Performance of the cERL LLRF System
Compact ERL (Energy Recovery LINAC)

Takako Miura (KEK)
LLRF'15, Shanghai, Nov 4, 2015 (T. Miura)

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Future Plan of 3GeV ERL Light Source at KEK[1] 3GeV ERL as VUV and X-ray SR source (high flux and short pulse)(10 mA – 100 mA, εn: 0.1 mm⋅mrad, bunch length:100fs@min)[2] 6GeV XFEL Oscillator (2 times acceleration by 2 circulations)

Recirculation Loop

Beams circulate only once.
=> Low emittance is preserved.

200 Superconducting cavities
6 GeV

1.3GHz CW
LLRF'15, Shanghai, Nov 3-6, 2015 (T. Miura)

6 GeV XFEL Oscillator (XFEL-O)
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Introduction of cERL
Compact ERL (cERL) has been constructed as a test facility of a 3-GeV ERL future plan.
The commissioning has been started from 2013.
Beam Dump
Circumference ~ 90m

Main LINAC
9-cell SC cavity x 2

QL = 1× 107
MargerInjector LINAC

RF frequency= 1.3 GHz
Design parameters of the cERL

©Rey.Hori/KEK

Photocathode DC gun

2-cell SC cavity x 3

Buncher

QL = 5×105

Nominal beam energy

35 MeV

Nominal Injector energy

5 MeV

Beam current10 mA (initial goal)

Normalized emittance

0.1 ‒ 1 mm⋅mrad

Bunch length

1-3ps (usual)
100fs (short bunch)

LLRF'15, Shanghai, Nov 3-6, 2015 (T. Miura)

3

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 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

3 MV/m3MV/m

Inj-32cell-SC
0.7 MV(15MV/m)(15MV/m)

QL

1.1× 105

1.2 × 106

5.8 × 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

R&K

R&K

16 kW SSA

8 kW SSA@Low beam current

BUN<Design>
100mA beam &Vc= 2MV at Inj.Cav

Inj1

2.6 kW

Inj2

Inj3
Vector-sum

200kW RF power isnecessary for each inj. cavity.

R&K

Toshiba

8 kW SSA

25kW Klystron

LLRF'15, Shanghai, Nov 3-6, 2015 (T. Miura)

Toshiba
300kW Klystron4Digital LLRF System at cERL
Fast Interlock(Arc, Pref, etc.)

Mechanical tuner : coarse tuning Frequency Tuner
Pieso Tuner : fine tuning

0 ~ 500V

KLY/SSA
Kly PfCavity pick-up signal
Pc

RF SWPf

LO (1.3GHz(1+1/128)≈1310MHz)

LOLO

IF (≈10MHz)IF

Field FB board

Tuner board
DAC-250V~250V

Digital I/O
Offset+250V

Piezo driver

1.3 GHz(CW/CCW pulse output)

Motor driver

IQ
MO(1.3 GHz)

Requirements of RF stabilities:
0.1%rms,0.1deg.rms for cERL
0.01%rms,0.01deg.rms for 3GeV-ERLLLRF'15, Shanghai, Nov 3-6, 2015 (T. Miura)

5

Digital LLRF Boards
16-bit ADC x 4 16-bit DAC x 4(LTC2208)(AD9783)
FPGA
Virtex5-FX

Field FBControl

Tuner Control

DigitalI/O

MicroTCA

Thermostaticchamber

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)

FB4

FB5

Tuner board

TN0TN1

TN2

TN4TN5TN3

 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.

LLRF'15, Shanghai, Nov 3-6, 2015 (T. Miura)

6

Frequency Feedback Control
TN4-piezoscan-20140206-13h12m38s.csv

5000

Vc

4000

Vc

2∆f

3000
2000
1000
-3Cav

θ f - θ(deg.)

100
50-2.5∆f =65 Hz for ML cavities (QL=107)-2-1.5-1

Narrow bandwidth for f0=1.3 GHz

Vc=Vpeak/ 2∆𝜃𝜃 = 𝜃𝜃𝑓𝑓 − 𝜃𝜃𝑐𝑐 : The phase difference between the input

0-0.5x 10
DAC value
Vc Maxpoint : Piezo= -16380 Phase offset : 3.9038e-005 degree

4𝑡𝑡𝑡𝑡𝑡𝑡∆𝜃𝜃 ≈ 2𝑄𝑄𝐿𝐿∆θTo keep resonance frequency,tuner should be controlled to maintain ∆θ at zero.

