Status ofSuperconducting Cavity(SCC)
Su p e r K E K B M AC 2 0 1 8
M arc h 1 5 , 2 0 1 8
M ic h ir u N is h iwak i

SuperKEKB MAC2018 M.Nishiwaki

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Contents
lSiC HOM damperlCavity Performance Recovery (HHPR)
lPiezo Actuator Test
lSummary

SuperKEKB MAC2018 M.Nishiwaki

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SCC for SuperKEKB
Eight superconducting accelerating cavity (SCC) modules are operatingin the electron ring (HER). In HER, RF systems are consist of 8 SCC and 8
normal conducting cavities (ARES).
A 509 MHz single cell cavity with a large iris diameter of 220 mm has
ferrite HOM absorbers on both sides and a coaxial-type power coupler.
All SCC modules were designed for KEKB and operated under thecondition of large beam intensity in KEKB and Phase-1 operation.
Door knob transformer Gate ValveSCC Modules
Input coupler
Gate Valve
Tuner

HOM damper

HOM damper

Nb cavity

N2 shield

Ion Pump

SuperKEKB MAC2018 M.Nishiwaki

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Issues for SCC
In a design of SuperKEKB, the total beam power will be 1.5 times larger
than that of KEKB achieved due to twice high beam current. The beam
power in a SCC module can be kept to be the same as that in KEKB bysharing the power with ARES.
Main issues for SCC
SCC-Related
KEKB
SuperKEKB n Large HOM PowerParameters(achieved) (design)ü twice high beam current
Number of Cavities
88ü shorter bunch lengthMax. Beam Current [A]1.4
2.6
ü In design current, HOM power in a
RF Voltage [MV/cav.]
1.0-1.5
1.5
SCC module is calculated as 37 kW.
n Degradation of Qo
External Q
5E+45E+4
ü FE caused by vacuum work, HeUnloaded Q at 2MV
1E+9
1E+9
leak and vacuum trouble
Beam Power [kW/cav.]
350-400
400
n Piezo Tuner Problem
HOM Power [kW/cav.]1637
ü electric breakdown in piezo stacks
SuperKEKB MAC2018 M.Nishiwaki

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HOM Dampers
Additional SiC Damper
SiC

Existing Ferrite Damper can absorb HOM
power up to 2 A
HIPped ferrite
operation.
For higher beam
current, we need toinstall additional SiC
dampers for all
cavity modules.
A pair of SiC dampers

CavityCooling pipeeGV

SiC damper can be installed outside of GV ofcavity module. There are no risks due todisassembling of cavity module.
A pair of SiC dampers has been installed
downstream of a cavity module last summer.
In Phase-2 operation, beam test will beperformed.

Pabs [kW]Ferrite SBP

Ferrite LBP

SiC 240mm

Tested max.

192636 (18x2)

Simulation*

91224* Beam current 2.6A, Bunch length 5mm, Bunch charge 10nC

SuperKEKB MAC2018 M.Nishiwaki

5Degradation of Qol Several cavity performances aredegraded by field emission caused
by vacuum work, He leak andvacuum troubles.






l Present cavity performances are
acceptable for SuperKEKB operation.
l Further degradation makes theoperation difficult.
l Performance recovery is desirablefor stable long-term operation.













 
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Horizontal High Pressure Rinse(HHPR)
HHPR is established as a recovery method of cavity performance in KEK.
We applied HHPR to three cavities degraded bystrong FE. All cavity performances weresuccessfully recovered.
First cavity module has been operated in Phase-1.
Second has been installed to replace a degradedcavity last summer. Third is kept as a spare cavitymodule.
We are planning to apply HHPR to otherdegraded cavities in the future.
After Agingafter HHPR in Tunnel

after HHPR

after HHPR
Degradedby Vacuum
Trouble CA-B04

Degradedby Vacuum
Trouble

Degraded
Before Leakat Repairing work
CA-B03
 CA-B03




















SuperKEKB MAC2018
 M.Nishiwaki

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Piezo Tuner Problem
lIn the last review, we reported,ü Six piezo actuators failed by electric breakdown in 3.5 months operation.
ü Those actuators were attached to replace old actuators used in the longterm operation.
ü The new piezo actuators were found to be sensitive to rapid change ofvoltage at the time of RF On/Off.
ü Time constant t of LPFs in the control system should be changed to slow
ones. t = 2 ms -> 20 ms (all cavities) -> 200 ms (two cavities)
lThe recommended voltage applying rate by manufacturer is slower than
800V/20ms.
lTo optimize the operating condition, the endurance tests of piezo actuators
were performed after Phase-1.
SuperKEKB MAC2018 M.Nishiwaki

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Endurance Test of Piezo Actuatort[ms]Voltage Cycles
Current
Note[V] (On/Off)[mA]

2005601000≤15 1000 cycles ≈ 10 years operation

200

800

1000

≤19 800 V is limit of piezo driver.

