RF System for SuperKEKB Contents: ◆ Base plan ◆ ARES and SC cavities ◆ High beam current and...

RF System for SuperKEKB

Contents:◆ Base plan◆ ARES and SC cavities◆ High beam current and measures◆ Crab cavity◆ Construction

K. AKAI

Jan. 20, 2004SuperB Factory Workshop Hawaii

Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 2

Base plan

• KEKB RF system– Excellent performance at 1.8A (LER) and 1.2A (HER) shows pote

ntial for operating beyond the design beam current of KEKB.• Strategy for SuperKEKB:

– Adopt the same RF frequency as KEKB and use the existing RF system as much as possible, with improvements as necessary to meet the requirements for SuperKEKB.

• If this scheme is feasible:– Construction cost is greatly reduced.– Technical uncertainties are relatively small.

• Important issues:– Very high beam current (4 times as KEKB) – Short bunch length of 3mm.


The ARES cavity

Storage Cavity

Coupling Cavity

Accelerating CavityCoupling Cavity DamperHOM damperEight SiC tiles per Groove

Two SiC bullets per WaveguideTuner Port

Tuner Port

Input CouplerPortPumping Port

Mode ShiftingGroove

Two SiC bullets per WaveguideRF Parametersof the π/2 Accelerating Mode

0.00010.0010.010.1

495500505510515520

π/2 mode0 modeQL≈100π modeQL≈100frequency /MHz

S21 responseHigh-Power PerformanceUa : Us = 1 : 9R / Q = 15 ΩQ = 1.1 x 105

Ua / Us = ks / ka22π / 2 - mode basics

Pc = 150 kW / ARES Cavitygenerating Vc = 0.5 MV (KEKB Design)Maximum ContinuousPc = 380 kWMaximum for 20 minutuesPc = 450 kW

HOM damper


0 0.5 1m

LHe

GATE VALVE

GATE VALVEFREQUENCY TUNER

HOM DAMPER (LBP)

HOM DAMPER (SBP)

N2 SHIELD ION PUMP

DOOR KNOB TRANSFORMER

INPUT COUPLER

Nb CAVITY

Superconducting Damped Cavity for KEKBSuperconducting Damped Cavity for KEKBT. Furuya


RF parameters for SuperKEKBRing 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


Problems to be solved

• Strong longitudinal CBI due to a large detuning of the accelerating mode, even with ARES and/or SCC. – Growth rate = (0.3 ms)-1

• CBI due to HOM and other parasitic modes• Large HOM power in each cavity

– HOM dampers

• Strengthening of RF power is required – 4 times as high as KEKB


Measures for CBI due to fundamental mode

• Two measures will be taken:

• (1) Modify LER-ARES– Remodel the A-C cavity of the ARES to increase the stored

energy further.

– The -1 mode growth rate is reduced from (0.3ms)-1 to (1.6ms)-1.• No modification on the HER-ARES: majority of the driving

impedance in HER is attributed to SCC.

• (2) RF feedback (-1 mode damper)– The growth time of 1.6ms (LER) and 1ms (HER) is still faster

than the radiation damping time by a factor of 20.

– The instability will be suppressed by the -1 mode damper.

– The -2 mode also needs to be suppressed by the feedback.


Modification of LER-ARES

• The ARES in LER will be remodeled to increase the stored energy further.

• By enlarging the coupling hole between the A-C cavities, Us/Ua will be increased from 9 to 15.

• Storage cavity is reused.

exsisting

modified

Energy ratio 1:9 1:15

Detuning (kHz) 65 45

Growth time (ms) 0.3 1.6

C-damper (kW) 41 26

100

101

102

103

104

9 12 15 18

Us/Ua

μ = −1

μ = −2

μ = −3

Coupling impedance for the p/2 mode

Growth rate as a function of Us/Ua

T. Kageyama, et. al.


The existing -1 mode damper at KEKB

• The -1 mode CBI occurs at more than 1A in KEKB-LER.

• It is suppressed by the -1 mode damper.• The damping time of 1 ms is required for

SuperKEKB.

∑

Beam

Circulator CavityKlystronRF reference

LPF

LPF

ƒrfƒrf

PickupElectrode0˚

0˚

0˚

-90˚-90˚

0˚0˚

-90˚-90˚

0˚0˚

0˚

DigitalFilter

-

+

Down conv.Up conv.SSB filter

Phase shifter

1600

1400

1200

1000

800

600

400

200

03:30 PM03.6.30

3:45 PM 4:00 PM

Date

Feedback off Feedback on

-120

-100

-80

-60

-40

-1 -0.99 -0.98 -0.97 -0.96 -0.95Frequency Δƒ/ƒrev

ƒrf - ƒrev ƒrf - ƒrev + ƒs ( )a

-100

-80

-60

-40

-1 -0.99 -0.98 -0.97 -0.96 -0.95Frequency Δƒ/ƒrev

ƒrf - ƒrev

ƒrf - ƒrev + ƒs

( )b

FB OFF

FB ON

S. Yoshimoto, et. al.


CBI due to the 0 and modes of ARES

• The large detuning of the A-cavity gives rise to imbalance of the 0 and mode impedance.

