Electron cloud feedback collaboration meeting Participants: ANL: Kathy Harkay SNS: S. Cousineau, S. Henderson, Jeff Holmes, Y. Sato SLAC: A. Chao LANL: R. Macek IU: Sara Breitzmann, S.Y. Lee, S. Wang, X. Huang, Fanglei Lin, Lingyun Yang, Qiong Wu, Fei Wang, Yingmei Su, Yue Hao

Program: 3/15: Kathy Harkay (ANL): e-cloud detector design issues Robert Macek (LANL): Overview of electron cloud effects at PSR 3/16: Robert Macek (LANL): Observations of the e-p Instability at PSR Stuart Henderson (SNS/ORNL): feedback basics, kicker, etc. Robert Macek: A compendium of e-cloud studies at PSR 3/17: Yoichi Sato (SNS/Indiana), Simulation of e-cloud using ORBIT Robert Macek: A compendium of e-cloud studies at PSR Jeff Holmes (SNS): ORBIT electron cloud model 3/18: Collaboration meeting

Experimental facts: The bandwidth of the instability for PSR can be up to 200 MHz. This seems to be related to the plasma frequency of electrons in the proton beams, i.e. ~(ρ) 1/2, where ρ is the effective density of the proton beam. The growth time ≈ 200 turns

Tasks: 1. Stuart Henderson: Stripline kicker 0.5 m, damping time 300 turns, corresponds to 300 W rf power with 200 MHz bandwidth. (The CIS stripline extraction kicker has a length of 1.3 m with 4.0 cm gap. Its usage is limited. We should talk to Fermilab to see whether we have a spare cooling feedback kicker. S.Y. Lee) 2. Control system, analog and digital signal processing, etc. (S. Henderson, SNS) 3. Effects of BPM resolution, amplifier noise on emittance and correction; Effect of sub-threshold coherent oscillations on the feedback. (A. Chao, SLAC + anyone interested.) 4. Availability of 200 MHz bandwidth Power amplifier (S. Henderson will check with J. Corlett) 5. Coordination, location of kicker and detector, Engineering, physical plan, and local support (R. Macek, LANL) 6. How to transform the current stripline (derivative) BPM signal into beam position information. (everyone should think about this task). 6. Website for collaboration information: 7. Timing: 2004, or Follow up meeting at SNS? ANL? Or PSR? (August?)

Puzzles, future experiments, and tasks to do: 1. Burst, sub-threshold? What causes the burst? Correlation with longitudinal distributions? 2. Properties of the sub-threshold coherent beam oscillations at a slightly lower frequency. Do we know the total spectral power in the sub-threshold condition? How does the spectral power depend on time? Bob’s experiments tell us that once ep instability is established, the total integrated betatron spectral power increase exponentially with time. The frequency extended up to 300 MHz. What causes it? 3. First pulse instability 4. Electron cloud recovery? Why not observed in numerical simulations? Bob says that when the sweep time is moved along the beam shape, he also see the electron cloud recovery phenomena. It would be nice to re-check this experiment. 5. What is the physics of neutralization factor in e-p instability?

6. Bunch shape dependence of electron cloud generation. These experimental results are very important to SEY modeling. 7. Dynamical range of RFA detector: A) Plotting the prompt electron distribution in log scale, the exponential growth factor may be related to electron cloud energy and transit time, and multipacting relevant to SEY. B) If one measure prompt electron distributions in energy bin, say 10 eV bin, one may be able to learn the electron energy distribution and understand the multipacting mechanism. C) The electron dissipation time is related to the space charge force and electron velocity distribution. D) The maximum energy of electron cloud observed from experiments is much larger than that derived in numerical simulations. Possible causes? sub-threshold coherent oscillation or transverse or longitudinal beam distributions? 8. Electron detection experiments with mylar strip in the dipole! How about in the quadrupole. If this work, one can use this method for electron multipacting prevention in accelerator magnets.