The 21th KEKB Accelerator Review Committee (2016.06.13)

Operation Status of
RF System
T. Kobayashi from SKB RF Team1

Outline
1. Introduction
2. Beam Operation Status
3. Status of High Power RF System (Kly, KPS, WG)
4. Status of Low Level RF Control System
5. Bunch Gap Transient Effect on Beam Phase (as a future issue)
6. Summary

Following talks:•Superconducting Cavity (M. Nishiwaki)•ARES -Normal Conducting- Cavity (T. Abe)

2

ARES

T. Abe@Oho, Fuji

Cavity Types

SCC

M. Nishiwaki@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. Abeconsists ofl HOM-damped accelerating cavity (A-cav),l Energy-storage cavity with TE013 (S-cav),(C-cav)l Coupling cavity
with a parasitic-mode damper.

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

Input Coupling Factor(Qext~50000) not changed

PHOM = 19 kW
Tested up to 19 kW.

58

Needs to be renewedsince some major parts
not available.
K. Akai et al. / Nuclear Instruments
and Methstraight section. The maximum current of HER
PHOM = 26 kW
has reached 870 mA so far.
Tested up to 26 kW.

7.2. Design and performance of cavity and its
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
surfacetreatmentusing electropolishing was alVc = 1.5
MV, Pbeam= 400 kW /cavity
most the same as that of the TRISTAN cavities.
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

ARES parameters
fRF

508MHzUs / Ua

9

R/Q0

15Ω

Q0

1.1 x 105

Vc

0.5 MVPc

150 kW

Table 6
Cavity parameters of the KEKB Superconducting cavity

for the π/2 mode

60 kW (A) + 90 kW (S)Frequency
Gap length
Diameter of aperture
R=Q
Geometrical factor
Esp =Eacc
Hsp =Eacc

Basically, KEKB RF systems are reused with reinforcement for SuperKEKB.

508.8
243
220
93
251
1.84
40.3

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

3

D

Intro.: RF System Arrangement (ultimate)
OHO

D4
1

C

e+: 8.0Gev x 1.4A

2

B

A

B

FUJI

D7

D5
2

1

C E

E

2

A

K. Akai

KEKB)RF
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

e-: 3.5Gev x 1.8A LERBeam Power/Cavity: ~200kW

SuperKEKB)RF,,(ul/mate)

Drive Power/cavity:
add050klystrons,0HP&LL0 ~350kW
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

add020klystrons,0HP&LL0
add020power0supplies

2

D

2

C

Max. RF Power Config.

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).
• increase and reinforce WG systems.
➡ Upgrade of input coupler for the ARES (up to β~6, 800-kW input power capable)➡ Addition of new HOM Damper for the SCC as a measure against beam-induced HOM-power rising.
4

RF System Arrangement for Phase-I
Reported ’15

Illustrated by T. Kageyama

KEKB

SuperKEKB (Phase 1)@D4
added 3 KLYs &added 3 new LLRFs@D5
added 2 KLYs &replaced all LLRFs

Relocation of ARES cavity from KEKB configuration for Phase-1• Oho D4: Two cavities were added.
• Oho D5: All six cavities were moved from HER to LER. → 1:1 config.

• Fuji D7: Two cavities were removed.
• Fuji D8: Two cavities were removed.

5

History of Start-up Work 2015
JFY201512

3

4

JFY2016
5

6

7

8

9

10

11

12

1

2

3

4

5

6

Acc. Operation
Last KEKB Review

Beam Operation

MR RF System Work
Wave Guide Connection
High Power Component & Cooling System Maintenance & Overhaul

LLRF StartUp Tuning
Klystron Aging& Cont. Tuning
ARES Cavity 10kW Operation& Control Calibration& Cavity Phase Adj.
ARES Cavity Aging
SCC Coupler Aging
SCC Aging& Control Calibration

Maintenance work, start-up tuning, system calibration and cavity conditioning were
progressed successfully in 2015.
6

Successful First Storage by RF-Power On
After Injection, BT and Optics Tuning
LER 10th Feb. 2016
with D7A~E (ARES, D7 all)powered-on & RF phase tuning

LER: 1st stored beam

HER

26th Feb. 2016

with D10A~D (SCC, D10 All) cavities
powered-on & RF phase tuning

HER: 1st stored beam

7

History of Ring Acc. Voltage (Total Vc)
Beam Current(LER, HER)HER Total Vc[MV]

LER Total Vc

RF Power - On
& Phase Tuning

2/26 HER
1st Storage

RF Power - On
& Phase Tuningµ=-1 mode damper
applied for HER

2/10 LER
1st Storage

Vc Up

Vc Up

[MV]

5/28
D10C
Piezo
Ins. DB+D4, +D11

Vc Up+D5,+D8
Only
D10

Only
D7

3/10
D10D
Piezo
Ins. DB

3/31
D10C
Piezo
Ins. DB

4/21
D7C
KPS
Trouble

5/6
D11A
Piezo
Ins. DB

5/24
D7D
Circulator
TroubleCommissioningStart

RF system has been providing sufficient acc. voltage without critical trouble.
Piezo insulation breakdowns (BD’s) occurred frequently in SCC stations. The BD piezo’s ware
replace with a spare, or otherwise, the SC-cavity tuning is controlled by only motorized mechanicaltuner without piezo. If no piezo control, the tuning phase stability degrades to be about ±2 degrees.

