The 23rd KEKB Accelerator Review Committee (2019.07.08)

RF System Status

T. Kobayashi from SKB RF Team1

Outline
1. Introduction (Overview Of RF system)
2. Beam Operation Summary
3. Normal Conducting Cavity (ARES Cavity, DR Cavity)
4. Superconducting Cavity
5. High Power RF System (Kly, KPS, WG)
6. Low Level RF Control System
7. Damper of Longitudinal Coupled Bunch Instability
8. Summary

2

ARES

Cavity Types of MR
Basically, KEKB RF systems are reused with reinforcement for SuperKEKB.

@Oho, Fuji

SCC
@NikkoAccelerator Resonantly-coupled with Energy Storage
3-cavity system stabilized with the π/2-mode operation
Successful Operation of the 32 ARES Cavities at KEKB

T. Abe8 modules have been installed in Nikko for HER.
Y. Morita
Pinput = 400 kW
Tested up to 750 kW.

58

Input Coupling Factor

K. Akai et al. / Nuclear Instruments and Meth
(Q ~50000) not changed
Needs to be renewed

ext

PHOM = 19 kW
since some major parts
Tested up to 19 kW.straight section. The maximum current
HER
not ofavailable.

has reached 870 mA so far.
consists of

PHOM = 26 kWl HOM-damped accelerating cavity (A-cav),l Energy-storage cavity with TE013 (S-cav),(C-cav)l Coupling cavity
with a parasitic-mode damper.

7.2. Design and performanceand its
Testedof
up cavity
to 26 kW.
accessories
7.2.1. Cavity
A cross-section view of the KEKB-SC cavity isshown in Fig. 10, and the cavity parameters of theaccelerating mode are summarized in Table 6.
The cavity was formed by a spinning method of
2:5 mm Nb sheet of RRR 200. The process of
surface treatment using electropolishing was althe same
as kW
that
of the TRISTAN cavities.
/cavityVmost= 400
c = 1.5 MV, Pbeam
beam
To obtain a carbon-free surface so as to suppress
discharging, hydro-preoxide rinsing was replacedby ozonized-ultrapure-water rinsing (OUR). The
OUR treatment completely removes any carbon

Vc = 1.5 MV, P
Vc = 0.5 MV,
Pbeam = 600 kW
ARES parameters
fRF

508MHzUs / Ua

9

R/Q0

15Ω

Q0

1.1 x 105

Vc

0.5 MVPc

150 kWfor the π/2 mode

60 kW (A) + 90 kW (S)= 400 kW

Table 6
Cavity parameters of the KEKB Superconducting cavity
Frequency
Gap length
Diameter of aperture
R=Q
Geometrical factor
Esp =Eacc
Hsp =Eacc

508.8
243
220
93
251
1.84
40.3

MHz
mm
mm
Ohms
Ohms
Gauss/(MV/m)

3

RF Related Parameters (design value)
Parameter

unit

KEKB (achieved)

Ring

SuperKEKB (design)

HER

LER

HER

LER

Energy

GeV

8.0

3.5

7.0

4.0

Beam Current

A

1.4

2

2.6

3.6

1585

1585

2500

2500

Number of Bunches
Bunch Length

mm

6-7

6-7

5

6

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 CaviQes

10

2

8

20

10

8

8

14

Klystron : Cavity

1:2

1:1

1:1

1:2

1:1

1:1

1:2

1:1

1.5

0.5

0.5

1.5

400

200

600

400

RF Voltage (Max.)

MV/cav.

Beam Power (Max.)

kW/cav.

0.5
200

550

0.5
200

600

Issues for RF systems•Beam current will be twice of KEKB.
•Beam power/cavity will be 3 times higher than KEKB for ARES cavity.
•Bunch length will be shorter than KEKB. HOM Power will be increased.
Reinforcement and reconfiguration of RF system are required.
4

RF System Arrangement (ultimate)
OHO

D4
1

C

e+: 8.0Gev x 1.4A

2

B

A

B

2

1

C E

E

2

2

D

C

B

A

1

2

2

A

D10

D8
B

C

D

E

2

NIKKO
2

2

D C B A

D11
2

1

A B C D E F

HER

SCC

ARES

e-: 3.5Gev x 1.8A LERARES

Beam Power/Cavity: ~200kW
add050klystrons,0HP&LL0
add030power0supplies0

add020more0klystrons,0HP&LL,00
add010more00power0supply
2

D4

2

2

D7

D5

2

H G F E D C B A22

A B C D E F

F E

2

2

crab cav.

