Stabilizing Beams in Particle Colliders and Synchrotron Light Sources


Date Thursday June 24th 2004
Time 4:00-5:00pm
Venue George E. Pake Auditorium

PARC Forum

Particle accelerators serve as fundamental tools for physics and synchrotron light sources are essential radiation sources for diverse applications in materials science, protein structure determination and fast reaction kinetics. All these applications drive accelerator designers to increase the stored currents in the machines – the intensity of the emitted synchrotron radiation, or the luminosity of a particle collider, are what makes experiments feasible. The latest generation of high-current particle accelerators and synchrotron light sources achieve their intensity performance goals by storing relatively large numbers of charged particles in discrete RF bunches. These particle bunches interact with the electromagnetic environment around the beam, leading to coupling mechanisms which drive unstable motion of the particles. These instability mechanisms limit the achievable intensities, as the particle motion grows unstably and the particles are lost from the accelerator. Such instabilities can be controlled with active feedback systems which sense growing particle oscillations, and act back with stabilizing electromagnetic signals on the beam.

Our group at SLAC has developed a digital feedback control system based on an 80 DSP parallel processor array. The technical challenges in such systems involve the detection of femtosecond scale particle oscillations, computational loads of 3.2e9 multiply-accumulates/sec., very wideband RF and baseband modulation techniques plus associated RF pickup and antenna structures to interact with the beam. These systems are in operation at 6 laboratories in the U.S., Europe and Asia.

This talk will give a brief overview of the physics and dynamics of the problem, and highlight the electronic technology and signal processing architecture of the system. Results are shown illustrating techniques to quantify instabilities and driving impedances via schemes where the system records the responses of the unstable particle beam while manipulating the control algorithm parameters.


John's interests span a diverse range but center of applications of electronic systems, signal processing systems and instrumentation techniques to physics experiments. He has earned degrees from Harvard University (B.A. Physics) and Stanford University (Ph.D. Applied Physics, Ph.D. minor Electrical Engineering).

He is group leader of the electronics research group at the Stanford Linear Accelerator Center, which focuses on applications of RF and high speed signal processing techniques, and a consulting Professor of Applied Physics at Stanford University. John teaches courses in electronic techniques as well as a seminar course "Energy Choices for the 21st Century" which covers basic physics on energy sources, with an assessment of both renewable and non-renewable energy technologies. John received the 2001 Stanford Dean's Award for Distinguished Teaching.

John's professional activities have spanned the early days of personal computers (project engineer for the IMSAI 8080), a brief stint at IBM Research, and a history at SLAC contributing to two generations of particle accelerators and storage rings. Among his more useful and unusual credentials are certificates in advanced engine performance, engine repair, engine tune-up, manual transmissions and rear axles, suspensions and steering, electrical systems, and brakes from the National Institute for Automotive Service Excellence (ASE). John is an avid recreational cyclist for balance, and a commissioner for the city of Menlo Park for bicycle, pedestrian and transportation issues.

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