Physical Description

The physical diagram shows how the electron passage produces infrared beams that are split, filtered, and converted to a voltage by means of a pyroelectric detector plus amplifier. The existence of 2 detectors is for redundancy, in case one fails. The infrared mirror can be moved out from the electron way, what causes the impossibility to measure the bunch length.

 "The light passes through a filter that transmits low frequencies (long wavelengths) and rejects high frequencies. As the bunch gets shorter, more of the light is in high-frequencies, and so the signal drops; the opposite happens if the bunch gets longer. We can’t measure the bunch length without a filter. There are actually two filters with different cut-offs to span different ranges of bunch length; only one is used at a time, and that’s why the filters are movable. Normally our bunches are short enough that only one filter is used routinely." (text by Alan S. Fisher).

Mirror and Filters Control

The mirror and 4 filters can be moved out from the beam or in front of the beam with electric actuators. Each of these 5 elements has a sensor for the IN or OUT position. The diagram shows how the control elements are connected to industrial pack modules responsible for digital input and output signals.

The EPICS database that gives access to the control system of the mirror uses a CALC record to show if the element is in the IN or OUT position, or if it is moving.

The EPICS database to control the filters is simpler. Each filter has an actuator and two position sensors.

Pyrodetector Digitalization Process

1. The EVR board receives event codes and associated timestamps. The IOC running in VME waits for a specific event code. When it arrives, the timestamp is registered.
2. Using the IP 445 module, the IOC running in VME sends a trigger to the digitizer, telling it to start collecting data from the pyrodetector.
3. The IOC running in VME tells the IOC running in the Digitizer that it is waiting for data as soon as the Digitizer finishes its digitalization. The VME IOC also sends a timestamp that will be used by the Digitizer IOC as a data label.
4. When the digitalization is complete, the Digitizer IOC sends an UDPComm package to the VME IOC with the digitalized data inside 4 waveforms. The data is labeled with the timestamp previously sent by the VME IOC. Now the VME IOC confirms the timestamp, reads the data, processes it and fill some EPICS records with its information.
5. The VME IOC sends an FCOM package to the Fast Feedback System, containing the received data.