...

Nov. 28, 2003 RF System Overview, K. Akai 1

RF System Overview

Contents: High beam current and measures Construction Damping ring RF system Crab cavity Impedance-related issues

K. AkaiNov. 28, 2003SuperKEKB mini workshop, KEK

Nov. 28, 2003 RF System Overview, K. Akai 2

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, 2003 RF System Overview, K. Akai 3

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,

exsisting modifiedEnergy ratio 1:9 1:15Detuning (kHz) 65 45Growth time (ms) 0.3 1.6C-damper power (kW) 41 26

Details will be given by Kageyama’s talk.

Nov. 28, 2003 RF System Overview, K. Akai 4

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.

-120

-100

-80

-60

-40

508.791508.790508.789508.788508.787

Frequency [x106 Hz]

Feedback on/off (Ib = 890 mA, Detuning -60 kHz)BW = 1kHz, Gain = 15 dB

-120

-100

-80

-60

-40

4.03.53.02.52.01.51.00.50

Time [Sec]

Feedback on/off (Ib = 1.0 A, Detuning -60 kHz)

Feedback off

Beam Abort

Σ

Beam

Circulator CavityKlystronRF Input

LPF

LPF

frffrf

PickupElectrode0˚

0˚

0˚

-90˚-90˚

0˚0˚

-90˚-90˚

0˚0˚

0˚

Filter

Block diagram of the -1 Mode Damping System

Nov. 28, 2003 RF System Overview, K. Akai 5

ARES HOM power

0.1

1

10

100

0.1 1 10

2 x GBP (Nb=1224, BL=7mm)2 x GBP (Nb=4896, BL=4mm)2 x GBP (Nb=4896, BL=3mm)4 x HOM WG (Nb=1224, BL=7mm)4 x HOM WG (Nb=4896, BL=4mm)4 x HOM WG (Nb=4896 BL=3mm)

HOM Power (kW)

Beam Current (A)

HOM WG Loads /CavityHPT verification up to 26 kW (KEKB)

GBP Loads /CavityHPT up to 2 kW (KEKB)

HOM WG~80 kW

GBP ~20 kW

HOM WG~14 kW

SuperKEKBHER 4.1 AGBP~3.4 kW

SuperKEKBLER 9.4 A

T. Kageyama

Nov. 28, 2003 RF System Overview, K. Akai 6

SCC HOM power and beam pipe

• Present HOM dampers in KEKB have been operated up to 10 kW/cavity.

Beam pipe diameter 150 mm (present) 220 mm (enlarged)

Loss factor for 3mm bunch (Furuya)

2.46 V/pC 1.69 V/pC

HOM power for 4.1A, 5000 bunches

83 kW/cavity 57 kW/cavity

Influence to other groups

No change Replace chambersLarge bore magnetsDevelop gate valves

Nov. 28, 2003 RF System Overview, K. Akai 7

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, 2003 RF System Overview, K. Akai 8

RF parametersRing LER HERBeam current (A) 9.4 4.1Wiggler magnets yes (half) noEnergy loss/turn (MeV) 1.2 3.5Loss factor, estimated (V/pC) 40 50Radiation loss power (MW) 11.3 14.3Parasitic loss power (MW) 7.1 1.7Total beam power (MW) 18.4 16.0Total RF voltage (MV) 14 23

(Total)Cavity type ARES ARES SCC ARES / SCCNo. of cavities 28 16 12 44 / 12Voltage /cav. (MV) 0.5 0.5 1.3Loaded-Q value (x10E4) 2.4 2.4 4.0Beam power /cav. (kW) 650 650 460Wall loss /cav. (kW) 233 233 -Detuning frequency (kHz) 45 20 74

Klystron power (kW) 930 930 480No. of klystrons 28 16 12 56Total AC plug power (MW) 42 24 10 76

Nov. 28, 2003 RF System Overview, K. Akai 9

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 cavity @Nikko– SCC for positron beam?

