# Presentation: 897804

## ILCDR06 WorkshopHighlights

- E. Gianfelice

- _[https://wiki.lepp.cornell.edu/ilc/bin/view/Public/DampingRings/CornellWorkshopTalks](https://wiki.lepp.cornell.edu/ilc/bin/view/Public/DampingRings/CornellWorkshopTalks)_

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## Participants

- Cornell University:
- Michael Billing, James Crittenden, Gerry Dugan, Don Hartill, Robert Meller, Mark Palmer, David Rice,David Rubin, David Sagan, Levi  Schachter, Eugene Tanke, Jeremy Urban
- SLAC:
- Karl Bane, Craig Burkhart, Yunhai Cai, Anatoly Krasnykh, Cho Ng, Mauro Pivi, Gennady Stupakov, Lanfa Wang
- LBNL:
- Christine Celata, Stefano De Santis, Ina Reichel, Marco Venturini, Michael Zisman
- ANL:
- Michael Borland,  Louis Emery, Katherine Harkay, Aimin Xiao

- KEK:
- Kazuhito Ohmi, Yusuke Suetsugu, Junji Urakawa
- INFN-LNF:
- Susanna Guiducci, Fabio Marcellini
- DESY:
- Ferdinand Willeke, Guoxing Xia
- FNAL:
- Panagiotis Spentzouris, Eliana Gianfelice-Wendt
- Gerald Codner (CLASSE), Robert Macek (TechSource/LANL), Thomas Mattison (Univ. of British Columbia), Art Molvik (LLNL),                      George Gollin (University of Illinois), Andy Wolski (University of Liverpool/Cockcroft Institute).

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## Goal

- Opening talk by A. Wolski:
- Not justified double addressed topics worry funding agencies.
- The GDE R&D Board has charged a 10 members task force (S3, chair: A.Wolski)
-    for coordinating efforts.
- S3 suggested meetings focused on the most design affecting issues (kickers, e-clouds, impedance driven instabilities) and comparisons between codes and possibly with measurements.

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-   Two major changes wrt November 2005 baseline:
- one e+ DR (instead of two)
- 650 MHz RF frequency (instead of 500)
- Under re-consideration:
- length
- one tunnel for both DRs

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## Impedance driven instabilities

-                                     Experiments
- K.Harkay  showed results from APS (impedance computations +  simulations vs. measurements). Agreement between theory and measurement is evaluated as ``70 %'', but for the microwave instability 80% larger than computed impedance was needed to get order of magnitude right! Not comforting for the design of new components.
-      Time demanding 3D-codes going to be used for a better estimate
-      of APS components impendance.
- J.Urakawa  summarized the past years attempts of  bunch length measurement and microwave instability detection at ATF in presence of IBS.
-       Large discrepancies between some theoretical  (Bane) and  experimental evaluations of the machine impedance. With new detectors (Silicon Bolometer,  Schottky Barrier Diode)  CSR
-       has been detected, but no microwave instability.
- K.Bane reported briefly on the “puzzling” experience with the 3 SLC DR designs.

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## SLC damping ring summary

| original | 1.1e10 | 1.5e10 |
| --- | --- | --- |
| old | 2.0e10 | 3.0e10 |
| new | 2.0e10* | 1.5e10 |

-                  threshold
-  version  calculated measured

- “sextupole” mode
- quadrupole mode

- *if add 2nH (0.1) inductance

-  **How to understand: from old to new ring reduced the impedance and threshold dropped?**
-    **old, inductive ring—strong mode—tune spread—weak modes Landau damped**
**    ****new, resistive ring—weak mode—little tune spread—no Landau damping**
** ****Note: old ring, SLC operation limited to 3e10, new ring—5e10**

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## Current dependence

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## Impedance driven instabilities

-                            Code developments
- M. Borland  presented the capabilities of  elegant for ``integrated modeling'': one code for (almost) all.
- The current DR design does not meet the Boussard (crude) criterion (for long bunches)!
- New tools for studying microwave instabilities has been presented by
- G. Stupakov (linearized Vlasov-FP equation solver in time domain, accurate but time consuming), S.Heifets and  K.Bane (tracking, fast but prone to noise)
-     and M.Venturini (Vlasov equation).

