# Presentation: 170595

## LARP Accelerator Systems  Accelerator Physics Task 1.4.1.5 LHC Electron Lenses         

*Vladimir Shiltsev** *

## Context

- LHC Electron Lenses – LARP CM9

- Fascinating Beam-Beam Compensation results in Tevatron – proton lifetime doubled by Electron Lenses
- BEAMS’07: “...Achievement by itself as first demonstration of active BBC in working hadron collider”
- Effect is believed to be mostly due to tune-shift compensation
- LHC-ELs for Head-on or/and LR BB Compen- sation of great interest (e.g., LARP IRUP)

## Recent events

- LHC Electron Lenses – LARP CM9

- New AP task  “LHC Electron Lenses for Beam-Beam Compensation” was proposed  at the previous CM8 (April 2007, Fermilab)
- May ‘07: “Gang of 5+1” recommended the task to start in FY08 (endorsed by CERN)
- June’07: LARP Executive Committee OK’d it
- Task Sheet drafted in July, recently modified
- FY08 budget guidance:
- 160k$ in FY08= 80k$ FNAL, 40k$ SLAC, 40K$ BNL

## Head-On Beam-Beam Compensation

- LHC Electron Lenses – LARP CM9

- Conditions for full footprint compression (tune-spread compensation) in *p-p* collider:
- Transverse electron profile should match proton profile at IP (presumably, Gaussian)
- Total number of electrons in the EL should be
-  e.g. for the LHC *N_p*=1.15e11, *N_ip*=3, for 10kV electrons (beta=0.2) one needs N_e=3.45e11 or **J_e=1.4 A in L=2 m long e-beam **
- Location of e-lens is not important in first order (footprint) but may be important for RDT, *β**_x=**β**_y*, *D_x*=0 desired

## Head-on beam-beam compensation

- LHC Electron Lenses – LARP CM9

*ca.1997*

## LHC Electron Lens : Footprint 

- LHC Electron Lenses – LARP CM9

- LHC Electron Lens : Footprint

*TEL ****off, ****LRBBWire ****off***

*TEL ****on, ****LRBBWire ****on***

*1.8A DC LEL with Gaussian current profile shrinks LHC     footprint  (LHC Lumi-upgrade, U.Dorda,et.al,  PAC’07)*

## Another Example: RHIC HO-BBC

- Electron Lenses: TeV, RHIC, LHC

- 10th

- 13th

- 16th

- 19th

- 3rd

**RHIC p-p ****ξ****=-0.01, ****dQ=-0.02**
**Beam-beam blowup @ start store**
**E-lens solution: fit btw ****2/3**** & ****7/10**
**Group is perf’ing simulations**

- Y.Luo, W.Fischer
- N.Abreu, et.al

- J=1.2A,σ=0.43mm

## Degree of Compensation

- LHC Electron Lenses – LARP CM9

- Is full tune-spread compensation needed?
- Single bunch coherent stability?
- Multibunch coherent stability?
- Gain in lifetime or emittance growth?
- higher the current more stable it should be
- What’s optimal?
- avoid “footprint folding”
- original thinking was to compensate to max tolerable *dQ_spread *= 0.010 ?
- Yuri Alexahin suggested to compensate to d*Q_spread=0.003*  - better coherent beam-beam

## 50% Head-On Compensation

- LHC Electron Lenses – LARP CM9

- Full LR-BBC and 50% HO-BBC (U.Dorda)

## Our Approach (see Task Sheet)

- LHC Electron Lenses – LARP CM9

- Obviously, just footprints are not convincing
- We will:
-  carry out relevant experiments with TELs
-  perform numerical simulations
-  do theoretical analysis
- Deliverables:  comprehensive summaries to conclude on  BBC in LHC with e-lens
- on numerical studies of head-on BBC
-  on general LEL layout
-  on BBC studies in Tevatron

## Experiments in Tevatron

- LHC Electron Lenses – LARP CM9

- Study effects of TEL on proton beam lifetime with smaller ~1-2 sigma electron beam size
- Same  with antiprotons
- b-b effect is small, not much to compensate
- Can we see footprint/BTF shrinkage?
- If results are interesting/promising  build and install Gaussian electron gun
-  15-20k$ M&S
- Installation time uncertain (mb ‘09)

## Experiments with TEL

- LHC Electron Lenses – LARP CM9

## Gaussian Electron Gun

-  BBC

- LHC Electron Lenses – LARP CM9

- V.Kamerdzhiev
- G.Kuznetsov

## Numerical Simulations

- LHC Electron Lenses – LARP CM9

- General Approach:
- show that beam-beam effects turn “bad” above certain intensity N_p/bunch
- either introduce wires or turn off log-range BB and see how much further increase possible
- Turn-on e-lenses and see improvement
- Indications of “bad” in simulations
- Dynamic aperture	   not  observable
- Beam lifetime    	   measurable
- Emittance growth     measurable
- Coherent stability     measurable

## Simulation Codes

- LHC Electron Lenses – LARP CM9

- All codes are good by definition
- Differences are:
- Whether all relevant  factors and effects are taken into account
- Who runs the code and critically questions results
- Benchmarking with reality of collider
- We intent to employ three groups
- FNAL   (A.Valishev + guest+VS):   LIFETRAC  w-s
- BNL     (Y.Luo and N.Abreau, W.Fischer)	  DA+
- SLAC  (A.Kabel)					s-s, w-s

