Injector RF and LLRF
Takako Miurafor the Linac RF GroupThe 23rd KEKB Accelerator Review Committee, July 8-10, 20191

List of Installation and Replacement
New Installations for SuperKEKB• Injector Master Oscillator Phase Shifter (HER/LER Injection Phase Control)• S-band Phase Shifter for DR Downstream (for Bucket Selection)• Phase Drift Compensation System between Linac MO and Ring MO• LLRF Control Unit (Amplitude/Phase Control, EVR, VSWR Meter)• RF monitor (AMP/Phase Detection, EVR) & Applications• Beam Induced RF Monitor• Klystron KL_DN/KL_DS Units• High Precision Pulse Modulator (installed in KL_A1A)
Replacement• SHB1 (114MHz) / SHB2 (571MHz) Solid State Amplifier(SSA) replacement to new one• RF Reference Signal Transfer Line : Coaxial Cable -> Phase Stabilized Optical Fiberto each sector• Seven pulse modulators were replaced to small inverter-type for making space2

List of Installation and Replacement
New Installations for SuperKEKB

Linac Reference RF Distribution System• Injector Master Oscillator Phase Shifter (HER/LER Injection Phase Control)• S-band Phase Shifter for DR Downstream (for Bucket Selection)• Phase Drift Compensation System between Linac MO and Ring MO• LLRF Control Unit (Amplitude/Phase Control, EVR, VSWR Meter)• RF monitor (AMP/Phase Detection, EVR) & Applications• Beam Induced RF Monitor• Klystron KL_DN/KL_DS Units

RF Monitor System• High Precision Pulse Modulator (installed in KL_A1A)
Replacement• SHB1 (114MHz) / SHB2 (571MHz) Solid State Amplifier(SSA) replacement to new one• RF Reference Signal Transfer Line : Coaxial Cable -> Phase Stabilized Optical Fiberto each sector• Seven pulse modulators were replaced to small inverter-type for making space3Linac Reference RF Distribution System
SuperKEKB Control Room

LINAC Main Station
LINAC-MO

Main MO

Sync
10MHz

571.2 MHz

1/51

1/51
510MHzMO Phase Shifter

φ1+φ2
Freq Multi/Div
Event
System114MHz2856
MHzPhase Shifter for DR

Master Oscillator Phase Shifter (MOPS) has been installed.
 RF phase for laser system is kept θHER.
 Linac RF phase is switched θHER /θLER

E/O
Sector3

571
MHz

EVR

Sector A/B/C/1/2/3
LLRF Cont Unit

571 MHz

Main Ring

Linac reference RF phase is changed to HER/LER
injection phases depending on the beam mode.
Laser system cannot accept such a high speed phase change.

LER: :θLER - θHER

φ 2 HER: 0

10.384 MHz
2856MHz

Sync
10MHz

508.9MHz

Injection phase
controller until Phase-I

φ 1 θHER
Freq Multi/Div

MR-MO

Sector4
O/E

O/E

Sector5
O/E

to RF Monitors

to RF Monitors

TD4V
Grid Pulser
Thermionic Gun

Laser
SystemSHB1 SHB2
KLY・・・・・・

RF
Gun
Sampling freq. for LLRF Control Unit, RF Monitor

DR

KLY

・・・・・・

LINAC

4

MO Phase Shifter (MOPS)
571.2 MHz

𝜙𝜙1

𝜙𝜙2 = 0 (HER, PF, PFAR)

𝜙𝜙2 = 𝜃𝜃𝐿𝐿𝐿𝐿𝐿𝐿 − 𝜃𝜃𝐻𝐻𝐻𝐻𝐻𝐻 (LER)
𝜙𝜙1 + 𝜙𝜙2

to Linacto Laser𝜙𝜙1 = 𝜃𝜃𝐻𝐻𝐻𝐻𝐻𝐻Specification of Phase Shifter

Phase Range
Resolution
Speed
LinearityMode-450.00 deg ~ + 450.00 deg
0.01 deg
1 deg/ms ~ 1000 deg/ms< 0.1 deg
High: LER / Low: HER

Phase change:
400deg → 0 deg @ 500 deg/ms

0.8 msIn the operation of SuperKEKB,
phase change speed :PS1 = 1 deg/ms
PS2 = 100 deg/ms
5Linac Reference RF Distribution System
SuperKEKB Control Room

