# Presentation: 102165

## Art Molvik
for the
Heavy Ion Fusion Science Virtual National Laboratory
Program Advisory Committee Review
August 9-10, 2006

- for the
- Heavy Ion Fusion Science Virtual National Laboratory
**Program Advisory Committee Review**
**August 9-10, 2006**

**Progress in e-cloud studies in both solenoids and quads**

_**Outline**_
- Accomplishments
- Why we made progress
- Opportunities on HCX, STX, NDCX,...
- Planning for future

**Notes:**
Give context for each major topic

	What were our objectives in 2005?
	Significance of each measurement presented

## Sources of electron clouds

** ****ion induced emission from**
** ****expelled ions hitting vacuum wall**
** ****beam halo scraping**

**Sources of electron clouds**

_**Primary:**_
_**Secondary:**_

*i**+*	= ion* *
*e**-**	*= electron
- g 	= gas
- = photon
- 	= instability

***Positive***
***Ion Beam***

***Pipe***

** ****Ionization of **
** ****background gas **
** ****desorbed gas**

** ****secondary emission from electron-wall collisions**

*e**-*

** ****photo-emission from synchrotron radiation (HEP)**

******

## HIFS-VNL has unique tools to study ECE

**WARP/POSINST code goes beyond previous state-of-the-art**
**Parallel 3-D PlC-AMR code with accelerator lattice follows beam ****	**_**self-consistently**_** with gas/electrons generation and evolution**
**HCX experiment addresses ECE fundamentals relevant to HEP (as well as WDM and HIF)**
_**trapping potential ~2kV**_** with highly instrumented section dedicated to e-cloud studies**
**Combination of models and experiment unique in the world**
**unmatched **_**benchmarking**_** capability essential to our credibility **
**‘****Benchmarking’ can include: a. Code debug**
**	****	****b. validate against analytic theory**
**	****	****c. Comparison against codes**
**	****	****d. Verification against experiments**
**enabled us to attract work on LHC, FNAL-Booster, and ILC problems**

## HCX is now dedicated to gas/electron effects studies 

- Capacitive
- Probe (qf4)

**Clearing electrodes**

**Suppressor**

***K******+***

**e****-**

**Short ****experiment => need to ****deliberately amplify**** electron effects: **let beam hit end-plate to generate copious electrons which propagate upstream.** **

**End plate**

**INJECTOR**

**MATCHING**
**SECTION**

**ELECTROSTATIC**
**QUADRUPOLES**

**MAGNETIC**
**QUADRUPOLES**

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

**HCX is now dedicated to gas/electron effects studies**** **

- Retarding  Field Analyser (RFA)

**Location of Current**
**Gas/Electron Experiments**

- GESD

## ~6 MHz signal is observed in simulation & experiment

**Good test of secondary module                   **- secondary electron emission turned off:
**run time ~3 days, **
**	**- without new electron mover and MR, run time would be ~1-2 months!

**~6 MHz signal is observed in simulation & experiment**

- WARP-3D
- T = 4.65s

**Oscillations**

**Beam ions hit end plate**

**e****-**

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

**Q4**

**Q3**

**Q2**

**Q1**

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

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

**       ****Electrons**

**“****Most successful benchmarking result in the world!” **
**M. Furman**

- _x0003__x0016_

**(c)**

**0.            2.      time (********s)       6.**

**0.**
**-20.**
**-40.**

**I (mA)**

**Potential contours****	**

**(c)**

**0.            2.      time (********s)       6.**

**I (mA)**

**0.**
**-20.**
**-40.**

**Electrons **
**bunching**

## HCX experiment and WARP simulations agree quantitatively on oscillation
frequency
wavelength
amplitude

**frequency**
**wavelength**
**amplitude**

**Array of BPMs in Quad 4 verified simulation results**

**Beam Position Monitor (BPM): **
**         ****electrode capacitively coupled to beam**

**Notes:**
... & this is why we want to keep HCX running.

## Retarding field analyzer (RFA) measures potential on axis = ion-repeller potential

+ beam/e- distr. => f=Ne/Nbeam

**Retarding field analyzer (RFA) measures potential on axis = ion-repeller potential**
**+ beam/e- distr. => f=N****e****/N****beam**