SuperKEKB)RF,,(ul/mate)

Drive Power/cavity: ~350kW

For the design
current

FUJI

D7

D5
2

A

K. Akai, 2014

KEKB)RF

add020klystrons,0HP&LL0
add020power0supplies

2

D

2

C

B

D8

2

A

A

B

C

D10
2

2

D E F

2

2

2

D C B A

D11
2

2

A B C D E F

e+: 7Gev x 2.6A
e-: 4Gev x 3.6A

add020SC0(opVon)0

add020ARES
remove040ARES

convert0to0LER

Beam Power/Cavity: ~600kW
Klystron,0HP&LLRF0system

2

Type0“A”0power0supply0(for0two0klystrons)

1

Type0“B”0power0supply0(for0one0klystron)

Drive Power/cavity: ~750kW (Kly Max: 1MW)

ARES0cavity

SC0cavity
Crab0cavity

• add 9 klystrons and 3 PS’s more.
➡ One-to-one configuration for every ARES (One klystron drives one cavity unit).
➡ Input coupler was reinforced for the ARES (β=5, 800-kW input power capable) at “1:1” stations➡ Addition of new HOM Damper for the SCC as a measure against beam-induced HOM-power rising.

5

RF System Arrangement (Present State)
OHO

D4
1

2

C

B

A

B

FUJI

D7

D5
2

A

K. Akai, 2014

KEKB-RF
2

1

C E

E

2

2

D

C

B

A

1

2

2

A

D10

D8
B

C

D

E

2

NIKKO
2

2

D C B A

D11
2

1

A B C D E F

HER

ARES

LER

SCC
ARES

Present
Layout
2

OHO

2

2

H G F E

HER
LER

SuperKEKB-RF(phase1)
(present
operation)

add 5 klystrons, HP&LL
add 3 power supplies

D4
C

1

A

A B C D E F

E

2

FUJI

D7

D5
2

2

crab cav.

2

D

2

C

B

A

1

2

2

A

D10

D8
B

C

D

E

2

NIKKO
2

2

D C B A

D11
2

A B C D

SCC

add 2 ARES
convert to LERKlystron, HP&LLRF system

remove 4 ARES

2

Type “A” power supply (for two klystrons)

1

Type “B” power supply (for one klystron)

ARES cavitySC cavitySC crab

At the OHO D4 section, two cavities were added.
At the D5 section, all ARES cavities were moved from HER to LER, and changed to the one-to-one configuration.
At the Fuji D7: two cavities were removed. And also at D8: two cavities were removed.
Accordingly, some klystrons and LLRF systems were added at D4 & D5.
6

DR Cavity

DR-Cav

Installed November, 2016

DR has an RF station with 2 cavities(the Up-stream and the Down-stream cavity)

HOM Damper

DR

here

Design Parameterse+
U-Cav.

D-Cav.

Dummy chamber for option to install an
additional cavity (the middle cavity) if necessary.

Opera/onal frequency

508.9 MHzRsh/Q0150 ΩQ0∼30000

Cavity Voltage (DR spec)

0.7 MV / cavity

Cavity Voltage (Cavity spec) 0.8 MV / cavity
Wall-loss power@ 0.7 - 0.8 MV / cavity~110 - 140 kW / cavity

0.95 MV/cavity has been achievedby RF conditioning

Two cavities are driven
by one klystronOperation Freq. : 508.9MHz
Cavity Voltage: Total 1.4 MV (0.7 MV/cavity) for the design

So far, this system has beensuccessfully operated at 1 MV (0.5 MV/cavity) without problem !

7

Overview ofOperation Status

8

History of Total Vc (Phase-2, 2018)
Beam Current

Total-Vc History[MV]

1MW-DL Water LeakHER Total Vc
LER Total Vc

D4G

PIEZO
Break Down
@D11A

1MW-DL Water Leak
@D5D

[MV]

HER Total-Vc

LER Total-Vc

DR Vc
HER
Storage

DR-Cav Vc

LER Storage
9

History of Total Vc (Phase-3, spring 2019)
940 mA
Beam Current

Total-Vc History

Beams were smoothly stored at RF start-up without phase search (with only
fine tune), so RF reference phase was properly remained from Phase-2.
And also the collision phase was successfully reproduced.

HER Total-Vc

HER Total Vc
LER Total Vc
Linac
fire trouble

LER Total-Vc
All RF stations worked wellwithout long-stop through the run!
DR-Cav Vc

DR Vc

10

<Topic>

ARES
DR-Cav

Normal-Conducting Cavity
ARES & DR Cavity

11

ARES

NC-Cavities Operation Summary
ARES & DR Cav
DR-Cavin Phase 3@Oho, Fuji

2019-03-11 to 2019-06-30

RF failure statistics for each station during Phase-3, 2019
OHO

RF condi*oning performed each maintenance day

Fuji

DR

No RF condi*oning performed during maintenance day(as an experiment)

ü Low trip rates (< 1 / 3_months)
ü No signiﬁcant diﬀerence in the trip rates between the ARES caviBes at D5 and D7/D8 for LER
12

<Topic>

SCC

Super-Conducting Cavity

13<Topic>

SCC
StatusSCC operation status
in 2019 spring operation• 8 cavi/es have been operated with good stability.
• Vc : 1.35 MV/cavity in present opera/on (1.5 MV is standard)• Beam Aborts caused by SCC• Breakdown of Cavity : 1• Peripheral problem : 4 (Piezo tuner trouble : 3, Water chiller trouble : 1)