LINAC Main Station
LINAC-MO

Main MO

Sync
10MHz

571.2 MHz

1/51

MR-MO
1/51

510MHzMO Phase Shifter

508.9MHzφ 1 θHER
Freq Multi/Div
10.384 MHz
2856MHzRF phase downstream of DR will be changed
for higher synchronization rate against MR bucket selection.
(Phase will be controlled by "bucket selection" and set by"EVG" for each pulse )φ1+φ2Freq Multi/Div
Event
System114MHz2856
MHzPhase Shifter for DR
E/O
Sector3

571
MHz

EVR

Sector A/B/C/1/2/3
LLRF Cont Unit

571 MHz

Main Ring

S-band phase shifter

LER: :θLER - θHER

φ 2 HER: 0

Sync
10MHz

Sector4
O/E

O/E

Sector5
O/E

to RF Monitors

to RF Monitors

TD4V
Grid Pulser
Thermionic Gun

Laser
SystemSHB1 SHB2
KLY・・・・・・

RF
Gun
Sampling freq. for LLRF Control Unit, RF Monitor

DR

KLY

・・・・・・

LINAC

6Test of S-band Phase Shifter
KBP phase was set by embedded-EVR via data-buffer of event record.
Phase was changed every 10 degree.

Phase Range : 0° - 400°
Resolution : 0.015°

0°

200°

RF

380°

test

LO

REF@sector2
RF monitor can detect phasedifference of Ref(LO) & RF.
RF is generated by using
Reference signal.
=> we cannot detectreference phase change.
By using upstream REF signal,
ref phase rotation can bedetected.

Monitored phase (deg)REF@sector3

KBE

KBP
390°

7

Reference RF Control Station
Thermostatic chamber : 28 ± 0.05 °C
Freq Mult/Div (#0)
MO Phase Shifter

Freq Mult/Div (#1)
Amplifiers

Reference Signal Generator(Frequency Multiplier/Divider)S-band Phase shifter(for sect.3- sect.5)

571.2 MHz

571.2 MHz

1/5

571 MHzphase det.
P/D

114.2 MHz

1/5

10.38 MHz

1/11

2856 MHz
VCO
2856 MHz
197 MHz

83 MHz3053 MHz
VCO

1/8
1/6

508.8 MHz

10.38 MHz
phase det.
P/D

Linac Master Oscillator
571.2 MHz

Sampling oscilloscope forphase monitoring of thereference signals

8

Block Diagram of MO Synchronization Systemlinac gallery

KEKB control room

510 MHz
1/51
10 MHzPSlinac MO
571.2 MHzNew

MOPS PS1

Phase Drift
Compensation System

PS2
REFSG1REFSG2

Laser
SystemGun Trigger
SystemRF GunThermionic Gun

MMO
510 MHz

PLL

O/E

10 MHzDR MO
508.9 MHz

MR MO
508.9 MHz

RF-Dist.&PLL

RF-Dist.&PLL

1/51

PS

372 m PSOF
PS

DR control roomDR

Injector linac

BCS

PS

PS

LER

HER

ECS

MR MO and DR MO phases have been locked by PLL.
 Linac MO phase had not been locked to Ring MO phase.
Phase monitor system for Linac MO (571.2 MHz) and Ring MO(508.9 MHz) was installed at Linac side.
The phase drift compensation system was also installed.
9Phase Drift between Linac MO & Ring MO
Linac MO & Ring MO phases are monitored with theclock based on Linac MO

This phase drift has strong correlation with Ring MO room
temperature (by T. Kobayashi)

Large phase drift between Linac MO and Ring MO Making BCS@RTL tuning difficult
BCS RF : 2856 MHz (Linac MO x 5)

 Drift of MR injection phase@571.2 MHz

10

Linac MO Phase Feedback
For the drift compensation between Linac MO & Ring MO,
Linac MO phase is changed to follow Ring MO phase by using MO Phase shifter.
Normalized to 571 MHz

5 deg∆PhaseLinac MO Phase
Ring MO PhaseFB ON@BCS arc

Slow drift wasdisappeared

11List of Installation and Replacement
New Installations for SuperKEKB

Linac Reference RF Control & Distribution System• Injector Master Oscillator Phase Shifter (HER/LER Injection Phase Control)• S-band Phase Shifter for DR Downstream (for Bucket Selection)• Phase Drift Compensation System between Linac MO and Ring MO• LLRF Control Unit (Amplitude/Phase Control, EVR, VSWR Meter)• RF monitor (AMP/Phase Detection, EVR) & Applications• Beam Induced RF Monitor• Klystron KL_DN/KL_DS Units