Refer Nishiwaki’s report for the detail.

8

Present Status of RF System
Basically, the RF systems are working well, and very stable now.
RF trip frequency is enough low in the present stage.
Cav. Trip Rate
State of 06/06 for example

ARES: ~1 /30 cavs./week
SCC: <1 /8 cavs./week

ARES
Saving the electricity cost

LER
H
D

D04

D11
A

Circulator Water Leak

A

D05

A

A

D10

D

910mA

A D07

F
E

D08

Cav. Vacuum Trouble

HER
Piezo Break Down

C

E

A

In the several stations (D5A,D5B, D7D,
D8D, D10A), the cavities are powered-off
and detuned to put out of operation forsome reasons.

RecoveredPresent state, D10A is recovered without piezo control.
830mA

SCC

Operation power of the klystron is still far
from the saturation. There is enoughmargin in the klystron performance.
9µ=-1 & -2 Mode Osc. due to Detuned Cavity(Power-off)
Even though the beam current was low, coupled bunch instability (longitudinal bunch oscillation) of theµ=-1 or -2 mode was occasionally induced by the detuned cavities (both of ARES and SCC), whichwere powered-off and put out of the operation because of trouble or saving cost, In that case, thetuner position of the detuned cavity had to be adjusted to reduce the instability.
Example of µ=-2 mode instability by a detuned ARES Cavity

frf − 2 frev
Before the tuner position
adjustment

After the tuner position
adjustment

frf − 2 frev + fs

frf = 508.877MHz
frev ~ 100kHz

10

The µ=-1 Mode Damper Applied for HER
In HER, over the 470-mA beam current, the µ=-1 mode instability due to the detuned (troubled)
cavities could not be suppressed by the tuner adjustment.Consequently, the -1 mode damper
system, which had been used in KEKB operation, was applied to the D4 station.
It worked well to suppress the µ=-1 mode successfully and the beam current could be increased.

HER: Ib ~ 470mA
Without µ=-1 mode damper

frf − frev + fs

frf − frev

Predicted threshold current of the µ=-1 mode instability due to the acc. mode : ~1.1A (HER)~1.6A (LER)
At an earlier stage than expected, the µ=-1 mode damper became required.

Single Sideband Filterµ=-1 mode damper ON

Digital Filter
The µ=-1 mode digital feedback selectively reduces impedance at the driving frequency.

For the µ-2 mode,
The predicted threshold current of the µ=-2 mode instability due to the acc. mode is near the design current value of SuperKEKB (Ref.
the 16th review committee). Therefore, the µ=-2 mode damper system is necessary for Phase-2.
New digital feed back system of the µ=-2 mode damper is now under development for Phase-2. It will be also available for the µ=-3 mode.
The µ=-2 and -3 mode damper is no less required for the suppression of the instability due to the detuned (power-off) cavities.

11

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.

12<Topic>

HPRF

Status of High Power RF System‣ Klystron• 30 Klystrons are operated smoothly without troubles.

Klystron Cooling
System‣ Klystron Power Supply (KPS)• The KPSs are also operated without serious trouble‣ High-power components (Waveguides, circulators and dummy loads)• The high power components are enough sound and stable without big
troubles except for the circulator water leak at D7D station.

‣ Cooling systems (for the Klystrons and the dummy loads)• Water leak troubles are happened due to the aging degradation ofcomponents. (**Many components of the cooling systems have been used

Air Cooled Heat
Exchanger

since the TRISTAN operation. **)• These components will be changed to new one or repaired as soon as
possible when the water leak is found.

13

<Topic>

HPRF

DR Status of HPRF System
The construction of high-power RF system for DR was started from October 2015.
The high power test without cavity is scheduled in winter 2016.

‣ Klystron• Klystron setup : finished. Fig. a

Cooling system(It was moved from D11-E to DR at Jan 2016)

Klystron‣ Klystron Power Supply (KPS)• Type-B KPS setup: finished. Fig. a

KPS

Vertical throughhole to tunnel(It was moved from D4 to DR at Dec 2015,
and the control console for KPS was renewed to new one.)‣ High Power Components• Connection of waveguide system: finished. Fig. a, b
• Construction of a stage for vapor cooling system: finished. Fig. c

Circulator

Fig. a‣ Current Works for the High Power Test (Winter 2016)• Construction of the vapor cooling system.
• Installation of the water cooling pipes.
• Wiring of the power and control cables.

stage for vapor cooling system

Details about DR cavity system are presented by T. Abe.

Fig. b

Fig. c14

<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.

