RF Acceleratingg Structure
for the Damping Ringat the SuperKEKB Injector
Tetsuo ABE
For KEKB‐RF/ARES/Cavity Group(T. Abe, T. Kageyama, H. Sakai, Y. Takeuchi, K. Yoshino)

The 15th KEKB Accelerator Review Meeting
February 16, 2010

Damping Ring (DR) / ARES
[Basic Conditions]A) Frequency: 508.887MHz (= f KEKBMR )B) Based on KEKB‐MR/ARES, but without S‐cav and C‐cav
C) Connection to 40 beam ducts (taper near the cavity)[Main Topics]
1. Determination of the Cavity Diameter2 Upgrade2.
Ud off theth HOM Damper
D(GBP)
3. HOM Impedances for Longitudinal CBIFebruary 16, 2010

RF Accelerating Structure for DR (T.Abe)1

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.

Along the beam axis
P
Perpendicular
di l tto ththe beambaxisi
February 16, 2010

RF Accelerating Structure for DR (T.Abe)

2

RF Model of DR/ARES
ver.2010‐02‐16
R Q  150 Q0  29000 (IACS90%)(Normal View)(Transparent View)

Bullet‐shaped HOM Absorbers (SiC; Hexoloy)

Input Coupler(Used one from APS)

Tuner

SiC Duct(Cerasic‐B)

Pumping
Port
February 16,
2010

RF Accelerating Structure for DR (T.Abe)

Taper(150<‐>40) with L=400mm

31. Determination of the Cavityy Diameterusing the Slater’s Tuning Curve Method
1d  d0 Qext
ntan 1
 f fa  fa f 22

 : gguide wave lengthg
fa: ACC‐mode frequency
n: integerRed: floating in fitting

dSimplifiedpmodelfor eigenmode analyses

Eigenmode Ananyses using CST MW‐STUDIOIIncrease
theh numberb off meshh cells
ll so thath fa < 100kHz
100kH
[GHz]

.LinesPerWavelength "40".MinimumStepNumber "40"
 5.9e+6 mesh cells
CPU time: 2 to 3 hours/mode(Preparation)

Adjust the Coupling Factor:
 

Q0Qext  1 (optimumti)

Simplified modelfor eigenmode analyses

Q0  a LoopAngle

UPwallQext  a PradPwall

UPradFitting with the Tuning Curvesfor Different Loopp Angles
gCavity Diameter: 438mm (KEKB‐MR) fixed

Fits with1Qextn1tan d  d0 2
f fa  fa f 2

Qext from the Fitting Results
as a function of the Loop Angle

Q0  29000 (IACS90%)

Error bars assuming   ndf  1

Fitting with the Tuning Curves
for Different Cavity Diameterswith the Loop Angle: 75deg

February 16, 2010

RF Accelerating Structure for DR (T.Abe)

9

Determination of the Cavityy Diameterfrom Fitting to the Tuning Curves
TTunerPPos.: 15 mm iinside
id ((normal)l)

443 9mm (438mm
443.9mm(438(KEKB‐MR))

Fitting Errors Assuming   ndf  1f KEKB MR102. Upgrade of the HOM Damper
f MoreforM
PowerP
CapabilityCbili
Grooved Beam Pipe with SiC Tiles Installed

In the case of SC cavities

Absorbs Horizontally‐Polarized Dipole Mode (TM11)

Needs large
g ducts,
which reduce Rsh.

In the case of ARES (NC)The Cutoff Freq. of TM11
can be made lower
without reducing Rsh.

Cutoff Freq. of TE11
in a Regular 150 Duct

SiC Indirectly water‐cooled(by T. Kageyama using MAFIA)2. Upgrade of the HOM Damper
MMorePPower CCapabilitybili
Grooved Beam Pipe with SiC Tiles Installed  Winged Chamber Loaded with SiC Bullets
Capability (1.3GHz )PHOM 1 kW

Capability (1.3GHz )PHOM
to be 5 kW

SiC Directlyy water‐cooled

Like the HOM damperat the Movable Mask Section
Y. Suetsugu et al., “Development of Winged HOM
Damper for Movable Mask in KEKB”,
Proc. PAC2003.

