The SPEAR3 synchrotron lightsource at SLAC relies on a sophisticated radio frequency (RF) timing system to maintain current – electrons – in the storage ring. One problem SPEAR3 operators have dealt with is the thermal expansion of one of the cables supporting this RF timing system. As the cable expands and contracts with the diurnal rise and fall of the sun, the phase of the RF in the cable shifts. This shifting phase affects the timing accuracy of electron injections into the storage ring.

A common feedback control algorithm PID (Proportional Integral Derivative) has countless applications in engineering. PID feedback can solve this problem of diurnal phase shift nicely. In general, feedback control of a dynamic variable requires the completion of a feedback loop; the variable is fed as input to the controller, which in turn modifies the variable. These principles were used to write a software program that controls a phase modulation box to compensate for the thermal expansion of the RF timing cable. The software was written and compiled with MATLAB, and interfaces with the EPICS control system at SLAC to control the hardware. The system also provides diagnostic tools and software control of the phase in this part of the timing system.


Controls and Control Theory | Engineering Physics | Hardware Systems | Plasma and Beam Physics


Jeff Corbett

Lab site

SLAC National Accelerator Laboratory (SLAC)

Funding Acknowledgement

This material is based upon work supported by the S.D. Bechtel, Jr. Foundation and by the National Science Foundation under Grant No. 0952013 and Grant No. 0833353. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the S.D. Bechtel, Jr. Foundation or the National Science Foundation. This project has also been made possible with support of the National Marine Sanctuary Foundation. The STAR program is administered by the Cal Poly Center for Excellence in Science and Mathematics Education (CESaME) on behalf of the California State University (CSU).


URL: http://digitalcommons.calpoly.edu/star/184


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