Compton Experiment at ATF

Tohru Takahashi Hiroshima University

for Collaborators(particularly Omori san for slides)

Experimental R/D in ATF

.

Make a fist prototype 2-mirror cavity

Put it in ATF ring

Hiroshima-Waseda-Kyoto-IHEP-KEK

Lcav = 420 mm

October 2007: Install the 2-mirror cavity into ATF-DR

4

Set up at KEK-ATF 1

Optical cavity

slit aperture

~0.26mrad

e - e -

beam

15.6m

detector set up

ray

First 2008 run~before summer shutdown~

DAQ Schematic

Continued to change the length of the external cavity.

Only picked up the data when the cavity was resonated.

2.16MHz

- e

cavity

Could pass Comparator

Gate was opened

for 100ns.

T = 463ns

PD

The appearance of light resonance signal

Reflected light

Transmitted lightIn this time, the optical cavity

was resonated state

Transmitted light

Mirror reflectivity : 99.6%

Mode locked laser

(Photo diode)

PD

time (ms)

Continued to change the length of the external cavity.1ms

8

Procedure of measurement 1

① Vertical scan Scanning to the laser vertical

position and find the best position to observe gamma

Vertical scan

② Horizontal scan Vertical was fixed to the best

position. Scanning to the Horizontal.

Moved accuracy ~ 0.8m

movable table

movable table

See from upper direction.At horizontal, cavity was leaned at 12 degree

Z

e-

e-

When Vertical scan,Moved the cavity to Z direction

Z

9

Procedure of measurement 2

We found the best collision point

③ Timing scan Vertical and Horizontal were fixed to the best position. And turned on the switch of phase locked loop . After that scanning phase.

Timing scan

- e bea

m

420mm

T=2.8ns

pulsed laser

beam

e -

10

Gamma Energy distribution 115.6

m

cavity

aperture 26mr

ray

detector

E [MeV]

E [MeV]

obserbed spectrum for single is:E(mean) ~23MeV =6MeV

11

Gamma Energy distribution 2

This graph shows the appearance of gamma energy distribution.

one of gamma had 16~28 MeV energy.

1 gamma

2 gamma#

of c

ount

s

12

The number of gamma

1 bunch : experiment ~3.3 simulated by CAIN ~ 4.5

20 bunches : experiment ~3.1 simulated by CAIN ~ 20

In the case of 1 bunch, the number of gamma seems to consist comparing our experiment data with estimate by CAIN.

However, the data of 20bunches were inconsistent.The reason of this,there was a possibility that not every electron bunches were collided.

We estimated the number of gamma to use a simulation software “CAIN”.

bunch distance : 2.8 ns

date bunch the number of electron transmitted power stack power estimate γ1/ pulse (included in one train) W W

2008/ 4/ 22 20 2.6E+10 (in 20 bunches) 1.55 388 3.12008/ 5/ 27 1 7.2E+9 (in 1 bunch) 1.09 272 3.27

Mirror reflectivity : 99.6%1 - 0.996

transmitted powerstack power =

Novmber - December run

Lcav = n Lcav = m Llaser

Laser freq = Ring RF

Feedback to Achieve 3 Conditions

PID HVPhaseDetector

RingRF

HV

BPF

BPF

DC +

keep resonance

PID

sync. to Acc.

Piezo

Piezo

PD

Ref-lightStacking

Cavity

Laser

laser lightpulses

offset

Previous Ssytem

QPD

PID HVPhaseDetector

RingRF

HV

BPF

BPF

DC +

keep resonance

PID

sync. to Acc.

Piezo

Piezo

PD

Ref-lightStacking

Cavity

Laser

laser lightpulses

offset

Previous System

QPD

can be SLOW

must be FAST

PID HVPhaseDetector

RingRF

HV

BPF

BPF

DC +

keep resonance

PID

sync. to Acc.

small mirror

FAST

large mirror

SLOW

Piezo

Piezo

PD

Ref-lightStacking

Cavity

Laser

laser lightpulses

offset

Normal Solution

QPD

can be SLOW

must be FAST

DC +

PhaseDetectorBPF

BPF

Piezo

Piezo

PD

Ref-lightStacking

Cavity

Laser

PID HV

QPD

PID HVRingRF

keep resonance

sync. to Acc.laser light

pulses

offset

(Sakaue)Cross-feedback Solution

offset

can be SLOW

must be FA

ST

small mirror

FAST

large mirror

SLOW

PhaseDetector

Piezo

Piezo

PD

Ref-light

StackingCavity

Laser

PID

RingRFke

ep r

eso

nan

ce

sync. to Acc.laser light

pulses

offset

(Sakaue)Cross-feedback=Closed loop

Energy Distribution

E [MeV}

1 bunch

<E>~117MeV ->5

Now, looks multiple photon genearation in laser-electron collision

previous run

data summary

Rough consistency check

÷ the number of electron ÷ stack power

1 bunch 1.715×10^-12/e/W

2 bunches1.718×10^-12/e/W

1 bunch data and 2 bunches data seem to consistent

The number of : 6.2 × 2.16×10E+6 [/second]

Simulated by Cain 1bunch : 5.7 2 bunches :6.7

date electronnumber of electrons

stacked power

# of g

bunches /pulse [W] /crossing

2008/11/20 1 7.2E9 413 5.1

2008/11/20 2 1.2E10 291 6.2

Summary1. Success : Resonance Feedback + Phase Lock on Acc RF

Before Summer No feedback Trigger : Acc + Transmitted LightPresent Separeted Feedback ---> Crossed(loop)-feedback Resonance Feedback + Phase Lock on ACC RF Trigger : Acc

2. Collision Experiment on going 5 gamma / crossing (single-bunch op.) 6 gamma / crossing (two-bunch op.) Consistent: Experiment <--> CAIN simulation Consistent: single-bunch <--> two-bunch We are now tying take up to 20 buch data

Summer 2007: Assembling the Optical Cavity

24

Set up at KEK-ATF 2

ray

Pure CsI scintillato

r

lead shield

15mm

UV-pass filter

light guide

PMT

UV-pass filter : Only pass the ultraviolet light.

Pure CsI : The maximum emission wavelength : 315nm

Emission decay time : 10-16ns

Emission decay time is enough to be faster than the data taking time and electron frequency.

electron frequency : 2.16MHz ~ 463 ns

data taking time : 100ns

300mm

slit aperture ~0.26mrade e - -

detector

set up

ray

beam

Energy Distribution single-bunch operation

Optical cavity condition

In summer time, we succeeded to keep condition of optical cavity timing lock and locking at resonance point.

Last week beam time, Optical cavity was to keep condition timing lock and locking at resonance point.

Transmitted light

Locking at resonance

Timing

locked Timing

Best collision point data in 1 bunch and 2 bunches

1 bunch 2 bunches

Scanning to Horizontal position Scanning to Timing

After that, we tried to take 3 bunches data.

However, gamma detector was broken.

Now, gamma detector is recovered.

Laser Stacking Optical Cavity in Vacuum Chamber