RF Monitor System• High Precision Pulse Modulator (installed in KL_A1A)
Replacement• SHB1 (114MHz) / SHB2 (571MHz) Solid State Amplifier(SSA) replacement to new one• RF Reference Signal Transfer Line : Coaxial Cable -> Phase Stabilized Optical Fiberto each sector• Seven pulse modulators were replaced to small inverter-type for making space

12

RF Monitor
RF monitors are installed for all RF sources (60 Klystron units & SHB1/SHB2)
Moni: 5 ch
Rep. rate: 50 Hz

Reference

KLY
SLED

Amplitude

KLY Pf
SLED Pf
Kly PfPb
Pf
Acc out

Phase(deg)"EVR" is built-in.
Identify the Event code & Shot ID

ACC timing

Stand-by timing

For each pulse, RF & BPM data can be linked by Shot ID

13

Short Term RF Stability
Measurement result of short-term KLYPF RF stabilities

Estimation of RF stability from KLY HV

Amplitude stability∆A/A(%)= 5/4 ∆V/V(%)= 0.063% rms

Amplitude

KLY HV stability：0.3% pk-pk (0.05% rms)

Phase stability∆θ = 4deg*∆ V/V(%)= 0.2 deg rms(from -4deg/%)∆A/A= 0.068% rms

K(Perveance) = I/V3/2
P= ηIV = η KV3/2V = η KV5/2.
∆P/P=5/2 ∆V/V.
∆A/A = 5/4 ∆V/V

Phase (deg)Consistent3 min∆θ= 0.18deg rms
14

Application of RF monitor

The Last Waveform Saving at Klystron Interlock
The cause of interlock is identified from the last RF waveform.

Reflection occurred
btw KLY & SLEDBreakdown?

15

Application of RF monitor

Klystron Pulse Shortening Detection
Klystron pulse-shortening events detected by using RF monitor data
KL_54

Normal

Short

Short

Beam might be injected the MR

KL_B4

1-day History of Klystron Pulse Shortening
If high voltage is reduced, pulse shortening decrease or disappear.
KL_C2
KL_54

16

Beam Induced RF Monitor
Motivation

Monitored RF phase is affected temperature drift of cable and monitor system.
By comparing the phase of driving RF and beam induced RF in the accelerating
structure, we can expect to get the beam phase against RF without system drift error.
Amplitude estimation
ACC Grad : 20 MV/m
-40.9 dB

small
Beam Induced:
180 kV/m @ 2nC, 3.3ps

Amplitude

Beam induced

Fast ATT switching module
HV

Beam & HV_off

ACC Timing

30dB or 40dB

STB Timing

ATT
Fast Switching

Phase

Judged bybeam trigger & HV trigger

2018/12/10

Installed Unit : A2, B7, C1, 12, 22, 38, 45, 53, 57

17

Measurement of Beam Induced RF
Amplitude of Beam Induced RF vs. Bunch charge
1.1

1.05

SP-46-4 Bunch charge (nC)

KL_45: KBE

y = 1.4773E-4 x + 2.9636E-3

1
0.95
0.9
0.85

@KL_45:KBE

0.8
5500

6000

6500

7000

7500

Amplitude of Beam Induced RF (a.u.)

Amplitude of beam induced RF is proportional
to bunch charge. (plotted at the same shot ID)
Beam-Induced-RF Phase
KL_45: KBE

When beam phase changed@2019/6/30 10:18,
beam charge increased.
Beam-Induced-RF Amplitude18

Summary• Linac reference RF control system are almost established by installing injector MOPS,
S-band PS, and MO phase drift compensation system.
• RF monitors are installed for all RF power sources.
Not only stability confirmation, they are utilized the investigation of interlock eventand the klystron pulse-shortening detection.
• Beam induced monitor is currently under development.
Beam phase information is so useful to confirm the operating condition.

