Resonance Control
at the Compact ERL in KEK
Takako Miura (KEK)on behalf of LLRF and SRF Cavity GroupLLRF Group
Takako Miura, Shinichiro Michizono, Feng Qiu, Toshihiro Matsumoto, Hiroaki Katagiri, Dai Arakawa (KEK),
Liu Na (Sokendai Univ.)
SRF Cavity Group
Eiji Kako, Takaaki Furuya, Hiroshi Sakai, Kensei Umemori, Taro Konomi, Masato Egi, Kazuhiro Enami (KEK),
Masaru Sawamura (QST)

ERL17 T.Miura (KEK)1

Introduction of cERLCompact ERL (cERL) is a test facility of 3-GeV ERL as a future light source.

Beam Dump

Circumference ~ 90m

Main LINAC
9-cell SRF cavity x 2

QL = 1 107
MargerInjector LINAC

RF = 1.3 GHz CWDesign parameters of the cERL

©Rey.Hori/KEK

2-cell SRF cavity x 3

QL = 5105

Photocathode DC gun

Buncher
Requirements of RF stabilities for 3GeV-ERL
0.01%rms,0.01deg.rms
ERL17 T.Miura (KEK)

Nominal beam energy

35 MeV

Nominal Injector energy

5 MeV

Beam current

10 mA (initial goal)

Normalized emittance

0.1 ‒ 1 mmmrad

Bunch length

1-3ps (usual)
100fs (short bunch)
2Current status of high power RF sources
CavityCavity Voltage

BuncherNC
114 kV

Field Gradient(Desgin)Inj-1
2cell-SC
0.7 MVInj-22cell-SC
0.7 MV

3 MV/m

3MV/m

Inj-3
2cell-SC
0.7 MVML-1
9cell-SC
8.6 MVML-2
9cell-SC
8.6 MV(7.5MV/m)(7.5MV/m)(7.5 MV/m)

3MV/m

8.6 MV/m

8.6 MV/m(15MV/m)(15MV/m)

QL

1.1 105

1.2  1065.8  105

4.8  105

1.3  107

1.0  107

Cavity Length
RF Power

0.068 m0.23 m

0.23 m

0.23 m1.036 m1.036 m3 kW

0.53 kW

1.6 kW

2 kW

ML1

ML2

@Low beam current

BUN

2.6 kW

Inj1

Inj2

Inj3
Vector-sum

The "vector-sum" operation
in low energy region, β<1,has some difficulties.
-> transit time change-> RF phase change

8 kW SSA

25kW Klystron
ERL17 T.Miura (KEK)
300kW Klystron

16 kW SSA 8 kW SSA
3

Digital LLRF System at cERL
Mechanical tuner : coarse tuning

Fast Interlock(Arc, Pref, etc.)

Resonance Tuning

Pieso Tuner : fine tuning

0 ~ 500V

KLY/SSA

Kly PfCavity pick-up signal

RF SWPcPf

LO (1.3GHz(1+1/128)1310MHz)

LOLO

IF (10MHz)IF (10MHz)

DAC

Q

Baseband

Digital I/O(CW/CCW pulse output)
Offset+250VI

RF FB board

Tuner board-250V~250V

1.3 GHz

Motor driver

Piezo driver
ERL17 T.Miura (KEK)MO(1.3 GHz)

Requirements of RF stabilities for 3GeV-ERL
0.01%rms,0.01deg.rms
4Tuner System

ERL17 T.Miura (KEK)5

Tuner system of Injector Linac
Slide-Jack tuner

E. Kako, IPAC2013

20 kHz/rotation
600 kHz

Drive Shaft
He jacket

Piezo tuner
0-500V
stroke= 4 m@2K

performance of slide-jack tuner

Piezo: 0-500V => 2 kHzTaper

2kHz

The same as KEK-STF tuner system

2Δf1/2 = f0 / QL

Inj1: QL= 1.2 ×106, 2Δf1/2 =1.1 kHz
Inj2: QL= 5.8 ×105, 2Δf1/2 =2.2 kHz
Inj3: QL= 4.8 ×105, 2Δf1/2 =2.7 kHz

