compton gamma stability - status of the drift source investigation - nobuhiro terunuma, kek march 17...

Compton gamma stability- Status of the drift source investigation -

Nobuhiro Terunuma, KEK

March 17th, 2014, LAPP, FJPPL-FKPPL ATF2 Workshop

1

Contents

• Jitter and drift of the Compton signal • Beam?• Laser?• Utilities?

March 17th, 2014, LAPP, FJPPL-FKPPL ATF2 Workshop 2

Drift of the Compton signalAfter December 2013, the beam size measurement by IPBSM has been difficult.• Sometimes the unacceptable level of drift (50% or more) on the Compton

signal was happened. It shows a periodic behavior about several tens of seconds.

• It accidentally fakes the modulation 0.2 or less.• We can eliminate such measurements by paying attentions for the

consistency of the modulation profile in a scan, and the repeatability in the several measurements.

• But it waste the time especially for the measurement of the bigger beam size in a crossing mode (lower modulation) and the Z-scan.

Cherenkov Signal (ADC raw data)

measuring the signals by keeping untouchedFringeScan

Fringe Scan


Drift of the Compton signal – continued (1) -


The survey of the jitter/drift source has been continued.• Stability of the electron beam

• There was no significant difference by • ON/OFF the ATF2 orbit FB, 1000bx optics, QD0 current

• The long periodic drift was measured by the FF BPMs.• No significant effect on the Compton signal was detected.• The BPM’s drift is due to the temperature change of the DR cooling water.• The extraction kicker used this water. The new cooling unit was installed to

stabilize the kicker. It seems the Compton drift was somewhat improved but not so significant.

– Even if so, we do not eliminate the possible drift caused by a beam.– The evaluation of the IP beam position is essential to understand the

beam stability.

• Stability of the laser– show later

Expanding the beam size at IP by QD0 reduces the amplitude of the drift.(Updated on 3/17/2014.)

Compton signal vs. FF BPM


y-position of the FF BPM (MFB2FF)

Cherenkov signal by a laser wire

Contents

• Need to stabilize the cooling water unit for the EXT-kicker.

• As a temporal approach to stabilize, we adjusted three air condfitioners in the kicker hut to relax the cooling water unit. These air conditioners had different settings such as 25-deg cooling, 20-deg heating and maximum flow with unknown setting.

• The temperature is still drifting after a few hours but the beam dift at MFB2FF is weaken.


y-position of the FF BPM (MFB2FF)

Temperature of the extraction kickerusing the cooling water for DR magnet

Drift of the Compton signal - continued (2)-


• Alignment of the Compton line is OK– If the Compton photons passes near the collimator, clipping of the signals

will be enhanced by a beam jitter and drift.– The alignment of this line was already done during the new year

shutdown by using the alignment laser.– Even if so, the x-y position scans for the collimators was done by using

the Compton signals. No improvement was obtained. • Compton gamma detector seems OK.

• Both CsI and Cherenkov detectors show the drift of the signal simultaneously.

• These detectors are controlled independently.– HV power supply, Charged ADC, gate and trigger

• The HV power supplies for these detector are connected to the same AC line. The specification of the HV stability is 5mV(p-p)/2kV or less and does not introduce the bigger signal drift.

Alignment of the Compton line


Removed #4,Laser ON

Removed #4,Laser OFF

with #4,Laser ON

#1 #2 #3(x-y movable) #4 Gamma detector

e-

Collimator scan (x-y)

Cherenkov vs. CsI


Cherenkov signal in the fringe scan

CsI signal in the fringe scan

Drift of the Compton signal - continued (3)-


• AC power stability for laser AC 200V, 50 HzPlot the maximum voltage of 20 ms sampling

Laser off2% fluctuation due to the automatic TAP of KEK main transformer

Laser turned ONadditional and steady 2% fluctuation due to the laser operation 6 Hz

6 Hz laser

Stabilization of Laser


What is a source of the drift?

Feb. 12th 2014, KEK, 17th ATF2 project meeting

We suspected the temperature related sources because of the drift interval, several tens of seconds.

– Cooling water; both external and internal– Clean booth Air conditioner

No significant improvement was obtained.

Survey of the laser condition


The survey of the laser condition with the company engineer was done on Feb/10th and 28th .

– Setting of the laser oscillator is fine as expected. – The cooling water unit is also working well and stable.– The signal drift was somewhat reduced by tuning the

temperature of the Harmonic Generator (1064532nm).– The flash-lamp needs to be exchanged about 30 M-shots

(~3 months). Does it introduce the instability of laser?• It was exchanged in October 2013.• Next exchange will be soon, before April or May run.

• The optical-flat viewports were installed to decrease the air turbulence in the laser transport.