19

Future Work• Amplitude & phase controllers with digital mode are required for SHB1/SHB2.
• Replacement of old coaxial cable in RF distribution line is necessary due to contact failure.
• Change RF drive line from sub-booster drive to SSA drive (Sect 1: already done)
Sub-booster
2856 MHz

LLRF
controlunit

0 dBm 23 dBm
MechanicalIφA

2856 MHz

LLRF
control
unit

not available

Solid state 60 kW
amp.
klystron

Solid state
amp.

IφA

IφA

IφA

IφA

IφA

IφA

IφA

IφA

IφA

IφA

IφA

IφA

IφA

IφA

IφA

IφA

High power
klystron

0 dBm 23 dBm
Mechanical
IφA
600W
Solid stateamp.
High power
klystronInstead of sub-booster,
600W SSA will be installedin each unit.
20

Back up21

Diagnostics of RF Stability by RF Monitor
Water Temperature vs. RF Phase of ACC Structures
5deg
ACC_PHASE@KL_B3

0.26°C

ACC_PHASE@KL_B5∆T = 0.26°C
Water Temperature∆θ = 5 deg

Cooling Water Temperature fluctuation is causing RF phase fluctuation

22

Application of Beam Induced RF monitor

Beam Phase Confirmation for Energy Spread Tuning

Beam Energy Profile

Beam tailcorrection(2) SHB1(114MHz) +1.5deg
Beam phase: -2deg(deg)(1) Beam energy is split@screen (SC61H1)(3A) Buncher +1deg.

Beam phase: recovered
Correct procedure

C1: ACC_RF_Phase

(2)

(3A)

(3B)

(deg)

(1)

(3B) All S-band RF -2deg(except for buncher)

Crest phase => shift
C1:ACC_Beam Induced_Phase23

LLRF Control Unit

presented in KEKB Review2014
IPAC2018, WEPAK018

Rear

Front

LLRF cont. unit
60 kW Sub-booster kly.

LLRF cont. unit
600W Amp

IΦA
8 klystrons
SLED

40 MW Klystron
SLED

Driveline by sub-booster klystron(left) andindependent driveline (right)
Frequency
RF output level
Linearity of amp.
RF pulse rise time
Phase setting-range

2856 MHz+10 dBm (100%)
0.3% rms and max < ±0.5%< 35 ns (0 - 90%)
0 – 400°< Functions of LLRF control unit >• Pulse modulation (AMP & Phase)• VSWR meter (Power detection)• 1ch RF monitor• Event receiver• Pulse shortening detection

24Installation of LLRF Control Unit
BUN, RF-Gun
B6, B5B7For BCS@J-arc

SB_B

SHB1 Thermionic GUN for
ACC. Buncher Prebuncher SHB2
Guide 2856MHz 2856MHz 571MHz 114MHz positron generatione-

Sector A

SB-B

10kW Solid State
Amplifier
40MW Klystron
IΦA
IΦA
60kW
Sub-booster
(SB)
LLRF
cont.
unit
SB-B

IΦA

IΦA
LLRF
cont.
unit

LLRF
cont.
unit
Event &
Clock
System

1/51

Receive digital data directlyfrom EVG via optical fiber
Low noise & good reproducibility

Coaxial cable line

E/O

Frequency
Multiplier/divider80m

Frequency
Multiplier/divider571 MHz
Phase shifter
30m

2856 MHz

LLRF
cont.
unit

SB-1

IΦA

IΦA

2856 MHz
Phase shifter

SB-5

Optical link
E/O

O/E

E/O

LLRF
cont.
unit

SB-2

SB-4

SB-3
Damping
Ring 1.1 GeV

IΦAThermostaticchamber

Optical fiber line

Main drive system

10 MHzLinac MO
571 MHzIΦAHigh power
ATT/phaseshifter (IΦA)

114 MHz571 MHz510 MHz

SB-C

I ΦA

RF phase is set in "Digital mode"

LLRF
cont.
unit

LLRF
cont.
unit

90m

509 MHzMR Cont.

IΦA
600W Solid State
Amplifer (SSA)

