# Presentation: 419791

## Lessons Learned from E-Lens Operation at the Tevatron

- LARP Mini-Workshop on E-Lens Simulations, BNL
- December 3, 2008
- Alexander Valishev, Vsevolod Kamerdzhiev (FNAL)

*BNL - FNAL- LBNL - SLAC*

_**US LHC Accelerator Research Program**_

## Electron Lens for Head-On Compensation at LHC

- Original idea (1997-1998) Shiltsev, Finley, Sery, Danilov
- Electron lens for compensation of beam-beam effects in _antiprotons_
- Linear EL – tune shifter. Bunch-to-bunch betatron tune spread =0.007. e- beam size ~3 mm, flat top transverse profile
- Nonlinear EL – tune spread compressor. =0.02
- Identified the following potential issues
- TMCI due to e-beam impedance (B > 1.75T)
- (anti)proton emittance growth due to e-beam current fluctuation (J/J<2x10-3)
- (anti)proton emittance growth due to e-beam position jitter (x<0.14m)

## TEL Experience

- TEL-1 tested in 2001 with flat top beam
- Tune shift observed in good agreement with expected
- Discovered that mis=steering of e-beam is by far the most important factor affecting (anti)proton life time
- Relative e-/p beam size matters, sharp edges deteriorating p life time
- Used for cleaning DC beam in abort gap

- TEL-1

- TEL-2

## TEL Experience Contd.

- TEL-1 upgrades in 2003
- Gaussian gun
- e-beam optics
- Better BPM system
- Modulator upgrade (<0.1% current ripple, <1 ns pulse stability)
- Better p beam life time observed
- Sensitivity to current ripple was studied
- Demonstrated suppression of antiproton bunch emittance blow up in a single HEP store
- Repeatability was poor due to problems with precise control of the machine and TEL parameters (no orbit stabilization in the TEV at that time)

## TEL Experience Contd.

- TEL-2 installed in 2006
- By then, adverse beam-beam effects shifted to protons!
- Specifically, bunch 12 in the train had considerably higher losses due to lower vertical tune
- Acting with TEL-2 on one proton bunch improved its life time
- Well repeated effect
- SEFT (smooth edge flat top gun) used
- Change of the proton bunch life time was consistent with a corresponding tune change
- Luminosity life time improvement was bigger than from a tune change!
- In 2008 after improvements in the machine optics bunch 12 is no longer different
- Ready to test Gaussian gun!

- 5155, Dec 2006, 2.5E32

- 6598, Nov 2008, 3.3E32

## Simulations and Analytical Studies

- Alexahin, Shiltsev, Shatilov 2001
- Found that footprint “folding” due to long-range interactions can affect life time
- Limit on dispersion re>Dx
- Second order chromaticity
- Variation of nonlinear component of EL
- Two ELs with 1>2 beneficial from the point of view of coupling resonance excitation
- Working point choice is important
- Studied e-beam imperfections
- 0.5 mm bend is tolerable
- 0.4 mm transverse misalignment for R=2 mm does not affect life time
-  J/J < 5x10-3 .
- Valishev 2007
- Demonstrated in long-term simulations the effect of TEL-2 on bunch 12 life time

## Summary

- Transverse misalignment less than 0.2-0.5 mm is critical (e-beam radius is 2 mm, p = 0.7 mm)
- Current ripple < 0.1%
- Pulse stability 1 ns
- Limit dispersion (or increase e-beam size)
- Beam size matching?
- Edge effects?