Status of the RF Accelerating Cavity
for the Damping Ring (DR)Tetsuo ABEFor SuperKEKB‐RF / ARES‐Cavity Group(T. Abe, T. Kageyama, H. Sakai, Y. Takeuchi, and K. Yoshino)

The 17th KEKB Accelerator Review Meeting
gFebruary 21, 2012

RF Accelerating Structure for the DR
Based on the ARES cavity with the long successful operation at KEKB
1. Accelerating-Mode Frequency: 508.887[MHz] (same as in the Main Ring (MR)
2. Cavity Voltage (spec.):
0.7[MV/cav] (Wall-loss power: 133kW/cav)
3.
3 Cavity Voltage (challenge): 00.8[MV/cav]
8[MV/cav] (Wall-loss power: 180kW/cav)
4. Max. stored beam current: 70.8[mA]
5. Grooved Beam Pipe (GBP) Common between cavities
6. Cavity-GBP Joint with a weld-ring gasket (not using a flange)
7 Multi Single Cell Structure
7.
8. Reuse of input couplers and tuners proven at KEKB-MR/ARES
9. Good vacuum in cav. (< 10^-6[Pa]) needed for high-power input couplers
5324 (< 5360)

1MW Klystronyto be used
Very low comparedto (Super)KEKB-MR

Pumping port on each cavity
2662

401550

72501501200128725050300150256 150727230050200
Bellows

Taper End

Taper End

400
Taperp30
Flange1100

110
GV(Dimensions in mm)

1

Specification of the Vc and Wall Lossof the DR Cavity
Based on the results of the HPT of the ARES Prototype
performed in the KEK/AR Tunnel (1997)
Vc[MV/cav]

Wall Loss
Power [kW]Wall Temperature(calc.) [degC]

KEKB Design

0.50

6050

Ma ContinuousMax.
Contin o s

0 70
0.70

13374

Max. Instantaneous

0.82

193

94
(Appendix A)

Note: The DR cavity has been designed with the same basic structure as the ARES/A-Cav(Appendix B)
on the basis of its successful experiences.

2Four Types of Components
1. Cavity (main body)
2. HOM(Higher-Order-Mode)-WG(WaveGuide) load
3 GBP (btwn)
3.
4. GBP (end)

Joint:

Welding for vacuum sealingRF shield inside31. Cavity (main body)Material: Highly-Pure Copper (C1011-C1)
except for the ports, GBPs, and HOM-WGs
Mirror symmetry except for the E-bends, tuner, and monitor ports.
Two input-coupler ports, one of which is to be used as a pumping port

(Along the beam axis)

110deg

70deg

R=150

R=150

Cross-section: 240mm x 28mm

150

340

Tuner Port (ICF2003)

525

Input-Coupler or Pumping Port (ICF203)

556
View Port(ICF70)(Cross-section perpendicular to the beam axis)
150

256

150 (Dimensions in mm)

4

2. HOM‐WG Load
6 SiC tiles as 1set
Cross-section: 240 x 28

2012

Material of the WG: SUS
HOM Absorber: SiC (Silicon Carbide) ceramics•Brazed on a copper plate•Water-cooled via the copper plate•Same as used in the KEKB-MR/ARESPower Capability: ~1kW/1set(@1.3GHz)
Max. HOM Power: ~30W/WG

HOM

Flange on thet WG

Flangeon the E-baand3005050((Dimensions in mm))500
5

A First Set of SiC Tiles
for the DR Cavity/HOM‐WG
Cavity/HOM WG or GBP
To be Delivered Soon
6 SiC Tiles

Copper Plate with a Cooling Channel

SUS Frame for Welding
Cooling-Water Pipe Joint

6

OLD

(Shown last year)NEW

7

HOM‐WG Load Optimized
for the Broadband Performance(Simulation Results using CST
CST-MWS/FD-Solver)
MWS/FD Solver)
Cutoff Freq
Freq. of TM01
in a 40mm circular duct(5.7GHz)

OLD

TM0122

TM0111

NEW (Single set of SiC tiles)

8TM011
TM012
TM013

TM010

CBI threshold for Total Vc: 1.4MV

Growth Time ＞ 30ms
＞ 5ms (rad. damping time)

Simulation by GdfidL for
9

3. GBP (btwn)
Material: SUS
4 sets of SiC tiles (same one as used for HOMHOM-WGs)
WGs)
Max. HOM + Accl.-mode: ~300W/duct

4 R10
4-R10

(Dimensions in mm)

4-R3
544
340

45deg
4-R230(Cross-section perpendicular to the beam axis)(Along the beam axis)

10

4. GBP (end)Material: SUS
4 sets of SiC tiles
MMax.
HOM + Accl.-mode:
A ld ~300W/duct
300W/d4-R10(Dimensions in mm)

544

4-R3340

25345deg
4-R230HELICOFLEX flange(Cross-section perpendicular to the beam axis)(Along the beam axis)

11

GBP(dummy)Material: SUS
No HOM absorbers
To be used for the two-cavity configuration
556

4-R10(Dimensions in mm)

4-R3340
30(Cross-section perpendicular to the beam axis)(Along the beam axis)

12

ARES
Joint btwn C-cav and S-cav

Cavity‐GBP JointSUS

Weld Ring Gasket with Lip Sealing, like:“Welding  Disassembly ReWelding”
Possible Several Times

Finger-type RF shield- Successful experience at KEK/PF:

Be-Cu, @KEK/PF(Fixed with 16 M12 bolts)

Single-Bunch-Mode Operation- BeamBcurrent:
t 70 mA
A ((max.))- Bunch length: 24 mm
13

Reasons why we adopted the structure
mentioned in the previous slide
for the Cavity‐GBP joint• Successful experience at KEKB‐MR/ARES (C‐cav and S‐cav) on
leakproof vacuum sealing during high power operation withh tdheatdeformationfti off ththe cavityit• We do not need to disassemble the structure so often. (twiceat maxmax. from our experience at KEKB‐MR/ARES)KEKB MR/ARES)– “WeldingDisassemblyReWelding” possible 3 times in the spec.

