Estimation of Loss Factors of Various
Vacuum Components
22/Feb/2004
K. Shibata (KEKB Vacuum Group)

Contents
Introduction
Estimation of loss factors for KEKB and SuperKEKB
Pumping port
Photon mask
Connection flange
Movable mask
Bellows
Comparison with measured loss factor (KEKB LER)
Improvement for SuperKEKB
Summary
2005/2/22

KEKB REVIEW

1Introduction
Upgrade to SuperKEKB
KEKB (design)

Loss factor and HOM power will
increase.

SuperKEKB

σz = 4 mm

σz = 3 mm

I = 1.1 A (HER)
2.6 A (LER)

I = 4.1 A (HER)
9.4 A (LER)

Some vacuum components of
KEKB need to be improved.

Vacuum components considered here
Pumping port
Photon mask
Connection flange

Antechamber

Movable mask
Bellows chamber

Method of estimation of loss factor
MAFIA T3 simulation code
2005/2/22

KEKB REVIEW

2Pumping Port – KEKB LER
Features“Hidden holes” structure
10 slots / 1 pumping port
Long slot in the beam-axis direction
Length : 100 mm, Width : 4 mm

r=47 mmLong slot

Beam Duct(LER)

6 mm

1800 pumping ports / 1 ring
Crossing bar

Loss factor (σz = 4 mm)
No stepk(4 mm) =0.64×109 [V/C]
×1800

Total : k(4 mm) =1.2 [V/pC]
Step with 1 mm heightk(4 mm) =1.97×109 [V/C]
×1800

Total : k(4 mm) =3.6 [V/pC]
2005/2/22

KEKB REVIEW

3

Pumping Port – SuperKEKB
FeaturesPumps are equipped on the upper and lower sides of the SR channel.
The pump channels are connected through many holes with typical
diameters of 4 mm.

Loss factor (σz = 3 mm)
k(3mm)/L = 8.8×105 [V/C/m]
× ∼2000 [m]Total :k(3mm) ≈ 0.002 [V/pC]

Pumping slots (holes) have littleeffect on the beam.
2005/2/22

KEKB REVIEW

4

Photon Mask
KEKB
SR masks are located at the side wall of the beam chamber.
47 mm

Loss factor (from KEKB Design Report)
k(4mm) = 4.6×109 [V/C]
Photon Mask
Height : 3∼10 mm

×1000(Mask height : 5 mm)

Total : k(4mm) = 4.6 [V/pC]

SuperKEKB
SR masks are located at the side wall of the SR channel.
112 mmLoss factor (estimated by MAFIA T3)k(3mm) = 1×104 [VC-1]
×1000

Photon Mask
Height : ex.10 mm

Total :k(3mm) = 1×10-5 [V/pC]

Loss factor for SuperKEKB is negligible small.
2005/2/22

KEKB REVIEW

5Connection Flange - KEKBFeatures

Helicoflex
GasketHelicoflex gasket

FlangeSame inner diameter as a beam duct
Double role of vacuum seal andrf bridge

2000 connections / 1ring

r=47 mm

2 mm

Beam

Loss Factor
Loss Factor k [×109 V/C]

1.5Total loss factor
KEKB LER (present)

1.0× 2000
0.502
2005/2/22

k(6 mm) = 0.2 [V/pC],
PHOM = 3 [kW]KEKB LER (design)k(4 mm) = 1.0 [V/pC],
PHOM = 14 [kW]345678Bunch length σz [mm]KEKB REVIEW

6Connection Flange - SuperKEKB
Connection of antechamber
It is difficult to use conventional connection
flange.

CopperGasketFlange

MO-type FlangeFeatures

r=47 mm1 mm

Developed for C-band wave guide
Smooth inner surface

Beam

Possibility with antechamber type aperture
Promising results were obtained.

Loss Factor (σz=3 mm, 0.2 mm steps)k(3 mm) < 6.8×107 [V/C]
× 2000Total: k(3 mm) < 0.1 [V/pC], PHOM < 4.4 [kW]The loss factor of MO-type flange is much less thanconventional one.
2005/2/22KEKB REVIEW

7

Movable Mask - structure
Movable mask with reduced HOM design (KEKB)
Features
Bellows Chamber
Mask Chamber
Bellows Chamber
Beam
Mask HeadA device to reduce the background noise in Belle detector
Wall of the bent chamber has the function as a mask head.
16 movable masks / 1 ring
Large loss factor
Strong HOM is excited at the mask head where the beam
passes of center of the beam chamber.
2005/2/22

KEKB REVIEW

8

Movable Mask – loss factor
Loss Factor
Total loss factor

Loss Factor k [×1012 V/C]

1.5rampKEKB LER (present)k(6 mm) = 7.2 [V/pC],
PHOM = 140 [kW]300 mmhead10 mm

1.080 mmKEKB LER (design)×160.5vertical:8,horizontal:8k(4 mm) = 19 [V/pC],
PHOM = 260 [kW]SuperKEKB LER (Expectation)

0.03456789Bunch length σz [mm]k(3 mm) = 32 [V/pC],
PHOM = 5655 [kW]It is difficult to use this movable mask at SuperKEKB.
2005/2/22

KEKB REVIEW

9Movable Mask - SuperKEKB
Proposal: Invisible Movable Mask (still only an idea)
Small mask head supported by ceramics and HOM absorber
Head is fixed to chamber.
Position is adjusted by moving the chamber.