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## Impedance driven instabilities

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## Impedance driven instabilities

- Consistent with Heifets macroparticle simulationsfor Broad-Band resonator model   (Venturini).

**Current  Threshold**

**Vlasov calculation**

**Macroparticle**
**simulation**

**Normalized current **

*Macroparticle simulation includes radiation effects*

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## Impedance driven instabilities

- Coasting beam: Oide-Yukoya frequency domain VFP solver indicates instability when there is none

**Eigenvalue spectrum**
** ****below  (theory) threshold**** **

-  Theory says all eigenvalues should
-   be on real axis...

**Eigenvalue spectrum**
** ****above (theory) threshold**** **

- only this
-  eigenvalue
- corresponds to a really
- unstable mode

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## e- clouds

- Compare options: simulations recent history

- Cloud density near (r=1mm) beam (m-3) before bunch passage, values are taken at a cloud equilibrium density. Solenoids decrease the cloud density in DRIFT regions, where they are only effective. Compare options LowQ and LowQ+train gaps. All cases wiggler aperture 46mm.

**e****- ****clouds**

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## e- clouds

- To be addressed:
-    e- production suppression through clever vacuum chamber design
-    surface material and conditioning to reduces SEY
-    clearing electrodes design compatible with
-    heat load and beam stability

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## e- clouds

**Some past experience**
- Laboratory measurements:
-         conditioning: SEY~1. In vacuum de-conditioning brings up SEY ~ 1.3
- KEKB tests:
-         conditioning *in situ*. [Cross-benchmarking with simulations gives low SEY~1]
- SPS-CERN:
-   conditioning in situ in the SPS. Minimum measured conditioned surface     SEY~1.5. De-conditioning effect. Electron cloud effects decreased in time
- PSR-LANL:
-       conditioning slow in time and de-conditioning. Still an issue. Measuring electron cloud since 1989!
- Dafne:
-         Luminosity reach is limited.  (Aluminum SEY ~2.0 after conditioning)
- Bfactories:
-         KEKB: smaller bunch spacing is limited by electron cloud. Still after years
-         PEP-II: no problem up to 2.7A.
**Ongoing tests ****	**
-         KEKB (effect of solenoid and fill pattern, see Ohmi presentation), CESRc
-         (no effect of solenoids &wigglers observed, see Rice presentation), Dafne,
-         PEP-II, PSR (e- production and trapping at quads, see Macek presentation).

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## e- clouds

| CLEARING ELECTRODES | BEND | PEP-II LER PR12 | 2007 | Design |
| --- | --- | --- | --- | --- |
| FINS TRIANG. | BEND | PEP-II LER PR12 | 2007 | Design |

|  | TEST in | LOCATION | Ready for INSTALLATION | Status |
| --- | --- | --- | --- | --- |
| SEY TESTS | STRAIGHT | PEP-II LER PR12 | November 2006 | Ready |
| FINS RECTANG. | STRAIGHT | PEP-II LER PR12 | November 2006 | Coating of extruded Al chambers  |

**Next chamber projects:**

- M. Pivi, SLAC

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## e- clouds

- Model for MWS

- Head (W:8 mm,T:7 mm, L:90 mm)
**Copper, 10 mm from beam**
- Support
**BN ****(W: 4 mm, T: 6mm)**
-  ***r* = 4.0, tan**= 0.0008
**Al****2****O****3 ****(W: 4 mm, T: 4mm)**
-  ***r* = 9.0, tan*** *= 0.0001
**Thin layer ****(*****t***** = 0.1mm)**** with conductivity (**********), as a coating**
- Duct
** *********** *****94, L: 300 - 500 mm**
- SiC
**Deby first-order dispersion**
** ***********s*****= 110, **************= 14, ********** = 1********10****-9****s**

- Port 1

- Port 2

- Beam duct

- Support

- Head

- SiC

- SiC

- Calculation
**S****11****between Port 1 and Port 2**
- Antenna: 10 mm
**Frequency mode**

- Debye type

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## e- clouds

-                                  Simulations
- Efforts of improving the e- clouds simulations.
-    Upgrade of ECLOUD and HEADTAIL.
-    New 3D self consistent simulation code by W.Bruns
-    being developed and tested against ECLOUD.
-    WARP-POSINST (LBNL): 3D (and 2D), any boundary, adaptive mesh size, self consistent, benchmarked by the High Current Experiment (HCX) at LLNL.
-    Simulations of e- clouds in wigglers with CLOUDLAND (Lanfa Wang, SLAC).