**First time-dependent measurement of absolute electron cloud density ****& major discrepancy with simulation**

**Absolute electron fraction can be inferred from RFA and clearing electrodes**
**Michel Kireeff Covo, PRL 97, 54801 (2006)**

| Beam neutralization | B, C, S on | B, C off 
S on | B, C, S off |
| --- | --- | --- | --- |
| Clear ElectrodeA | ~ 7% | ~ 25% | ~ 89% |
| RFA | (~ 7%) | ~ 27% | ~ 79% |

**/RFA**

**Sim~89%**

**•****	****Clearing electrodes provide independent measurement of e****-**** density, confirms RFA**
**•****	****Both RFA and clearing electrodes measure unattenuated transport of electrons through 3 quads whereas WARP finds x0.5 attenuation at each gap.**
**•****	****We are adding diagnostics and a controllable source of electrons (e-gun) to study electron transport and compare with WARP to resolve discrepancy.**

**Notes:**
... & this is why we want to keep HCX running.

## Electron effects on beam more accurately simulated

**Beam loading in simulation now uses reconstructed data from slit-plate measurements **
**leads to improved agreement between simulation and experiment**

**Semi-gaussian load =>**
**New load from reconstructed data =>**

**X'**

**X**

**X**

**X'**

**X'**

**Low e-**

**Hi e-**

**Hi e-**

**Hi e-**

**No e-**

**No e-**

## Improved model for beam energy and angle of incidence scaling of ion-induced electron yield*

**Improved model for beam energy and angle of incidence scaling of ion-induced electron yield***

**Gas-Electron Source Diagnostic (GESD) measures ion-induced electron yield near grazing incidence**** **

***Michel Kireeff Covo, PRSTAB 9, 063201 (2006).**

**Better agreement with data at low-energy (≤400 keV) range where 1/cos(********) dependency breaks**

**Notes:**
... & this is why we want to keep HCX running.

## Intense beam excitation of gas – enabled measuring velocity distribution of desorbed gas

**Observation: desorbed gas in beam emits light**

**View expanding gas cloud from side – f(v****0****) normal to hole plate [with gated camera or streak camera]**

**Notes:**
1st bullet: RPA will also measure beam potential, from peak of ion energy distribution. It can also be biased to measure electrons that detrap during the current fall time.

4th bullet: data from HCX and STS-500 is consistent with the electronic component of dE/dx responsible for gas desorption with no significant contribution from nuclear scattering, so we've identified the energy source driving desorption. Experiments up to 4 MeV, with a variety of ions and targets will recheck this conclusion, but more importantly will begin to study the various particle sources. [The HCX/STS work will be submitted to a major journal, probably Nature - so maybe leaving 4th bullet on S18 as you have it is best.

## Optical gas measurement has other applications

**Velocity distribution of desorbed gas measured**
**[Further details from Frank Bieniosek]**

**Future plans:**
**•****	****Absolute calibration to obtain desorption coef. by injecting  beam through gas of known pressure**
**•****	****Then can measure desorption from Non-evaporable Getter (NEG), ...**
**	****[Collaborate with GSI vacuum group]**

**Notes:**
1st bullet: RPA will also measure beam potential, from peak of ion energy distribution. It can also be biased to measure electrons that detrap during the current fall time.

4th bullet: data from HCX and STS-500 is consistent with the electronic component of dE/dx responsible for gas desorption with no significant contribution from nuclear scattering, so we've identified the energy source driving desorption. Experiments up to 4 MeV, with a variety of ions and targets will recheck this conclusion, but more importantly will begin to study the various particle sources. [The HCX/STS work will be submitted to a major journal, probably Nature - so maybe leaving 4th bullet on S18 as you have it is best.