Piezo tuner can cover the band width.
f1/2f0f

ERL17 T.Miura (KEK)

performance of piezo tuner
6Tuner system of Main Linac
H. Sakai, SRF2013 @Paris

Shaft of slide-jack tuner

Cavity flange is fixed here
Piezo tuner
0V - 500V (offset=250V)
Stroke= 4 m @ 2K40 m @ 300K

He jacket(1 m: 300Hz)

Slide-jack tuner

QL=1 × 107
2Δf1/2 = f0 / QL=130 Hz

Load Cell
Piezo
Module

1kHz

Screw

Shaft
SlideJackring

7

ERL17 T.Miura (KEK)7

Mechanical Resonance of Inj Cav<Injector>

Eacc: 1MV/m
INJ2

409Hz

Sinusoidal wave (40Vpp) was fed to piezotuner.
Mechanical resonance is scanned bysweeping the input frequency.
Phase detector : 20 mV/deg

INJ1

260Hz

435Hz

423Hz

INJ3

68Hz

Large mechanical resonance exists around 400 Hz.
ERL17 T.Miura (KEK)8Mechanical Resonance of ML Cav
M. Satoh, IPAC2014

Impulse hammer response

Large mechanical resonance exist near 50 Hz.

ERL17 T.Miura (KEK)9LLRF System

ERL17 T.Miura (KEK)10Digital LLRF Boards
16-bit ADC x 4 16-bit DAC x 4(LTC2208)(AD9783)
FPGA
Virtex5-FX

RF FB
Control

Tuner Control

DigitalI/O

MicroTCA
AMC(Advanced Mezzanine Card)(Mitsubishi Electric TOKKI Systems Co.,Ltd.)

Total 11 boards are used for operation.
BUN

Inj1

Inj2

Inj 3

ML1

ML2

RF FB board

FB0

FB1

FB2 (Vec-sum)

FB4FB5

Tuner board

TN0

TN1TN2TN4TN5

TN3

ERL17 T.Miura (KEK)◼ Embedded Linux is working in thePowerPC on FPGA.
◼ Each board acts as an EPICS IOC.
◼ Data acquisition is performed
through GbE bus on the backplane.
11Field Feedback Control
LO
Down-convertor

MPS
InterlockRF switch
RF ON/OFF
External Interlock

1300 MHz

Digital I/O

FPGA
80MHz

Cav

CLK
LTC2208

Pf

MO cos  − sin  A  
 sin  cos  
Vector-sum
Correction

ADC

I
Q

I
Q

ADC

I
Q

I
Q

ADC

I
Q

IQ

I
Q

IQ

Cav

ADC

1300 MHz
MO

I_FF

I_Set

LPF:100kHz

ILimitAD9783

IIR Filter

PI++DACIIR Filter

PI

DAC+++Q_Set

Q_FF+IQ
QDACInternal Interlock
High Limit
Low Limit
Judgement
Waveform data

CPU PPC440LinuxEPICS IOC

DAC

Ring Buffer
RAM256MBQ

RAM256 MB

Ethernet PHYA

Gb Ethernet

I

ERL17 T.Miura (KEK)Wave Forms

Parameter set

12

IQ modulator

IF=10MHzCavity Resonance2Δf1/2
Amplitude (dB)

-3dB

f1/2 =65 Hz for ML cavities (QL=107)
Narrow bandwidth for f0=1.3 GHz

f0∆𝜃 = 𝜃𝑓 − 𝜃𝑐 : The phase difference between the input
RF and the cavity pickup signal45deg-45deg

Detuning Δf=fc-f0∆𝑓𝑡𝑎𝑛∆𝜃 ≈ 2𝑄𝐿𝑓
To keep resonance frequency,
tuner should be controlled to maintain  at zero.