15

<Topic>

LLRF

Status of new LLRF System@OHO D4 Control Room
Old systems

SCC

3 new LLRF
systems

KLY+LLRF

ARES+@OHO D5 Control Room

6 new LLRF
systems
Integrated Vacuum control system

Status@DR Control Room

• At 9 stations of Oho D4&D5 (6@D5 + 3@D4) , the LLRF control systems were replaced with new digital control systems.
• Vacuum gate-valve control-integration system at OHO RF section is also upgraded to make matching with the new digital LLRF systems for flexibility
and convenience. Details are presented by M. Nishiwaki.

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

The DR-LLRF control system has already installed in DR control room. It is almost the same as MR one, except 3-cavity vector-sum control isneeded. In the present stage, the number of cavities is two.

16

<Topic>

Existing Analog LLRF System

LLRF

Most stations are still operated by existing old 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

49

Low-level RF for KEKB Superconducting cavity

Block Diagram of SCC LLRF
interlocks

from RFreference line

Phase Lock Loop
combiner for klystron

klystron circulator

Fig. 2. RF station for the SCC cavities.

Tuning Control Loop

S-cav

SW
out

FBC
ref.

out

FBC

FBC

FB

φ det.

ref.

FB

ref.

DL

FB

φ det.

FBC
FB

Gain Control
for klystronout

klystron out

FBC
Vc setTuner
Controller

ARES Tuner Control
Configuration

tuner

c-damper(RF ON)

cavityDirect RF Feedback
SW

Amplitude Control for Vc

pick up (Vc)

beam signal

A-cav

s-tuner

BPF

beam

FB

coupling
accelerating
cavitycavitystorage cavity

out

ref.
offsetRF input

φ det.

BPF

out

a-tuner
BPF

BPF

BPF

φsg
φsb

φac

(RF OFF)for ALC and PLL

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 aaway from frf : It is done by controlling the storage
cavity tuner according to the relative phasebetween the beam signal and the beam-induced
voltage. When the cavity trips, the reference signal
for the energy-storage cavity is switched from theincident 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 as well as operated in the KEKB operation without serious troubles,
3.3. Protection against trips

however, many old defective modules were replaced with spares in the maintenance works.

3.3.1. Trips and recovery

17

<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)18

Bunch Gap Transient Effecton Beam Phase
T. Kobayashi and K. Akai, Phys. Rev. Accel. Beams 19, 062001 (2016)
Published 9 June 201619

Simulation of Bunch Gap Transient Effect
New time domain simulation code was created to estimate the transient loading in ARES.
TABLE
II. KEKBof
operation
parameters usedsystem
for the simulationof the observed
condition.
Observed
beam phase in KEKB operation
This simulation can calculates the RF time
evolution
the three-cavityof ARES.
HER(SCC/ARES)

Beam current [A]

0.66

0.47

Bunch gap length [%]1010Beam power/cavity [kW]68

165 / 72

RF voltage/cavity [MV]0.33

1.25 / 0.35

Number of cavity

16

6 / 10R/Q of cavity [Ω]14.8

93/14.8

Loaded Q of cavity [×104]

3.0

7.0/3.0

Coupling factor

2.7- /2.7

Wall loss/cavity [kW]100

Acc. phase φacc [deg]72Cavity detuning Δf [kHz]⎡ ARES)(A-CavV n ⎤ of−B ⋅V n ⎤0 ⎤ ⎡detuning

-8.1
(-81)

ARES Cavity (3-Cav. System)

Illustrated by T. Kageyama⎡ V n+1 ⎤ ⎡ Wa⎢ ar ⎥ ⎢⎢ Vajn+1 ⎥ ⎢ Da⎢
⎥ ⎢⎢ Vcrn+1 ⎥ ⎢ 0⎢ n+1 ⎥ = ⎢⎢ Vcj ⎥ ⎢ −K ac⎢ n+1 ⎥ ⎢⎢ Vsr ⎥ ⎢ 0⎢ n+1 ⎥ ⎢V0⎣⎢ sj ⎦⎥ ⎢⎣

−Da

0

K aa

0

Wa

−K aa

0

0

K ac

Wc

−Dc

0

0

Dc

Wc

−K sc

0

0

K ss

Ws

0

−K ss

0

Ds

ωµ
⎧
⎪ Δω µ = ω µ − ω rf , ω µ /2 = 2Q ,µ⎪⎪ G = 2 β Δt ⋅ ω , C = β , B = Δt ⋅ ω ,
s
s/2
s
a/2
⎪
⎪ Wa = 1− Δt ⋅ ω a/2 , Wc = 1− Δt ⋅ ω c/2 ,⎨⎪ Ws = 1− ( β s + 1) ⋅ Δt ⋅ ω s/2 , Dµ = Δt ⋅ Δω µ ,⎪kk ⋅ Δt ⋅ ω ν⎪ K µν = µ ⋅ Δt ⋅ ω ν /2 ⋅Qν = µ,
2
4⎪⎪ µ,ν : a, c, s,⎩

Beam Phase [deg.]

