71st ATF2 meeting

1. Results of beam test from Shintake monitor group, M.OROKU

The beam test results were updated. the detector consist of 4 1cm-thick layers in front and a 30cm-thick layer of CsI crystal whose radiation length is 1.85cm/Xo.

Energy distributions of signal and background have been estimated to have each distinct peaks at 0.8Xo and 3Xo, respectively, by simulation (GEANT4). The beam test results shall be compared with those expectation, where the signals are calculated by background subtraction, i.e. distribution with laser (laser-wire) minus one without laser. The signal distribution was shown with the expectation in page-11.

The background has been simulated from 1.3GeV beam hitting beam pipes, while the experimental one was measured without laserwire as mentioned above (page-12). Also, the simulated one is consistent with the measured one with the metal wire scanner in page-13.

The simulated distributions agree with the measurements, especially for the first 4 layers.

With the experimental verification of two distributions, the signals can be estimated by fitting with signal and background functions.

Q : How much is the simulation error in page 11?

A/C : The error is negligible for the simulation has large statistics. However, the 5th layer has not been well calibrated. So, the systematic differences are seen in distributions of the 5th layer.

Q : How did you evaluate the error in the measurements ?

A : They are statistical errors.

Q :The carbon wire scanner will use the same detector as the Shintake monitor. Did you see any saturation in the wire scanner signals ?

A : We measured both signals with changing the PMT gains .

Q : How much is the change ?

A : The HV was 800V at laserwire, while it was 300-400V at wire scanners.

Q : We would like to know a non-linearity of the detector response with the carbon wire scanners?

A : The signal strength can be tuned with collimator in front of CsI. We were aware the case for the carbon wire scanner. We will consider the wide dynamic range of detector.

Q : How much is the minimum S/N for the beam size measurement ?

A : The answer will be prepared in Yoda's Master thesis on the Shintake monitor. In General, the smaller S/N case needs more statistics, so more time for the measurement.

2. Status of the carbon wire scanner and the commissiong plan, D. McCormick

The 4um carbon wires have been used originally 10 years ago. There is no production at present for danger to health ( lung cancer ). 4um tungsten wire is easily broken by heating.

Instead, 7um carbon wire can be used, where the resolution will be 7um/4, i.e. 1.7um . Is it OK for the beam tuning ?

Since the SLAC technician will retire soon, ATF personnel needs to lean how to attach wires. He/she should be patient with microscope.

Another major questions are (1) size and type of 45 degree wires, (2) control method of SLAC or ATF, (3) need to read back position with 100nm accuracy or rely on accuracy of the stepping motor.

In terms of (1), we can use SiC 15um wires to measure 20um beam size . Also, 34um carbon wire can be used.

Q : How many the ceramic cards do you have at SLAC ?

A ; There are 2 for each types. It takes usually a half hour for replacement with 5cm long wires for string.

Q : How large is the signal strength with the carbon wires?

A : A cherenkov detector has been used. It is better to measure it at present beam line.

Q : What is the precision of horizontal wire position ( for vertical scan)?

A : Machining error, alignment one etc., they are accumulated. So, it is well below a degree for well-machined devices.

Q : How many wires are there in a card ?

A : There are 6 wires on the card, which are horizontal and slihgtly tilted.

Q : Why does it have tilted wires ?

A : It is for flat beam.

3. Initial setting method using spacers and mortar, T. Kume

Initial setting of the Shintake monitor was shown. The level will be adjusted with shims ( spacers ) and the gap will be filled with mortar.

C : This method has no flexibility when we like to change the setup.

C : Can we use a removable glue ? Some glue can be removed by heating up to a specific temperature. e.g. "glue disintegrate when heated" and found a link to http://www.sierraclub.org/sierra/200507/perfectfix.asp ( A.Seryi).

C : We may polish a flat floor, but it must be expensive.

KEK site meeting

4. Minimum hardware for "1um beam" at the laserwire location , T. Okugi (KEK)

The minimum sets were evaluated for 1um beam at laserwire and both planned beam sizes at laserwire and NanoBPM which are installed in the matching section. The former requires 9 additional power supplies, and the latter requires 2 more in addition where two skew quadrupoles are needed for coupling correction.

Color codes in the PS list; yellow=existing, light blue=30A-PS for 6cm thick Qs, pink=a PS of polarized positron bend in series for 3 Qs and orange=J-PARC PS.

C : There must be monitors and BPMs. Especially, 7 and 9 QEA-magnets have QBPMs in the former and latter cases, respectively. We must ask SLAC colleagues for readiness of QBPMs.

5. Installation of Shintake monitor, Y.Kamiya (ICEPP, The University of Tokyo)

We discussed the location of laser hut for the Shintake monitor and the working area before the final installation. The hut location is fine as shown in the presentation. The working area can be off-beam line near the north wall. The area must be controlled with an interlock system during the laser operation.

The laser transport line were shown too as in above presentation.