Nov. 28, 2003 RF System Overview, K. Akai 10

Construction

• Before 2008– Construct 14 units of RF system

• To change to 1 ARES/1 klystron configuration– 2 RF stations for Crab crossing experiment @Nikko

• 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, 2003 RF System Overview, K. Akai 11

Schedule

2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 201510 (20) 6 (12) 8 (8)

20 (20)10 (10) 8 (8)

20 (20)16 (16) 8 (8)

20 (20)20 (20)12 (12)

20 (20)24 (24)12 (12)

4.6 4.6 18.0 20.2 12.0 12.0 12.0 12.0 8.0 7.0 0.8

# Stations (# cavities)

RF system

FujiOhoNikko

14 Klystrons18 Klystrons8 sets of Power supplies16 sets of High power and Low-level systemCooling system

ARES-AC modify Prototype Beam test

ARES-AC modify 20 sets ARES (LER-Oho)

10 sets

SCC 4 sets

6 ARES install 4 ARES install 4 ARES install

4 SCC install

RF system for Crab exp.

2003. 9. 12003. 9. 5 revisedK. Akai

Super-KEKB Adiabatic Construction --- RF Group

6 sets of Power supplies14 sets of High power and Low-level systemCooling system

R&D for ARES-HOM damper SCC-HOM damper ARES-plating Couplers Control and Feedback

SCC beam pipe radius increase

ARES (LER-Fuji) assemble

RF system for Crab@Tsukuba

Total111.2

Cost for RF system (unit oku-en)Related InfrastructureConsruct (D4, D7, D8) Construct (D10)

Nov. 28, 2003 RF System Overview, K. Akai 12

New buildings to be constructed

Building for Power Supply (hight=5m)

Control room Schedule

D4 455 m2 (35m×13m) 170 m2 2005〜 06

D5 - -

D7 273 m2 (21m×13m) 100 m2 2005〜 06

D8 304 m2

(16m×13m+12m×8m)- 2005〜 06

D10 81 m2 (9m×9m) 50 m2 〜 2009

D11 - -

Total 1113 m2 320 m2

Nov. 28, 2003 RF System Overview, K. Akai 13

Cost estimation

• Total cost = 111.2 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, 2003 RF System Overview, K. Akai 14

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 charge 2.5 nC

Number of bunches 4 (2x2)

Circumference 131.3 m

Beam current 23 mA

Energy loss/turn 0.073 MV

RF frequency 508.9 MHz

RF voltage 0.261 MV

Wall dissipation 42 kW

Beam power 1.7 kW

Number of cavity 1

Nov. 28, 2003 RF System Overview, K. Akai 15

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.

Absorbing materialNotch filter

Absorbing material

Squashed Crab cavity for B-factories

Coaxial beam pipeCooling for inner conductor

(axial view)

inner conductor

"Squashed cell"

(K. Akai et al., Proc. B-factories, SLAC-400 p.181 (1992).)

Nov. 28, 2003 RF System Overview, K. Akai 16

Coupling impedance of new crab cavity

Zx

Z//

Zy

Nov. 28, 2003 RF System Overview, K. Akai 17

Impedance and loss factor

• Crabbing mode– R/Q = 41.4Ω, Q = 41100 (Type-I cavity: R/Q = 47.2)

• If NC, Vkick = 0.35 MV@Pc=72 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.

unit Type- I Type- IIZT kÉ∂/ m 25 2.6Z/ / Å~f[GHz] É∂ 2050 290kloss@3mm V/ pC 1.23 0.56

Nov. 28, 2003 RF System Overview, K. Akai 18

Crab experiment in KEKB@Nikko

Type- I (SC)No. of cavities 1É—(transverse) 28msÉ—(longitudinal) 96ms

KEK B (LER)É¿crab=50mVÅ€=1.32MV

Total HOM power 23kWNo. of cavities 1É—(transverse) 26msÉ—(longitudinal) 440ms

KEK B (HE R)É¿crab=250mVÅ€=1.35MV

Total HOM power 6kW

For the crab crossing experiment in KEKB,beam instability is OK with present crab cavity.