LER(ARES)

LER: 660mA

Measured Beam Phase
Simulation
Simulation (old)- /105
With including
the three-cavity structure of ARES in the calculation, therapid phasechangeat the leading part of the bunch train can be
74 / 64(*)
FIG.
6.
Comparisonof the resultof the new
simulation
fortheLER rapid(dashedphase
red line) withthe observe
reproduced by the simulation.
It wasclarifiedthatchange-9.5 / the-5.1 parasitic (0&pi) mode of ARES.
is attributed
datato(dots)
and the previous simulation (solid black line). The observed data and the previobr⎥ ⎢ ar ⎥ ⎢
⎥
n ⎥
n ⎥
⎥
⎢
⎢
Input
coupling
β
2.7
0
Vaj
−B ⋅Vbj⎥⎢⎥⎢⎥(*) Synchronous
phase of HER: 71 degrees
K sc ⎥ ⎢ Vcrn ⎥ ⎢⎥0⎥⎢ n ⎥ + ⎢⎥0 ⎥ ⎢ Vcj ⎥ ⎢0⎥⎥⎢ n ⎥ ⎢⎥−Ds ⎥ ⎢ Vsr ⎥ ⎢ G ⋅Vgrn ⎥⎥⎢⎥ ⎢⎥Ws ⎥ ⎢ Vsjn ⎥ ⎢ G ⋅Vgjn ⎥TABLE
used for the simulation.
⎦ ⎣ cavity parameters⎦⎦ ⎣III. ARES

Q-value of A-cavity (Qa)26000

Q-value of C-cavity (Qc)100

Q-value of S-cavity (Qs)

180000

Coupling between A and C cavity (ka)5%

Coupling between S and C cavity (ks)

1.6%

(-51)

simulation- / 2.7 are replotted from Fig. 2-(a).

A-Cavity Phase measured by new LLRF Systemin this SuperKEKB commissioning@LER,D5F
Ib=840mA

Simulation result agrees well with the measurement.
The behavior of the phase ringing at the head of thebunch train depends strongly on Q-value of the coupling
cavity of ARES: Lager Q-value of C-cav. makes larger
phase ringing at the train head.

21

20

AI

(σ z ) is 5 mm (rms).

Bunch Gap Transientz

Estimation of BGT for Design Current

VI. MITIGATION OF THE RELATIVEPHASE DIFFERENCE BETWEENTHE TWO RINGS FOR SUPERKEKB

PHYS. REV. ACCEL. BEAMS 19, 000000 (XXXX)LER: Ib=3.6 A
HER: Ib=2.6 A

In the KEKB operation, no degradation was observed ofthe luminosity due to the bunch gap transient. However, in
the SuperKEKB
operation,
the beam AKAI
phase difference at the
TETSUYA KOBAYASHI and KAZUNORI AKAI
PHYS. REV. ACCEL. BEAMS 19, 000000 (XXXX) TETSUYAKOBAYASHI
and KAZUNORI
Vector-Sum
of ARES and SCC PHYS. R
Parameter
LER
HER
leading part of the train due to the gap transient will become
Beam energy [GeV]47much larger than that of KEKB, as presented !ðΔϕin theHER −Δ
Beam current [A]
3.6
2.6
previous section. Because the crossing angle between
the theexcludingBunch gap length [%]220.125-degree
two beams at the collision point is larger in SuperKEKB
displacement
Beam power [MW]88.3%
and the vertical beta function (βy ) is much smaller thanfor(σ z ) is 5 mm
Bunch length [mm] (rms)65
KEKB, the effect of the large phase difference at the
F11:1
FIG. 11. Phase modulation of the vector sum of ARES and SCC
RF frequency [MHz]508.887
leading part of the train of the colliding beams might be a
VI. M
F11:2
voltage simulated for HER.
Harmonic number
5120
crucial issue to achieve high luminosity. Beam blowup or PHA
2.5 deg.
Revolution frequency [kHz]99.4
even beam loss might happen in the worst-case scenario. InTHE
2.0deg.
Cavity type
ARES
SCC/ARES
the future, a detail study of this effect from the point ofInview
the KEK
From the simulation results shown in Figs. 7–11, the484
Number ofdue
cavities
8/8 arephase (right) modulation
to the 2% bunch gap in22
ARES. The calculationsof beam-beam interactions is needed for the SuperKEKB
theluminosity
rapid phase change in the leading part of the bunch train
485
Total RF voltage [MV]
10~11
15~16
operation. We also propose measures to mitigate thethephase
SuperKEK
due
to
the
bunch
gap
will
be
significantly
largerin486
4
Loaded Q of cavity [×10 ]2.4
7.0/2.0
difference between the colliding beams as a cureleading
if thepart ofSuperKEKB. Figure 12 shows the phase difference487
ds on thestored beam
currents
will be approximately
twice as- /5high as440
much larger
Coupling
factor(β)
4.3
beam-beam interaction effect turns out to be critical.
t with thethose in KEKB operation were (LER 2 A and HER 1.4 A).
441
between
LER
and
HER
(Δϕ
−
Δϕ
),
obtainedfrom488
previous secti
HER
LER
RF voltage/cavity [MV]0.48
1.5/0.5
oncluded
The beam power per cavity will be more than twice as high442
two beams at
Figs. 7 and 11. In the figure, the solid red line indicates the489
Wallloss/cavity[kW] were. Therefore,140- /150he train isas thoseof KEKB
the input-coupling443
and the vertica
A. Gap delay for the mitigation of the phase difference
relative phase. A plot zoomed in around the gap is
490
Beam
[kW]
400/600
ations, or
factorpower/cavityof the ARES
cavity should460
be increased anda larger
444
KEKB, the epresented
in duethe toright
side
plot
of
Fig. 12.
As seenF11:1
in
491 (right)
FIG. The
11. Phasemodulation of method
the vector sumof ARESmaking
and SCC a delay
first
mitigationissimplyF7:1
FIG.
7.
Simulation
resultsoftheamplitude(left)
andphase
modulation
the
2%
bunch
gap
in
ARES.
The
calculationsare
ES cavity.
cavitydetuning
willberequired
for
the
beam
loading445
leadingofpart oCavity detuning [kHz]-28-18/-44
F11:2
voltagesimulatedfor
HER.
the figure, the maximum phase difference will be
492
F7:2
done On
for LERat SuperKEKB.
the HER gap timing with respect to the LER gap at thecostissue twith thecompensation.
the otherhand, the length of the bunch446
crucial(A-Cav detuning of ARES)(-280)(-180)
by about
gap will be reduced from 5% of the ring in KEKB to 2% of
447
5.5 degrees at the leading bunches. Besides the leading
493
eventhisbeam losof a reduced number of colliding bunches. With
Number18
8/8of theconsistent
the ringofinklystrons
SuperKEKB by improving
the rise time448
thefuture,bunches,thephasedifference
along
the
train
is
not
so
large.
494
method,collisionis shown
avoidedfor theleadingpart of a deFrom the thesimulation
results
in Figs.
7–11,
the
484as
of ARES.
stored beam currents will be approximately twice asHER
high
407 kicker.
440
Klystron
power[kW] The ringing~600duration definitely~450/~800 depends
ent cause
abort
449 on theofbeam-beam
LER
495
The relativephase
at theinteraction
bethe
LER change
train inthat
has thepartlargechange.
the leadingof therapid
bunch phasetrain
ofsimulation
the C-cavity), andit is consistent
those inRelative
KEKBshiftoperation
were(LER 2 point
A and(IP)HERwill
1.4485A). rapid
408
441 phase
Figure Q-value
7 shows theresult(Qofctheamplitude
andour new
Phase
450with thetween thecaused by
cts in theam phasenstability
so called
d by thisoperation.
a point at
rom otherat bucket
ment thisef. [12]).
physicalNSIENT