• Cavity performances• All cavi/es almost reproduced the performance of Vc limits and Q factors ofPhase-2. (not degraded)• Vc.max > 2.0MV, Qo : >1e9 at 1.5 MV

Piezo Tuner Problem• Six piezo actuators were broken in Phase-1. Then the slower low-pass ﬁlter andthe voltage limita/on were applied in piezo tuner control (reported in the last
review) . As the result, piezo actuator failure was drama/cally decreased.
• However, the increase of leakage current of piezo actuators is s/ll observed andseveral piezo actuators were broken by electric breakdown in Phase-2 and2019-spring-opera/ons. -> The piezo-broken cavi/es were operated with only
mechanical motor tuner if it was possible.
14<Topic>

Piezo Problem Study:
Exposure Experiment - Drying by silica gel SCC

We invesBgated the eﬀect of environments on piezo insulaBon.
For the experiment, we tried to expose piezo actuator to various environments, such as vacuum,
dry N2 gas, the air and synchrotron radia/on. According to the results, we found that the
moisture in the air degrades insula/on between electrodes of piezo stacks.

From the exposure test,
It was found that drying by silica gel is eﬀecBve to reduce leakage current of piezo tuner!
Piezo enfolded in plas/c bag with silica gel packs

Leakage Current

in plas/c bagwith silica gel packs

in the air--> As a trial, we a.ached silica gel packs to piezo tuner in the tunnel.

15

<Topic>

SCC

Attaching silica gel to piezo
at D11A SCC in the operation

As a trial, we a.ached silica gel packs to piezo tuner at D11A SCC in the tunnel.

Piezo Tuner with silica gel
Motor Tuner

Leakage Current of Piezo Tuner
A.ached Silica Gel
degradaBonof electric insulaBon

Piezo Tunerwith lead shield

Silica Gel

Increase of the leakage current of piezo due to degrada/on of electric insula/on wasobserved at D11A SCC. Then, silica gel was abached to piezo. Acer that, the increaseof leakage current was eﬀec/vely stopped.
The good eﬀect of drying by silica gel was also conﬁrmed in the prac/cal opera/on.
We will con/nue to study moisture control around the piezo in the tunnel.

16

<Topic>

HPRF

High Power RF System
Klystron
Kly. Power Supply
Waveguide system

17

<Topic>

HPRF

Water Leak from High Power LoadIn Phase2,
Water leak troubles occurred in two cylindrical type water loads at
D04G (April 2018) and D05D (July 2018),
because, ceramic RF windows were broken by mechanical stress.
They were replaced with spares, and a[er Phase2, were repaired.

1.2 MW high-power water loads
Two types:

Cylindrical type

Rectangular type
Water leakfrom load
First /me at D04G (April 2018),
There were no interlock systems for water leak. The water went throughout the
waveguide system because it was delayed to recognize the water leakage. It took
long /me to dry it. -> A water-leak detector was mounted for all water-loads.
Second /me at D05D (July 2018)
The water-leak detector worked well. So the water leakage was able to be found before the water enter
the waveguide system. The opera/on was recovered within few hours.

Fortunately, during Phase-3 (2019), no water leak trouble occurred in the water loads.
New design of a ceramic window is under consideraBon for the robustness against mechanical stress.

18

<Topic>

HPRF
at DR

Anode Voltage Controller Failure
in Klystron Power Supply at DR
June 18, 2019

Cockcro&WaltoncircuitCollector

Klystron

R1

Vk=
Vk
70kV

R2

GroundX

RF out

Vk

Vk=
70kV

X

Va out toanode

TemporaryCure
To Heater incathodeThen we applied temporary cure.

Va=
Va=
30kV
30kV

Outputresistance toanode(20 MΩ)Vg

To Ground

R2

R3

The power supply was replacedwith voltage divider resistance.
R1= 100 MΩ

Va out(R2= ~60 MΩ)

Vk
Va

(kV)

(kV)

R3= 50 MΩ
groundingresistance(200 MΩ)R1

Vk out (kV)to cathode

Va

Anode voltage controller failed. The
cause of failure could not be identified.

VkVk=
=
70kV
70kV

Va

R3

Vk Input(kV)

Anode-V was
fixed at 30 kV.

Vg

(kV)

Cockcro>-Walton circuit togenerate anode voltage.

In this case, the efficiency (collector loss) cannot be optimized.
So, it is difficult to apply this cure method to MR klystron forlarge beam loading. Although, idling operation of cavity might
be possible with no-loading phase instead of detuning cavity.

<Topic>

LLRF

Low Level RF Control System

20

<Topic>

New Digital LLRF System

LLRF

Digital LLRF control system has been newly developed for high accuracy and flexibility.
@OHO D4 Control Room
Old systems

new LLRF control
systemSCC

3 new LLRF
systems

KLY+LLRF

ARES+@OHO D5 Control Room

6 new LLRF
systems• Consisting of µTCA-platformed FPGA boards & PLC• I/Q components are handled by FPGA@DR Control Room

StatusRegulation Performance• 9 stations of Oho D4&D5 (6@D5 + 3@D4) are operated with the new
digital LLRF control systems.