• Longitudinal CBI can be excited. The growth time is 4ms. • It is outside the bandwidth of the klystrons.

Top: Re [Z//] of the 0 and modes

Bottom: Re [Z//] imbalance R+-R-


Summary of CBI due to RF cavities

LER HERItem Freq.(MHz) # cav. Growth

time# cav. Growth

time

Cure

ARES-HOM 1850 28 5ms 16 47ms B-BSCC-HOM 1020 - 12 49ms B-BCrab-HOM and LFM 655 2 41ms 2 214ms 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 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-HOM 773 2 4ms 2 12ms B-B

Longitudinal

Transverse

Longitudinal bunch-by-bunch FB is needed. Required damping time is 4ms.

The instability can be suppressed by the present transverse bunch-by-bunch FB.


ARES HOM dampersHOM LOADSBullet-shape sintered SiC Ceramic Absorber

• Two absorbers (ø55mm x 400mm) per HOM waveguide. • Power capability tested up to 3.3 kW (CW) per absorber.

SiC Ceramic Tiles for GBP HOM Load

• Eight SiC tiles (48mm x 48mm x 20mm, or 10mm) per groove.• Power capability upgraded up to 0.5 kW by brazing tiles to a copper plate cooled by water.SiC TileOFCSUSCooling Circuit

OFCOFC Compliant Layer


HOM power of LER-ARES

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 A

GBP~3.4 kW

SuperKEKBLER 9.4 A

KEKB

SuperKEKB

WG

dam

per

GBP

dam

per


Improve the ARES-HOM dampers

• The waveguide dampers– High power tested up to 3.3 kW/bullet (26 kW/cavity).– Upgrade needed to 80 kW/cavity.– Will be tested at higher power with a new high power source.– The number of bullets/waveguide will be increased.

• The grooved beam pipe dampers– High power tested up to 0.5 kW/groove (2 kW/cavity).– Upgrade needed to 20 kW/cavity.– A new type of damper? Such as a winged chamber with SiC bull

ets?

Y. Suetsugu, et. al.


SCC HOM power and beam pipe

• Present HOM dampers in KEKB have been operated up to 12 kW/cavity.

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

Loss factor for 3mm bunch

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 chambers

Large bore magnets

Develop gate valves


Improve the SCC-HOM damper

• The present HOM damper will be bench tested to see its performance limit.

• The points are effective cooling, surface temperature, and outgas.

• 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.

• In addition, the beam pipe diameter will be changed to 220 mm to reduce the loss factor.


Strengthening of RF power

• Required RF power provided to beam is 18 MW (LER) and 16 MW (HER), four times as high as those of KEKB.

• The required RF voltage is relatively low.• The number of cavities should be kept as small as possible

to reduce the total impedance in the ring.

• Change to one ARES/klystron configuration.– KEKB: two ARES/one klystron

• The input power to each cavity will be nearly doubled.

• The number of klystrons will be more than doubled.


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 + TbkothersIb

2

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


Input couplers

• Performance at KEKB– Operating typically at 300-350 kW/coupler (ARES, SCC).– The ARES coupler tested up to 950 kW (through).– The SCC coupler tested up to 800 kW (through), 300 kW (total r

eflection).• Requirement for SuperKEKB

– Operation at 900 kW/coupler (ARES), 500 kW/coupler (SCC).• Plans and prospect

– The present couplers can be probably used in SuperKEKB.– Improvements and tests planned.

• A new high power test setup is being constructed.• R&D to suppress multipactoring (TiN coating) is going on.• Increasing the operating power of SCC > 400kW in 2004.


Number of RF units

KEKB SuperKEKB

LER HER LER HER

Oho D4 3 14

D5 3 8 2

Fuji D7 5 10

D8 5 10

Nikko D10 4 6

D11 4 6

Total 24 56


New buildings needed

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


Construction plan

• 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 2015

10 (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 Klystrons

18 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)


Crab crossing

Kick

Kick

head-on collision

crossing angle

crab cavity crab cavity

Recent simulations by Ohmi showed significant increase of luminosity by several times by the crab crossing.

Palmer for LC (1988)Oide and Yokoya for storage rings (1989)


Parameters for the crab crossing

KEKB SuperKEKB

Plan Backup scheme Adopted as baseline

Ring LER HER LER HER

Beam energy (GeV) 3.5 8.0 3.5 8.0

Beam current (A) 2.6 1.1 9.4 4.1

RF frequency (MHz) 508.887 508.887

Crossing angle (mrad) ±11 ±15

βx* (m) 0.33 0.33 0.2 0.2

βx, crab (m) 20 100 100 〜 200 300 〜 400

Required kick (MV) 1.41 1.44 1.10 〜 0.78 1.46 〜 1.26


Damping parasitic modes

• Accelerating cavities– Operating mode (TM010) is th

e lowest frequency mode.