unch gap
g the new
ed for the
EKB, theGap 2% (200ns)

LER

HER

Δφ

filling time
the C-cavity.
Consequently,
concluded
409 modulation
phasein theofARES
cavity causedby the bunchit is 451

− Δφ

486
The beam power per cavity will be more than twice as high487
as those of KEKB were. Therefore, the input-coupling488
factor of the ARES cavity should be increased and a larger
489
cavity detuning will be required for the beam loading
490
compensation. On the other hand, the length of the bunch491
gap will be reduced from 5% of the ring in KEKB to 2%
492of
the ring in SuperKEKB by improving the rise time of493
the494
abort kicker.
Figure 7 shows the simulation result of the amplitude 495
andphase modulation in the ARES cavity caused by the bunchthat the rapid phase change in the leading part of the train is410
attributed to parasitic mode (0 and π mode) excitations, or411
in other words, the mode dispersion in the ARES cavity.
412
The ringing of the phase corresponds to a beat with the413
0 or π mode, the frequency of which is separated by about414
3 MHz from the π=2 mode [4]; the beat period is consistent415
with the 3-MHz mode separation. Thus, the apparent cause416
of the rapid phase change is demonstrated by our new
417
6.5 deg.
418
simulation.
In Fig. 6, there still appear slight differences between the419
measurement and the simulation, which may be caused by420
some other effects. One of the possible other effects in the421data that are not captured in the model is beam phase422
oscillation due to longitudinal coupled-bunch instability
423
associated with the detuning of the cavities (so called424
μ ¼ −1 mode). Actually, the oscillation caused by this425
instability was often observed during the KEKB operation.
426
Another point is that in the measurement one data point at427
the bucket ID about of 400 significantly deviates from other
428
FIG.
8.
A
plotpoints.
of the simulated
phase
in data
F8:1
data
The reason
ofmodulation
the outliershownof theat bucket
429
F12:1
FIG. 12.
Fig. 7, enlarged to show the empty gap region.
F8:2
ID of about 400 is not clear. In another measurement this430

Phase (zoomed)Δ

due
442to the bunch gap will be significantly larger inSuperKEKB.
Figure 12 shows the phase difference443
between LER and HER (ΔϕHER − ΔϕLER ), obtained from444
Figs. 7 and 11. In the figure, the solid red zoomedline indicates the
445 phase. A plot zoomed in around the gap isrelative446
presented
in the right side plot of Fig. 12. As seen in447
the figure, the maximum phase difference will be
5.5448degrees at the leading bunches. Besides the leading
bunches,
the phase difference along the train is not so large.
449
The
relativephase shift at the interaction point (IP) will be
450

operation. We
difference bet
beam-beam in

A. Gap delay

The first m
the HER gap tof a reduced
method, the cthe LER trai

451

0.9 deg.

