RF system upgrade - Overview
K. Akai
Feb. 16, 2004
KEKB review committee
Contents:◆ Base plan
◆ High beam current and measures◆ Construction◆ SummaryBase plan
• KEKB RF system– Excellent performance at 1.8A (LER) and 1.2A (HER) shows
potential for operating beyond the design beam current of KEKB.

• Strategy for SuperKEKB:– Adopt the same RF frequency as KEKB and use the existing RFsystem as much as possible, with improvements as necessary tomeet the requirements for SuperKEKB.

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

• Possible problems to be investigated:– Issues related to very high beam current (4 times as KEKB)– Short bunch length of 3mm.
Jan. 20, 2004

RF System for SuperKEKB (K. Akai)

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Jan. 20, 2004

RF System for SuperKEKB (K. Akai)

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RF System for SuperKEKB (K. Akai)

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Superconducting Damped Cavity for KEKB%<')=>=?@

311*'9-1:'%*$-7)1*2&*
8-4,%'.1,4!&*#$%&'($!(&!H"#$%&'($!(&)*&+,&-./'''''''%,-&*

012'3$24&*''''5 SBP)

012'3$24&*(LBP)-;''.$(8%/81-'4,24- 6 '708&!30

Jan. 20, 2004

RF System for SuperKEKB (K. Akai)

0.51m5

Jan. 20, 2004

RF System for SuperKEKB (K. Akai)

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RF parameters
Ring
LER
Beam current (A)9.4
Wiggler magnets
yes (half)
Energy loss/turn (MeV)
1.2
Loss factor, estimated (V/pC)
40
Radiation loss power (MW)
11.3
Parasitic loss power (MW)
7.1
Total beam power (MW)
18.4
Total RF voltage (MV)14
Cavity typeNo. of cavities
Voltage /cav. (MV)
Loaded-Q value (x10E4)
Beam power /cav. (kW)Wall loss /cav. (kW)
Detuning frequency (kHz)

ARES
280.5
2.4
650
233
45Klystron power (kW)No. of klystrons
Total AC plug power (MW)

930
28
40

Jan. 20, 2004

HER
4.1
no3.5
50
14.3
1.7
16.0
23
ARES SCC
16120.5
1.3
2.4
4.0
650
460
150
3174
850
16234801210

RF System for SuperKEKB (K. Akai)(Total)
ARES / SCC
44 / 125673

7

Issues to be solved• Strong longitudinal CBI due to a large detuning, evenwith 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)

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Measures for the fundamental mode instability• Modify LER-ARES– Remodel the A-C cavity of the ARES to increase the stored
energy further.
– The growth rate is then reduced from (0.3ms)-1 to (1.6ms)-1.
– This modification will not be used on the HER-ARES (majority ofthe driving impedance is attributed to SCC).

• Powerful feedback using a comb filter– The growth time of 1.6ms (LER) and 1ms (HER) is faster than
the radiation damping time by a factor of 20.
– Further study to test the performance limit of existing -1 mode
damper in KEKB and the R&D to improve the performance, ifnecessary, will continue.
– The -2 mode damper will be added.
Jan. 20, 2004

RF System for SuperKEKB (K. Akai)

9Modification of LER-ARES•The ARES in LER will be
remodeled to increase thestored energy further.
By enlarging the coupling holebetween A-C cavities, Us/Ua
will be increased from 9 to 15.
T. Kageyama, et. al.

exsisting modified
Energy ratio
Detuning (kHz)

1:965

1:15
45

Growth time (ms)

0.3

1.6

C-damper (kW)41

26

Coupling impedance for the p/2 mode
104

Growth Rate [ s-1 ]•µ = !1103
102µ = !2101
100µ = !3
91215
Us/Ua

18

Growth rate as a function of Us/Ua
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RF System for SuperKEKB (K. Akai)

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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.
FB OFF

FB ON

S. Yoshimoto, et. al.
Jan. 20, 2004

RF System for SuperKEKB (K. Akai)

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CBI due to the 0 and π modes of ARESTop:
Re [Z//] of the 0 and π modes

Bottom:Re [Z//] imbalance R+-R-•••

The large detuning of the A-cavity gives rise to imbalance of the 0and π mode impedance.
Longitudinal CBI can be excited. The growth time is 4ms.
It is outside the bandwidth of the klystrons.

