Accelerating Cavities
for the Damping Ring (DR)Tetsuo ABE
For KEKB‐RF/ARES/Cavity Group(T. Abe, T. Kageyama, H. Sakai, Y. Takeuchi, and K. Yoshino)

The 16th KEKB Accelerator Review Meeting
February 8, 2011

Old RF Modelshownhin theh 15th KEKB AcceleratorlReview Meeting, Februaryb16 (2010)()
R Q  150 Q0  29000 (IACS90%)
Vc  0.5 MV(Normal View)

Loss Factor : 1.9 [V/pC]

Bullet‐shaped HOM Absorbers (SiC; Hexoloy)(Transparent View)
Input Coupler(Used one from APS)

Tuner

SiC Duct(Cerasic‐B)

Pumping Port

Taper(150<‐>40) with L=400mm1

(Changes after Feb. 2010)[Basic Conditions]A) Frequency: 508.887MHz
508 887MHz (= the freqfreq. of the MR)B) Based on KEKB‐MR/ARES, but without S‐cav and C‐cav
C) Connection to 40 beam ducts (taper near the cavity)
D)••

Max Total Vc: 0Max.
0.55  2MV

Against microwave instabilities from CSR effects
Should be higher enough than the current design value: 1.4MV(SSpace conserrving)[Main Topics]
1.
2
2.
3.
4.
4
5.
6.
77.

3 Cavities (max) with 0.7MV/cav in the RF section (~5m‐long)
SiC tiles for all the HOM dampers
Grooved Beam Pipe (GBP) made common between the neighboringcavities
Connection between the cavity and GBP
HOM Impedances for CBIs
RF‐absorption power in each HOM damper
C
Coupledl d oscillations
ill tioff theth accelerating
l ti moded2

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 s0 700.70

13374

Max. Instantaneous

0.82

193

94
(Appendix A)(From T. Kageyama’s presentation @DR mtg)

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.

3

New RF Model

Pumping Portsver.2011‐02‐08
2011 02 08
 3 cavities with 0.7MV/cav
 GBP common betweenb ttheth neighboringi hb i cavities
iti HOM dampers with SiC tiles
 SiC tiles on the duct work similarly to SiC ducts.
 Loss Factor : 2
2.55 [V/pC]
Input Couplers(from KEKB‐MR)

Tuner

Taper End

SiC tiles

400
Taper30Flange

1100
72300

200
Bellows

256

Taper End(Dimensions in mm)

110
GV53242662

4

Two Types of Components
1. Cavity
2. Grooved Beam Pipe (GBP) with SiC tiles

Connection:

Welding for vacuum sealingRF shield inside
We do not use flanges because of•No space for bellows•Non-circular duct (GBP)•Thermal stress by the ACC mode 5

C-Cav
A-Cav

Connection between
the Cavity and GBPS-Cav

Lip welding for vacuum sealing, like:
Cycle: “Welding  Cutting”
possible several times

Vacuum340mm
3

between C-Cav and S-Cav of ARES

FiFinger-typet
RF shield,
hi ld lik
like:
Safe for low beam currents,
such as 70mA
30mm

(Based on the Y. Takeuchi’s drawing)(Conceptual)in the flange for KEK/PF;
Courtesy of T. Honda.

6

HOM Absorbers
The basic HOM damped structure is the same as that of the KEKB-MR/ARES cavity,
but the HOM absorbers are all SiC tiles: t20mm x 48 mm x 48mm.
Bullet-shaped SiC absorbers
used for the KEKB-MR/ARES

SiC tiles used in the GBPof the KEKB-MR/ARES(Electric Field)
SiC tiles are:- brazed on a copper plate.
- water-cooled via the copper plate.

