Yoshiyuki Morita
MAC2014Superconducting Cavity
HOM power
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：1.37V/pC @σ=5mm– HOM power per cavity：37 kW– at KEKB: 16 kWFerrite HOM damper– SBP damper:φ220x4x120– LBP damper:φ300x4x150

HOM power
Beam current (A)HOM power (kW)

222

2.637

Need to reduce HOM power load
HOM damperHIPped ferrite （Thickness：4mm）

Beam pipe: 150Φ

SBP

LBP

Cupper pipe (3/8”) for water cooling
Stainless steel flangePower flow simulation for superconducting cavity module
Area integral of power flow on each surface

Monitor wake fields using CST Particle Studio, wakefield solver

Beam-out signal
LBP damper
SBP damper

SBP damper

LBP damper
Power flow at outlet

Beam-in signal
not shownPower flow at inlet

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

Inlet(pJ)

Outlet(pJ)

SBP(pJ)

LBP(pJ)Stored energy(pJ)

Total energy
(pJ)

1.367

0.05340.50280.27550.36010.1205

1.312

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

Load＠2.6A
(kW)

Inlet

0.061

1.6

Outlet

0.576

15.6

SBP

0.315

8..5

LBP

0.412

11.1

Total

1.367

36.9

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.
Results showed SBP and LBP damper loads were not large.
Large amount of HOM power is emitted through the beam pipe outlet.
The energy becomes additional load to cavities in the downstream.

Effects of HOM power emission to the downstream cavity
Wake field simulation using CST Particle Studio
A loss structure introduced in front of cavity
Calculated energy gain of each component

Equivalent LF gain

SBP damper

SiC:240mm

Eq LF(V/pC)

Fraction(%)

Outlet0.130459

SBP

0.088540LBP

0.0035

1Total0.227

100

40 % of the HOM power is absorbed in the SBP damper
while 60 % goes through the cavity. The HOM poweremission increases the power load of the SBP damper.
The power emission has to be reduced.

LBP damper

Pill box as a loss structure
Energy gain
Additional power flowEffects of additional SiC damper
Wake field simulation using CST Particle Studio
Additional SiC damper set on the beam pipe

Eq. LF of emitted and absorbed energies

HOM power emission

Equivalent LF and HOM loads at 2.6A
SiC:240mm

Eq LF(V/pC)

Load＠2.6A(kW)

Overall
(kW)

Inlet

0.064

1.7

Outlet

0.204

5.5

SBP

0.333

9.0

13.7

LBP

0.436

11.812.1

SiC(240mm)

0.905

24.5

26.8

Total

1.942

52.5

Additional SiC damper can absorbs more HOM power
emission as the length becomes longer. In practice,
HOM load of additional SiC damper has to be less than
30kW (1.1 V/pC ). 240 mm is a good choice.

Power emission from the upstream and downstream
Preliminary simulation results showed that 80% of thepower emission from the upstream was absorbed in
the SBP damper (SiC damper:240 mm), while 5 % goes
thorough the cavity. The backward power emission
from the downstream was absorbed in the SiC damper.
Overall damper loads are given in the table.

Prototype SiC dampers and those high power tests
SiC dampers absorbed RF power up to 7 kW

Prototype SiC damper of 120 mm in length

HPT for higher power absorption will be done soon

High power test standSurface temperaturesSummary of measures for large HOM power
••

•

•

Developed a new HOM power calculation method– Damper loads can be calculated
Damper loads– SBP and LBP HOM loads are not large– Large amount of HOM power is emitted through BP– Become SBP damper load
Additional SiC damper– Additional SiC damper can absorb power emission– 240 mm SiC damper is suitable for our cavity– SiC can be set without vacuum breaking of the cavity
R&D for SiC dampers is ongoing– Fabrication of prototype dampers– HPT up to 7 kW
Beam pipe: 150Φ
SBP

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

13.7

LBP

12.1

SiC(240mm)

