RF Synchronization, control and stability

Takuya Natsui

• Laser oscillator must be synchronized to RF in linac.

• Linac is driven with 2856 MHz RF.

• Low level RF system uses 114 MHz (= 2856/25) and 51.9 MHz (= 2856/55).

• The oscillator frequency must be 114 MHz or 51.9 MHz.

• 51.9 MHz RF was chosen for oscillator frequency for L-band (1.5 GHz) operation. Because initially, it was planned to use L-band accelerating tube.

• A lot of product oscillators are about 80 MHz. 51.9 MHz will be special order product.

• We developed oscillator due to budged.

Oscillator and frequency

Basic synchronize system

Beam trigger, laser pulse and RF synchronization

KEKB ring RF frequency : 508 MHz

Basic synchronize frequency : 10.38 MHz (2 bunch pulse distance)

LLRF frequency in linac : 114 MHz (10.38 x11) and 51.9 (10.38 x5)

linac RF : 2856 MHz (10.38 x11x5x5)

Beam trigger : 50 Hz

Beam trigger, laser pulse and RF synchronization

Beam trigger: 50 Hz

Synchronized 51.9 MHz RF is used in linac system.Laser oscillator is synchronize the 51.9 MHz RF.

Fine phase tuning is done using 571 or 2856 MHz RF. RF gun and accelerator is driven by the 2856 MHz RF.

52 MHz

2856 MHz

INPUT 1

INPUT 2

INPUT 3

INPUT 4

2856 MHzBPF

52 MHzBPF

Oscillator signal

Oscillator phase detect

52 MHz IQ signal

2856 MHz IQ signal

52 MHz phase detect PID (Proportional-Integral-

Derivative) Controller.CPU control

voltage control cycle : >10 kHz

Piezoelectric controller

2856 MHz IQ signal

52 MHz IQ signal

Nd:YAG laser oscillator at 3-2

LD Pump Nd:YAG

Piezoelectric actuator

Photo diode

52 MHz ： resonant length 2.88 m x2

to Amplifire

Control circuit

IQ signal571 MHz

Nd:YAG oscillator

Nd:YAG oscillator

• The Nd:YAG oscillator is used at 3-2 RF gun.

• Frequency : 51.9 MHz

• Phase lock RF frequency : 51.9 MHz and 571 MHz

• Phase stability : 2.27 deg

Yb:YAG laser oscillator at A-1

Yb:YAG fiber oscillator

LDPump

WDMcoupler

Isolator Yb-doped fiber

SMF SMF

Collimator

Collimator

Polarizing

/4l/4l

Output

/2l

250mW976 nm

1000-grooves/mmGrating pair

PEZ

P.D./4l

Synchronization controller

Laser signal

2856 MHz 52 MHzPiezo control voltage output

Yb:YAG fiber oscillatorWe have two oscillators. Basically, they are same.However their stability is not same.

Second oscillator is very stable

Phase stability (sigma)Oscillator1 : 2.38 degOscillator2 : 0.58 deg

Yb:YAG fiber oscillator

Cavity length of oscillator1 is varying greatly

Cont

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d pi

ezo

disp

lace

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Yb:YAG fiber oscillator

• The Yb:YAG oscillator is used at A1 RF gun.

• Frequency : 51.9 MHz

• Phase lock RF frequency : 51.9 MHz and 2856 MHz

• Two oscillators are provided

• Phase stabilityOscillator1 : 2.38 deg Oscillator2 : 0.58 deg

Laser transport and spot control at cathode

2w (515 nm) is transported to near RF gun

telescope

BBO (2w to 4w)

Remote control mirror

By using the reflection of the wave plate, laser profile is being monitored.

Plan

• 114 MHz oscillator being developed. (114 MHz synchronize RF can be used. L-band was no longer required)

• Menlo Systems company product laser oscillator will be install.Frequency : 114 MHzSynchronize frequency : 114 MHz and 2856 MHz