For constant acceleration field,
double input power is necessary at f = f1/2

ERL17 T.Miura (KEK)13

Block Diagram of Resonance Control
Feedback Control: Δθ = θf (Pf) − θc (cav) => 0Piezo Tuner

DAC

CW

Mechanical Tuner

Digital I/O
CCW

Stepper motor

FPGA Board
Amplitude
Level judge

CLK80MHzCav

ADCPfADCQθ

ROT1IQ

ROT2IIR LPF
Δθ

+-IIR LPFPolarity
change𝑛8

14

ERL17 T.Miura (KEK)

0<0>

Kp∙ 𝑉 𝑛 , 𝑄 = σ7𝑛=0 sin 2𝜋

OffsetLPF

Δθ'fc=20Hz

14I

FB on/offKi

IQ

𝐼 = σ7𝑛=0 cos 2𝜋

Aoffsetθoffset𝑛8for protection

DACCW
Digital I/O
CCW∙𝑉 𝑛14

Cavity field Stability & Microphonics

ERL17 T.Miura (KEK)15

Waveform of ML Cavities
T. Miura, IPAC2014 @Dresden
1.664

A = 0.012% rms
 = 0.014 rms

x 10

Amplitude
0.012302%rms

4Phase01.663

FB:OFF
FB:ONPhase(deg.)

Amplitude

-0.4

1.66
1.659
1.658

1.655

1.64-1.6
050

100

150

200

250

300

350

400

-1.8

050

100x 10200

250300350

Phase
0.014572deg.rms

1FB:OFF
FB:ON
0

1.636

-1

1.634

1.632

-3

1.63-4

1.628

-5

050

100

150

200

Time (ms)

250

300

350

400

50Hz Microphonics-2-64deg

Phase(deg.)

1.638

1.626

400

Time (ms)

Amplitude
0.012572%rms

4150

FB:OFF
FB:ON

AmplitudeA = 0.15% rms
 = 0.6 rms-1

Time (ms)ML2
A = 0.013% rms
 = 0.015 rms-0.8-1.4

1.656

Vc: w/o RF Feedback-0.6-1.2

1.657

Vc: w RF Feedback

FB:OFF
FB:ON-0.2

1.662
1.661

A = 0.035% rms
 = 0.3 rms

0.013717deg.rms

0.2

1.4deg

ML1050

100

150

200

250

300

350

400

Time (ms)Field fluctuation
by Michrophonics is stabilized by RF Feedback
ERL17 T.Miura (KEK)16

Phase noise jitter measurement
using Signal Source Analyzer Agilent E5052B
M.Egi, PASJ2016 (MOP025)
T. Miura, IPAC2014 @Dresden-20

Vibrational state of "ﬂoor" around Main Linac

FB5-PT-HGFB-1.5kW-8.6MV-ssa-20140521-2.csv

50Hz-40

Pf: w/o FB
Pc: w/o FB
Pc: w FBMO

RP: Rotally pump-60

dBc/HzdBc/Hz-80-100-120-140-160

ML2-180010101102

1034

10105106HzHzVc Phase Noise with RF FB (10Hz-1MHz)=0.017deg
Vc Phase Noise w/o RF FB (10Hz- 1MHz)=0.73 deg
Microphonics is observed at 10 Hz - 400Hz.
Phase noise by Microphonics was suppressed well by RF FB.
Phase noise of Vc with FB was almost the same as that of Master Oscillator.
ERL17 T.Miura (KEK)17

Countermeasure against Scroll Pump Vibration
For constant input RF power

9-cell SC cavity: QL=107
Before(15 MV/m : Design)

2
1.5

1.005

1Phase(deg.)

Amplitude/mean(Amplitude)

1.01

Field gradient
8.3 MV/m : Operation point

vibration by scroll pumps

50 Hz

10.9950.5
0-0.5-1-1.5

0.99

0

100

200

300

-2

400

0100

Time (ms)200300400300400Time (ms)The rubber sheet was inserted
under the scroll pump.
The 50 Hz vibration is suppressed.

1.01

21.5

1.005

1Phase(deg.)