SiC Indirectly water‐cooled

12Position of SiC Bullets
Looking at |S11|
Freq. Domain Computation using CST MW‐STUDIO

30

150February 16, 2010

RF Accelerating Structure for DR (T.Abe)

13

Permittivity Measurements (by Y. Takeuchi) of SiC andthe General 2nd‐order ModelHexoloy 0  j r ( )   r  0  j1   2 2
S. Gutschling, H. Krueger and T. Weiland,Int. J. Numer. Model. 2000; 13:329‐348

14Number of Mesh Cells Increased
This Simulation

Default

February 16, 2010

RF Accelerating Structure for DR (T.Abe)

15

Positions to be Considered
ParaH
ParaL

(J t for(Justf reference)f)

Slope3Sl
Slope2
2
Slope1 (Just for reference)
RF Accelerating Structure for DR (T.Abe)

16

Clearance: 10 mm

Clearance: 5 mm

Clearance: 0(Just for reference)17

Computation Results
ClClearance:5mm
5ClClearance:0mm0ClClearance:10mm
10ParaHPH
ParaLーSlope1‐‐‐ Slope2・・Slope3

ParaLFebruary 16, 2010

ParaH

ParaL:best, ParaH:worst
Steeper slope worse
Smaller clearance better

RF Accelerating Structure for DR (T.Abe)

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Final Position of the SiC Bullets
Flange for SiC Bullet

φ253

340

φ150

3440

72

15
5R10February 16, 2010

Helicoflex Flange

RF Accelerating Structure for DR (T.Abe)

3019

Mockup (Al) of the Winged Chamber arrived (Dec. 24, 2009)
A test chamber (SUS) for highhigh‐power
power tests is coming soon.
soon

RF Accelerating Structure for DR (T.Abe)

20

Caution! Leak of the ACC‐Mode heats the SiC Bullets
due to the asymmetry caused by the TunerTh tails
Thet il are magnified!
ifi d!

Tuner Pos.: 0 [mm] (outermost)

Tuner Pos.: 15 [mm] (normal)

Tuner Pos.: 30 [mm]Tuner Pos.: 50 [mm] (innermost)February 16, 2010

RF Accelerating Structure for DR (T.Abe)(96, Hexoloy)

21

Heatingg Power of the ACC‐modeEstimated from Eigenmode Analyses using CST‐MWS
1111


Q0
Q0 (encl.) Q0 (Tuner ) Q0 (SiC)
Q0  a

UPtot

Q0 (encl.)  aQ0 (Tuner )  a

UPencl .

Q0 (SiC)  a

UPTuner

UPSiC

Max. Heating Power= Q0(encl.)/Q(encl )/Q0(SiC) x Pwallll= 0.24%/2 x 60kW(max) = 72 W<< 5kW (capability/Groove)
InnermostFebruary 16, 2010

RF Accelerating Structure for DR (T.Abe)22

3. HOM Impedances and Longitudinal CBIAny Troublesome Resonances?

Bunch Length: 5.0mm
Simulator: GdfidL
Full geometry
Mesh Size: 0.5mm in Z, 1.0mm in X,Y9e+9 grid cells, 40 GB Memory
Using 64 cores in parallel computing~1..5 m~3 m

February 16, 2010

RF Accelerating Structure for DR (T.Abe)

23

Computation Results of GdfidL/FDTD
Longitudinal CBI Threshold Line forGrowth Time: 30[msec]
HOM LossFactor/ring: 4.88[V/pC]
DR parameters on 2009‐10‐26

February 16, 201024

Computation Results of GdfidL/FDTD
Longitudinal CBI Threshold Line forGrowth Time: 30[msec]
HOM LossFactor/ring: 4.88[V/pC]
DR parameters on 2009‐10‐2625

Computation Results of GdfidL/FDTD
Longitudinal CBI Threshold Line forGrowth Time: 30[msec]
HOM LossFactor/ring: 4.88[V/pC]
DR parameters on 2009‐10‐2626

Computation Results of GdfidL/FDTD
Longitudinal CBI Threshold Line forGrowth Time: 30[msec]
HOM LossFactor/ring: 4.88[V/pC]
DR parameters on 2009‐10‐2627

Computation Results of GdfidL/FDTD
Longitudinal CBI Threshold Line forGrowth Time: 30[msec]
HOM LossFactor/ring: 4.88[V/pC]
DR parameters on 2009‐10‐2628

SummaryRF Model
d l off theh Accelerating
li Cavityi ffor DR hhasbeen designed.
Based on the successful KEKB‐MR/ARESWingedg Chamber loaded with SiC Bullets
For more capability of HOM powers (appl. to MR/ARES)
The test chamber is coming soon.
soon  High‐power
tests to be done in the L‐band test stand.

No serious HOM impedance for LCBI = 30 msec (from ReZll at 11.75GHz)
February 16, 2010

RF Accelerating Structure for DR (T.Abe)29