# Presentation: 509595

## Filling in the Roadmap for self-Consistent 

**Electron Cloud and Gas Modeling**

**Particle Accelerator Conference**
**May 16-20, 2005**
**Knoxville, TN, USA**

**J.-L. Vay**
**Lawrence Berkeley National Laboratory**
**and the**
**Heavy Ion Fusion Virtual National Laboratory**** **

## OUTLINE

**Who we are and why we care about e-cloud**
**The “roadmap” to self-consistency**
**Our simulation tools**
**Example of comparisons of WARP-POSINST with HCX**
**Application to High Energy Physics: 1 LHC FODO cell**
**Conclusion**

## OUTLINE

**Who we are and why we care about e-cloud**
**The “roadmap” to self-consistency**
**Our simulation tools**
**Example of comparisons of WARP-POSINST with HCX**
**Application to High Energy Physics: 1 LHC FODO cell**
**Conclusion**

## Heavy Ion Inertial Fusion or “HIF” goal is to develop an accelerator that can deliver beams to ignite an inertial fusion target 

**Heavy Ion Inertial Fusion or “HIF” ****goal is to develop an accelerator that can deliver beams to ignite an inertial fusion target**** **

**Target Requirements:**
**   ****3 - 7 MJ     x    ~ 10 ns               ******** *****~ 500 Terawatts***
**   ****Ion Range:     0.02 - 0.2 g/cm****2****  ********  *****1- 10 GeV*****                            **

***Near term goal: ***
***High Energy Density Physics (HEDP)***

**For A ~ 200  ******** ****	*****~ 10 ******16****** ions***
***	******	******~ 100 beams***
***	******	******1-4  kA / beam****** ***

**DT**

## The Heavy Ion Fusion Virtual National Laboratory:
			LBNL
			LLNL
			Princeton Plasma Physics Laboratory
Working on e-cloud (in addition to R. Davidson and H. Qin):
		Miguel Furman  (LBNL)
			 LBNL is lead lab for LARP on e-cloud
		Ron Cohen  (LLNL)
		Jean-Luc Vay  (LBNL) 
		Alex Friedman  (LLNL)
		Dave Grote (LLNL)
		Art Molvik  (LLNL)
		Peter Seidl   (LBNL)
		Frank Bieniosek  (LBNL)
		Michel Kireef-Covo  (GS, LLNL)
     Also:	Peter Stoltz, through coordinated SBIR at Tech-X
		Prof. John Verboncoeur, UCB NE 				

- 			LBNL
- 			LLNL
- 			Princeton Plasma Physics Laboratory
- Working on e-cloud (in addition to R. Davidson and H. Qin):
- 		Miguel Furman  (LBNL)
- 			 LBNL is lead lab for LARP on e-cloud
- 		Ron Cohen  (LLNL)
- 		Jean-Luc Vay  (LBNL)
- 		Alex Friedman  (LLNL)
- 		Dave Grote (LLNL)
- 		Art Molvik  (LLNL)
- 		Peter Seidl   (LBNL)
- 		Frank Bieniosek  (LBNL)
- 		Michel Kireef-Covo  (GS, LLNL)
-      Also:	Peter Stoltz, through coordinated SBIR at Tech-X
- 		Prof. John Verboncoeur, UCB NE

**Simulation & theory**

**Experiment**

**HIF-VNL/e-cloud team (LDRD’s at LLNL & LBNL)**

## Why do we care about electrons?We have a strong economic incentive to fill the pipe.

- (from a WARP movie; see http://hif.lbl.gov/theory/simulation_movies.html)

- Time-dependent 3D simulations of HCX injector reveal beam ions hitting structure

**Notes:**
Show movie.

## OUTLINE

**Who we are and why we care about e-cloud**
**The “roadmap” to self-consistency**
**Our simulation tools**
**Example of comparisons of WARP-POSINST with HCX**
**Application to High Energy Physics: 1 LHC FODO cell**
**Conclusion**

## “Roadmap” toward self-consistent modeling of beam with e-cloud & gas effects.

- Key: operational; partially implemented  (5/6/05)

- WARP ion PIC, I/O, field solve
- 
- fbeam, , geom.

- electron dynamics
- (full orbit; interpolated drift)

- wall electron source

- volumetric (ionization) electron source

- _gas module_

- emission from walls

- ambient

- charge exch.