Power Capability: ~1
1 kW/Set(@1.3GHz)TM ModeTE ModeAbsorbing both TM & TE modes

7

Longitudinal Impedance of the RF section:

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

GGrowthh TimeTi
＞ 20ms20＞ 5ms (rad. damping time)8Transverse Impedances of the RF section:and CBIEstimated 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)9Power of RF Absorption in Each Set of SiC Tiles
HOM Power from the Long
Long-Range
Range Wakefield
Estimated from the time-domain computation of GdfidL (smax=1000m)
with the conditions:- Bunch charge: 8nC- Bunch length: 6mm- Beam offset: 2mm (X,Y)

Scalar sum over four bunches~15W~15W
1 W

~14W
14W

~58W

~19W
~58W

14W
~58W

~18W
~52W

~21W
21W

~20W
20W

~18W
18W

~16W

~15W

~16W

<< (Power Capability: 1kW/set)10

Heating Value by the ACC Modefor SiC Tiles
Eigenmode Analysis•Using CST-MWS•With 40 MeshLines/WaveLength
Electric Field of the ACC mode
T il off theTailth El
Electrict i Fi
Field
ld off ththe ACC moded(magnification)(6 SiC tiles are approximated by one plate.)
11

Heating Value by the ACC Mode
Simulation Results(“All-SiC” means these 4 plates(=sets).)

For the mechanically innermost position( All  SiC )Ploss 0.1 %
(Wall )
(WallPloss(Wall )Ploss 133kW for 0.7MV/cav( All SiC )Ploss 133 W

Heating value < 100W/set << Power Capability: 1kW/set

12

Coupled Oscillations of the ACC Mode
Electric Field

Coupled Oscillations of the ACC Modemight be non-negligible via the TE mode.

TE modedTM mode
Cutoff: 1.51 GHz Cutoff: 588 MHz
Close to the ACC-mode Frequency: 508.9MHz13

Step 1: Two‐Cavityo Ca ty Syste
System“Electric Short” or “Magnetic Short”
Conditions:- Lossfree approximation- Cavity interval: 956mm- 6 SiC tiles approximated by one plate

Computep
Mode Frequencies
qusing CST-MWS and GdfidL.

14

Two‐Cavity System<<f acc
509MHz 20kHz
Q030000
15

Step 2: Periodic Structure
One Unit

Periodic Boundary Condition witha phase shift: 0 or 180 deg

16Periodic Structure<<f acc
509MHz 20kHz
Q03000017

Two-Cavity System

Periodic Structure

The Coupled Oscillations of the ACC Mode are negligible.
18

Schedule
JFYCavity No. to be madeRemarks

20110(prototype)

HPT to be done by May 2012;
Could be a spare.

2012

1Feedback from the HPT of theCavity No.0No 02013

2Get ready for the commissioningwith the two cavities.

201X

3If needed19Starting the commissioning with two cavities:
Dummyy GBP
Total Vc: 1.4MV

Total Vc: 2MV

Install the 3rd Cavity if needed20Summary
The design of the accelerating structure for the DR
has been modified for the total Vc: 2MV(max).
 Based on the KEKB‐MR/ARES Three cavities with 0.7MV/cav
 GBP made common between the neighboring cavities

SiC tiles are used for all the HOM dampers.
dampers
 Based on the established technology used for KEKB‐MR/ARES (RF absorption power)/set < 180W << PowerCapability: 1kW/set

CBIs driven by the HOM impedances Longitudinal
Lit di l GrowthGth TimeTi
＞ 20 ms ＞ 5 ms (rad.
( d dampingdi time)ti ) Transverse Growth Time ＞ 30 ms ＞ 10 ms (rad. damping time)Co pled Oscillations of the ACC‐mode:Coupled
ACC mode negligible
 OK21

Fin.
Fin22

Appendix AAssumptions 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 : 22.2e4
2 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

23

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
PPerpendicular
di l tto ththe beambaxis
i24

Backup Slides

25

Horizontally‐Polarized Dipole Mode in the Cavity
Couples to the TE mode in the GBP.

TM110 (630MHz)

26

ACC-Mode Frequency with or without the Input Coupler
TTunerPosition:
P iti
00mm

Symmetric

Asymmetric507.191 MHz

506.286 MHz＝ 0.905
0 905 MHMHz
facc = 40 kHz / mm (by the tuner) “0.905MHz” corresponds to 22.6 mm in the tuner position.

ACC-Mode F
Frequency [MHzz]

Shift=10mm & LoopAngle=79.5deg

Cavity Diameter [mm]28

2. Upgrade of the HOM Damper
f MoreforM
PowerP
Capability
Cbili
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)

29

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‐cooled30