2013.3.4
MRC2013
Yoshiyuki Morita

Superconducting Cavity
1. Measures for large HOM power
2. Performance recovery

Expected beam-induced HOM power in SuperKEKB/HER•••

Machine parameter of SuperKEKB/HER– Beam Current ：2.6A/2500 bunches– Bunch length：5mm
Expected beam-induced HOM power– Cavity loss factor：1.2V/pC @σ=5mm– HOM power：31kW– LBP damper load：26kW• Self loss=0.26 V/pC
– SBP damper load: 20kW
• Self loss=0.30 V/pC
– Total HOM load per cavity：46kWTotal HOM power at KEKB: 16 kW

Expected damper loads
Beam current

SBP load

LBP load(A)

(kW)

(kW)

21215

2.6

2026

HOM damper
HIPped ferrite （Thickness：4mm）

Beam pipe: 150Φ

SBPLBP

Cupper pipe (3/8”) for water cooling
Stainless steel flange

Monitor-damper surface area

Monitor-inlet area

Monitor-outlet area

New calculation method for damper load
Power flow monitor (CST-PS wake-field)
Area integral of power flow on each area

Beam in

Absorbed power in damper
can be directly calculated

Beam-in signal
Beam-out signal(not included in time integral) (not included in time integral)
Energy absorption signal

Energy absorption in damper

Area integral of power flow on the inlet area (magnified)Bunch charge: 1pC

Time integral (pJ)

Normalized (pJ)

Eq. LF (V/pC)

Inlet area

0.000536

0.000636

0.000636

Outlet area

0.00797

0.009460.00946

Damper surface

0.112

0.133

0.133

Stored energy @ 2ns

0.00353

00Total energy

0.124

0.143

0.143

From loss factor

0.143

0.143

Energy emission through the inlet BPBeam out

Energy emission through the outlet BPPower flow simulation for superconducting cavity module
Area integral of power flow on each surface
Beam-in signal
not shown

Wake field simulation using CST Particle Studio-The damper’s shape was approximated by a cylinder

Beam-out signal

LBP damper

Φ150

SBP damper

SBP damper
PinCavity cell
LBP damper

Taper:300 mm

Power flow at outlet

SBP: Φ220

Taper:600 mm
LBP:Φ300

Φ150

Power flow at inlet
Pout

Emitted/absorbed/stored energy in the cavity
LF(V/pC)

Inlet(pJ)

Outlet(pJ)

SBP(pJ)LBP(pJ)Stored energy(pJ)

Total energy
(pJ)

1.414

0.062290.35730.28850.3798

0.104

1.192

Eq. LF and HOM loads at 2.6A
Eq. LF(V/pC)

Load＠2.6A
(kW)

Inlet

0.081

2.2

Outlet

0.464

12.5

SBP

0.375

10.1

LBP

0.494

13.3

Total

1.414

38.2

σ=5 mm, q=1pC Energy deposit of 1pJ corresponds a loss factor of 1V/pC

Total energy is consistent with energy deposit calculated from the loss factor.
SBP and LBP damper loads are not large. Those loads can be absorbed by presentdampers. On the other hand, large energy is emitted through the beam pipe outlet.
The energy becomes additional load to cavities of downstream area. Therefore theenergy has to be absorbed by an additional damper.

Effects of additional SiC damper
Wake field simulation using CST Particle Studio-The damper’s shape was approximated by a cylinder
SBP

LBP

SiC

Pout

Pin

Eq. LF and HOM loads at 2.6A
SiC:240mm

Eq LF(V/pC)

Load＠2.6A
(kW)

Pin

0.09

2.4

Pout

0.22

5.9

SBP

0.31

8.4

LBP

0.44

11.9

SiC1.1029.7

Total

2.16

58.4

Additional SiC damper

Eq. LF of emitted and absorbed energies

Additional SiC damper can absorbs more energy as thelength becomes longer. It also reduces SBP and LBP
damper loads. In practice, HOM load of additional SiC
damper has to be less than 30kW (1.1 V/pC ). 240 mm
damper is suitable for our cavities.