5.5-> Displacement@IP : 0.44 σz in around
Plot of the phase difference between LER and HER (red solid line ¼
Δϕdeg.
HER − ΔϕLER ). The right side is zoomed21disaster of beam performance deterioration due to aaberrant beam-beam interaction caused by the large relati
phase difference in the colliding bunches could be avoidewith this method.

Measures to reduce phase difference (1)B. Varying bunch currents at the leading
bunches with gap delay

Considering that the phase change due to the BGT effect will be critical for the high luminosity,
For further mitigation, we also investigated a measur
F13:1
FIG. 13. Phase difference between LER and HER (red solidmeasures are proposed to mitigate the phasedifference
betweenthecolliding
beams
as
awith
cure.
F13:2
line) for a HER gap delay of 200 ns. The phase difference at thementa changing bunch fill pattern. We assume that th
F13:3

leading part of the train is reduced to 2.4 degrees for the collision.

bunch current in the main part of the train is set at th
maximum allowed bunch current from the viewpoints
As a simple method, making a delay of the HER gap timing with respect to the LER
is considered
optics,gap
dynamic
aperture, beam-beam, etc., and that n
Figure 13 shows the phase difference when the HER gap is
527
bunch
current
can
exceed this value. Then, in the followinat the cost of a reduction of number of colliding
bunches.
being delayed by a gap length of 200 ns. In this case, the528
we consider only the reduction of the bunch current fro
phase difference between the two beams is reduced to529
this nominal (¼maximum allowed) value. By appropriate
2.4 degrees at the leading part of the colliding bunches,
530
adjusting the bunch current at the leading part of the trai
while
the
phase
difference
in
the
other
part
of
the
train
531
the ringing
behavior in the rapid phase change can b
ADVANCEDSIMULATIONON BUNCH
PHYS. REV. ACCEL. BEAMS 19, 000000(XXXX)
Case of making
200-ns.STUDY
gap delayin HERGAP …
along the revolution period is similar to the case of no532
mitigated. For example, by gradually increasing the bunc
delay. As another example, we evaluated a 3% gap in both533
current as a function of bunch number from the start bunc
of by
3%
gap
and
gap
delay
rings with
the HERCase
gap
delayeda gap
lengthof 300300-ns.
ns.
difference
between
the
two
beams
almostatthe534
537 period (∼300 ns) we cou
upcancels
to HERa few cyclesof theringing
Here, thesame bunch
as for14,
the 2%
gap.However,535
reduce theringingmagnitude.
leading
partcurrentof theis assumed
train (Fig.
left).
thephase
538Various fill patterns inclu
536
The result is shown in Fig. 14. In this case, the phaseing the above one can be attempted to search for the be

Δφ HER − Δφ LER

F13:1
F13:2
F13:3

527
528

F14:1
F14:2

difference along the entire bunch train in the revolution
period is increased to 1.6 degrees (Fig. 14, right), whichcomes from the increased gap length, as envisaged from
Eq. (1). These results are summarized in Table V. The
number of colliding bunches is reduced by 2% (2% gap
with 200-ns delay) or 4% (3% gap with 300-ns delay)
compared to the original fill pattern (2% gap, no delay).
Although the reduced number of colliding bunches results
in a luminosity reduction by the same amount, the possible
disaster of beam performance deterioration due to an
aberrant beam-beam interaction caused by the large relative
phase difference in the colliding bunches could be avoided
with this method.

539
540
541
542
543
544
545
546
547
548
549
550
551

B. Varying bunch currents at the leading
552
FIG. 14. Phase difference for bunches
a 3% gap withwith
HER gap
delay.
The phase difference at the leading part
gap
delay
553of the train is almost cancele
while the phase difference of the other part in the train increased to 1.6 degrees.

For further
mitigation,
we alsoinvestigatedmeasureFIG. 13. Phase difference between LER and HER (red solid
In this case,the phasedifference
betweena thetwo beams554
almost cancels
In this case, the collision avoids the largest rapid phase change atline) for a HER gap delay of 200 ns. The phase difference at thement withachanging
bunch
fill
pattern.
We
assume
that
the
555
11
at the leading part of the train. However,the phase difference along thethe
LER part
leadingThen,the degrees
phase fordifference
for theleadingof the bunches.
train is reduced
to 2.4the collision.
bunch current in the main part of the train is set at the556

entire bunch train in the revolution period is increased to 1.6 degrees fromcollision is reduced to 2.4 degrees from 5.5 for the collision.
maximum allowed bunch current from the viewpoints of557
no-delay case.
However, colliding bunches is reduced to 4% bunch gap equivalent. optics, thedynamic aperture, beam-beam, etc., and that no558

Figure 13 shows the phase difference when the HER gap isbeing delayed by a gap length of 200 ns. In this case, thebunch current can exceed this value. Then, in the following,
we consider only the reduction of the bunch current from

559
560

22

TABLE V.

