rf system for superkekb contents: ◆ base plan ◆ ares and sc cavities ◆ high beam current and...
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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.
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 3
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
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 4
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 5
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
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 6
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 7
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
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 8
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
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 9
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.
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 10
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.
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 11
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.
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 12
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-
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 13
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.
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 14
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
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 15
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
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 16
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.
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 17
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
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 18
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.
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 19
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.
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 20
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
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 21
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.
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 22
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
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 23
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
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 24
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
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 25
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)
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 26
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)
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 27
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
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 28
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.
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 29
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).)
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 30
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.
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 31
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.
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 32
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')
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 33
New crab cavity (1/4 cell)
K. Akai and Y. Morita,to be submitted.
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 34
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
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 35
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.
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 36
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.
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 37
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.
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 38
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
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 39
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
Jan. 20, 2004 RF System for SuperKEKB (K. Akai) 40
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.