First, noise level in the electronics was measured at a test bench. Detected signals were digitized by a 12-bit ADC (1000pC full scale). Since the input signal has -10dBm (70nsec width), 1 um offset signals were simulated by inserting 30dB attenuator for -36dBm/um (-96dBm/nm). [dBm=10 log (mW)] The ADC count was 870 with pedestal subtraction, while the rms one was 5. Therefore, 5nm resolution can be expected in the electronics.
Second, the electronics was tested with existing cavity BPMs at the ATF extraction line, which are a reference cavity behind the SLAC/LLNL nanoBPM system, #3 cavity in front of FEATHER and #4 cavity behind the ODR. A stripline BPM of ML10x is very close to #3 cavity. Signals were propagated in long cables with 10dB attenuation from the cavity BPMs to the electronics; i.e. converter -> detector -> 1/25 att. -> 14bit ADC with 200pC for equivalent count to the 12bit ADC. The position signals of #3 cavity were calibrated with ML10x. The calibration coefficient was 150 counts/um. Dividing the 10dB cable attenuation, the coefficient becomes 450 counts/um. Since pedestal has 15 counts rms, the resolution is estimated to be 33nm. The pedestal's rms did not depend on 10dB attenuator insertion in front of the electronics. Therefore, there is difference between the bench and beam test, which shall be understood.
"Current status of LASER FRAME", Y. Higashi
(transparencies, 10 pages, pdf,1.9MB )
Design of the laser frame configuration has been completed as explained in the previous meeting, where both floor and reference bar movements can be measured by laser-BPM system with two laser beams. Four laser-BPM have been fabricated for a performance test. Stability of the KEK system will be monitored by this laser frame configuration, where three dummy cavity BPMs will be also fabricated. Since there is only one mover system at present, the two BPMs will be directly mounted on the granite table.
"Measurement of vibrations on the granite table (girder) and the reference bar", H. Yamaoka
(transparencies, 11 pages, pdf,2.1MB )
The granite table was bolted on the floor, and the reference bar system was bolted on the granite table. Vibrational properties of this supporting system have been measured by servo accelerometers. First, the granite table has large amplifications of floor motions in horizontal directions at frequency of around 20~30Hz, while the vertical motions has no significant amplification. There were good coherency at frequency from 1 to 10Hz between the granite table and the floor. Second, movements of the reference bar have been investigated by measurements and FEM-analysis. The measurements show four resonant peaks below 100Hz ( 1st at ~23Hz), while the FEM has the 1st resonance at 104Hz. Comparing these two, rigidness of the reference bar must be too strong in the FEM.