IΦA

Laser
systemSector R

26 (+1) LLRF cont. units
in operation

RF GUN for low
emittance 5nC beam

Sector B
B-5

B-6

Installed this summer

A4, A3, A2, A1A, A1B

Energy Knob

KEKB Review2014
IPAC2018, WEPAK018

I ΦA

I ΦA

I ΦA

LLRF
cont.
unit

LLRF
cont.
unit

I ΦA

6-1
LLRF
cont.
unit

60kW kly.
For PF
2.5 GeV,0.1nC X 1

I ΦA

For PF-AR,6.5 GeV
Bunch
Compression

e+ capture
sectionSector C

SB_C

Sector 1

SB_1

e- bypass orbit

15,16,17,18

21, SB_2

EnergyCompression

Sector 3

Sector 2

27, 28For LER
4.0 GeV,4nC X 2

DS, DN

E-Knob BCS, ECS

SB_3

Sector 4

SB_4

SB-5

5-1

5-2
Sector 5

SB_5

51,52

61

E-KnobECSFor HER
7.0 GeV,5nC X 2

25

Phase Drift between Linac MO & Ring MO
Monitored phase with the clock based on Linac MO

Phase drift between Linac MO and Ring MO Making BCS@RTL tuning difficult
BCS RF : 2856 MHz (Linac MO x 5)

 Drift of MR injection phase
Strong correlation with
Ring MO Room Temp.
(by T. Kobayashi)@571.2 MHz

26

Under-sampling Technique for Linac MO & Ring MO
LMO(571.2 MHz):RMO(508.9 MHz)=55:49

fs=124.63MHz

𝑓𝑓𝑠𝑠 =

𝑓𝑓𝐿𝐿𝐿𝐿𝐿𝐿
7
4+
12

LMO: 571.2 MHz

RMO: 508.9 MHz

ADC1
ADC2

DDC1
DDC2

I1
Q1
I2
Q2

M1=12
N1=7
M2=12
N2=1

𝜑𝜑𝐿𝐿𝐿𝐿𝐿𝐿 = tan−1 ( 𝑄𝑄1 ⁄𝐼𝐼1 )𝜑𝜑𝑅𝑅𝑀𝑀𝑀𝑀 = tan−1 ( 𝑄𝑄2 ⁄𝐼𝐼2 )27

Measurement of Beam Induced RF

Phase (deg)Amplitude

Trend graph of beam induced RF @KL_38:KBE

Pulse shortening @KL_B4
Normal2018/12/10 18:36:59 KBE

5deg

Peak amplitude was almost the same,but pulse width became shorter.

Amplitude is not so high.
Phase jitter (error) is 5 deg pk-pk.
For more high precision, parameters of attenuator and amplifier will be revised.
28

Linac RF System
RF GUN for low
emittance 5nC beam
Sector B
B-5

B-6

SHB1 Thermionic GUN for
ACC. Buncher Prebuncher SHB2
Guide 2856MHz 2856MHz 571MHz 114MHz positron generatione-

Sector A

SB-B

10kW Solid State
Amplifier
40MW Klystron

LLRF
cont.
unit

IΦA
IΦA
60kW
Sub-booster
(SB)
LLRF
cont.
unit
SB-B

IΦA

IΦA

LLRF
cont.
unit
Event &
Clock
System

90m

510 MHz

1/51

Coaxial cable line

E/O

Frequency
Multiplier/divider80m

IΦA

Frequency
Multiplier/divider571 MHz
Phase shifter
30m

2856 MHz

LLRF
cont.
unit

SB-1

IΦA

IΦA

2856 MHz
Phase shifter

SB-5

Optical link
E/O

O/E

E/O

LLRF
cont.
unit

SB-2

SB-3
Damping
Ring 1.1 GeV

IΦAThermostaticchamber

Optical fiber line

Main drive system

10 MHzLinac MO
571 MHz

SB-C

High power
ATT/phaseshifter (IΦA)

114 MHz571 MHz509 MHzMR Cont.

I ΦA

LLRF
cont.
unit

LLRF
cont.
unit

Laser
systemSector R

IΦA
600W Solid State
Amplifer (SSA)

IΦA

I ΦA

SB-4

I ΦA

LLRF
cont.
unit

I ΦA

6-1
LLRF
cont.
unit

LLRF
cont.
unit

I ΦA

For PF
2.5 GeV,0.1nC X 1

I ΦA

For PF-AR,6.5 GeV
e+ capture
sectionSector C

Sector 1

e- bypass orbit

Bunch
Compression

Sector 2

EnergyCompression

For LER
4.0 GeV,4nC X 2
Sector 3

Sector 4

5-1

5-2
Sector 5

SB-5

For HER
7.0 GeV,5nC X 229