# 2017-Mar-03 Comp. Phys. Biweekly Report

From Administrative

He Zhang

- Cooling simulation - Found and fixed one bug when implementing tracking in the cooling simulation. Performed some simulations with various parameter sets. In these simulations, the transverse rms bunch size of the ion beam changes from 33% to 100% of the electron beam radius, and the longitudinal rms length of the ion beam changes in the same manor to the electron bunch length. Made plots of the dynamic invariants of the ions w.r.t. their initial positions or initial dynamic invariants. I did observe different patterns for different ion bunch sized, compared with the electron bunch size. However, now I can’t explain the results and draw a solid conclusion. In these simulations, the ions with similar initial position have different dynamic invariants and different momentum. The ions with similar dynamic invariants have different position and momentum. Averaging of the inhomogeneous parameters makes it more difficult to understand the results. I’m planning to make more simulations with more specific parameter values, which may help to more deeply investigate the problem.
- Dust particle transport - Read more about the longitudinal motion of the dust particles. Now I understand there are two mechanisms for the dust particles to gain longitudinal momentum. One is due to the change of the electron bunch profile. The other is the Moller scattering of the beam electrons with the atomic electrons inside the dust. The latter one dominates when the mass-to-charge ratio is very large. Finished the slides to summary the dust particle transport theory and formulas. Had a discussion with Rongli about the value range of the parameters. Rongli provides his estimates on some parameters and also provides some documents. I haven’t got time to do any calculations. Rongli also points that the dust particle may moves in the opposite direction of the beam motion, according to their observation.
- Cooling theory study - Read Chapter 1.1 (till page 20) of Slava’s thesis and made slides on the contents. Had a two-hour meeting to present and discuss the slides with Slava and Yuhong.
- Trip rate/heat load optimization - Generates new plots to compare the gradients of the multi-object optimized setting with those of the trip rate optimized setting used in operation. In the new plots, both groups of gradients are normalized by the maximum gradient in the group.
- LDRD for FY2018 - Proposed to write a proposal for LDRD fund for FY2018. The purpose is to extend the capability of GHOST for the simulation of non-Gaussian beam collisions, for which the FMM will be used to calculate the Coulomb interaction of non-Gaussian beams. The proposed work includes: 1. Investigate parallel FMM framework: pkifmm and exafmm; 2. Select one of them and make sure it runs with good parallel efficiency in CPU-GPU hybrid cluster; 3. Insert our FMM kernel into the selected parallel FMM framework; 4. Implement FMM in GHOST; 5. Run a few benchmark cases for beam-beam with Gaussian or non-Gaussian beams. I am writing the LOI.
- Submit a proposal for SULI summer student program. - Got the following notice: “The offer extended to Zachary Abrams Dunlap-Tunnage was accepted on 2/17/2017 11:34:39 PM. The offer was to work with He Zhang on Space charge field calculation with a boundary of arbitrary geometry.”

Yves Roblin

- Organized the simulation parallel session for the upcoming collaboration meeting. All speakers are now confirmed:
- Ji Qiang TBD (Beam beam 3D simulations with FFB and crabbing but he has not send me the title yet)
- Jean Luc Vay "Berkeley Lab modeling tools for electron cloud build-up and effects on beam transport"
- Balsa Terzic "Beam-beam with gear Change for JLEIC"
- Dan Abell "“Computational Considerations for Spin Tracking in Electron-Ion Colliders”
- David BruhWiler ""A New Approach to Calculating Magnetized Dynamical Friction for JLEIC"

- Ran meeting on simulations for JLEIC, gave an update on BeamBeam simulations. Next meeting is 3/17/2017.
- Working with B. Terzic to benchmark GHOST and BB3D together.
- CEBAF:
- discussed 2R optics error investigation with Mike T. and Todd.
- met with Tim Maxwell (SLAC) regarding high level apps
- BEM for HALLD investigated. Added a segment using the tagger.