Jan. 20, 2004

RF System for SuperKEKB (K. Akai)

12Summary of CBI due to RF cavities
Longitudinal
ItemFreq.
(MHz)

ARES-HOM
SCC-HOM
Crab-HOM and LFM
ARES - 0/pi modes
Fundamental –1 mode
Fundamental –2 mode

1850
1020
655
504
508.79508.69LER# cav.
Growth
time
28
5ms
2
41ms
28
4ms
28
1.6ms
28
20ms

HER
# cav.
Growthtime
16
47ms
1249ms2214ms1629ms16+121ms
16+1221ms

Cure

B-B
B-B
B-B
B-B
RFRF

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

Transverse
ItemFreq.
(MHz)

ARES-HOM
SCC-HOM
Crab-HOM

633
688/705773

LER# cav.
Growthtime
28
4ms
24ms

HER
# cav.
Growthtime
16
33ms
1212ms
212ms

Cure

B-B
B-B
B-B

The instability can be suppressed by the present transverse bunch-by-bunch FB.
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RF System for SuperKEKB (K. Akai)

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ARES HOM dampers

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RF System for SuperKEKB (K. Akai)

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HOM power of LER-ARES#!!

89:% ;'
S4!% @;$%&%'()%*+,-#$$./%(0-1223$%&%'()%*+,-.456/%(0-.223$%&%'()%*+,-.456/%(0-7223.%&%89:%;'%*+,-#$$./%(0-1223.%&%89:%;'%*+,-.456/%(0-.223.%&%89:%;'%*+,-.456%(0-7223TCP>?QRQ(
0RU% 5".% F'()%S$!% @;89:% ;'% 0<AGH% IBAJKEL8)M% J>?KNKOAEK<D%CP% E<% $6% @;% *QRQ(3#!

89:% ;'S#.% @;TCP>?QRQ(
8RU% ."#% Fmper

89:% )<=>?% *@;3SuperKEKBer'()% 0<AGH% IBAJKEL
8)M% CP% E<% $% @;% *QRQ(3GBPdamp#KEKBW

Gda'()
S7".% @;

T. Kageyama!"#!"###!

(>A2% BC??>DE% *F3

Jan. 20, 2004

RF System for SuperKEKB (K. Akai)

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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 SiCbullets.

Y. Suetsugu, et. al.
Jan. 20, 2004

RF System for SuperKEKB (K. Akai)

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SCC HOM power and beam pipe
Beam pipe diameter

150 mm (present)

220 mm (enlarged)

Loss factor for 3mmbunch (Furuya)

2.46 V/pC

1.69 V/pC

HOM power for 4.1A,
5000 bunches

83 kW/cavity

57 kW/cavity

Influence to othergroups

No change

Replace chambers
Large bore magnets
Develop gate valves•Present HOM dampers in KEKB have been operated up to 12
kW/cavity.

Jan. 20, 2004

RF System for SuperKEKB (K. Akai)

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Improve the SCC-HOM damper• The present HOM damper will be bench tested to see its
performance limit.
• The point is effective cooling, surface temperature, andoutgassing.
• 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 to220 mm to reduce the loss factor.

Jan. 20, 2004

RF System for SuperKEKB (K. Akai)

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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)

19Loss factor and Number of RF units
Required number of RF units
is expressed as:
N cav =2b others b
2b cav b

U 0 Ib + T kI
Pb 0 " T k I

U 0 = 1.2 "10 6 (V )kcav = 0.67 "1012 (V /C)!

N cav =!

11.3 + 0.174 " k others (V / pC)
Pb 0 (MW ) # 0.117

%"

$#$"

28 unit!#!"!

kothers is loss factor except cavities, andPbo is beam power by each unit.
Jan. 20, 2004'()##"*+,-./0'()1""*+,-./0'()1#"*+,-./0%#

Tb = 1.965 "10#9 (s)Ib = 9.4(A)!

#"234(567897:;7<=.=>8?<7>?7@A:

•

"&"!"

$"

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@8<<79.-=8675B-5C=7-./>=>5<7DE,CFG

RF System for SuperKEKB (K. Akai)

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

• Requirement for SuperKEKB– Operation at 900 kW/coupler (ARES), 500 kW/coupler (SCC).

• Plans– A new high power test setup.
– R&D to suppress multipactoring (TiN coating).

