Minutes of ATF2 weekly meeting, 22 June, 2011

June 22 15:00 - 16:00 (JST time), Webex and ATF LC meeting room, KEK

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Recovery Status of ATF, N.Terunuma

A change of DR frequency in the tuning indicates that the DR circumference has shortened by 3mm after the earthquake. Recent survey of the DR magnets confirmed this change. Therefore, all the frequencies were changed accordingly. At the LINAC, the cavity volumes had to be adjusted by cooling water temperature. The magnets were aligned only in transverse direction with accuracy of 0.3mm. The fine alignment of 50um will be done in this summer shutdown.

The laser wire optical cavity and the Compton 2 mirror one were commissioned. The detectors were aligned. Checkout of the Compton 4 mirror system is just started in last Monday.

The beam tuning has been executed in evening shifts and the vertical emittance has been measured to be about 30pm by XSR in DR. The beam intensity was raised to 1 x 10¹⁰/bunch in DR. The beam was dumped without loss in the final focus system and the extraction line. The beam intensity is limited for lower power of the modulator-0 which has been converted from no.10 modulator. The Compton signals were detected.

BPM progress report, S. Boogert

Nominal performance of c-band BPMs is 200nm and 20nm resolutions w/ and w/o 20dB attenuators, respectively. The s-band BPMs have 1um because of 15dB attenuation in the cables which were replaced with shorter ones now. The vertical resolution of the IPBPMs is 100nm with good IP steering.

While the earthquake damage is small, we upgraded the DAQ and analysis especially for multi-bunch performances. Also, the hardware was upgraded, i.e. 16 bit SLAC digitizers with 120MHz were installed. So, the electronics for the 4 BPMs including IPBPMs around IP were fully integrated in the 22 slot crate. There is a problem, i.e. there are reflections in the signals due to mismatch of the input impedance.

Q : Can you check this problem by CALTONE ?
A : Yes, but there are still reflections.

The DC impedance will be checked. It is high > 1 MOhm, but also might be some unwanted capacitance. The problem will be with the reference cavity as it has a long decay time.

Clocks of 714 MHz and C-band LO were checked in the c-band RF distribution. There was small damage in the temperature interlock in water cooling, which was repaired. CALTONE system was also checked out.

For the S-band BPM system, a new MVME3100 was installed as a VME CPU board. The clock/trigger/processing is still an issue when the DR RF is ON. So, we should have an internal clock. The signals are attenuated by the 15dB loss in the cables. Hybrid circuits will be installed at the front-end. The LO and CAL will be completely unlocked from the 714MHz of ATF.

We also checked the Zygo straightness monitor system, since we were asked by Mike. The laser and the computer are OK, while the VME system seems to be OK. The laser paths should be re-aligned and some locking signals should be checked. While the fibers may be damaged, they are easily replaced.

The software was changed in details as it has totally automatic system configuration which can be written in ASCII code. It is expected to be more stable database, e.g. the panel shows no control device in red and new BPMs can be easily added.

We observed a digitizer noise in the amplitude during the BPM processing. It is to be checked, for it may come from phase noise and cooling sources. Typical frequency shifts from temperature change are -112kHz/K and -50 to -60kHz/K at the BPM and beam pipe, respectively. We will monitor the temperature there.

The T0 resolution is observed to be a function of beam intensity(I), which indicates substantial jitter and longer term drifts. Measured T0 RMS's are 602, 160, 33 and 32 psec at I=0.3, 0.5, 0.8 and 1 x 10¹⁰/bunch, respectively.

In the calibration, slow orbit drift and jitter can be removed. The scale errors are normally 1% with the jitter subtraction. In the multi(3)-bunch study, the IQ diagram shows an effect by the subtraction.

Future works are to monitor the temperature at the cavities which needs 30ch and to prepare the high charge operation requested by Terunuma-san. We see signal-saturation in the dipole cavity and in the reference cavity even at I=1x10¹⁰/bunch .

Q Philip: What is the limit of calibration error after the subtracion of jitter?
A : It is 1 % scale error, i.e. from 10% with 5 calibrations to 1 % with the jitter subtraction.
Q : Can it be better than 1% ?
A : It is not an absolute error, also it is a result by the simulation in figures. The measured error goes to 1 %.
Q : Is it the same for the IPBPMs ?
A : No, they have systematic errors.
Q : Is 1% error enough for IPBPMs , since they are sitting in large beam divergence ?
A : The relative errors between IPBPMS can be better, i.e 0.1 %, in an absolute sense around 1%.
Q : Is it the measured one ?
A : Yes
Q Oroku: IPBPM works well. The data can be read by EPICS ?
A : Yes. You must remember that the signal saturation effects the resolution. There is a flag to show the saturation, i.e. check list is given in the database.
Q Jackie: How long does it take the calibration of IPBPMs ?
A : It takes an hour to calibrate IPBPMS, assuming small orbit deviations. It depends on the external condition, orbit and charge.
Q : IPBPMa are important for the IPBSM background generated from halos jittering around IP. We would like to see any correlation between orbit and the background. Is it possible?
A : At present, the S-band BPMs have 1um resolutions limited by DR-RF ramp. We expect that it can be improved to 200nm by changing cables. So, the IPBPM calibration must be improved too.
Q : What causes the IQ change ?
A : It is a phase relative to beam.
Q : IPBSM group will work with you, i.e. exchanging information for background reduction.
A : The best person is Glen White with respect to the calibration and the orbit reconstruction.
C Okugi: There is an issue of synchronization between data.
A Terunuma: In order to have coincidence between servers, they must have scalars with the same clock.
C Stewart : EPICS synchronization is easy.
C Okugi : ICTs at EXT and IP have not been synchronized.
Q : How do we check the BPM quality, e.g. saturation?
A : There is a flag in the EPICS data.
C : Please ask Glen for the check.
Q Philip : What is the status of synchronization in the data?
A Glen : In March, DR and EXT, FF, c-band, s-band systems were checked. EPICS hardware has time stamps within 100 msec. Actually, a few 100 msec was checked, so 1.5Hz is easy.
C Philip : So, it should be easy for background study ?
C Glen : The operation system of EPICS is OK.
C Philip : LLRL group has data with synchronization, too.
Q Okugi : Can you rematch the impedence ?
A : Yes, it can be matched.
C Glen : It must be 50 Ohm.
C : There are broken capacitors ? The work should be collaboration with Glen and Stewart.

IPBSM Status, M.Oroku

I would like to briefly report on the 2nd collimator/detector and a problem of the laser chilling water system.

We are considering movable stages for the 2nd collimator and the detector. The former stage has a vertical movement in 1cm for the total weight of 50Kg ( 2nd collimator). The latter one has x and y movements both in 1cm for the 100Kg.

Are such moving stages available ? The IPBSM group has spare newport controllers.

Q : Is it 50Kg for the 2nd collimator ? It seems too heavy.
C : It must be about 20Kg, since a lead block is about 10Kg.
Q : The collimator stage is only vertical movement?
A : Yes, the collimator is a slit for it shields the vertical aperture of beam pipe in front of the last bending magnet.

We could not re-start the laser after refilling the chilling water. It must be due to air bubbles. We asked the company for the check.

Q : Will you check it again today ?
A : No
C : We should check it again for explanation to the company.

We will prepare a simple clean hut covering the IPBSM ( the vertical-optical table ), because we saw dust on mirrors after we cleaned them a week ago.

Next meeting is 29th June, 2011.