• All of new LLRF systems are successfully working well without
problem. Some software bugs found during the operation were fixed.

• At DR, also the new digital system is applied, and it is working
properly without problem. It is almost the same as MR one, except 2cavity vector-sum control is needed.

21

<Topic>

LLRF

Existing Analog LLRF System

Most stations are still operated with old analog LLRF systems, which had been used in KEKB operation
Existing LLRF used in KEKB
K. Akai et al. / Nuclear Instruments and Methods in Physics Research A 499 (2003) 45–65

Low-level RF for KEKB Superconducting cavity

Block Diagram of SCC LLRF
from RFreference line

interlocks
Fig. 2. RF station for the SCC cavities.

Phase Lock Loop
combiner for klystron

klystron circulator

Tuning Control Loop

SW
out

out

ref.

out

FBC

FBC

FB

φ det.

ref.

FB

ref.

DL

FB

φ det.

FBC
FB

Gain Control
for klystron

storage cavity

A-cav

Tuner
Controller

out

c-damperklystron out

FBC
Vc setcoupling
accelerating
cavitycavityout

ref.
offsetS-cav
RF input

φ det.

tuner
beam

FB

(RF ON)

cavityDirect RF Feedback
SWpick up (Vc)s-tuner

BPF

beam signal

BPF

FBC

ARES Tuner Control
Configuration

a-tuner
BPF

BPF

BPF

φsg
φsb

φac

(RF OFF)for ALC and PLL

Amplitude Control for Vc
Fig. 3. Tuning control.

Phase Lock Loop for Vc

phase of the accelerating cavity to the coupling
cavity.
When an RF station operating at nominal
power is tripped off, the resonant frequency of
the ARES tends to decrease at first by about
100 kHz in about 80 s; and then turns to increase if
no tuning control is applied. This is caused by thethermal deformation properties of the end platesof the storage cavity. In order to avoid the m ¼ "1mode instability caused by tripped cavities and alarge amount of beam-induced power, that canaway from frf : It is done by controlling thecavity tuner according to the relative
between the beam signal and the beam-i
voltage. When the cavity trips, the reference
for the energy-storage cavity is switched fr
incident RF to the beam signal [10].

• These systems are composed of combination of NIM standard analogue modules.
• They are controlled remotely via CAMAC system.
• All systems are soundly working without serious troubles.

3.3. Protection against trips

Trips spares.
and recovery
However, some NIM modules failed during operation. They were replaced3.3.1.
with

22

The RF system is designed so that an

<Topic>

LLRF

Damper System forLongitudinal Coupled Bunch Instability
due to Acc. Mode23

Growth Rate Estimation for SuperKEKB
Estimation of Growth Rate of LCBI due to the Acc. mode

K. Hirosawa

LCBI: Longitudinal Coupled Bunch Instability

LER（22 (b)x ARES）
Growth rates for LER

HER （8 x ARES + 8 x SCC）
(a) Growth rates for HER

Design Beam Current

Design Beam Current

µ=-1

µ=-1

Dashed line:
one SCC parked

Rad. Damping Rate

µ=-2

µ=-2

µ=-3

µ=-3
ΔfSCC ~ -44 kHz @ 2.6A
(optimum tuning)

Growthrates for LER
Dashed line indicates the case that one SCC is parked (b)withdetuning
at -150 kHz.

: Calculation results of growth rates for HER (a) and LER (b). Solid curves
frequency)
0 = 100 kHz
the results under RF worked ideal, and dashed curvesfindicate
the (revolution
results under
onducting (HER) or normal conducting (LER) cavity detuned manually.

(center between -1 and -2 modes)

In SuperKEKB, the µ=-1 and -2 modes of LCBI will be serious problem forthe design current.

New LCBI damper system with new digital filters has been developed forSuperKEKB. It 10
can suppress the µ=-1, -2 and -3 modes in parallel.

24

New LCBI Damper System for SuperKEKB
For SuperKEKB, new LCBI damper was developed.
It can suppress µ＝-1, -2 and -3 in parallel by new digital filter.
Block diagram of FB loop of RF system with LCBIs damper for SuperKEKB.

RF

RF control system

Vc FB control

Reference Signal

frf =508.9 MHz

Pickup signal＋

DriverAmp

LCBIs damper(μ= -1, -2, -3 mode ﬁlter)

Klystron

Beam
Pickup Signal

CavityBeam

f0 = 100 kHz (revolution frequency)

伝送特性と模擬空洞を用いたループ特性
Transmission
Newley developed
LCBI
damper(mode
filter)(a) The block diagram of the new LCBIs damper.

frf = 508.9 MHz

f0 =100 kHz
800 kHz
Single sideband
filterofand
band pass filters (a parallel comb filter)(b) Illustrations
signaldigitalprocessing.