Effects of the proposed mitigation methods on reducing the phase difference between colliding beams.

Figure w
15s shows
patterneters
and thedg fillwith
a considered
step of here.
10 Thensbunch current at the leading part of the LER train i
guidelines were used: (1) the phase chang
Longitudinalincreased in two steps with a time interval ws and the firs
(jΔϕHER − ΔϕLER j) [degrees]
displacement
Bunch
HER
Rate of num. of
andbunchsecondstepshouldcancelareeac
stepcurrent
increaseof bs .mostly
The gap lengths
gL
Methodgap
delay
Leading part The rest of train @IP (σ z ¼ 5 mm) colliding bunches
andgH for LER
respectively, and the HER gap i
secondstepand(wHER,
s should be about half of thedelayed
by
d
.
The
gap
lengths are set to 2%g"""2%
no delay
5.5
0.9
0.44 σ z
and
(2)
the
LER
phase
ringing
after the
se
As
a
next
method,changing
the
bunch
fill
patternofLER
isinvestigatedforthemitigation.
(g
¼
g
¼
200
ns),
which
is
the minimum
lengthLH2%
2% (200 ns)
2.4
0.9
0.19 σ z−2%
HER gap delay
be synchronized
HER
phase
chan
requiredfrom the risewith
time theof theabort
kicker.
Fo3%
3% (300 ns)
1.6
0.13 σ zfill pattern for−4%
F15:1 <0.2
FIG. 15. Illustrationof a bunch
more effective
simplicity,
b
is
set
to
half
of
the
nominalbunch
currents HER train. The best result was opart of the
LER 2 steps þHER gap delay2%
160 ns F15:2 0.4
0.5bunch current0.07
σ z leading part−1.6%
mitigation. The
at theof the LER train
The simulations were performed by changing the paramand w160
ns forphasew andringing
d , respectively.
LER bunch train is filled up in two
steps
F15:3
is increased in twotime interval
Thesteps
HERwithgapadelay(gH) is w
decidedsynchronize
theLER
with the Th
eterss and thetobunchs and dg with sa step ofg 10 ns. The following
F15:4
current
at thestepphaseby bstrain.change.
Thecombined
gap Thelengths
gLof
and
for
were The
used: (1)the phasechanges dueto the firs
in
16.
phase
difference
betweenwith
HERofgap
delay.
result. From theviewpoint
practical
beam operation,
leading
partfirst
of
the
LER
witharethe
HER
573stepguidelines
HER
interval
thegHfirst(wFig.
s) was optimized to mostly cancel
andsecondstepshouldmostlycanceleach
other
after the
HER, respectively, and the HER gap is delayed by d574
F15:5
g.
significantly
reducedto0.4
degreesat thhowever, a simpler fill pattern would be favored.
Con- LER
gapanddelay.
the phase change each other after the second step.
second step (ws should be about half of the ringing period)
sequently,
we investigate
the caseof increasea simple fill(bs) Figure 15 shows the fill pattern considered here. The
575
For
the simplest
case,below
the firststep
and (2) the LER phase ringing after the second step should
bunch current at the leading part of the LER train is
with
only
of bunchcurrentcurrent.
increase at the576
ispattern
set tohalf
oftwo
thesteps
nominalbunch
be synchronized with the HER phase change at the leading
F15:1
FIG. 15. Illustration of a bunch fill pattern for more effective
increasedF15:2
in twomitigation.
steps withatimeinterval
w
and
the
first
part of the HER train. The best result was obtained with 140577s
The bunch current at the leading
part of the LER train
and 160 ns for ws and dg , respectively. The result is shown
F15:3
is increasedin twowith gapa timeinterval are
ws andstep bunch
current
increaseof bsteps
lengths
gL the bunch578
s . The
H=160ns
F15:4
current
at
the
first
step
by
b
.
The
gap
lengths
are
g
and
g
for
in Fig.g16.
The phase difference between LER and HER is
LHand gH for LER and HER, respectively, and the HER gap is579
LER and HER, respectively, and the HER gap is delayed by dg.
F15:5
significantly
reduced to 0.4 degrees at the leading part o
ws=140ns
delayed by dg. The gap lengths are set to 2%580(gL ¼ gH ¼ 200 ns), which is the minimum length581
required from the rise time of the abort kicker. For
582
simplicity, bs is set to half of the nominal bunch current.
583
The simulations were performed by changing the param584
eters ws and dg with a step of 10 ns. The following
585
guidelines were used: (1) the phase changes due to the first586
and second step should mostly cancel each other after the587
second step (ws should be about half of the ringing period),
588
571
572
Phase difference

sequently, we investigate below the case of a simple fillpattern with only two steps of bunch current increase at the

Measures to reduce phase difference (2)
569
570
571
572

and (2) the LER phase ringing after the second step should
be synchronized with the HER phase change at the leading
F15:1
FIG. 15. Illustration of a bunch fill pattern for more effective
Then,
the
HER
gap
delay
and
the
time
intervalofthepart of the HER train. The best result was obtained with 140
F15:2
mitigation. The bunch current at the leading part of the LER train
first
step
(w
)
are
parameterstobe
optimized.
sand 160 ns for ws and dg , respectively. The result is shown
F15:3
is increased in two steps with a time interval ws and the bunch
F15:4
current at the first step by bs. The gap lengths are gL and gH forin Fig. 16. The phase difference between LER and HER is
TABLE
V.
Effects
the proposed
mitigation
methods
on reducing
the byphase
betweenLER
and of
HER,
respectively,
and theHER gap
is delayed
dg. difference
F15:5
significantly reduced to 0.4 degrees at the leading part of

589
590
591
592
593
594

colliding beams.