Summary of measures for large HOM power••••

Established new HOM power calculation method– Each damper’s load can be calculated
HOM power calculation– SBP and LBP HOM loads are not large (can be absorbed)– 30% of beam-induced energy is emitted through BP
Additional SiC– Additional SiC damper can absorb energy emission– Also reduce ferrite damper loads– 240 mm SiC damper is suitable for our cavity– SiC can be set without opening the cavity module
Fabrication and high power test of SiC dampers

Beam pipe: 150Φ

SBP

LBP

Additional SiC damper

Summary of HOM power loads
Load＠2.6A
(kW)
Inlet

2.4

Outlet

5.9

SBP

8.4

LBP

11.9

SiC(240mm)

29.7

Total

58.4Performance recovery of degraded cavities
•••

•

•

Vacuum leakage happened at cooldown in May 2010
– Suspected leakage at indium-sealed flange
Opened the cryomodule, retightened volts.
– Bolts of the flange were loose (60kgｆcm)– Those bolts were retightened (150kgｆcm)
High power test
– No vacuum leakage– Q degradation with field emission• Voltage reached 1.3 MV with degraded Qo value• Limited by the radiation safety rule at test stand• Contaminated with micro-particle
Other degraded cavities– D10A, D10C, and D11C at high fields– Still acceptable for SuperKEKB operation– Performance recovery is desirable
High pressure rinsing– HPR is effective to clean cavity surface– HPR in a cryomodule can save time and costs– We are developing horizontal HPR (HHPR)

Leakage at indium sealed flange

10%Degraded

Otherdegradedcavities

Horizontal HPR of the test cavity in clean room
••••
•

••

•

Horizontal HPR test in clean room
EPII (10μm)
Baked at 120 ℃
Cold test after EPII
1st HHPR– Rinsed cavity cell, iris and BP– Evacuated in vertical position– Residual water dropped on BP flange
Cold test after 1st HHPR
–Without baking
2nd HHPR– Evacuated in horizontal position– Residual water in cavity cell
Cold test after 2nd HHPR
– Without baking– Observed no degradation

We confirmed that HHPR is applicable to our cavity

HHPR in a clean roomImprovement of HHPR for application to cryomodule
HHPR in a clean booth at assembly area•••••Developed automated nozzle driving system
Wasted water is aspirated through stainless steel pipe at equator
Installed new ultrapure water system at assembly area
Parameters of HHPR
– Ultrapure water jet (7MPa) from a stainless steel nozzle– Nozzle: 6 holes of 0.54 mm diameter– Driving speed: 1mm/sec– Rotation speed: 60 deg./10 sec– Total time: 15 min– Rinsing area: +200/-250mm (cell and iris areas covered)
After HHPR
– Aspirate residual water in pickup port

Stainless steel nozzle

Teflon tube to aspirate water inpickup port

Horizontal HPR in clean booth•••••••

EPII (10μm) and baked at 120℃
Cold test– Fields reached to 13MV/mHHPR(3rd HHPR)–HHPR in clean booth at assembly area
– Used new HHPR system– Rinsed cell and iris areas for 10 min.
– Evacuated with residual water
Cold test after 3rd HHPR w/o baking– Fields reached to 8 MV/m after RF processing– Fields degraded to 6 MV/m with FE
Inspected in clean room,–Found a small pit <1 mm near LBP iris
HHPR(4th HHPR)– Rinsed cell and iris area for 15 min.
• Wider SBP iris area
Cold test after 4th HHPR w/o baking– Fields successfully recovered to 12 MV/m
– No field emission observed

Effectiveness of HHPR was demonstrated.

RecoveredDegraded

HHPR at assembly area

HHPR application to our spare cavity module
Dismounted end parts and HPC
Moved the cavity to assembly area

High pressure water jet in cavity cell

Water jet nozzle and aspirator

Set HHPR apparatus in clean boothEvacuate with residual waterSummary of performance recovery••

Horizontal HPR was established– Degraded test cavity recovered its performance after HHPR
– Rinsed cell and iris areas– Evacuated with residual water– Cold tested without baking
We applied HHPR to our spare cavity module– High power test will be done this month

We hope performance recovery

HHPRed spare cavity just before setting in the pit

Our plans for the next two years••

Measures for large HOM power– Studied additional SiC dampers– Fabrication and HPT of SiC dampers– Assembly of φ200mm beam pipe module (continued)• For lower beam-induced HOM power structure
Performance recovery– High power test of HHPRed spare cavity will be done soon
– Exchange one of installed cavities with the spare cavity– Attach φ200mm beam pipe module to exchanged cavity– If the performance will not recover…
• Dismount cavity cell from the cryomodule• HPR or EP, CT and HPT

Measures for large
HOM power

FY2012FY2013

FY2014High power test for 4mm thickdampers with double coolingstructure

Fabrication and HPT of SiC
dampers

Install SiC dampers in the
SuperKEKB ringIf not recover
Dismount cavity cell
HPR or EP

Study for additional SiC
dampers

Performancerecovery

Assembly of 200φ BP modules

200φ BP (continued)

HHPR in cryomodule
High power test

Exchange one of cavities withthe spare cavity

Install 200φ BP cavity
Cool-down test of all cavities

Attach 200Φ BP for low LF
High power test