• Finger
Finger‐type
type RF shield– Measure against heat deformation of the cavity during high power
operation– Should be safe for low beam currents, such as the DR.
– Successful experience at KEK/PF.
– Negligible
N li ibl wakefieldk fi ld andd HOM heatingh ti (see(theth followingf ll i slides)
lid )

• x14

Solid Model of the Cavity‐GBP Joint
with RF Fingers(Created by using CST STUDIO SUITE)

Fingers

Blue Region: Vacuum1516

The Geometry Converted to GdfidL(Dimensions in mm)

Wakefield Simulation
By GdfidL with 00.1mm
1mm Mesh Size
Finite-Difference Time-Domain parallel computation
using 64 cores in the PC cluster

17

Results of the Calculation (1/2)

Suppressed and Damped!

No Resonance!

18

Results of the Calculation (2/2)
Loss Factor[V/pC]

Loss Powerfrom the Loss Factor[W]

Without the Fingers

0.017

9.7

With the Fingers

0.00048

0.27
For the DR Parameters:- Bunch Charge: 8nC- Bunch Length: 6.5mm- # of Bunches: 4/ring- Circumference:135.5m

This loss power is negligible!!

19

Current Status of CavityNo.0(prototype)~ Low
Low‐Level
Level RF Measurement Done ~Movable Tuner (mockup)

HOM-WG

GBP(mockup)

HOM WG
HOM-WG

Network Analyzer
Input Coupler

M it (antenna)
Monitor( t)

WG-Coax. Transformer

Coupling Loop of the Input Coupler

20

Examples of the Measurement Results

For =1.0@operation
For =1.2@operation

By sccraping the tuninng bump(-7000kHz at max)For =0.8@operation

Measurement
TargetQ0@operation@ti = ~26000
26000 (80%IACS)
21

Simulation by CST‐MWS
CST MWS
An Example

Curved Tetrahedrons
5 Steps per Wavelength

Port1

Fit with60 Stepsp pper Wavelengthg

 ff arg  S11    2 tan 1 Qext   a     0
 fa f (Red: floating parameters in fitting)22

Tuning Bump (2.5mm)

23Schedule
JFY

Items

Remarks

2011

CavityNo.0 (prototype) x 1
HOM‐WG load x 1
GBP(bt ) x 1
GBP(btwn)→to be high‐power tested at the D1A test stand→to be high‐power tested at the D1C test stand→t be→tob hihigh‐powerht t d att thtested
the D1C ttestt standt d

2012

CavityNo.1 x 1
HOM‐WG load x 4
GBP(btwn) x 1
GBP(end) x 1
GBP(dummy) x 1←Feedback from the High Power Test of CavityNo.0

2013

CavityNo.2 x 1
HOM WG load x 4
HOM‐WG
GBP(btwn) x 1
GBP(end) x 1

Start of DR commissioning with Cavity No.1 and No.2

201X

CavityNo.3
HOM‐WG load x 4

If needed24

Summaryy The accelerating structure for the DR
 Based on the KEKB‐MR/ARESKEKB MR/ARES cavity with the long successful operation at KEKB HOM‐WG Load Optimized
 2 sets  1 set of SiC tiles /WG
 Better Performance Cavity‐GBPyJoint byy Weld‐Ring Gasket with Lip Sealing Successful experience at KEKB/ARES (C‐cav and S‐cav) on leakproof vacuum sealing
during high power operation with heat deformation of the cavity
 “WeldingDisassemblyReWelding” possible 3 times (enough from our experience) Finger‐type RF Shield Flexible for heat deformation of the cavity during high power operation
 Should be safe for low beam currents
 Successful experience at KEK/PF Negligiblel bl HOM heatingh(<<( 1W))

 The prototype cavity almost in the final stage

25

Fin.
Fin

Appendix A
Assumptions for estimating wall temperatures of the DR cavity- Cooling-water flow: 200 L/min- Cooling-water temperature: 30 degC- Cooling
Cooling-water
water velocity:
velocity 2.0 m/s- Hydraulic equivalent diameter of the cooling-water channel: 9.1e-3 m- Reynolds
Rld number:b : 22.2e42 4 (turbulence)(t b l)- Heat-transfer coefficient from the channel to the water: 8.9e3 W/m^2/K- Thermal conductivity of copper: 4.0e2 W/m/K

27

Appendix B

Accelerator Resonantly‐coupled with Energy Storage

3-cavity system stabilized with the /2-mode operationconsists off
 HOM‐damped accelerating cavity (A‐cav), Energy‐storage cavity with TE013 (S‐cav), Coupling cavity(C‐cav)
with a pparasitic‐mode damper.
p
We use only this for the DR.

Along the beam axis
Perpendicularthe beamaxisP
di l tto thbi28

Starting the commissioning with two cavities:
Dummyy GBP
Total Vc: 1.4MV

Total Vc: 2MV

Install the 3rd Cavity if needed29Transverse Impedances of the RF section:

and CBI

Estimated from Finite-Difference Time-Domain parallel computations of GdfidL
with the PC cluster (256 cores & 512GB memory)
CBI threshold for Total Vc: 1.4MV(Tuner Position: 30mm inside)

Growth Time ＞ 30ms
＞ 10ms (rad. damping time)30