Nov. 28, 2003 RF System Overview, K. Akai 19

Crab cavity in SuperKEKB

Type- I Type- IISC SC NC

No. of cavities 1Å~2 1Å~2 2Å~2É—(transverse) 0.9ms 8.4ms 4.2msÉ—(longitudinal) 21ms 146ms 73ms

Super-KEKB(LER)É¿crab=170mVÅ€=0.7MV Total HOM power 214kW 97kW

No. of cavities 1Å~2 1Å~2 3Å~2É—(transverse) 2.7ms 25ms 8.4msÉ—(longitudinal) 107ms 763ms 254ms

Super-KEKB(HE R)É¿crab=300mVÅ€=1.2MV Total HOM power 44kW 20kW

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, 2003 RF System Overview, K. Akai 20

Impedance-related issues

KEKB @4mmin Design Report

Super-KEKB @3mm

Number of items Loss factor(V/pC)

Number of items Loss factor /item(V/pC)

Loss factor(V/pC)

Comment

ARES cavity 20 10.6 28 0.667 18.7Resistive-wall 3016 m 4.0 3016m - 6.5 CopperPhoton Masks at arc 1000 4.6 800 1E-8 8E-6 ante-chamberPumping slots at arc 10x1800 0.37 - 0.0019 ante-chamberPumping slots @straight + 800 +BPMs 4x400 0.79 4x400 +Masks at IP 1 0.08 1 + pendingIR chamber 1 0.29 1 + pendingRecomb. chambers 2 1.6 2 + pendingBellows 1000 2.5 800 4E-3 3.2Flange gap + 800 1E-4 0.08Gate Valve + 40 3.1E-3 0.12Feedback kickers + +Injection/Abort kickers + +Septum + +Movable masks + 16 1 16HOM absorbers (RF end) + 4 Å 0.5 Å 2 150É”Tapers (RF end) + 4 0.04 0.16 94ÅÃ150É”Tapers (others) + 72 3E-3 0.22Total 25.7+ 46.9+ tentative

(Suetsugu, Shibata, Stanic, Kageyama, Akai)

Loss factor of LER

Nov. 28, 2003 RF System Overview, K. Akai 21

Loss factor and Number of RF units

• Required number of RF units is expressed as:

20

25

30

35

40

45

50

0 10 20 30 40 50

Pb=550kW/cav.Pb=600kW/cav.Pb=650kW/cav.

Loss factor except cavities (V/pC)

€

Ncav = U0Ib + TbkothersIb2

Pb0 −TbkcavIb2

€

€

Tb =1.965 ×10−9(s)Ib = 9.4(A)

U0 =1.2 ×106(V )

kcav = 0.67 ×1012(V /C)

€ €

€

Ncav = 11.3 + 0.174 × kothers(V / pC)Pb0(MW ) − 0.117

kothers is loss factor except cavities, andPbo is beam power by each unit.

28 unit

Nov. 28, 2003 RF System Overview, K. Akai 22

Instabilities due to RF cavitiesLER HERItem Freq.

(MHz) # cav. Growthtime

# cav. Growthtime

Cure

ARES-HOM 1850 28 5ms 16 47ms B-BSCC-HOM 1020 - 12 49ms B-BCrab (II) -HOM 1260 4 73ms 6 240ms B-BCrab (I) -HOM 410 - 2 102ms B-BARES - 0/pi modes 504 28 4ms 16 29ms B-BFundamental –1 mode 508.79 28 1.6ms 16+12 1ms RFFundamental –2 mode 508.69 28 20ms 16+12 21ms RFCrab (II) -Lower mode 390 4 4ms 6 20ms RF

LER HERItem Freq.(MHz) # cav. Growth

time# cav. Growth

time

Cure

ARES-HOM 633 28 4ms 16 33ms B-BSCC-HOM 688/705 - 12 12ms B-BCrab (II) -HOM 1360 4 4ms 6 8ms B-BCrab (I) -HOM 1050 - 2 2ms B-B

Only the fastest mode is listed in each item.Crab (II) and Crab (I) are alternative in HER.Beta_x@crab is assumed to be 170m in LER and 300m in HER.B-B means bunch-by-bunch feedback.RF means feedbacks in RF control system.

Longitudinal

Transverse