100800

1000

≤36

20800

1000

≤130 Higher than max. current of piezo driver

200

800

12000

≤69200

560

10000

≤11 Adopted as operating conditionlNo electric breakdown was found all tests.
lIn the condition of LPF of 20ms, the voltage applying rate is almost the operating
limit of the piezo actuator and the current exceeds the limit of the piezo driver.
lThe combination of LPF of 200 ms and voltage of 560 V was very stable conditionin 10000 cycles. We adopted the combination as the operating condition.
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Summaryl Cavity performance after the 1.5-year shutdown
Vc and Qo : almost reproduced the Vc limits and Q factors of Phase-1
l Degraded cavity replacement and HHPR◦ One cavity module degraded by vacuum trouble was replaced with HHPRed one.
◦ HHPR was applied to the degraded cavity.
◦ Performance was recovered.

l SiC HOM damper◦ A pair of SiC dampers has been installed.
◦ In Phase-2 operation, beam test will be performed.

l Piezo actuator◦ The endurance tests for piezo actuators were carried out.
◦ The combination of the time constant of LPF of 200 ms and the maximum
voltage of 560 V was adopted as the operating condition.

SuperKEKB MAC2018 M.Nishiwaki

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Thank you for your attention!

SuperKEKB MAC2018 M.Nishiwaki

11SuperKEKB MAC2018 M.Nishiwaki

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backup
SuperKEKB MAC2018 M.Nishiwaki

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SuperKEKB Parameters (RF Related)
Parameter

unit

KEKB (achieved)

Ring

SuperKEKB (design)

HER

LER

HER

LER

Energy

GeV

8.0

3.5

7.0

4.0

Beam Current

A

1.42

2.6

3.6

1585

1585

2500

2500

Number of Bunches
Bunch Length

mm6-76-7

56

Total Beam Power

MW~5.0

~3.5

8.0

8.3

Total RF Voltage

MV

15.0

8.0

15.8

9.4

ARES

SCC

ARES

ARES

SCC

ARES

Number of Cavities

10282088814

Klystron : Cavity

1:2

1:1

1:1

1:2

1:1

1:1

1:2

1:1

1.5

0.50.51.5400200600400

RF Voltage (Max.)

MV/cav.

Beam Power (Max.)

kW/cav.

0.5200550

0.5200Issues for RF systems• Beam current will be twice of KEKB.
• Bunch length will be short.
• Beam powers is so large, 1.5
times
HER and twice in LER of KEKB. 14
SuperKEKB
MAC2018in
M.Nishiwaki

550

SuperKEKB MAC2018 M.Nishiwaki

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The risk of degradation of the cavity performance can be avoided.
KEKB Superconducting Cavity Module
SBP

LBP

Additional SiC Damper

HHPR Parameters
Water Pressure

7 MPaNozzle

f0.54mm x 6Driving speed

1 mm/sec.

Rotation speed

6 deg./sec.

Rinsing time
15 min.
Stainless Steel Nozzle

We applied HHPR to degraded cavities.

Removing Coupler

Before HHPR, input couplerand HOM dampers weredismounted in a clean booth.

Removing HOM dampers and vacuum system

Nozzle and Aspirator HeadSetting HHPR Apparatus

Opening Dummy Flange

Rotating Water Jets
Insert Automatic Drive Nozzle

Evacuation after HHPRHigh Pressure Water Pump

Aspirator Pumps

Cavity was dried up by evacuation before setting thecoupler and HOM dampers.Tuner for SCC

Motor

Tuner

Piezo actuator

Piezo Stroke :80 µm in 1000 V
44 µm in 560 V
MAC2018 M.Nishiwaki
In the usual
operation, the strokeSuperKEKB
is enoughfor a tuner of our SCC.
2016/7/22
SuperKEKB SCC

2020