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


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


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.


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


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


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


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.


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


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?


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


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)


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


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.


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


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).)


Coupling impedance of new crab cavity

Zx

Z//

Zy


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


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.


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.


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


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


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

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