0-50-100-3∆𝑓𝑓𝑓𝑓

RF and the cavity pickup signal-2.5-2-1.5-1-0.50

DAC value
DAC(piezo scan)x 10

Forward RFVf

Vc
Cavity pickup

4Block diagram of frequency FB control

Amplitude
Level judge

ADC
ADC

I/Q
I/Q

ROT
ROT+offset

Ki

LPF
LPF

FB On/Off Offset

Σ∆𝜃𝜃

Kp0<0>

HoldCW
CCW

LPF

DAC

Piezo tuner

Digital I/O

Mechanicaltuner
Stepping motor

LLRF'15, Shanghai, Nov 3-6, 2015 (T. Miura)

7Field Feedback Control
LOInterlock

RF switch
RF ON/OFF
External Interlock

1300 MHz

Digital I/O

FPGA
80MHz
Cav
Cav

Pf
MO

CLK
LTC2208

 cosθ sinθ A ⋅ 
 − sinθ cosθ 
Correction

ADC

I
Q

I
Q

ADC

I
Q

I
Q

ADC

I
Q

I
Q

I
Q

I
Q

ADC

I_FF

I_Set

Vector-sum

LPF

I

IIR Filter

Q

IIR Filter+‒‒+LimitPI++PI++

DAC

DAC

I
Q

DAC

Internal Interlock

Waveform data

AD9783

Q_FF

Q_Set
High Limit
Low Limit
Judgement

1300 MHzMOIQ modulator

IF=10MHzDown-convertor

MPS

CPU PPC440LinuxEPICS IOC

DAC

Ring Buffer

40MHz
77𝑛𝑛=0𝑛𝑛=0RAM
256MB1𝑛𝑛1𝑛𝑛
𝐼𝐼 = � cos 2𝜋𝜋 � 𝑉𝑉 𝑛𝑛 , 𝑄𝑄 = � sin 2𝜋𝜋 � 𝑉𝑉 𝑛𝑛
4848RAM
256 MB

Ethernet PHY

Gb Ethernet
Wave Forms

Parameter set

EPICS is used for control
communication. 8

Results of Frequency Control∆θ (degree)∆𝜃𝜃 = 𝜃𝜃𝑓𝑓 − 𝜃𝜃𝑐𝑐

ML1, ML25h∆𝜃𝜃 = ±3𝑑𝑑𝑑𝑑𝑑𝑑.

∆𝑓𝑓
𝑡𝑡𝑡𝑡𝑡𝑡∆𝜃𝜃 ≈ 2𝑄𝑄𝐿𝐿𝑓𝑓𝑄𝑄𝐿𝐿 ≈ 107 ⇒ ∆𝑓𝑓 ≈ ±3.4 Hz

LLRF'15, Shanghai, Nov 3-6, 2015 (T. Miura)

9Performance of RF Feedback Control
Waveforms of cavity pick-up

ML1x 10Phase

Amplitude
0.012302%rms

40

1.663

1.658

-0.6-0.8-1050

100

150200

250

300

350

400

-1.8050100

150x 10200

250300

Amplitude
0.012572%rms

4-160

400

-1Phase(deg.)

1.636

1.634

1.632

1.628

-5150

200

Time (ms)

250

300

350

400

-6103

10

4

105

10

6

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

Vc: FB OFF

Pf: w/o FB
Pc: w/o FB
Pc: w FBMOML2-80-3-42-60

Vc: FB ON-2

1.63100-40

FB:OFF
FB:ON010Hz

Phase
0.014572deg.rms

11.63850350

Time (ms)FB:OFF
FB:ON

Amplitude-120-180 110ML20-100-140-1.6

Time (ms)1.626

ML1-1.4

1.656

1.64

Pf: w/o FB
Pt: w/o FB
Pt: w FB
MO

-80

-1.2

1.657

FB4-PT-HG-1.5kW-8.6MV-ssa3.csv

-60

-0.4

Vc: FB OFF

1.659

FB:OFF
FB:ON

dBc/Hz1.66

FB:OFF
FB:ON

Phase(deg.)

Amplitude

1.661-40-0.2

Vc: FB ON1.662

1.655

0.013717deg.rms

0.2dBc/Hz

1.664

Phase noise measurement using
signal source analyzer-100-120-14050Hz peak in Pf is fake:leakage from reflection port indirectional coupler.
-180 1
43
2-160

0

50

100

150

200

Time (ms)

250

300

350

400

1010

10

10

Fluctuations by microphonics have been well suppressed by FB control.