## Electron accumulation and effects on beam transport in solenoidal field – commissioning

**Electron accumulation and effects on beam transport in solenoidal field – commissioning**

**                                 ****Short electrodes in                  **
**                      ****solenoids expel or attract **
**               ****electrons, long electrodes **
**       ****collect or emit electrons along solenoidal field lines between magnets.**

## WARP/POSINST applied outside HIF program

**In collaboration with CBP (M. Furman)**
**LARP funding (started FY06, 0.2 FTE): simulation of e-cloud in LHC**
**FNAL funding: study of e-cloud in MI upgrade (hiring post-doc)**
**ILC (with C. Celata, M. Venturini): start work this summer**

**Quadru****poles**
**Drifts**
**Bends**

**WARP/POSINST-3D - t = 300.5ns**

**1 LHC FODO cell (~107m) - 5 bunches - periodic BC (04/06)**

## CERN staff interested in our capabilities

**Simulations show tenuous electron clouds (below instability threshold) increase emittance of LHC beam.**
**Request from Frank Zimmermann and Elena Benedetto to compute initial electron distribution for her simulation starting point, using our self-consistent 3-D code WARP.**
**Repeat simulation with WARP, when it can do many turns in LHC.**
**Jean-Luc Vay invited to speak at CERN Oct. 6, 2006.**
**Above results may increase interest of CERN management**

## VNL has capabilities for High-Brightness Studies

**Issues**
**Beam potential**
**Beam transport**
**Duration (μs)**
**Access**

**HCX**
**2 kV**
**Quads**
**5**
**Between quads and ends**

**	****      ****NDCX**
**STX (****Solenoid****)**
**0.4 kV**
**Solenoids**
**≤****~20**
**End**

**NDCX (quads)**
**0.4 kV**
**Quads**
**≤****~20**
**End**

**Exploit other capabilities such as Paul Trap at PPPL or UMER at Univ. Maryland for testing some slowly-growing phenomena, to supplement our short accelerators.**

## Expectations for electrons in quadrupoles and solenoids

**Transport**
**Quadrupoles**
**Solenoids (********)**
**Solenoids (********)**

**Axial flow**
**Electrons drift slowly**
**Electrons flow freely over entire length**
**Electrons flow freely for 1-magnet length**

**Radial flow**
**Electron flow along B is slightly impeded by magnetic gradient**
**Electron flow suppressed**
**Electron flow suppressed except between magnets**

**Not yet clear which is superior for WDM/HIF needs, motivates present STX-ECE experiments**

## Our present plan for future

**WDM/HIFS**** **
**Continue coordinated experiments and simulation of electrons and gas effects on HCX magnetic quads in search of complete quantitative agreement – publish areas of agreement and work on areas of disagreement**
**Beginning solenoid studies, for near-term support of WDM**
**Study mitigation techniques**
**HEP**
**implement hybrid (3-D beam though 2-D e- slabs) “quasi-static” mode to study slow e-cloud driven emittance growth, which is a growing concern for LHC**
**study e-cloud in ILC, FERMILAB, possibly RHIC**
**develop experiments/diagnostics on HCX/NDCX relevant to HEP**
**Collaborate with GSI to study beam-induced desorption from Non-Evaporable Getters (NEG).**

## Reconvene High-Brightness Planning Group

- Goal: What do we need to know to initiate larger HIF facility ~2010 [After NIF ignition and ITER spending-peak]
- Or – Learn enough to add validated effects into IBEAM systems code
- &  – Apply to near term WDM accelerators
**Issues: **
**E-cloud, gas-cloud (quads vs sols, transport, conditions to assure non-degraded operation)**
**Halo**
**Beam transport limits**
**Emittance growth**
**Mitigation ...**
**Strategy: **
**Benchmark codes over wide parameter range for verified predictive capability **
**Verify codes with HCX, NDCX, STX, PTSX, UMER... (The Paul Trap Simulation Experiment and U-Maryland Electron Ring can test effects that occur over 100’s of lattice periods).**
**Use lists of issues from previous workshops**

## External recognition of High Brightness program

**Significant publications:**
**PRL – Measure electron cloud density**
**PRSTAB – Measure & model e- emission by ion impact**
**POP – e- mover successes**
**Recognition with invited papers**
**PAC05 ****	****	****2**
**HB2006****	****	****2**
**HIF06****	****	****3**
**CAARI-06****	****	****1**
**ICAP06****	****	****1**
**DPP05/06 ****	****	****1/1**
**AVS06****	****	****1**
**Invitations from CERN, FNAL for talks and assistance**

## BACKUP

**Slides**

## WARP-POSINST code suite is unique in four ways 

**WARP-POSINST code suite is unique in four ways**** **

**  ****merge of WARP & POSINST**