Jan. 20, 2004

RF System for SuperKEKB (K. Akai)

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Number of RF units
KEKBLER
OhoFujiNikko

HER

D43D53LERHER
148

D7510

D85102

D1046

D1146Total

Jan. 20, 2004

SuperKEKB

24

RF System for SuperKEKB (K. Akai)

56

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New buildings needed
Building for Power
Supply (hight=5m)

Control room

Schedule

D4

455 m2 (35m×13m)

170 m2

2005~06

D5--

D7273 m2 (21m×13m)

100 m2

2005~06

D8304 m2-

2005~06~2009(16m×13m+12m×8m)

D1081 m2 (9m×9m)

50 m2

D11--Total

1113 m2

320 m2

Jan. 20, 2004

RF System for SuperKEKB (K. Akai)

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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)

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Schedule
2003. 9. 1
2003. 9. 5 revised
K. AkaiSuper-KEKB Adiabatic Construction --- RF Group2004# Stations(# cavities)

2005

2006

2007

Fuji
10 (20)Oho
6 (12)
Nikko 8 (8)

2008

2009

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

2010

2011

2012

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

2013

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

2014

2015

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

RF system
14 Klystrons
RF system for
Crab exp.

ARES-AC modify
Prototype
Beam test

6 sets of Power supplies
14 sets of High powerand Low-level system
Cooling system
ARES-AC modify
20 sets

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

Cost for RF system(unit oku-en)
Related InfrastructureJan. 20, 2004!"#!"#

18 Klystrons
8 sets of Power supplies
16 sets of High power and Low-level system
Cooling system$%"&Consruct (D4, D7, D8)

6 ARES install

4 ARES install

4 ARES install

ARES (LER-Oho)
10 sets

ARES (LER-Fuji)assemble

SCC 4 sets

4 SCC install

SCC beam pipe
radius increase
RF system for Crab@Tsukuba'&"'$'"&$'"&$'"&$'"&%"&("&&"%

Total
111.2

Construct (D10)RF System for SuperKEKB (K. Akai)

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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.
Jan. 20, 2004

RF System for SuperKEKB (K. Akai)

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RF system for Damping Ring••

Base plan assumed•

RF-related parameters– Same RF frequency as KEKB
– Use ARES (full set)

Bunch charge

Construction

Number of bunches– 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.)Circumference

4 (2x2)131.3 mBeam current

23 mA

Energy loss/turn

0.073 MVRF frequency

508.9 MHzRF voltage

0.261 MV

Wall dissipation

42 kW

Beam power

1.7 kW

Number of cavity

Jan. 20, 2004

2.5 nCRF System for SuperKEKB (K. Akai)

127Summary of SuperKEKB RF system_1• Base plan:– The existing RF system will be used as much as possible, withimprovements as necessary.

• To suppress the CBI due to the accelerating mode:– LER-ARES will be modified to increase the stored energy.
– The -1 mode damper will handle the growth time of 1 ms.

• CBI due to RF cavities:– Transverse modes can be suppressed by the present BbyB FB.
– Longitudinal BbyB FB is required with a damping time of 4 ms.

• HOM dampers to absorbe a large power:– Performance limit of the present dampers will be tested.
– A new damper may by necessary, particularly for the GBPdamper.
Jan. 20, 2004

RF System for SuperKEKB (K. Akai)

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Summary of SuperKEKB RF system_2• Strengthening of RF power by a factor of 4.
– Improvement of the couplers will continue to double theoperating 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)

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Impedance-related issues
Loss factor of LER
KEKB @4mm
in Design Report
Number of items Loss factor(V/pC)
ARES cavity
2010.6
Resistive-wall
3016 m4.0
Photon Masks at arc
1000
4.6
Pumping slots at arc
10x1800
0.37
Pumping slots @straight
+
BPMs
4x400
0.79
Masks at IP
10.08
IR chamber
10.29
Recomb. chambers
21.6
Bellows
1000
2.5
Flange gap+
Gate Valve+
Feedback kickers+
Injection/Abort kickers+
Septum+Movable masks+
HOM absorbers (RF end)+
Tapers (RF end)+
Tapers (others)
+
Total
25.7+

Super-KEKB @3mmNumber of items Loss factor /item(V/pC)
28
0.667
3016m
800
1E-8
800
4x400
112800
4E-3
800
1E-4
40
3.1E-3164472

1!0.5
0.04
3E-3

Loss factor(V/pC)
18.7
6.5
8E-6
0.0019
+++++
3.2
0.08
0.12+++
16!20.16
0.22
46.9+

Comment

Copperante-chamberante-chamber

pending
pending
pending

150"
94#150"tentative(Suetsugu, Shibata, Stanic, Kageyama, Akai)

Jan. 20, 2004

RF System for SuperKEKB (K. Akai)

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