Glossary



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Glossary

actuator
This is the generic term for a device which feedback uses to control the beam. Examples are an XCOR (horizontal correction magnet) and PHAS (a phase shifter controlled via a PAU)
BPM
Acronym for Beam Position Monitor. This device determines the position of the beam. A Processing module connected to it (BPMP) converts the analog voltages to digital values which can be read by the micro
calibration
A procedure by which all the actuators of a feedback loop are varied and the changes of the states are recorded. In control theory jargon this is called identification. It is done to directly measure some of the transfer matrix elements used in the design of a loop.
feedback loop
The necessary hardware and software needed to stabilize a number of states. Some number of sensors and actuators will be needed to do this.
gold orbit
The values of all the measurements used by a feedback loop typically recorded at a time when the accelerator is in a good (golden) state that you want to maintain. These values can be used as offsets to be subtracted from the present feedback measurements. In this way a feedback loop can be set to maintain a particular saved setup.
launch loop
This is the most common type of feedback loop. It controls the launch of the beam from one part of the accelerator to another. The states controlled are the horizontal and vertical position and angle and sometimes the energy. Some loops do this for a single beam and others do it for both electrons and positrons. The sensors used are BPMs.
measurement
The result of reading a sensor. A typical measurement is the value of the beam position.
plant
This is the generic control theory term for the device being controlled by a feedback loop. In our case this is the accelerator and the description of it includes a lot of transfer matrix elements and any dynamics of the actuators such as a finite slew rate or LR time constant.
ring buffer
This contains data (such as measurements or states) recorded for each pulse of the accelerator for the last few hundred pulses. It is also sometimes used to refer to a plot of this data. It is used for diagnostic purposes to check the response of a loop.
robust
An adjective describing a desirable feature of a feedback loop. A loop is robust if it keeps working properly even if the real plant is different than that which was used to design the loop. Examples of things which could be different are the time response of an actuator and the values of transfer matrix elements.
sensor
A device which is used to make a measurement for a feedback loop. Examples are a BPM which measures the beam position and a profile monitor which measures the size of the beam.
states
Numbers used to describe the present state of a system. The estimates of the states for pulse are calculated from the state estimates for pulse and the measurements for pulse . Examples of states are the horizontal position and angle of the beam at a point, the beam energy, the energy spread, and an estimate of the present magnetic field of a corrector.



next up previous contents
Next: About this document Up: Fast Feedback Users Guide Previous: Feedback status shows



SLAC Controls Software
Fri Nov 4 11:34:56 PST 1994