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## thr

- e- build-up for ILC 2(1)x6 km DR – 2 (ECLOUD)

- _example simulations_
- centre density (m-3) vs. time (s),
- primary photo-electron rate:
- d/ds= 0.001 m-1,
- bunch train followed by gap,
- arc & straight, log scale

- max=1.3, 14.4 ns

- max=1.5, 14.4 ns

- max=1.3, 7.2 ns

- thr

- thr

- thr

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## e- clouds

***WARP***

***POSINST***

- Python

**field calculator**

**ion mover**

**image forces**

**electron source**
**modules**

**kicks from beam**

**diagnostics**

**lattice description**

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

***interpreter***
***& ***
***user interface***

**electron mover**

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## e- clouds

** ****1.**  **2D vs. 3D**
**  ****Head-tail instability**
**  ****Effect of gaps and resultant ecloud**
**  ****Electron cloud & beam in wiggler**

*CPU time is estimate-- depends on problem.  *

**Computer Time will to be Requested (‘07)**
**              ****for WARP-POSINST**

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## CLOUDLAND 3D PIC code for e-cloud (PRST-AB 124402)

- Simulation Key parameters
- (beam,ring,SEY,electrode, ...)

- Mesh Generator

- Magnetic and electric fields input

**Space charge solver**

**Charge mesh**

- Update particle positions

- Advance particle positions using the new beam and e-cloud space charge fields

- Preliminary electron generator when beam passing

- Secondary electron generator

- Preliminary electron generator

**Wake field** Instability code

**Future plan** --Parallelize for consistent instability study

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## Train gap effect (2767bunches)

**Bunch Train gaps reduce the electron cloud density by a factor of 10**

**One  train**

**Short train**

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## Comparison with dipole  

**Dipole, B=0.194T**

**Wiggler**

**There is a lower electron density in Wigglers (one order)! (assuming the same initial electrons rate )**

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## e-clouds

- Experimental tool at LBNL for studying
-  e- production and effect of clearing electrodes
- (see Molvik presentation).

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## A tool for ecloud experiments at LLNL

**INJECTOR**

**MATCHING**
**SECTION**

**ELECTROSTATIC**
**QUADRUPOLES**

**MAGNETIC**
**QUADRUPOLES**

**Focus of Current**
**Electron Cloud Experiments**
**(2 m length)**

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

- low energy heavy ions

- 2 m

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- Marx

- matching

- 10 ES quads

- diagnostics

- diagnostics

- ESQ injector

- 10 Electrostatic quads

- diagnostics

- 4 Magnetic quads

***Parameters***
-   K+ Beam
-   0.2 - 0.5 Amp
-   1 - 1.7 MeV
-   4.5 s pulse

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**MA4**

- 8 “paired” Long flush collectors (FLL): measures capacitive signal + collected or emitted electrons from halo scraping in each quadrant.

- 3 capacitive probes (BPM); beam capacitive pickup ((nb- ne)/ nb).
- 2 Short flush collector (FLS); similar to FLL, electrons from wall.
- 2 Gridded e- collector (GEC); expelled e- after passage of beam
- 2 Gridded ion collector (GIC): ionized gas expelled from beam

- BPM (3)

- BPM

- FLS(2)

- FLS

- GIC (2)

- GIC

- Not in service

- FLS

- GEC

- GEC

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**Notes:**
In the third magnet we have: 
-8 paired FLush collector Long (FLL)

In the fourth magnet we have:

4 capacitive probes (BPM); @ 0, 90, 180, 270 DEGREES, NOT GRIDDED, RECESSED FROM WALL TO REDUCE ION SCRAPING.