- ioniz.

- nb, vb

- fb,wall

- fb,wall

- 

- sinks

- ne

- ions

- Reflected
- ions

- fb,wall

- gas transport

## OUTLINE

**Who we are and why we care about e-cloud**
**The “roadmap” to self-consistency**
**Our simulation tools**
**Example of comparisons of WARP-POSINST with HCX**
**Application to High Energy Physics: 1 LHC FODO cell**
**Conclusion**

## WARP has many well-tested features ...

**Geometry: ****3D, (x,y), or (r,z)**
**Field solvers:**** FFT, capacity matrix, multigrid**
**Boundaries:**** “cut-cell” --- no restriction to “Legos”**
**Bends:**** “warped” coordinates; no “reference orbit”**
**Lattice description:**** general; takes MAD input**
**solenoids, dipoles, quads, sextupoles, ...**
**arbitrary fields, acceleration**
**Beam injection: ****Child-Langmuir, and other models**
**Diagnostics:**** Extensive snapshots and histories**
**Parallel:**** MPI**
**Python and Fortran: ****“steerable,” input decks are programs **
**a GUI is also available**

## ... and new features advancing the                                         state of the art ...

**	****- LHC ****3-D ****simulation: Cell count reduced ****20,000x**
** **
**New electron mover that allows large time steps**
**E-cloud and gas models**
**Prototype Vlasov solver (for halo)**

**... ****and *****new features***** advancing the****                                         state of the art ...**

*Beam coming off source ****x 11 speedup***

## Problem: Electron gyro timescale 
     << other timescales of interest
	 brute-force integration very slow due to small t
Solution*: Interpolation between full-particle dynamics (“Boris mover”) and drift kinetics (motion along B plus drifts)	

**     ****<< other timescales of interest**
**	******** ****brute-force integration **_**very**_** slow due to small ********t**
**Solution*:**** Interpolation between full-particle dynamics (“Boris mover”) and drift kinetics (motion along B plus drifts)****	**

**We have invented a new “mover” that relaxes the problem of short electron timescales in magnetic field***

**Magnetic quadrupole**

**Sample electron motion in a quad**

- *R. Cohen et. al., Phys. Plasmas, May 2005; ROPA009, Thursday, Ballroom A, 16:45

- small t=0.25/c
- Standard Boris mover
- (**reference case**)

- large t=5./c
- New interpolated mover

- large t=5./c
- Standard Boris mover
- (**fails in this regime**)

**Test:**** Magnetized two-stream instability****	**

## POSINST has been used extensively for e-cloud calculations

**Follows slice of electrons at one location along beam line  **
**	****	****2-D PIC  for e****–**** self force**
**	****	****analytical kick for force of beam on electrons**
**Effect of electrons on beam -- minimally modeled**
**	****	****dipole wake**
**Good models for electron production by:**
**	****	****synchrotron radiation**
**	****	****residual gas ionization**
**	****	****stray beam particles hitting vacuum wall**
**	****	****secondary electron production (detailed model)**

_***POSINST calculates the evolution of the electron cloud***_

**POSINST has been used extensively for e-cloud calculations**

## We have merged WARP and POSINST (with support of coordinated LBNL & LLNL LDRD’s)

***POSINST***

- Python

**field calculator**

**ion mover**

**image forces**

**electron source**
**modules**

**kicks from beam**

**diagnostics**

**lattice description**

***x******i******, v******i***

***framework***
***& ***
***user interface***

**electron mover**

**We have merged WARP and POSINST (with support of coordinated LBNL & LLNL LDRD’s)**

## Recent additions

- Gas module
- emit neutrals (as macro-particles) from beam ion impact according to incident particle energy and angle of incidence
- Ionization module
- create macro-ions and macro-electrons resulting from impact ionization of gas molecules

## OUTLINE

**Who we are and why we care about e-cloud**
**The “roadmap” to self-consistency**
**Our simulation tools**
**Example of comparisons of WARP-POSINST with HCX**
**Application to High Energy Physics: 1 LHC FODO cell**
**Conclusion**

## Current HCX Configuration(High Brightness Beam Transport Campaign, 2005)

**INJECTOR**

**MATCHING**
**SECTION**

**ELECTROSTATIC**
**QUADRUPOLES**

**MAGNETIC**
**QUADRUPOLES**

**Focus of Current**
**Gas/Electron Experiments**

_**Additional Experiments:**_** Fill-Factor Measurements,                Head-Tail Correction, Wave Experiments**