Amplitude/mean(Amplitude)

After

10.9950.5
0-0.5-1-1.50.990100200

Time (ms)
ERL17 T.Miura (KEK)

300

400

-20100200

Time (ms)18

Momentum Error due to Vector-sum Error&Improvement by tuner feedback parameter

ERL17 T.Miura (KEK)19

RF Performance
RF Stabilities for Short Time
Inj1

Inj2 & Inj3

ML1

ML2

Amplitude

0.006% rms

0.012% rms

0.003% rms

0.003% rms

Phase0.009 rms

0.022 rms

0.010 rms

0.009 rms

Almost satisfied the requirement of 3-GeV ERL

Measurement of Beam Momentum Stability
for confirmation of RF stability
dP/P= 0.013115 %rms

0.06

<Measurement condition>
Beam: 5Hz, 3ps rms, 23 fC, total
Energy=19.9 MeV

dP/P(%)

0.04

36 min.

0.02
0-0.02
-0.04

0500

1000

1500

2000

2500

time(sec)

Momentum stability = 0.013% rms
ERL17Momentum
T.Miura (KEK) drift of ~15 minutes period was observed.
20

What causes Energy Drift ?

Detuning phase∆𝜃 (deg.)Time interval of detuning is similar to the interval of energy drift.
Inj2~15 min.

Inj3Large ripple depends on valve control
for liquid N2.
Input-couplers of injector are cooledby liquid N2.

Inj1
TimeCavity Phase<RF source : cavity =1:1 >Cavity phase is stabilized by RF FB.

ML1
Inj2

10deg

Cavity Phase(deg.)

ML2

Inj3

<Vector-sum operation>
Vector-sum is constant,but each cavity phase fluctuates.

Inj1

Vector-sum error may cause energy drift.
ERL17 T.Miura (KEK)21

Vector-sum Error
Possibility of momentum drift caused by vector-sum error(1) Vector-sum calibration error
Amplitude & Phase calibration error(2) for low beam energy ( < 1),transit time is affected by cavity field.
Injection energy : 1.63MeV@Inj2, 2.36 MeV@Inj3

Cavity fields changes => Beam phase changes.

In order to minimize the momentum fluctuation due tothe vector-sum error,“detuning” should be stabilized.

ERL17 T.Miura (KEK)22

Result of Resonance FB Control Improvement
Higher FB gain in resonance control is adopted for small detuning.

Detuning Phase(rms)f Hz(rms)

INJ1

0.23

2.2

INJ2

0.10

2.0INJ3

0.09

2.1

ML1

0.09

0.08

ML25h
Detuning due to liquid N2 flow has been compensated.

0.16

0.18

Detuning phaseΔθ (deg)

Cav deg

Cavity Phase
Cavity phaseθc (deg)

Inj2&Inj3 cavity phasebecome stable.

ERL17 T.Miura (KEK)23

Stability of Beam Momentum (2)Measurement after modification of tuner feedback gain
for Inj2 & Inj3 only

FB gain is optimized

dP/P= 0.0063913 %rms

0.05

Momentum Jitter= 0.0064% rms

0.04

The latest result P/P = 0.003% rms

0.03

0.03

0.02

0.020.01

0.01

dP/P(%)

dP/P(%)

dP/P= 0.0033939 %rms

0.04

0-0.010-0.01

-0.02
-0.02

-0.03

50 min.

-0.04
-0.05
0500

1000

1500

30 min.

-0.03

2000

2500

3000

-0.04

0200

400

600

800

1000

1200

1400

1600

time(sec)time(sec)

Large momentum drift disappeared.
=> Beam momentum jitter ΔP/P =0.003% is achieved.
ERL17 T.Miura (KEK)

24

1800

2000

Summary• Digital control boards are applied to RF feedback and tuner control.
• Owing to the stiff cavity structure, so detuning by Michrophonics does notinfluence to the operation.
• The field fluctuation due to Michrophonics is well suppressed by RF feedback.
• Vector-sum operation has some difficulty for low beam energy due to different
transit time.

• By applying high FB gain for piezo tuning, the detuning fluctuation due toliquid N2 flow rate has been suppressed.
=> Beam energy drift caused by vector-sum error has become small.
0.003% momentum stability is achieved.
ERL17 T.Miura (KEK)25