# Presentation: 359820

## E-P Meeting					09/01/2004

**ORBIT e-p simulation results**
**Update**
**Y. Sato **
***SNS/ORNL; Indiana University, Bloomington***
**J. Holmes, A. Shishlo**
***SNS/ORNL***

- Y. Sato	Indiana University;   SNS, ORNL

## Outline

- Y. Sato	Indiana University;   SNS, ORNL

-  Try to reproduce some PSR results using cold proton pulse in ORBIT:
- 	Prompt and Swept Electrons
- 	Recovery after “Clearing Gaps
- ECloud growth v.s. Proton pulse slope (cold proton)
- 	The same head p-pulse
- 	The same tail p-pulse
-  PSR ring simulation
- 	Setup in ORBIT and current situation
-  Conclusion

## Prompt and Swept Electrons vs. Beam Intensity (1)

- PSR data (IU ep meeting 03/17/04)

## Prompt and Swept Electrons vs. Beam Intensity (2)

- ORBIT result (to cold proton bunch)

- Common parameter set (max=2.0,
- LossRate=4e-6) shows saturation in the swept electrons at 6~7μC as the PSR data, but both of prompt and swept slopes are much weaker than the PSR data.
- Lower loss rate gives steeper slopes.

**Notes:**
We can expect “prompt” and “swept” electrons are proportional to the eCloud line density. 

## Prompt and Swept Electrons vs. Beam Intensity (3)

- ORBIT result (to cold proton bunch)

- Low max gives steeper slopes on swept electrons,
- but it is hard to see the saturation in swept electrons at 6~7μC.

## Recovery after “Clearing Gap of electrons

- PSR data (IU ep meeting 03/17/04)

## Recovery at E-sweeper and nearby E-Detector

- PSR data (IU ep meeting 03/17/04)

## Recovery with low proton loss rate

- ORBIT result (to cold proton)

- Common proton loss rate 4e-6 does not show any recovery as Pivi and Furman’s: PRST-AB **6**, 034201 (2003).
- The flat lines corresponds to the electrons where proton line density is increasing and most of them stay inside the beam pipe. So, only E-sweeper with HV can count them.

## eCloud growth to same head (cold) proton pulse

- We set p-pulses having the same line density in their 180ns-long-heads but having different tail slopes to cut off the effect of stored electrons during the increasing process of the proton bunches.
- eClouds show almost the same growth but different decay slopes in the first turn and following turns.

## eCloud growth to same tail (cold) proton pulse

- We set p-pulses having the same 100ns-long-tails but different heads to concentrate on the effect of the amount of primary electrons
- eClouds show the same growth and decay.
- The amount of primary electrons affect on the surviving electrons after the gap.

## eCloud growth to triangle (cold) proton pulse

- The factors of eCloud growth:
- Energy of electrons hitting the wall  SEY                                                 *Energy distribution of electrons hitting surface in the same-head-p-pulse data*
- Electron traveling time wall to wall  SEY, p-pulse slope and line density                                      *Hard to see*
- Amount of primary electrons          no effect                                            *The same tail p-pulses data*

**Notes:**
Low pBunch slope holds almost same proton line density during 10-20ns fitting
High pBunch slope include the change from top line density to bottom during 20ns fitting
Lower line density reduce growth rate.
Blue “H”s are affected by proton line density (not only by SEY)

## Energy distribution of electrons hitting the surface

- We may use a simple estimation to the growth rate:
- The “hitting_freq” have no big difference among  the same head p-pulses.

**Notes:**
pBunch-same-head energy distribution and SEY graph explain the linear relation of growth rate vs. pBunch slope in the previous page.

## Ring simulation   --- ORBIT script

- Uniform focusing lattice
- 90m long
- Qx = 3.21,  Qy = 2.19
- 1/ρ = 0.07

- [eCloud region 10cm] × [effective coefficient to kick protons 10]

- Number of p-pulse slices:  2048
- Time steps:  6000 or more /turn
- Number of macro protons:  ~10M
- New macro primary electrons: 50K/turn

- Stainless steel, δmax=2.0, LossRate=4e-6

- To save calculation time, we adopt the effective length approach.

**Notes:**
2048 > 80*20 see attachment

## Ring simulation  --- current situation

- Before exploring ep-instability, we use short effective length, 1m, and try to optimize our numerical parameters as time steps, macroSize of electrons and protons and so on, to satisfy numerical stability.
- We are going to use NERSC cluster.

## Conclusion 

- We saw saturation of swept electrons as PSR data, but both slopes of primary and swept electrons are much weaker than the PSR data. Lower loss rate could help. We should develop a new ORBIT tool “surface_monitor” especially for prompt electrons but not for swept electrons.
- We prepare the same head p-pulses and the same tail p-pulses. The growth rate depends on mostly SEY but not on the amount of primary electrons. The electron traveling time from wall to wall may not change largely with varying slopes of p-pulse tail.
- We are optimizing numerical parameters to simulate PSR bunched beam case to assure numerical stability. We are going to use ~64 CPUs in NERSC .
- Discussion:
-  pBunch shape dependency of prompt-swept electron slopes and eCloud growth rate
-  recovery correlation between opposite ES and ED in PSR
-  spectrum calculation of pBunch in the ep ring simulation
- and so on.

## Energy distribution to same head p-pulse (2)

**Notes:**
The energy spectrum of electrons hitting the surface explains the similarity of these growth rates.

## Estimation of computational requirements for PSR bunched beam case

*Two stream model for PSR:*

- For PSR bunch we need to think:
-  About 80*20 longitudinal nodes to simulate the PSR ring
-  The simple case, no boundary, no 3D proton-proton space charge and no longitudinal momentum spread, will require about 80 times as much CPU time as our benchmark calculation (80 min. for 1 turn with SNS 16 CPUs)
-  Setting primary electron production and secondary emission surface instead of linear neutralization factor

**Notes:**
From my talk in ECloud04 (April 2004), Napa, CA.

## “Electron burst” phenomenon

**“****Electron burst” phenomenon (PSR data, IU ep 03/2004)**