Integrated VacuumControl System for RF
Operation Status of SCC
SuperKEKB MA C2016
J une 13, 2016
Michiru Nishiwak iIntegratedVacuum Control
System for RF
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Integrated Vacuum Control
System for RF
The integrated vacuum control system with PLC has been developed
together with digital LLRF system.
The basic purpose of the system is to protect the cavities from vacuum
pressure rise as an interlock system.
The PLC is embedded with ladder-CPU and EPICS-IOC on Linux-CPU. Thesystem with PLC can control vacuum components overall and build asimple and flexible interlock system.
Our system can absorb a variation in the number of cavities andconfigurations of vacuum components and GVs depending on RF section.
The configurations of cavities can be set simply by dip switches at a
local control panel. Therefore, LLRF system can be used withoutarrangement to fit the configurations of vacuum components.
The system has been installed to two RF sections, D4 and D5 area withdigital LLRF and is operating with no issues.
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Schematic ViewlMonitor and judge
the status ofüPirani GaugesüGVsl Interlock signal
output to LLRF,
abort system andother groupsØRF offØGV closeØBeam AbortØetc.

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Control Panels
Dip Switches
Gauge Statuses

Remote Control Panel

GV Status
GV control switches

Local Control Panel

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Summary of IntegratedVacuum Control System for RF
The integrated vacuum control system has been developed together
with digital LLRF system.
The system is flexible and simple interlock system by using PLC withladder and EPICS.
The system is functioning well in Phase-1 operation.

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Operation Status ofSuperconducting Cavity(SCC)

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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 operation.
Door knob transformer Gate ValveSCC Modules
Input coupler
Gate Valve
Tuner

HOM damper

HOM damper

Nb cavity

N2 shield

Ion Pump

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8Issues for SCC
In a design of SuperKEKB, the total beam power will be 1.5 times larger
than that of KEKB achieved. But the beam power in a SCC module canbe kept to be the same as KEKB by sharing with ARES.
Main issues for SCC in SuperKEKB• Large HOM PowerSCC-Related
KEKB
SuperKEKBØ Additional SiC dampers canParameters(achieved) (design)absorb effectively.
Number of Cavities
88Ø Install in Phase-2 or -3
Max. Beam Current [A]1.4
2.6• Degradation of Qo
RF Voltage [MV/cav.]
1.0-1.5
1.5
Ø Possible risk in the future
External Q
5E+4
5E+4
operation
Unloaded Q at 2MV
1E+9
1E+9
Ø Horizontal HPR for 2 modules
Beam Loading [kW/cav.] 350-400400Ø Qo have been recovered.
Ø One module is operating in
HOM Loading [kW/cav.]
1637
SuperKEKB.
SuperKEKB MAC2016 M.Nishiwaki

9HOM Dampers
Additional SiC Damper

Existing Ferrite Damper
SiC

Copper Pipefor cooling

HIPped ferrite

Cooling pipe

SBP : L=120mm, ID=220mm, t=4mm
LBP : L=150mm, ID=300mm, t=4mm

Existing ferrite dampers can absorb
HOM power up to 2 A operation. SiC
dampers will be installed to outside of
GV of LBP in Phase-2 or -3 for higher
beam current operation.

SiC : L=120mm, ID=150mm, t=10mm
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 MAC2016 M.Nishiwaki

10Horizontal High Pressure Rinse(HHPR)The system can apply HPR to cavity without disassembling cryomodule. Thesystem is equipped with automatic nozzle driving system in horizontal androtational. Only cell and iris area are rinsed. Water in the cell is pumped up by
aspiration system during rinsing.
We have already applied HHPR to two modules
degraded by strong FE. Both cavity performanceswere successfully recovered.
One module is operating in beam commissioning.
CA-B03

Before
Leakafter Agingin Tunnel

after HHPR

after HHPRCA-B04



Degradedby VacuumTroubleDegradedat Repairing work











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Summary of Operation Statusof SCC in Phase-1l Cavity performance after the 5-year shutdown
Vc : almost reproduced the Vc limits within 0.15 MV before shutdown
Qo : almost reproduced Q factors before shutdown◦ One cavity slightly degraded its Q factor at 2 MV (D10A). Further conditioning
may help to increase its Q factor.
◦ One cavity significantly degraded its Q factor by dust contamination during
start-up work (D11B). The Q factor at the operation voltage of 1.5 MV is below
1x109. The cavity is still acceptable since the operation voltage is still lower. We
have to replace it before the full current operation.

l Cavity operation parameters during the commissioning◦ Operation Voltage : 1.1-1.38 MV/cav.
◦ RF Power delivered to beam : 250 kW/cav.
◦ HOM Power : 3.5-4 kW/cav. at 0.8 A operation◦ Trip rate has increased significantly after vacuum bump beam study for Beast II
background study.
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Summary of Operation Statusof SCC in Phase-1l Cavity performance during the commissioning
Trip : Beam aborts due to cavity problem were 7 times. (~6/12)◦ 4 quenches/breakdowns (3 in D11A, 1 in D10D)◦ 3 discharges in input coupler and cavity (D11A, D11B)

Other trouble : Piezo tuner problem◦ Six piezo stacks (in four cavity modules) failed by electric breakdown in 3.5
months operation. In two modules, broken piezo stacks were replaced to newones, and in others, cavities are operating by using motor tuner only.
◦ Piezo stacks have been renewed because the model used in KEKB wasdiscontinued. But, the new model is found to be sensitive to rapid change ofvoltage in operation. We have took measures of replacement of LPFs of control
system to slow ones. We will continue to investigate the problem.

SCC operation is totally stable in Phase-1.
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Thank you for your attention!

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backup
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The risk of degradation of the cavity performance can be avoided.
KEKB Superconducting Cavity ModuleSBP

LBP

Additional SiC Damper

HHPR Parameters
Water Pressure

7 MPaNozzle

φ0.54mm 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 NozzleEvacuation after HHPRHigh Pressure Water Pump

Aspirator Pumps

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