Our klystron bandwidth is about 100 kHz (The gain and phase are not flat at µ＝-2 and -3 modes ).
The feedback gain and phase can be controlled independently for each mode by the digital filter.

ループ

25

Demonstration of the new LCBI Damper
in HER in Phase-2 Operation (Ib ~ 0.7 A）
frf = 508.9 MHz

f0 = 100 kHz

The µ=-1 mode was excitedby a parked
SCcavityof damper
Δf~-150(a) Beam
pickupsignals without
for µ = −1kHz.
modeµ=-1 mode

frf-f0frf-frev+fs

fs = 2.3 kHz
We purposely excited the µ=-2 mode by detuninga SC cavity
atdamperΔf=-200
kHz.
(a) Beam manually
pickup signals without
for µ = −1 andµ = −2 modesµ=-2 mode

frf-2f0

frf-2f0+fs
sync. osc.

sync. osc.

10 kHz (@µ=-2)

10 kHz (@µ=-1)(b) Beam pickup signals with damper for µ = −1 mode

The new LCBI damper
applied(b) Beam pickup signals with damper for µ = −1 and µ = −2 modes

The µ=-1, -2 modes weresuccessfully damped.

This new damper was also practically used in Phase-3 (2019)
Figure 15: Spectrum of beam pickup signals without feedback(a) and with feedback(b)Figure 16: Spectrum of beam pickup signals without feedback(a) and with feedback(b)and worked well to damp the µ=-1 modein HER, even though Ib < 1 A.
for the µ = −1 mode.
for µ = −2 mode.
26

Summary• Steady operation has been continued without serious problem in RF
systems.

• ARES cavity and DR cavity has also operated without trouble and thetrip-rate is enough low at present.

• In SCC operation, piezo actuator frequently failed with electric

breakdown. From our study, it was found that the moisture degrades its
insulation, and that drying piezo with silica gel is effective to preventfrom the degradation.
We ill continue to study moisture control around the piezo in the tunnel.

• Newly developed digital LLRF control systems, applied to 9 stations at
OHO section, is properly working without fatal trouble.

• New LCBI damper system with new digital filters has been developed.
It can suppress the µ=-1, -2 and -3 modes in parallel. In Phase-2,
successful damping of µ=-1 and -2 was demonstrated by the new
damper.

27

Thank you
for your attention!

28

Backup Slides

29

e-

e+

1.5 MV

7 GeV x 2.6 A

4 GeV x 3.6 A

P beam 400 kW

Vc = 15~16 MV

Vc = 9.4 MV

Pbeam = 8.0 MW

Pbeam = 8.3 MW

by

by

Vc

D11

8xARES + 8xSCC

22xARESNIKKOD10LER ARES

1 : 1

1 : 2

Vc

0.48 MV

0.34 MVP wall140 kW

70 kW

P beam

460 kW

230 kW

Input β

4.3

4.3

PPMD

14 kW

7 kW

Vc

0.5 MVP wall150 kW

P beam

600 kW

Input β

5.0

PPMD

21 kW

OHO

HER SCCHER ARES

D4SuperKeKB L = 8 x 1035 cm-2s-1

T. Kageyama, 2011.02

D5

RF Power for Ultimate Stage

Klystron
SCC
ARES

D8

FUJI

D7

2010.11.25

30

Instability due to RF cavities and cure
Instability due to RF cavities and cureT. Kageyama, 2011.02

Ring

Longitudinal/Transverse

Cause

Frequency (MHz)Growth time (ms)

Cure

LER

Longitudinal

ARES-HOM

1850

12

B-by-B FB

ARES-0/π

504

21

B-by-B FB-1 mode508.794-1 mode damper

LER

Transverse

ARES-HOM

633

7

B-by-B FBHERLongitudinal

ARES-HOM

1850

59(no need)

SCC-HOM

1018

58(no need)-1 mode508.794-1 mode damper

ARES-HOM

633

39(no need)

SCC-HOM

688

14

B-by-B FBHERTransverse

Longitudinal bunch-by-bunch FB will be needed
to suppress coupled bunch instabilities driven by RF cavities.
31

22 ARES Cavities
operated for LER (Ib=3.6A)
T. Kageyama, 2011.02

RF frequency

508.869 MHz

Flywheel Energy Ratio US /UA

9unchanged

Cavity Voltage Vc

0.48 MVP(wall) = 140 kW

Detuning Frequency Δfπ/2 / ΔfAC

-28 kHz / -280 kHz

P(beam) = 460 kW

Input Coupling Factor β

5.0

β (optimum) = 4.3

CBI (-1 mode) due to the Acc. modeτ = 4 ms

RF feedback

CBI due to the 0 and π modesτ = 21 ms

bunch-by-bunch FB

32

HOM Power Estimation for LER
T. Kageyama, 2011.02
KEKB LER
Sep. 21, 2004

SuperKeKBLERPower Handling Capability
verified at 1.25 GHz

Factor of Safety

Ibeam [A]

