# 2017-Jan-13 Comp. Phys. Biweekly Report

From Administrative

He Zhang

- Electron cooling simulations for the new "strong cooling" baseline.
- Found an equilibrium solution for the higher CM point (at a reduced luminosity from minimal)the strong cooling scheme, which provides a 2.0/3.2 nC/bunch cooling electron beam. The result shows, the IBS rate is about ten times higher than the cooling rate in the horizontal direction, but much lower in the other two directions. Introducing transverse coupling could transfer the horizontal IBS effect into the vertical direction, so that the extra cooling in the vertical direction can be utilized. Introducing dispersion function at the cooling could transfer the longitudinal cooling into the transverse directions. This tricks help to find the equilibrium of the cooling and IBS effect. However, due to the high electron beam density, even if we can transfer some longitudinal cooling into the transverse directions, the extra cooling in longitudinal direction could reduce the momentum spread of the proton beam very fast, which results in a fast reduction of bunch length and increase of IBS in the transverse directions, especially in the horizontal direction. It will breach the equilibrium in the horizontal direction and the proton beam start to expand horizontally. If we can find a way to compensate the extra longitudinal cooling, the equilibrium could be constructed relatively easy. Also calculated the scaling of proton current in equilibrium with different cooling electron current, and the scaling of the proton current in equilibrium with different emittance. In these two scaling calculation, the extra longitudinal cooling is assumed to be compensated.
- Trip rate and heat load optimization for CEBAF 12 GeV RF system - Ran the optimization for the CEBAF 12 GeV RF system. First, clean and load the parameters for all the cavities into the simulation code. Second, test the four optimizers, nspso, nsga-II, spea2 and sms_emoa, to find the best parameters for each of them, and then find the most efficient one. Third, find the optimized curve with all the 200 cavities on. Forth, find the optimized curve with 195 cavities on and compare with the operating parameters, which only used 195 cavities. It shows that the current operating parameter have the lowest trip rate. We can further reduce the heat load with the same or slightly higher trip rate.
- Electron cooling theory study - Spent some time to study Slava’s paper on electron cooling theory. We have formed a electron cooling theory study club, including Slava, Yuhong, Vasiliy and me. We have met once and will continue the meeting after Yuhong comes back from his trip.
- Paper on Fast Multipole Method (FMM)- After River give me back his revisal of our FMM paper, I went through it again and made some changes in the introduction and the appendix. Now the paper is handled to Prof. Luo, River’s mentor at ODU.

Yves Roblin

- Worked with He on the various strategies for the strong cooling. Looking at higher order harmonic cavities to control the bunch length in the ring and ease the equilibrium also at emittance transfer methods and running the ring in coupled mode.
- Beam Beam code (GHOST) is now installed on GPU at lab. Ran the code and documenting it for others to use. Will perform simple tests and comparisons with BeamBeam3D to validate. This version of Ghost also Handles the gear changing. It does not yet have the electron damping. I Will add it.
- Systematic studies of bpm/dipole systems in the ARCs to assess the accuracy of dp/p determinations.
- Working on matching CEBAF by using raytrace and the bpm system to calculate the twiss parameters in front of the next spreader. Tech note almost finished.
- Considering the way to move forward regarding the impedance budget estimates.