Loss Factor k [×1012 V/C]

SiC absorber is combined to damp HOM excited at the mask head.
1.5
Loss factor is about 1/10 ofconventional one.
ceramics rod
More R&D is necessary.

New movable mask
(conceptual drawing)
2005/2/22

1.0

conventional

0.5

0.0

KEKB REVIEW

metal rod345678
Bunch length σz [mm]910Bellows – KEKB
Bellows chamber with a finger-type RF shieldStructure1 mm

RF finger

Taper

Inner tube10 mmStepBeamr=47 mm

Loss Factor
Total loss factor
KEKB LER (present)

Loss Factor k [×109 V/C]

12108× 1000

6KEKB LER (design)

4k(4 mm) = 6.3 [V/pC],PHOM = 68 [kW]202

2005/2/22k(6 mm) = 1.9 [V/pC], PHOM = 37 [kW]SuperKEKB LER
34 5 6 7 8 9Bunch length σz [mm]10k(3 mm) = 11 [V/pC],PHOM = 1944 [kW]KEKB REVIEW

11Bellows - SuperKEKB
Bellows chamber with a comb-type RF shieldFeatures
RF shield : nested comb teeth
Length: 10 mm, Width: 1 mm
Radial thickness: 10 mm,High thermal strength
No radial step on the inner surface
Loss Factor (estimated by MAFIA T3)
Loss Factor k [×109 V/C]

12Comb-type RF-shield

108× 1000

6Total : k(3 mm) = 4.1 [V/pC]
PHOM = 707 [kW]420

2005/2/22k(3 mm) = 4.1×109 [V/C]

Finger-type RF-shieldk(3mm) reduces to ∼40 %.
234 5 6 7 8 9Bunch length σz [mm]10KEKB REVIEW

12Comparison with measurement in KEKB LER - 1
Estimation (σz = 4mm)

Total loss factor : k(4mm) = 60∼62 + α V/pC
Total k [V/pC]

1.5×109
2.0×109
5.1×108
6.3×109
4.6×109
1.0×1010

Number ofitems
2200 [m]
1800
2000
1000
1000
30

Movable mask (ver.1)

1.2×1012+α’

1619.2 +αCalculation(4mm)

IR chamber
Mask at IP
Recomb. Chamber
Dummy chamber for
Crab cavity

2.9×1011
8.0×1010
1.6×1012

1110.29
0.08
1.6

Design report

1.8×1012

2

3.2〜4.0

Measurement(6mm)

Cavity (ARES)

8.3×1011

1613.3

Design report

BPM

2.0×109400

0.8

Design report

Feedback system

3.2×1012

13.0〜3.8

Calculation(6∼7 mm)Componentk [V/C]Resistive wall
Pumping port
FlangeBellows
Photon mask
Gate valves

2005/2/22

KEKB REVIEW

3.2
3.6
1.0
6.3
4.6
0.3

FormulaCalculation(4mm)Calculation(4mm)Calculation(4mm)
Design report
Calculation(4mm)

Design report
Design report13Comparison with measurement in KEKB LER - 2
Experimental result (by Ieiri-san)Measurement in 2000
Cavity: ARES×16
Movable mask: Ver.1×16k(σz=4mm) = 87±30 V/pC

Comparison ( KEKB LER, σz=4 mm )Measurement ≈ Estimation
87±30 V/pC

60∼62 + α V/pC

Measured loss factor agrees with estimated loss factor.

2005/2/22

KEKB REVIEW

14

Improvement for SuperKEKB
Loss factor and HOM power (σz = 4mm)
KEKB (design)(σz=4 mm, I=2.6 A, nb=5000)

SuperKEKB(σz=4 mm, I=9.4 A, nb=5000)

Componentsk [V/pC]

PHOM [kW]k [V/pC]

PHOM [kW]Resistive wall

3.2

43

3.2971

Pumping port

3.649

Negligible

Negligible

Flange1.2

140.01

2.0

Photon mask

4.662

Negligible

Negligible

Bellows

6.3

85

1.96346

Gate valves

0.340.06

10

Movable mask

19.2+α260+α1.5+α269+αTotal

38+α517+α6.8+α1200+αLoss factor reduces to ∼18 % for a 4 mm bunch length.
Other components
IR chamber, IP mask, Recomb. chamber, Cavity, Crab cavity,Feedback system, BPM, etc.
2005/2/22

KEKB REVIEW

15

Summary
Estimation of the loss factors of the vacuum components ofKEKB and SuperKEKB
Pumping port
Photon mask
Connection flange
Movable mask

Antechamber
MO flange
Invisible movable mask

Bellows

Comb-type RF shield

Comparison between estimation and measurement in KEKB (2000)
Estimation ≈ MeasurementImprovement for SuperKEKB
Loss factor of improved vacuum components for a 4 mm bunch
length reduces to 18%. (if everything goes well.)FutureEstimation of all other components
Investigation of the beam instabilities
2005/2/22

KEKB REVIEW

16