**1 MeV, 0.18 A, t ≈ 5 ********s, **6x1012 K+/pulse

## We are looking at fundamental questions*

- Primary electron emission
- yield & velocity distribution
- Secondary emission
- yield & velocity distribution
- Desorbed gas
- mechanism, yield & velocity distribution
- Accumulation & retention in quads
- loss mechanisms, sources
- Effects of electrons on beam
- harder - must exaggerate sources because of short experiment
- Efficacy of mitigation methods

- *A. W. Molvik et. al., ROPB002

## Beam hits end-plate in HCX to generate copious electrons leading to observable effects on the beam

- Capacitive
- Probe (qf4)

**Clearing electrodes**

**Suppressor**

- Time-dependent beam loading in WARP from moments history from HCX data:
-  current
-  energy
-  X-Y (assume semi-gaussian)
-  RMS envelopes, emittances
-  slopes
-  beam centroids
-  slopes average
- (4-D phase-space reconstruction in develop.)

***200mA K******+***

**e****-**

## Comparison sim/exp: clearing electrodes and e-supp. on/off

**Comparison sim/exp: clearing electrodes and e-supp. on/off**

*  ***beam ions**

*  ***secondary electrons**

*  ***electrons from ions hitting surface**

***200mA K******+***

## Comparison sim/exp: 3 clearing electrodes biased (no sec.)

**Comparison sim/exp: 3 clearing electrodes biased ****(no sec.)**

**(a)**

**(b)**

**(c)**

**(qf4)**

## Comparison sim/exp: 3 clearing electrodes biased

**Comparison sim/exp: 3 clearing electrodes biased**

**(a)**

**(b)**

**(c)**

**(qf4)**

## Comparison sim/exp: 3 clearing electrodes biased

**Comparison sim/exp: 3 clearing electrodes biased**

**(a)**

**(b)**

**(c)**

**(qf4)**

**(a)**

**(b)**

**(c)**

***200mA K******+***

**e****-**

**+9kV                 +9kV                     0V                            0V**

**(qf4)**

## Comparison sim/exp: first clearing electrode biased

**Comparison sim/exp: first clearing electrode biased**

**(a)**

**(b)**

**(c)**

**(qf4)**

**(a)**

**(b)**

**(c)**

***200mA K******+***

**e****-**

**+9kV                   0V                       0V                           0V**

**(qf4)**

## OUTLINE

**Who we are and why we care about e-cloud**
**The “roadmap” to self-consistency**
**Our simulation tools**
**Example of comparisons of WARP-POSINST with HCX**
**Application to High Energy Physics: 1 LHC FODO cell**
**Conclusion**

## Study of e-cloud in LHC FODO cell

- SPS sees surprisingly long-lasting e-cloud  (~ second)
- The problem:
- 	Simulate “multibunch, multiturn” passage of beam through FODO cell (100 m):
- 			   	dipoles
- 				quadrupoles
- 				drifts
- 	Electrons    synchrotron radiation, secondary emission
- Study:
- 	Electron accumulation and trapping in quads
- 	Power deposition from electrons

## We are beginning to use WARP to study e-cloud in LHC

**(particles colored according to radius)**

**beam (scaled 10x)**

**electrons**

**We are beginning to use WARP to study e-cloud in LHC**

**1 LHC FODO cell**

**F B  B   B D B   B   B**

**T=2********s**

## OUTLINE

**Who we are and why we care about e-cloud**
**The “roadmap” to self-consistency**
**Our simulation tools**
**Example of comparisons of WARP-POSINST with HCX**
**Application to High Energy Physics: 1 LHC FODO cell**
**Conclusion**

## Conclusion

- Near completion of a new capability that follows “roadmap” toward self-consistent modeling of beam with e-cloud and gas
- PIC; Lattice; AMR; new electron mover; secondary e-; photo-e-; neutrals generation and tracking; ionization.
- Comparison with HCX experiment are very encouraging
- demonstrated importance of secondary electrons,
- inclusion of desorbed neutrals and ionization from halo, using newly developed modules, should help to close remaining gap.
- Started to apply to High-Energy physics
- first 3-D time-dependent simulation of LHC FODO cell,
- study application to RHIC, and maybe others.