Working Group 1 Synchrotrons/LHC Summary Report Mike Brennan Philippe Baudrenghien Four Talks, and much discussion (LHC)

1.Development of LLRF control system for J-PARC RCS, by Dr.Tamura Rapid cycling implies 1. High gradient cavities 2. Fast frequency sweep 3. Finemet cavities are the solution 4.Two harmonics are imposed on the cavities simultaneously (Q=2) Direct Digital synthesizers are used to generate the waveforms Feedforward beam loading compensation is used DDS is used to extract the harmonic component of the beam current, up to h=6

2. Experiments of Low Level Control Based on Analog IQ Technique, by Mr. Zhao 1.At the Shanghai Synchrotron Radiation Facility both analog and digital I/Q processing are being considered 2.So far an analog prototype system has been built and tested 3.Some suggestions were proposed on how to extend the bench tests to better simulate a real cavity

3. An IQ-based low-level RF prototype for ALBA, by Mr. Hassanzadegan ALBA is the light source being built in Spain (near Barcelona), 350 meter 3.5 GeV ring Tests of the IQ hardware demonstrate 1% amplitude and 1 degree phase regulation A high-Q pill box cavity has been built and will soon be added to the test setup

4. (Digital version of IQ control for ALBA), by Angela Sarasqueta 1.Rather similar to IQ board reported on by Tony Rohlev 2.Angela invited suggestions by the experts in the house

Issues of particular interest to LHC 1.RF noise and longitudinal emittance control 2.Klystron gain saturation and phase noise remedies 3.Beam Control topics (not presented in talks)

RF Noise Is there an optimal value for rf noise –Too much costs luminosity (bunch lengthening) –Some rf noise may balance synchrotron radiation damping (too small emittance enhances IBS) –There were many opinions about if controlled noise can be beneficial in emittance blow-up –Consensus (perhaps?) that the noise spectrum should be shaped in a controlled way

RF Noise J. Tuckmantel reported on his study (via simulation/analytic calculation) of noise versus synchrotron radiation damping

RF Noise We discussed if narrowband noise and can cause de-bunching Lebedev, “In theory… it’s impossible” Brennan, “In practice…I’ve seen it” Linnear has seen something similar in the SPS (ICFA 2004) Probably some other mechanism is involved, such as IBS or instability De-populated spot in momentum distribution First synchrotron sideband at 4 GHz

Klystron Gain/Noise All agree that the klystron makes phase noise, and we must have feedback to reduce it J. Fox showed how to keep the gain high even when the klystron saturates (linearizer) Philippe B. showed results of tests of direct feedback in reducing phase ripple the “polar loop” has basically the same effect at the linearizer

Beam Control for LHC Loops (store with open or closed loop?) –Phase, programming the gain, opening the loop,… –Radius, used only in commissioning –Synchronization, conflict with phase loop? AC coupled phase loop Cogging –Keeping it adiabatic –Operations interface –Direct measurement (WCMs) of vertex phasing

Beam Control for LHC Technology –Noise floor of phase detecor –Phase noise in VCXO vs state-of-the-art DDS Diagnostics –How do you reduce the flood of data on a fault (post mortem) –Out-of-range trapping should be engineered into firmware designs –Templates of good system states should be readily available Beam Inhibits (not a casual matter) –A 100 Hz frequency jump would de-bunch the beam