26.8

Total

52.6

LBP

Additional SiC damper

Performance recovery
Motivation to develop HHPR•••

RF Performance of SRF cavities degraded in the long term operation at KEKB
– Qo of several cavities significantly degraded at ~2MV with FE– Due to particle contamination during• repair of vacuum leakage• Exchange of coupler gaskets– Present degradations are still acceptable for SuperKEKB (1.5MV)– Further degradations make the operation difficult– Performance recovery is desirable
HPR is effective to clean the particle contamination– If we can apply HPR to the cavity in the cryomodule,• We can save time and costs; no need for cavity disassembly• We can avoid the risk of leakage; no need for re-sealing at the indium joint
HHPR was developed for performance recovery– Horizontal insertion of the HP water nozzle– Water evacuation by the aspirator pump

HHPR system•••••

Developed automatic nozzle driving system
Water evacuation through the same BP
Installed new ultrapure water system at assembly area
Rinsed cell and iris area only
After HHPR
– Evacuate residual water in pickup port

HHPR in clean booth at assembly area

Recovered

Degraded

HHPR parameters (automatic operation)
Water Pressure

7 MPaNozzle

Φ0.54mm x 6Driving speed

1 mm/sec

Rotation speed

60/secRinsing time

10-15 minOnce degraded but recovered after 2nd HHPR

Stainless steel nozzle

Teflon tube to aspirate water inpickup port

HHPR application to the spare module
Taking out the inner conductor of the HPC

End beam pipes and HOM dampers were dismounted

Before we applied HHPR, HPC and HOM
dampers were dismounted in a clean booth.
Then the HHPR driver was set to the cavity.

Setting the HHPR apparatus

HHPR application to the spare module
Opening the dummy flange

The degraded cavity was HHPR’ed with a newautomatic drive and water evacuation system
Water jets
Automatic driveHigh pressure water pump

Aspirator pumps
Evacuation after HHPR

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

Successfully recovered

HHPRed spare cavity just before setting in the pitHHPR to another degraded cavity
Recovered cavity installed into the HER ring

HHPR setup for another degraded cavity

After the successful performance recovery, recoveredcavity was installed in the HER ring. On the otherhand, another degraded cavity was took out of thering, then HHPR’ed in the assembly area. This cavity
was installed in the test stand. The high power testsof this cavity have been conducted.

Performance recovered drasticallySummary of performance recovery••••We have developed HHPR
– Horizontal insertion of the HP water nozzle– Water evacuation by the aspirator pump
We applied HHPR to the degraded spare cavity module– RF performance recovered successfully– The recovery is sufficient for the operation at SuperKEKB– However, the recovery is not perfect• Further optimization (rinsing time/area)?
• Re-contamination?
Recovered cavity: Installed in the HER ring
Another degraded cavity: HHP rinsed– Performance recovered drasticallyOur plans for the next year•••

Measures for HOM power Fabrication and high power tests of prototype SiC dampers– Continue R&D for additional SiC dampers– Install SiC dampers into HER, if possible
Performance recovery
 High power test of HHPRed spare cavity
 Exchange one of installed cavities with the spare cavity– Attach φ200mm beam pipe module to exchanged cavity– If the performance will not recover…
 HHPR to another cavity and its high power test
Cooldown tests of all cavities and then cavity operation for SuperKEKB

Measures for large
HOM power

Performancerecovery

FY2012FY2013

FY2014High power test for 4mm thickdampers with double coolingstructure✔Study for additional SiC
dampers✔Fabrication and HPT of SiCdampers□Fablication of SiC dampers□Install SiC dampers into HER

Assembly of 200φ BP modules

200φ BP (continued)✔HHPR in cryomodule✔High power test

✔Exchange one of cavities
with the spare cavity✔HHPR to another cavity✔High power test
Attach 200Φ BP for low LF
High power test

Cooldown tests of all cavities
Cavity operation for SuperKEKB
Install 200φ BP cavity

Horizontal HPR R&D using prototype test cavity
Horizontal HPR was applied to our test cavity in the clean room
Large BPTest cavity
Small BP
Water evacuation pipe(connected to aspirator)

Horizontal insertion of HP water pipe

High pressure rinsing

Manually operated

HHPR parameters (manual operation)
Water Pressure

6 MPaNozzle

Stainless steal
Φ0.54mm x 6

Driving speed

0.33 mm/sec (cell)
0.66 mm/sec (BP)Rotation speed

120/sec

Rinsing time

20 minWe tried HHPR two times: No degradation occurred