By 7th October, all the fine machining processes will be completed with checking all the dimensions. Also, brazing test of feedthroughs will be done by 7th October. Before the brazing, the resonant frequencies will be measured by 12th October. The brazing will be completed by 20th October, where the 4 sets are brazed at the same time with twice the brazing processes. After the brazing, the frequencies will be measured again to be compared with those before the brazing by 22nd October. The packing and shipping will be completed on 26th October, which is to be confirmed.
Although the QBPM has a capability of tuning the frequencies, i.e. 5MHz (about 100um) with tuning ports, we should not use it in this fabrication in order to see the machining accuracy and the brazing effect directly.
We discussed if we should visit to PAL from KEK for checking the brazing procedure as well as the machining properties. Yes, Hayano will visit to PAL on 3rd and 4th October after his participation in the ICFA seminar. He can see the fine machining process on 4th October, while the 3rd is a national holiday in Korea. (Hayano's trip report in Japanese) Also, Honda will visit to PAL for 10th through 13th October, in order to see the brazing setup and the brazing result with the frequency measurement as above schedule. (Honda's report in Japanese)
Test items of the prototypes have been sent to PAL on 14th September. There are two major item of the port measurement without using the tuning port by network analyzer and vacuum tightness. The most relevant parameters are the resonant frequency, its width and the depth of absorption in the S11 and S21 measurements in order to determine Qload, &beta and Qo .
The port and antenna measurements will be completed by end of October. Also, the effect of misalignment between cavity and wave guide will be measured. They will be installed in the beam line of the LINAC end in the first week of November. The signal will be checked for the sensitivity and pulse shape with a simple diode detection for 11/7-18 .
We will receive the PAL prototypes in 11th November at the latest. One of the two will be installed in the ATF extraction beam line for a beam test in 11/14- . The second one will be checked with the cold test in the same way as the KEK prototypes. This second prototype replace the first one on 11/28 for the beam test. These tests will be done with the diode detection (analog electronics), since the SLAC digital electronics will arrive in December.
We discussed on participation of PAL group in the beam tests. Certainly, the PAL group is willing to participate. We will communicated for the detailed schedule via emails.
We need to fix the design of the production model as soon as possible after the beam test of the prototype. The discussions so far are summarized as follows; (1) copper long beam pipe without bellows with flanges at both ends, (2) detailed brazing method, difficult? , (3) quality correlation with the prototype ? and (4) the mount mechanism on the Q-magnet, where QBPM is mounted on an aligned adapter, however the PAL adapter design was not understood well. PAL group explains that the brazing process will be the same as the prototype but with different jig to hold the long beam pipe, and that the adapter design of half-split type is based on experience at PAL. Specification of the QBPM properties ( on the catalog) should be determined soon after the prototype tests; i.e. the port measurement and vacuum tightness. The check items are same as the prototype, while the acceptable ranges will be determined after the prototype-test results.
M.Ross expressed a concern on this adapter method, i.e. the adapter is mounted on the iron tips of Q-magnets. Cavity-BPM must be very sensitive to the temperature; e.g. about 100nm / 0.1 degree, while the cooling water temperature changes 1 degree during the ATF operation. So, the magnet temperature change may significantly affect the QBPM performance. One solution is to use hinge structure with position-feedback for the support of QBPM on Q-magnet. Also, the magnetic center itself of the Q-magnet may change by the temperature. We need to know tolerance of position difference between QBPM and Q-magnet, which should be asked to the Optics group. The temperature variation of Q-magnet (iron tips) and QBPM mounted with adapter must be measured, which can be done with the prototypes .
The detailed design will be discussed during Honda's visit to PAL on 10/10-13.
KEK must provide the hybrids, whose number is 2 per a QBPM, and the reference cavities. Number of the reference cavities depend on the phase variation with different cable length, while a reference cavity is assumed in one digitizer module.
On 29 September (SLAC time), the prototype electronics is submitted for printing. The parts are on hand except for limiters ( 4 to 6 weeks) and power meter. The prototype test begins on 12th October. The prototype is expected to be tested with the prototype QBPM at the ATF extraction line in December. One electronics expert will be available for the beam test from SLAC. Total channel number of the prototype electronics is 10 .
Using this method, the displacements were calculated in each X and Y directions of the three KEK cavity-BPMs. They are within ±10um except for Y-direction of #3 cavity-BPM; i.e. -54 and -39.5 um . The #3 cavity-BPM has behaved in similar way at the beam test. So, it is expected to have some problem inside in Y direction; e.d. it may be brazing trouble.
In conclusion, the antenna method was improved with accuracy of less than 10um for the electrical center measurement. It is enough performance for the cold test.