1.6

3.6

-

-

Nbunch

1293

2503

-

-

σz [mm]

7

6

-

-

k [V/pC]

0.40 (0.39†)

0.44

-

-

PHOM /ARES
[kW]

5.4†

17

-

-

PHOM /HWG
[kW]

1.05†

3.3

5.0

5.0/3.3 = 1.5

PHOM /Groove
[kW]

0.3†

0.93

1.2

1.2/0.93 = 1.3†based on calorimetric measurement

33

Coupled Bunch Instability (CBI)
driven by the Accelerating Mode (π/2)

T. Kageyama, 2011.02

Δfπ/2 = -28 kHz
KEKB LER
20 x ARES (0.4 MV, β＝3)Δfπ/2 = -17 kHz for 1.8 A

Re(Z//) / Cavity [Ω]SuperKeKB LER
22 x ARES (0.48MV, β = 5)Δfπ/2 = -28 kHz for 3.6 A
Δfπ/2 = ΔfAC / (1+US/UA )( f - frf ) / frev

34

Cavity Impedance and LCBI modes
Longitudinal Coupled Bunch Instability

LER - ARES Cavity Impedance ( Ib=3.6 A ){∞1= AI b ∑ f p( µ + ) Re Z f p( µ + ) − f p( µ − ) Re Z f p( µ − )
τµ
p

(

)

(

)}

f p( µ + ) = pfrf + µ f0 + fs

f p( µ − ) = ( p + 1) frf − µ f0 − fs

frf =508.9 MHz
Revolution freq.
f0 = 100 kHz
Figure 1: The illustration of the relation between LCBIs modes and longitudinal resonant
impedance of an RF cavity.

Synchrotron osc. freq.
fs = 2~3 kHz
35

SCC Operation Parameters and Trip2019
spring8
0.94
1.35
4.7 7.2E+4

DesignPhase-1
achieved

Phase-2
achieved

Number of Cavi/es

8

8

8

Max. Beam Current [A]

2.6

0.87

0.8

RF Voltage [MV/cav.]

1.5

1.2

1.35

External Q

5E+4

4.3 6.8E+4

4.3 6.8E+4

Beam Loading [kW/cav.]

400

80 - 170

Unloaded Q at 2MV

1E+9

1.6E8 - 1.1E9

80 - 100
1E8 - 1.6E9 0.2 - 1.5E9

at 1.5MV

3.3E8 - 2.2E9

3.1E8 - 3.0E9

1.0 - 2.8E9Max. Vc [MV] at aging

1.74 - 2.36

1.75 - 2.48

2.00 - 2.49

Beam Aborts cavity trip

91

peripheral

16

4

1
4

SuperKEKB-SCC
Parameters

100 - 12036

<Topic>

New LLRF Control System

LLRF

was developed for higher accuracy and flexibility for SuperKEKB.

New LLRF System

Block Diagramof FB & Tuner Cont.

for one klystronuTCA-platform
FPGA Boards(AMC Card)µTCA crate

16-bit ADC x 4ch,
16-bit DAC x 2ch

EPICS-IOC embedded• Consisting of µTCA-platformed FPGA boards (AMC), & PLC.
• EPICS-IOC with Linux-OS is embedded in each of them.
• Common hardware for both of ARES & Superconducting Cavity.
• Klystrons (LLRF) : Cavity unit = 1 : 1 (SuperKEKB)

Completely remote controllable• New LLRF control system is built on recent digital technique. It is dominated byµTCA-platformed FPGA boards for higher accuracy and flexibility.
• In this system, I/Q components are handled by FPGA for vector control instead of
amplitude and phase.
• The good performance was demonstrated in the high power test with ARES cavity.,
The regulation stability was 0.02% in amplitude and 0.02 deg. in phase.

37

<Topic>

LLRF

RF Reference Distribution
with digital optical delay control for phase stabilization• RF reference signal is optically distributed into 8 sections by means of “Star” topology configuration from the central
control room (CCR).
• “Phase Stabilized Optical Fiber”, which has quite small thermal coefficient, is adapted : < 1ppm/°C• For the thermal phase drift compensation, optical delay line is controlled digitally at CCR for all transfer lines.
• The phase noise (time jitter) is enough low.

Variable Optica DelayLines (VODLs)
for 8 transmissions

uTCA-platformed FPGAs
for the VODLs control

Low SSB Phase Noise

Short term stability (time jitter) : ~0.1 ps (rms)Long term stability (pk-pk) : ±0.1° @508.9MHz = ±0.55 ps(expected by the optical delay control)38

Linac/DR/MR Synchronizing MO System
MR Circumference
Compensation

Freq. Change
for DR Dispersion
Measurement

For dispersion measurement in DR, the RF frequency has to be controlled independently for only DR.
->A dedicated master oscillator for DR (DR-MO) is required.
Linac-MO, DR-MO and MR-MO are synchronized each other by the external 10-MHz reference generated byfrequency dividing of 510-MHz into 1/51, which is distributed from the central control room.
After the end of the dispersion measurement (frequency change), RF phases between each other can be immediately
recovered by a phase shifter, and bucket-ID (the revolution signal) is reset for successive injection.