## LIFETRAC simulation: TEL on P12

- LHC Electron Lenses – LARP CM9

- A. Valishev

## Analytical approach

- LHC Electron Lenses – LARP CM9

- Yu.Alexahin

- The10***x*+6***y* resonance driving term for *a**x *=* a**y *=* a*/21/2: 1 – 2 TELs with flat-top e-beam (Fig.4, curve 2), 2 - 2 TELs with Gaussian e-beam, 3 – 1 TEL with Gaussian e-beam at location with ***x *= ***y*

## Plans

- LHC Electron Lenses – LARP CM9

- Given the status of the codes and groups,  budget guidance and available resources we, most probably, will be able to accomplish the task in FY09
- In FY08 we can:
- Get LHC lattice and load it into all codes
- Scan tunes around nominal
- Scan chromaticity dependencies
- Observe “bad” b-b-effects vs N_p
- We will work in close contact with BBLR team

## Back up slides

- LHC Electron Lenses – LARP CM9

## Long Range Compensation

- LHC Electron Lenses – LARP CM9

- DC wire can do the job better
- simpler
- cheaper
- ... but only for reasonable beam-beam separations
-    (3...4...5? Sigma)
- Electron Lens can
- act as “electron wire” at ANY separation
- not infinite current! (enough for 2-4 parasitics)
- current variable bunch-by-bunch
- can compensate b-b-b tune spread in *XX *crossing with many parasitics (next slide)

## Bunch tunes for XY and XX

- LHC Electron Lenses – LARP CM9

- Bunch tunes for *XY* and *XX*

## Location in LHC – I (55 cm)

- LHC Electron Lenses – LARP CM9

- J.Johnstone
- LARP-doc-560

- D_x < 9 cm
- σ = 1.1 mm
- @ *β**=2300m*

## Where are we now?

- LHC Electron Lenses – LARP CM9

- There is interest at FNAL, BNL, CERN :
- FNAL wants to study and understand TEL effects and put TELs in Tevatron Collider operations
- Tevatron stops in Sep 2009 (Sep 2010 possible)
- BNL wants to simulate, build and install RELs for head-on BBC in RHIC
- 1 year for simulations, 1-2 years to build and install
- CERN wants to explore LEL possibilities for the  LHC luminosity upgrade(s)
- The first upgrade in 2012 (?), big upgrade in 2016(?)
- We all want to collaborate and get others in

## Resources

- LHC Electron Lenses – LARP CM9

- Fermilab:
- V.Kamerdzhiev and full time Engineer, 10% VS
- A.Valishev, Yu.Alexahin (part-time, theory & simulation support)
- Brookhaven:
- Y.Luo and his group to simulate and develop
- W.Fischer – management and operation support
- CERN:
- Excellent work by U.Dorda, hope for T.Pieloni
- Support/interest from FZ, JPK, OB
- LARP will support ELs in FY08 : 1-1.5 FTE

## High priority items

- LHC Electron Lenses – LARP CM9

- Fermilab:
- Continue studies:
- Beam size effect
- Quantify Improvement vs e-current *R(J_e)*
- Induce and detect pbar tunespread reduction or proton tunespread broadening
- Simulate and explain TEL results and “puzzles”
- Provide design help to BNL team (m.b. hardware)
- Brookhaven:
- Long list of HO-BBC questions to answer (next slide)
- Start the design (and later build) RELs, integration
- CERN:
- U.Dorda to contribute to LEL design considerations
- Very desired: T.Pieloni on Tev spectra and LEL effect

## Questions: Analysis and Simulations

- LHC Electron Lenses – LARP CM9

- Will truncated Gaussian e-current density distribution work (improve lifetime and reduce diffusion rates)?
- Straightforward tracking with a weak-strong code
- Is partial compensation helpful?
- Is there a better distribution?
- from first principles, theory, analytical consideration
- Effects are beta_EL/beta*/sigma_z; or dP/P
- check in numerical tracking
- Importance of e-p interaction in bending sections
- Which configuration is better? Pi-shape or S-shape
- Is the choice tune dependent?
- Lifetime deterioration due to e-p misalignment:
- e-beam straightness tolerances
- relative e-p displacement, angle
- Effect of _low-frequency_ variations dJ, dX on beam lifetime
- Ion cleaning efficiency tolerances
- Interference with wires in LHC – if there is any
- e-beam effect on coherent stability or strong-strong beam-beam effects

##     e-Lens configurations

- LHC Electron Lenses – LARP CM9

-     e-Lens configurations

## Is Technology Available?   

- LHC Electron Lenses – LARP CM9

- Is Technology Available?

*+ Marx HV Modulator, SEFT gun, 2 Cryo *
*bypasses, 4-plate BPMs & Cables*

- TEL-1 (2001)

- TEL-2 (2006)

- 600ns
- 50kHz
- 1-2A

## What is Electron Lens?

- LHC Electron Lenses – LARP CM9

- ~2 mm dia 2 m long very straight beam of ~10kV ~1A electrons (~1012) immersed in 3T solenoid

## How strong is it?

- LHC Electron Lenses – LARP CM9

- For many applications
- electron beam size
- needs to be nxσ protons
- e.g. n=1 for head on BBC

**Figure of merit- tuneshift dQ:**
- Similar to space-charge  and beam-beam

- this product is const(E)
- RHIC
- Tevatron
- LHC

**SAME!**

## TEL2 In The Tunnel (A0)

- LHC Electron Lenses – LARP CM9

## LHC footprint (design)

- LHC Electron Lenses – LARP CM9

- 6/19

- 5/16

- 4/13

## LHC footprint (x2 Np/bunch)

- LHC Electron Lenses – LARP CM9

- 6/19

- 5/16

- 4/13

## 50% Head-On Compensation by LEL

- LHC Electron Lenses – LARP CM9