RF Signals Shift
RF Master Oscillator Signal
The CEBAF accelerator is controlled by a Master Oscillator Clock running at 1497 MHz, corresponding to 499 MHz (2.004 ns spacing) per hall during 3-hall operation. The precise 499 MHz RF clock is delivered both to the tagger and to Hall D to be used for accurate timing of beam bunches arriving to the experimental area. As part of 4-hall operation, the beam is almost always delivered to Hall D at 249.5 MHz with arrival times synchronized to the RF signal provided by accelerator. This clock is too fast for our detector electronics, so we pre-scale the signal by a factor of 128 to provide clock edges every 256.51 ns to our electronics. The timing of the leading edge of the clock is aligned with the 499 MHz RF signal, but the phase is arbitrary and must be calibrated.
The nominal pre-scale factor for the RF signal is 128, which is settable with the RF EPICS GUI shown in Fig. 1. (There are actually two sub-factors, 16x8=128, corresponding to two electronic stages, accessible using the "MO Boards" button.) Shift personnel should not need to change the pre-scale factor, but if the EPICS IOC that controls the pre-scale boards is rebooted, the value may need to be restored to that shown in the figure. The hall IOC is located in the crate containing PSC electronics.
For details of the calibration system see RF Calibration
The individuals responsible for checking that the RF is ready to take data and setting its operating parameters are shown in following table. Problems with normal operation of the RF signal should be referred to those individuals and any changes to their settings must be approved by them. Additional experts may be trained by the system owner and their name and date added to this table.
|Name||Number||Date of qualification|
|Fernando Barbosa (hardware)||JLab: 7433||Sep 20, 2018|
|Elton Smith||JLab: 7625||Sep 20, 2018|