39

Longitudinal Coupled Bunch Instability

LCBI Damper System
In KEKB operation, the µ=-1 mode damper has
been used to suppress the LCBI due to the Acc.
Mode in KEKB operation.
In SuperKEKB operation, the LCBI damper is alsoneeded:at Ib > 800 mA, the µ=-1 mode was excited in HER,
and a parked cavity also excites µ=-1 mode at Ib >500 mA in both rings.

Example of SKB Phase-1 operation
The µ=-1 mode excitation
due to a parked SC cavity.

frf − f0
w/o µ=-1 mode damper

Ib > 0.5 A
frf − f0 + fs

Single Sideband Filterµ=-1 mode damper applied

Up Converter
Digital Filter

Down Converter

40

Klystron Characteristics
Our klystron bandwidth ~ 130 kHz
Modulation Amplitude(a) The gain frequency characteristics of the klystronPhase(b) The phase frequency characteristics of the klystronµ=-1 -2 -3(b) The phase frequency characteristics of the klystron

frf = 508.9 MHz

Figure 5: Frequency characteristics of the klystron used in KEKB and SuperKEKB. Blue
dots and curve are measured data and fitting function, respectively.

f0 = 100 kHz (revolution frequency)
15

Klystron bandwidth is not so wide (gain and phase are not flat).
The feedback phase and gain should be controllable for each LCBI
mode independently in our RF system.
41

SSBF and DBPF
Transmission(a) The block diagram of the new LCBIs damper.

K. Hirosawa

伝送特性と模擬空洞を用いたループ特性

frf = 508.9 MHz

f0 =100 kHz
800 kHz
we adopted actually. The calculation
Eq. (4) agrees
thesimulation. As the result,(b)ofIllustrationsof withsignalprocessing.
resonance points of each polyphase filter (= 1/RC) were 20 kHz, 40 kHz, 80 kHz, 160

Single Side-Band Filter (SSBF)

kHz, 320 kHz, and 900 kHz.

ループゲイン
Digital Band Pass Filter (DBPF)

Figure 7: (a) The block diagram of the new LCBIs damper with parallel bandpass filtersfor µ = −1, −2, and −3 modes. (b) Illustrations of signal processing of SSBF (left) Figureand 11: A functional block diagram of the digital bandpass filter on the FPGA.
DBPF (right).
Figure 8: The functional blockfdiagramof the single
side-band filter.
MHzrf = 508.9
Transmissionω µ = − µω 0 − ω s

f0 = 100 kHz
1 MHzµ = −1, − 2, − 3

The center frequency(-μf0-fs) of BPF,
phase and gain are precisely adjustablefor each mode individually by remotecontrol42

Feedback Loop Test with a Simulant Cavity
frf = 508.9 MHz
f0 = 100 kHz (revolution frequency)
fs = 2~3 kHz (synchrotron osc. freq.)

43

Concern Issue of CBI damper
In the demonstration,
the new damper was applied to only one klystronstation at the D04G station in HER or at the D05F
in LER. (In these stations, one klystron drives one
ARES cavity) .
Then, the instabilities were suppressed as
expected at up to about 0.9-A beam current inPhase 2.
However, the target current of SuperKEKB design is 3.6 A which is much higher.
According to the calculating evaluation, there is possible that applying the damper
to only one station could not reach the required loop gain to damp instabilities forthe nominal beam current.
We will try to apply the damper system to two or more klystron stations.
We need enough time for tuning of several dampers systems to apply them toseveral klystron stations.
44<Topic>

DR-Cav

Damping Ring Cavity

45

<Topic>

DR-Cav Check of the relative cavity phasebetween Upstream and Downstream
Cavities for the DR• The rela(ve phase was adjusted during the advance low-power RF measurement.
è This (me, we veriﬁed the result by using the beam.

• Method based on the beam
① Operate the cavi(es with a constant RF power based on klystron-loop feedback• To establish that the synchrotron frequency (fs) does not change② Change the rela(ve cavity phase by moving the phase shiIers③ Record fs from the spectrum analyzer

To U-Cav

Magic TeeTo D-Cav

rom
f
r

e
ow stronp
RF e klyth

The adjustment of the WG phase shifter
was confirmed by using the beam.

46

<Topic>

DR-Cav Check of the relative cavity phase between
Upstream and Downstream Cavities for the DR
Measurement Results

Measurements

Max. of the ﬁOed parabolic func=on -0.7°
Klystron output power maintained to be constant

40.4
40.3

fs [kHz]

40.2
40.1

y = -0.0007x2 - 0.001x + 40.311

Original (deﬁned to be 0)

40
39.9
39.8
39.7

The result based on the beam is very good agreement withthe result of the advance low-power measurement!