• The outer part of the laser image at the laser hut was jittered more than others. Clipping it makes profile better.

IPBSM Laser


HarmonicGenerator1064532nm

Rear Mirror(Oscillator Tuning)

BeamLok(pointing stabilization)

Water cooled

Water cooled

Water cooledN2 purged

Monitors for the IPBSM laser


Laser time structure

(PIN-photo Diode)

Laser imageInjection (CCD camera)

IP screen can be used for an enlarged image.(focal lens)

Laser hut

Laser image (CCD camera)

Laser time structure(PIN-photo Diode)

Laser image174L (CCD camera)

Stability monitoring of the laser profile


hut V-tableIP screen

or 174Lhut

V-table

IP screen or 174L

Laser buildup, water temp

No significant correlation between the drift of the weighted center of the CCD image and the Compton signal was observed.

Clipping the unstable part on the laser image


• The profile was getting worse during the transport to IP.• It was found that the outer ring at the laser hut fluctuated much compare to

the inner rings.• Clipping the outer ring makes the better LW profile than before. It has been

applied since Mar 3rd .

Outer ring is jittered so much.

Clip the outer ring by Iris in the laser hut

Not saved sorry!It seems better but still looks triangle.

Which detector is best? Use both!

CsI• better stability (20%) than

present Cherenkov (30%)• need to maintain the non

standard PMTs– Noisy or dead PMTs

Cherenkov• better S/N • better linearity• fast response

– two bunch separation

• but poor stability especially for the lower signals


We can use both detectors simultaneously.

500 ns/div 500 ns/divLaser

BeamADC Gate (80 ns)

Cherenkov

ADC Gate(4 us)

50 ns/div 2000 ns/div

Compton DAQ condition (2014/3/7); 4e9/bunch, but under IPBPM study

CsI

System checkout to understand the sensitivity of the recent measurements by Cherenkov and CsI. N.Terunuma

CsI: 6 mV (peak)Cherenkov: 150 mV (peak)

Fringe scans by CsI


waiting the next scan but signal drift much

Signal fluctuation by detectors

• Jitter and drift of the Compton signal • Beam?• Laser?• Utilities?


Cherenkov signals

CsI signals

Signal fluctuation is dominated by a statistical reason.Lack of the number of detected Compton photons.

CsI signals -Mar/12/2014-


Noisy

Dead Noisy

OK?

OK?Dead

Dead

Dead

Shut the air flow in the laser transport by optical-flat windows


Laser IP

transport on the shield block

Air turbulence in the transport


• Just put a window on the hole to IP area on Feb.10th (Monday) evening.• No tools to store the data was prepared at that time. Monitoring only.• Comparing the displayed history, It seems the CCD image was somewhat

stabilized after putting a window as follows.

Before

After (30min later) It looks small and stable (flat).

20 min History of the laser image center on the CCD (at vertical table)

• Another side of the transport was also closed by a viewport.• Therefore no air flow is expected in the laser transport since Feb. 12th.

Summary


• The drift of the Compton signal is undesirable on the beam size measurement.

• A lot of surveys to reduce the jitter and drift of the Compton signal were done.

• The situation has been improved somewhat but the source of the drift is not identified yet.

• The effort should be continued.

backup


Stability at the exit of laser head


PIN Photo Diode located 0.5m from the exit of laser head

• for timing adjustment• for tuning of the laser oscillator

Note: It measures a part of laser profile because a laser is 10 mm but a sensor is only 0.5 mm.

Results• Timing jitter

– typically < 2 ns– sometimes < 4 ns

• Power jitter– resulting by the timing jitter– for beam (if sit on peak)

• typical 0.5/8div ~ 6%• sometime 1.5/8div ~

20%

Persistence10 sec

The waveform drifts sometime but it is fast and small. It does not explain the amount of a drift measured on the Cherenkov signal.

Stability at the exit of laser head –continued -


PIN Photo Diode 0.5 m from the exit of laser head

• No significant difference to the 10 sec measurement.

• It looks same as before; i.e. 65 nm measurement.

• not sensitive to find the source of drift.

• Tuning of the laser oscillator improves/recovers the jitter level.

Persistence~ 600 sec

Stability at the Vertical Table -


PIN Photo Diode 20 m from the exit of laser head

• Amplitude of PIN-PD signal jitters about 30% at IP but a few for @hut.

Note: It measures a part of laser profile because a laser is 10 mm but a sensor is only 0.5 mm.

• It suggests the enhanced jitter after the transport. – pointing jitter– laser profile jitter

Persistence~ 60 sec

Stripline

PIN-PD@IP

PIN-PD@hut

compton gamma stability - status of the drift source investigation - nobuhiro terunuma, kek march 17...

Documents