2 FLush collector Short (FLS); @ 45, 135, 225. NOT GRIDDED, 

2 Gridded Electron Collector (GEC); GRIDDED, RECESSED FROM THE WALL, @ 315 DEGREES, CORRESPONDING LOCATION TO FLS POSITIONS  - MEASURES EXPELLED SECONDARY ELECTRONS AFTER PASSAGE OF BEAM PULSE/TAIL.  ***NOT WORKING YET***

2 Gridded Ion Collector (GIC), DOUBLE GRIDDED TO SUPRESS TO HIGH DEGREE THE CAPICITIVE SIGNAL.

## ILC DR Test Facilities

- New propsed DR Test Facilities:
- M.Palmer presented the plan for transforming
-  CESR in a ILC DR Test Facility (starting in 2008, 50%
-  time sharing with SR experiments, Touschek lifetime:
-  7 minutes).
- F.Willeke presented the plan for transforming
-   HERA-e into a ILC DR Test Facility.
- Suetsugu speculated about the possibility of transforming KEKB into a DR  Test Facility (if Super KEKB get not support from the japanese HEP community?).

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## 1) What Can CESR Offer?

- CESR offers:
**The only operating wiggler-dominated storage ring in the world**
**The CESR-c damping wigglers**
- Technology choice for the ILC DR baseline design
**Flexible operation with ****positrons***** and***** electrons**
**Flexible bunch spacings suitable for damping ring tests**
- Presently operate with 14 ns spacing
- Can operate down to 2 ns spacings with suitable feedback system upgrades
**Flexible energy range from 1.5 to 5.5 GeV**
- CESR-c wigglers and vacuum chamber specified for 1.5-2.5 GeV operation
- An ILC DR prototype wiggler and vacuum chamber could be run at 5 GeV
**Dedicated focus on damping ring R&D for significant running periods after the end of CLEO-c data-taking**
**A useful set of damping ring research opportunities...**
- The ability to operate with positrons and with the CESR-c damping wigglers offers a unique experimental reach

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## Lattice Comparisons

|  | CesrTF | ATF | TESLA | ILC 6.7 km |
| --- | --- | --- | --- | --- |
| Cicumference (m) | 768 | 139 | 17000 | 6695 |
| Energy (GeV) | 2.0 | 1.28 | 5.0 | 5.0 |
| Horizontal Emittance (nm) | 2.25 | 1.0 | 5.1 | 0.515 |
| Vertical Emittance (pm) | 5.0 (target) | 4.5 | 1.4 | 1.4 |
| Energy Spread (x10-3) | 8.6 x10-4 | 5.5 x10-4 | 1.3 x10-3 | 1.3 x10-3 |
| Jx | 1.0 | 1.6 | 1.0 | 1.0 |
| Jy | 1.0 | 1.0 | 1.0 | 1.0 |
| Qx | 14.53 | 15.141 | 76.310 | 52.397 |
| Qy | 9.59 | 8.759 | 41.180 | 49.305 |

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## Pulse generator 

**Pulse generator**

**Specifications**
**Amplitude at 50 ohm : 5 kV**
**Rise time :****	****	**** 1-1.4 ns**
**Pulse width at 50% of amplitude : **
**                                     ****2-3 ns**
**Maximum Pulse Repetition Frequency **
**in burst mode :     **_**3 MHz**__** **_

***FID Technology has very fast and high repetition rate pulse generators. The specification meets our requirements for the high voltage pulse source. We tested the kicker performance by using the pulse PS.****   *

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## Beam kick experiment at ATF DR

**Beam kick experiment at ATF DR**

***The kicker pulse is applied to the strip-line electrode when the beam goes through the electrode.***
***The beam kick is observed by a turn-by-turn BPM as the amplitude of the oscillation of the betatron frequency component.***
***The kick effect is measured by scanning the pulse timing precisely. ***

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## Measurement result of FPG5-3000M

- The achieved resolution is 0.2rad.

- Rise time~3.2ns
- Kick angle ~91rad
- (calc.	94.7rad)

- Expanded horizontal scale

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- Comments (Zisman)
**existing “FID” tests seem to have been DSRD pulsers!**
**concerns about robustness**
**single-source issue**
**Alternative solutions need to be studied.**
**A working kicker design meeting impedance and vacuum properties is still to be demonstrated. **
**HV feed-through are critical. **
**Consider use of an injection bump for relaxing**
**   ****kicker requirement: is it feasible?**

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