39.6
39.5
39.4
-40.0

-35.0

-30.0

-25.0

-20.0

-15.0

-10.0

-5.0

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

Rela=ve cavity phase [deg]

47

High Power RF System<Topic>

HPRF(above-ground part)NS

to FujiOho

PS build.
D5 (for LER)+e

Water Pool-e

D4 (for HER)F

D5-F (1:1)

A

A C

KlystronH

D4-A (1:2)

Kly. Power Supply

1.2-MW water load
(Cir. port#3)
to the tunnel(ARES)to IP

PS build.

Klystron(for 2 ARES’s)

Magic-T

30-kW dummy load
(Cir. port#4)
1.2-MW water load
(Magic-T port#4)

WR-1500

1-MW UHF circulator

WR-1500

400-kW
water load
(Cir. port #3)

30-kW dummy load
(Cir. port#4)

Examples of HPRF System

1-MW UHF circulator

Many components used in TRISTAN operation were reused. Regular maintenance of them is needed.

48

<Topic>

HPRF

KPS Issues

In Phase 2 (2018),
MR: One KPS (D4-GH) was tripped due to reducing a ground resistance in anode power supply byleaking of rain from the roof at May 13, then an interlock to detected anode over-current wasworked. At May 16, this KPS was retuned to operation after set-up a simple rain cover on this
KPS in the building.
: A stucco work to repair on a part of outer wall at D4 building was made until March 2019 before
Phase 3 commissioning. We will continue the repair work for other region of outer walls.
DR: Successfully operation.
In Phase 3 (2019),
MR: Troubles did not happened during Phase 3. -> Successfully operation.
DR: A failure of control board in anode power supply was happened at June 18. We could not search
immediately specifying a failure point in control board. To retune for operation without taking time,
the anode voltage power supply was disconnect to KPS. Then, the voltage divides to anode bychanging the value of resistance between the cathode, anode and ground. The anode voltage
can controls roughly as a function of ratio of resistances. It was worked well, therefore, the KPS
of DR was retuned at evening in June 19.
: We are planning a repair work for this KPS in this summer.

<Topic>

HPRF

KPS : connection of anode power supply

Anode power supply to generate Va
To Heater in(kV)
Vk InputcathodeConventional
Collector(kV)

Va out toanode
Vk out (kV)to cathode

GroundOutputresistance toanode(20 MΩ)RF outVkgroundingresistance(200 MΩ)To Ground

Cockcroft-Walton circuit togenerate anode voltage.

<Topic>

HPRF

Anode Voltage divides replacing byresisters after disconnect the CockcroftEquivalent circuit
Waltoncircuit
Vk Input
Without Cockcroft-Walton circuit
Vk outVa out(R2= ~60 MΩ)

Vk =
70kV

R1= 20 MΩ

Va=
30kV

R1

R2

R1= 100 MΩ
Va out(R2= ~60 MΩ)Vk

R3=
200 MΩVa
Vk

To Ground

(kV)

Vg

R3

(kV)

(kV)

R3= 50 MΩ

Equivalent circuit (Conventional)

Vg (kV)

Cockcroft
WaltoncircuitVk

Conventio
nal

R1
R2

After disconnect the CockcroftWalton circuit and replacing theresistors.

R3

Va

<Topic>

HPRF

High-power components Issue 1•1MW UHF Circulator (Total 31 circulators used for SuperKEKB)
Number of overhaul: Three circulators repaired from April 2018 to March 2019.
Before starting Phase2, they were replaced to other circulators which a repair
should be necessary. We are planning that two circulators repair until Dec 2019.
New production: One circulator was manufactured until March 2019.
We propose the next production for one circulator until March 2022.

<Topic>

HPRF

High-power components Issue 2•1.2 MW high-power water loads(Two type loads used which are the rectangular type (18) and the cylindrical type (12).)In Phase2,-> Water leak trouble was happened from two cylindrical type water loads.
A cause of water leak is that a ceramic rf windows was broken by mechanical stress.
After Phase2, the broken loads were repaired.
D4-G (HER) -> At April 5, a water leak trouble happened, then the leaked water was infiltrated toinside waveguide system. It was detected by checking with eyes, after
judged the monitoring values of LLRF are abnormal. The cavity was detuned andremoved to operation after drying inside waveguide by blower.
At evening on April 6, the operation of HER was restarted.
-> The load changed to spare until May 16, then rf station was retuned to operation.
-> After this trouble, a water-leak detector was installed for all water-loads.
D5-D (LER) -> At July 1, a water leak trouble happened.
-> Water-leak detector worked well before infiltrating leaked water to insidewaveguide system.
-> So, the cavity was detuned and removed to operation within few hours.
In the Phase3, the trouble of loads are not happened never.

<Topic>

HPRF

空洞からのBeam induce
powerはロードで終端。
導波管内は送風機にて区間を分けて乾燥中。

To the tunnel

D4-G

54

<Topic>

HPRF

To cavity

55