– Any parasitic mode (HOM) has higher frequency than the operating mode.

– Wave guides or beam pipe with cut-off frequency higher than the operating mode can damp all HOM’s. (ARES, SCC, PEP-II cavity, etc)

• Crab cavity– Operating mode (usually

TM110) is NOT the lowest frequency mode.

– There exists lower frequency parasitic mode(s).

– Wave guides can damp higher frequency modes. However, special care is needed for the lower frequency modes.


Original crab cavity

• Squashed cell operating in TM2-1-0 (x-y-z)

• Coaxial coupler is used as a beam pipe

• Designed for B-factories (1 〜 2A)

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).)


Crab cavity with 10A beam

• The original cavity is designed for 1 〜 2A beam– Simple structure, suitable for SC → High kick voltage is obtaine

d by one cavity.– Sufficient damping of parasitic modes.– Not necessarily optimized for a 10 A beam.

• Possible problems at 10A– Large HOM power (200kW)

• Loss factor is not very small, because the radius of coaxial beam pipe can not be widely opened.

• Additional loss factor comes from the absorber on wide beam pipe.– Much heavier damping of HOM’s may be needed, particularly for

horizontal polarization of transverse modes (large x_crab).• A new crab cavity has been designed, which can be use

d at 10A.


Design concept of new crab cavity

• Squashed cell operating in TM2-1-0 (same).

• Waveguide dampers are attached.– Much heavier damping of parasitic modes can be obtained.

– Larger HOM power is allowed for the dampers.

• Coaxial dampers are used, but not as a beam pipe.– The TM1-1-0 is well damped.

– Loss factor is reduced since widely opened beam pipes can be used.

• Optimization has been carried out for both the SC and NC versions independently.


Schematic drawing of new crab cavity

• (Left) The cross-shaped waveguide dampers and coaxial dampers are attached at the squashed-cell.

• (Right) Cross section of the coaxial damper at the cut plane of Y-Y’.

coaxial damper

cross-shapedwaveguide dampers

Y

Y'

absorber

(cross section at Y-Y')


New crab cavity (1/4 cell)

K. Akai and Y. Morita,to be submitted.


Coupling impedance

Crabbing modeLower frequency mode

Longitudinal Horizontal

Ohm/mOhm

Original New(SC) New(NC) unit

Highest value of ZT (H) 25.0 5.6 4.4 k/m

Highest value of ZT (V) 15.0 3.2 10.1 k/m

Highest (Z// x freq./GHz) 2070 1020 760 GHz

Kloss@3mm 0.73 0.56 0.56 V/pC


Comparison of cavities for SuperKEKB

Original New designSC SC NC

No. of cavities 1Å~2 1Å~2 2Å~2Growth time (horizontal) 0.9ms 8.4ms 4.2msGrowth time (longitudinal) 21ms 146ms 73ms

SuperKEKB(LER)É¿crab=170mV kick=0.7MV Total HOM power 214kW 97kW

No. of cavities 1Å~2 1Å~2 3Å~2Growth time (horizontal) 2.7ms 25ms 8.4msGrowth time (longitudinal) 107ms 763ms 254ms

SuperKEKB(HE R)É¿crab=300mV kick=1.2MV Total HOM power 44kW 20kW

New crab cavity has advantages for Super-KEKB, especially in LER.Original crab cavity could be used in HER, if HOM absorber is OK with 50kW.


Summary of new crab cavity

• Parasitic modes are sufficiently damped.– The lower frequency mode is also damped.– Instability can be suppressed with the present FB system, even

at a beam current of 10A.

• The problem for the dampers due to a large parasitic power is greatly eased: – Loss factor of the cell is reduced.– The absorbers do not contribute to the loss factor.– The parasitic power to each damper is further reduced since it i

s divided into the waveguide and coaxial dampers.

• The new crab cavity can be used in SuperKEKB.


Summary of SuperKEKB RF system

• Base plan:– The existing RF system will be used as much as possible, with improvements as

necessary. – The ARES (LER, HER) and SCC (HER) will be used.

• CBI due to the accelerating mode– LER-ARES will be modified, that eases the growth time from 0.3ms to 1.6ms.– The -1 mode damper will suppress the CBI with a growth time of 1 ms.

• HOM dampers– Performance limit of the present HOM dampers will be tested.– A new HOM damper may by necessary, particularly for the GBP damper.

• Large RF power– Improvement of the couplers will continue to double the operating power.– The number of RF unit will be doubled.

• Crab cavity– A new crab cavity is proposed, which can be used at 10 A. – The design is completed. It has sufficient property for SuperKEKB.


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


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 0̀.5 Å 2̀ 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


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 SuperKEKB Contents: ◆ Base plan ◆ ARES and SC cavities ◆ High beam current and...

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Transcript of RF System for SuperKEKB Contents: ◆ Base plan ◆ ARES and SC cavities ◆ High beam current and...