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Abstract
An intra-pulse Interaction Point fast feedback system (IPFB) has been designed for the Next Linear Collider (NLC), to correct relative beam-beam misalignments at the Interaction Point (IP). This system will utilise the large beam-beam kick that results from the beam-beam interaction and apply a rapid correction to the beam misalignment at the IP within a single bunch train. A detailed examination of the IPFB system is given, including a discussion of the necessary electronics, and the results of extensive simulations based on the IPFB concept for fast beam correction are presented. A recovery of the nominal luminosity of the NLC is predicted well within the NLC bunch train of 266 ns.
The FONT experiment — Feedback On Nanosecond Timescales — was proposed as a direct test of the IPFB concept and was realised at the NLC Test Accelerator at SLAC. As part of FONT, a novel X-band BPM was designed and tested at the NLCTA. The results of these tests with the NLCTA short and long-pulse beam are presented, demonstrating a linear response to the position of the 180 ns long-pulse beam: measurements show a time constant of ~1.5 ns and a precision of better than 20 μm. A novel BPM processor for use at X-band, making use of the difference-over-sum processing technique, is also presented in detail, with results given for both short and long-pulse beams.
The FONT design concepts and modification of the IPFB system for use at the NLCTA are described. The design of a fast charge normalisation circuit, to process the difference and sum signals produced by the BPM processor, forming part of the FONT feedback circuit, is detailed extensively. Bench tests of the feedback electronics demonstrate the effectiveness of the normalisation and feedback stages, for which a signal latency of 11 ns was measured. These bench tests also show the correct operation of the normalisation and feedback principles. Finally, the results of a full beam test of the FONT system are presented, during which a system latency of 70 ns was measured. These rigorous tests establish the soundness of the IPFB scheme and show correction of a mis-steered bunch train within the full NLCTA pulse length of 180 ns.
“Any intelligent man needs to maintain his intelligence. Intelligence isn't a static property, its dynamic, permanently increasing, yes, but also shifting, moving, sliding, jumping and sometimes leaping into different planes, dimensions, boxes and tunnels. You can't catch it, you can't quantify it, you can't qualify it, you can't see it and you can't understand it. All you can do is feed it, and if it doesn't like the food then give it something tougher to chew on …”
Simon James, MMII
ME SAY NOW. A surprisingly large number of people have participated in the formulation of the work contained within this thesis, without many of whom it is unlikely that much of it would have seen the light of day. As such I have the pleasure of thanking all those who have made this research possible. I must first extend both my thanks and admiration to an outstanding group of physicists at SLAC. Firstly, to Marc Ross, Tonee Smith, Doug McCormick, Keith Jobe, Chris Adolphsen and Janice Nelson who gave an unwarranted quantity of their valuable time and expertise in helping FONT find such success at the NLCTA, and to Dave Brown, Mike Brown and Bill Roster for making most of the important bits work in the first place. My thanks also go to Dave Burke, Tom Markiewicz, Marty Breidenbach, Peter Tenenbaum and Tor Raubenheimer for their help in various aspects of FONT, and Glen White for his simulation work and the various stolen plots that appear throughout this thesis.
I am particularly grateful to Steve Smith for his expertise in the intricacies of beam position monitors and fast feedback systems, and for having the patience to explain them all to me whenever I turned up on his office doorstep. To Joe Frisch, an accelerator physicist of astonishing skill and knowledge, I am indebted for his invaluable help in virtually every aspect of my research, without whom it is unlikely FONT would have achieved anything close to the success we experienced. Another expert whose input was of enormous value is Colin Perry, master of the dark arts of analogue and tube electronics, and with whom I had the pleasure of sharing the bewildered euphoria that everything had actually worked …
For services above and beyond the call of duty, my thanks go to Gavin Nesom, who braved the world of FONT while he had better things to do, argued with me till we were both blue in the face and applied himself with a quiet diligence while all hell was breaking loose in the NLCTA control room. Finally I must thank my two supervisors: Phil Burrows, who fought my corner when no-one else would in engineering my PhD transfer, provided superlative guidance throughout my research and under whom my abilities as a physicist have benefited immeasurably; and Adrian McKemey, who provided a young student with more inspiration than he will ever know.
Lastly, my thanks go to Rich Sloane, Paul Jackson and Ed Hill for keeping me sane in California; Rich Steward, Claire Gwenlan, Chris Smith and Ed Moyse for showing me the light; Keith Hamilton, Thilo Pauly and Mike Ramage for their patient assistance with particle theory; the UCL HEP group for providing me with a home away from home in the early days; various assorted Monkees for keeping me in my place; Nick, Neil and Stuart for surviving the Stoke; Jason Johal and Tom Lyford for making Brunel a brighter place to be; and Liz, AJ and MJ for just being great.
© Simon Jolly 2003