Hz

10

5

10106

RF Stabilities
Monitored with IIR LPF(5kHz)

Inj1

Inj2 & Inj3

ML1ML2

Amplitude

0.006% rms

0.007% rms

0.003% rms

0.003% rms

Phase0.009° rms

0.025° rms

0.010° rms

0.009° rms

Requirements:
0.1%rms,0.1deg.rms for cERL
0.01%rms,0.01deg.rms for 3GeV-ERL
x 10

Amplitude

Phase

moni: 0.003349%rms

0.015%

Amplitude

1.64381.64371.64361.64351.64340100

200300moni: 0.0085591deg.rms

23.02

400

23.01
230.04deg.

1.64394Phase(deg.)

ML2

22.99
22.98
22.97
22.96

0100

msec
LLRF'15, Shanghai, Nov 3-6, 2015 (T. Miura)

200300

400

msec
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Stability of Beam Momentum (1)Screen Monitor
CAM14Injector~3MeV

Main Linac
20 MeV

Dispersion : ηX= 0.487m
Beam: 5Hz, 3ps rms, 23 fC, total Energy=19.9 MeV

Screen Monitor
63.7 um/pixel

dP/P= 0.013115 %rms

0.06

dP/P(%)

0.04
0.02
0-0.02
-0.04

0500

1000

1500

2000

2500

time(sec)
12
Momentum drift in the period of ~15 minutes was observed.

Reduction of the Effect of Vector-sum Error(deg.)(deg.)

𝑡𝑡𝑡𝑡𝑡𝑡∆𝜃𝜃 ≈ 2𝑄𝑄𝐿𝐿∆𝑓𝑓𝑓𝑓

The time interval of detuning is similar to theinterval of energy drift.

∆𝜃𝜃 = 𝜃𝜃𝑓𝑓 − 𝜃𝜃𝑐𝑐θcInj2~15 min.

Blue: Inj1, Red: Inj2, Green: Inj3

Higher tuner FB gains were adopted in Inj2 & Inj3.

The amount of phase variation became small.

Inj3
Inj1

If error is included in vector-sum calibration, energy drift can occur.
In the region of Inj2 and Inj3 cavities, β < 1. Transit time is different in each cavity.
=> weight of vector-sum is different between Inj2 and Inj3.

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Stability of Beam Momentum (2)Measurement after modification of tuner feedback gain for Inj2 and Inj3
dP/P= 0.0063913 %rms

0.05

Momentum Jitter= 0.0064% rms

0.04
0.03

0.04%dP/P(%)

0.02
0.01
0-0.01-0.02

50 min.

-0.03
-0.04
-0.05
0500

1000

1500

2000

2500

3000

ti me (se c )Large momentum drift disappeared.
Good stability of beam momentum was achieved.
=> It was confirmed that the RF field for the beam is stable.
LLRF'15, Shanghai, Nov 3-6, 2015 (T. Miura)14

By H. Sakai

Demonstration of Energy Recovery (I0 = 30 µA)
ERL operation

Non-ERL operation
Cavity 2: deceleration Cavity 1: acceleration(Vc=8.57 MV/cavity)
E=2.9 MeV

Beam loading (+ and -)(Vc=8.57 MV/cavity)

Cavities 1 and 2: acceleration (1st pass) anddeceleration (2st pass)
E=2.9MeV

E=2.9 MeV

E=2.9 MeV

E=19.9 MeV

Cavity 1:Pin-Pref

No beam loading

Energy recovery: 100-98.6%(within accuracy of the measurement)

Cavity 2: Pin-Pref

Cavity 2:
Pin −Pr
Beam current

Cavity 1: Pin −Pr

Beam current
30 µA

30 µA

(Power lost in cavity) = (Pin : input power to cavity) - (Pref : reflected power from cavity)

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Summary RF stabilities satisfied the requirement for cERL, and almost
satisfied the requirement for 3GeV ERL.
 The beam momentum jitter of 0.006% rms was achieved.

Future Plan Tuner feedback parameters have not been
optimized enough.
We will optimize the tuner control parameters.
 Beam current will increase and burst mode
operation is planned.
Beam loading compensation is necessary.
[Feng Qiu (KEK), this afternoon]

10 mA

Prospect

1 mA
100 µA The evaluation of the long-term stability isnecessary.
LLRF'15, Shanghai, Nov 3-6, 2015 (T. Miura)

16Thank you for your attention.

LLRF'15, Shanghai, Nov 3-6, 2015 (T. Miura)17