Use of Electron Lens in Tevatron and LHC

1
Use of Electron Lens in Tevatron and LHC

• Xiaolong Zhang

2
Beam-beam Compensation with Electron Beam
to compensate (in average) space charge forces
of positively charged protons acting on
antiprotons in the Tevatron by interaction with
a negative charge of a low energy high-current
electron beam (1997)
3
Compensation with Two TELs
Yu.Alexahin

• Tev Run II 36x36 bunches in 3 trains
• compensate beam-beam tune shifts
• a) Run II Goal
• b) one TEL
• c) two TELs
• d) 2 nonlinear TELs
• requires
• 1-3A electron current
• stability dJ/Jlt0.1
• e-pbar centering
• e-beam shaping

4
TEL1 in Tevatron
5
Use of Electron Lens in Tevatron (TEL)

• Beam-beam compensation studies
• Tune shift beam lifetime vs. electron beam
  parameters, etc.
• DC beam studies
• DC beam cleaning efficient, DC beam measurement,
  calibration of the abortgap monitors, etc.
• Beam diagnostics tool
• Pbar tune measure by exciting pbar bunches,
  controlled proton or pbar remover, noise vs. beam
  emittance growth, etc.

6
Beam Tune Shift
Three bunches in the Tevatron, the TEL acts on
one of them Tuneshift dQhor0.009
7
Tuneshift vs. Electron Current
8
Tuneshift vs. e_Beam Timing
9
Electron Beam Profile
10
Collimation Effect
Need electron gun with smooth edge.
11
Beam Lifetime vs. Tune
With dQTEL0.004
Flat e-beam
Gaussian e-beam
12
Gaussian Gun

• Beam profile controlled by special electrode
• Somewhat reduced current density in the center ?
  need of higher voltage
• Beamsize smaller ? Difficult to align the beams
• New gun flat top with smooth edge

13
New Electron Gun
14
Beam-beam Compensation
Emittance Scallops
15
Beam-Beam Compensation
Store 2540 May 12, 03
A9 4.1 ? mm mrad/hr
A21 2.2 ? mm mrad/hr
A33 1 ? mm mrad/hr -TEL on it
16
Beam Loss vs. Electron Position

• Beam loss 1/R3, R is distance between P/Pbar
  beam and e-beam.
• No effect on protons while e-beam acting on Pbar,
  and vice versa.

17
Beam Loss vs. Electron Position
18
DC Beam Cleaning
19
Calibration of the Abort Gap Monitor
Calibration of the SL abort gap monitors AGIGI1,
AGIGI2, AGIGI3, and SLPAH37.
20
DC Beam Cleaning

• Fire TEL in 3 gaps every 7
• turns to excite resonance
• TEL is equivalent to 100kW
• tickler
• Exciting 4/7th order
• resonance in vertical.
• Reduces DC beam intensity.
• Protect CDF detector by
• eliminating the proton loss
• spikes.

21
Noise vs. Emittance Growth

• TEL e-current turn-by-turn noise amplitude dJ_e
  3-5mA p-p
• while operating for BBC
• with dQ gt 0.005
• ? 0.1-0.2 ?/hr
• That is less though comparable with natural
  emittance growth of 0.2-0.5 ?/hr

22
Exciting Pbar for Tune Measurment
Enable us to measure Pbar tune at the EOS by
21MHz Schottky System
23
P/Pbar Remover
Remove p/pbar in a controlled manner to enable
the End-of-store single beam study.
24
The 2nd Electron Lens (TEL2)

• 57 electron beam bend with strength solenoids
• Upgraded BPMs

• TEL2 under testing
• at E4R
• Magnetic fields
• meet requirement
• Will be installed
• coming shutdown

25
Main Difficulties to Overcome

• Modulator
• Short pulse
• Higher output voltage gt7KV
• Reliable, stable and no afterpulse
• BPM need offset between e-pulse and P/Pbar bunch
  lt 0.2mm, now 1-1.5mm
• Resolution of bunch-by-bunch tune measurement
  lt0.0002 needed, 0.0010.002 achieved Data
  acquiring speed from a few minutes (now) to a
  few seconds (future).
• Orbit stabilization
• Alternating transverse electron beam position for
  beam-beam compensation and DC beam cleaning

26
Using Tevatron Electron Lens for LHC

• The two TELs will be available upon the
  termination of the Tevatron
• Electron beam is more flexible than the wire
• Transverse position can be changed when needed
• Dont need to be cooled
• Dont pose any aperture limitations
• Can do both head-on and parasitic beam-beam
  compensation
• Can be used for nonlinear beam-beam compensation
• May be used for other purpose (help beam
  diagnostics DC beam cleaning etc.)
• More studies needed on Tevatron

27
Summary

• TEL1 is running successfully and reliably for
  Tevatron, and is crucial for daily RunII
  operation.
• We had one successful attempt to use it for
  beam-beam compensation, despite its main function
  as DC beam cleaning and limited machine study
  time.
• The 2nd TEL is tested 90 successfully so far and
  will be installed this coming shutdown.
• We have plans for the upgrades and bring TEL for
  beam-beam compensation.
• More studies are ahead of us

28
Tuneshift vs. e_Beam Position