Summary of effects of the proposed mitigation methods.
MethodHER gapdelay

LER 2 steps+
HER gapdelay

Phase difference (|ΔφHER-ΔφLER|)[degrees]

Longitudinal
Rate of num.
F16:1
FIG. 16. Simulation result of phase difference for the best case of the fill pattern shown in Fig. 15. The gap length of both rings is 2%
displacement@IPofcolliding
F16:2(200Asns),
thecurrentheightdifference
atthe
the initial
step
the
LER
(bs ) fillis halfofthe nominal
current,
the lengthof thegap
initiallength
step (ws
F16:1
FIG. 16. Simulation
resultof result,phase
forofthebestleadingcase partof
thepatternshown
in Fig.
15. Thethephasedifference
between
two
rings
is
significantly
bunches
The rest of train(σz = 5 mm)
is 140 ns and the delay of the HER gap (d ) is 160 ns.
F16:3

Bunch
gap

HER delay2%

no delay

5.5

0.9

2%

2% (200 ns)

2.4

0.9

0.19 σz-2%

3%

3% (300 ns)

< 0.2

1.6

0.13 σz-4%2%160 ns0.4

0.5

0.07 σz-1.6%

Leading partgLER leading part (b ) is half of the nominal current, the length of
F16:2(200 ns), the current heightat theinitialstep of thes the collision, while the entire
reducedto0.4
degreesatthe leading part of0.44
σz
is 140 ns and the delay of the HER gap (dg ) is 160 ns.
F16:3

phase difference along the train is kept sufficiently
small.
12

The LER fill pattern change with a HER gap delay gives a more
effective mitigation compared with only the gap delay cases.

It is an example of certain conditions. 12
In reality, the optimization depends on strongly operation conditions.
The operation conditions will be optimized for the luminosity in future
SuperKEKB.
The best optimization for the fill pattern and gap delay will be
investigated based on the best operation conditions.

23

Summary• RF system has been successfully operated without fatal problem, except
several stations are powered off and put out of operation for variety reasons.
Many old components and modules were repaired or replaced with spares• Newly developed digital LLRF control systems are applied to 9 stations at
OHO section, and successfully working.

• Th µ=-1 mode damper is applied to HER, and the coupled bunch instability
due to detuned cavities is suppressed successfully. The µ=-2 mode damper
system is now under development for Phase-2.

• Phase modulation due to bunch gap transient effect will be be too large at
the leading part of the bunch train for design beam current.
--> Simulation study proposes the measures to mitigate the phase difference:
the relative phase change at the IP can be reduced by optimization of thegap delay and bunch fill pattern of LER.
24

Tank youfor your attention!

25

Backup Slides

26

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.
Reinforce and reconfiguration of RF system is required.
27

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.
28

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

29

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

30

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

31

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

32

CBI due to the Accelerating Mode (π/2)
T. Kageyama, 2011.02

10µ = -1µ = -2µ =- 3Rad. damping time

Growth Time [s]

1

0.1

0.01
SuperKeKB LER

0.001

22 x ARES (0.48 MV, β = 5)

τ (-1 mode) = 4 ms for 3.6 A
0.0001
0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Beam Current [A]33Response Property -Klystron Bandwidth(open loop)

Measured Result
Amplitude @dBD
10

10k

100k

Magnitude

1M

Frequency @HzD

Modulation Frequency [Hz]Td : Delay

Magnitude [dB]0fitting curve with

H kly [s] =

-10

-20

1
1+ s / ω kly + s 2 / αωkly=130 kHz

Phase

Td=650ns
α=2.1x1012-30

Phase@deg.D
180i e− s⋅Td

10k

100k

1M

Frequency @HzD
Phase@deg.D
180

10k

100k

1M

Frequency @H

Phase [deg.]

90
90

0

-90

Phase（delay=0）

0

-90

-180

-180

34
31

Disturbance Rejection Characteristics
x

fN

+
+

KLY

Delay

PI-cont+

CavityDelayin the closed loopyy=H[s]•x

Ref.
Amplitude @dBD
Magnitude
(h11)
10
0

1k

Calculation & Measurement
10k

100k

Frequency @HzD

1M Phase@deg.D
180

OpenLoop

1k90Frequency

10k

100k

1M

10k

100k

1M

Phase

-10
-20

0

P20,I20-90-30

P8, I40-40

P20,I20-180

Phase@deg.D
180

P20,I801kFrequenc

90

-50

0

P8, I40-90

Sync. Osc.

fs

Revolution-18035