tevatron electron lenses and its applicationselectrodes in tels x. zhang - fnal cool'09,...

COOL'09, Lanzhou,9/3/2009

Tevatron Electron Lenses and Its Applications

MS341, PO BOX 500, Batavia, Illinois 60510-0500, USAzhangxl@fnal.gov

Xiaolong Zhang

Fermilab – Accelerator Div./Tevatron Dept.

Acknowledgement

• V.Shiltsev (Project Leader), D.Finly, A.Valishev, Yu.Alexahin, H.Pfeffer, J.Crisp, J.Fitzgerald, M.Olson, A.Semanov, D.Wildman, G.Saewert, V.Scarpine, N.Solyak, L.Nobrega, R.Hively (Fermilab)

• V.Kamerdzhiev (FZ-Julich, IKP, German)• I. Bogdanov, S. Kozub, V. Sytnik,L. Tkachenko, S. Zintchenko, V.

Zubko, V. Pleskach (IHEP, Russia)• G. Kuznetsov, M.Tiunov, A.Romanov (BINP, Russian)• A. Sery (SLAC)• K.Bishofberger (LANL)

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Tevatron Collider

1.96 1.96 TeVTeV ProtonProton--Antiproton Antiproton ColiderColider

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Overview

• Tevatron

– 1 km radius superconducting synchrotron at 980 GeV beam energy

– Tevatron 36×36 proton-antiproton collisions to CDF & D0 experiments

– 3 trains of 12 bunches each with 396 ns separation

– Protons and antiprotons circulate in single beam pipe

• Electrostatic separators keep beams apart in helical orbit except @CDF &

D0

• Beam-beam interactions (head-on & long range) play major role

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Tevatron Bunches

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• The Tevatron operates with 36 bunches in 3 groups called trains

• Between each train there is an abort gap that is 139 RF buckets long

– RF bucket is 18.8 ns Abort gap is 2.6 μs

139 buckets

21 buckets 1113 RF buckets totalTrain

Bunch

Abort Gap

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Tevatron RunII Total Integrated Luminosity

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Tevatron RunII Peak Luminosities

Recycler-only pbars & 28 cm β*

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Theory of Beam-Beam Effects for Antiprotons and Compensation

• Head-On tune shift 2 IPsξ=0.020-0.024

• Bunch-by-bunch tune spreaddQ=0.004-0.006

• Two electron lenses can compensate (in average) space charge forces of positivelycharged protons acting on antiprotons in the Tevatron by interaction with a negativecharge of a low energy high-current e-beam

• Major requirements:– 1-3 A e-current – 6-12kV e-energy– modulated t~800ns– ~2 m long, ~3mm diameter – transverse shape control– e-p position control <0.2mm

No compensationOne Linear TEL

Two Linear TELs Two Non-Lin TELs

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Tevatron Electron Lenses: #1(F48) and #2 (A0)

pe

pee

e

eyxyx ace

rLJdQ

γββ

πβ

⋅⋅⋅⋅±⋅= 2

,,

12

m

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Tevatron and TEL Parameters

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BEAM-BEAM COMPENSATIONTELs as

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Tuneshifts Due to E-beam

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TEL2

TEL1-Pbar

TEL1-P

TEL1-P

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Bunched Beam Loss During HEP

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At present, beam-beam effects are relatively stronger on protons, accounting for some 10-15% loss of the integrated luminosity. Proton loss rates vary greatly from bunch to bunch. The Tevatron Electron Lens #2 aligned on proton beam.

Protons Antiprotons

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2003: Pbar Blowup Suppressed by TEL#1

Store #2540Store #2540

May 13, May 13, 20032003

A33 1 π mm mrad/hr

-TEL1 acts on it

Only few stores!operations

A21 2.2 π mm mrad/hr

A9 4.1 π mm mrad/hr

Emittance evolution at the start of the store

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Long-range effects as seen in stores

Bunch-by-bunch tune spread as a result of parasitic beam-beam interaction

• 36 bunches: 3 trains of 12 – 3-fold symmetry• Lifetime and emittance growth vary bunch-by-bunch

Measured by 1.7GHz Schottky monitor

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in space in time

P12

P11P10P9

A24

TEL

Transverse e-p alignment is very important for minimization of noise effects and optimization of positive effects due to e-beam. Timing is important to keep protons on flat top of e-pulse – to minimize noise and maximize tune shift.

E_beam Position

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TEL2 on P12: 1st hour of Store #5119

TEL2 current

Bunch P36 –not affected by TEL2

Bunch P12 –TEL2 acts on it

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TEL2 Improves Proton Bunch Lifetime

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THE COLLIMATION EFFECTFlat Top Gun

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Three current profiles from TEL-1 e-guns

E-beam is strongly magnetzed in 2-40 kGmagnetic field Profile in theinteraction region isthe same (justscaled) as on cathode

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TEL-1 Studies: Sensitivity to position and profile

• The very first e-beam profile (~’02) was uniform =flat-top & sharp edges

• Very cumbersome tuning to get good lifetime (max ~40 hrs and dQ=0.005) and centering e-beam on antiprotons or protons

• The second one had Gaussian profile (’02-’05) – still hard to center but better lifetime (140 hrs max)

• 3rd one has flat-top and smooth edges

Beam study, 2002:980 GeV protons collide with 7kV ~1.5A electrons

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STACKED TRANSFORMER MODULATOR

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•RF Modulator: Can’t operated at 50KHz; Constant on; Power line harmonics;

•Marx generator:Low voltage output; Can’t operated at 50KHz;

•Stacked transformer:Good repetition rate and duty factor; low noise; adequate voltage;

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UNCAPTURED BEAM REMOVER

TEL as:

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Uncaptured Beam

• Mechanism Generating Uncaptured Beam:Come from Main Injector coalescing process;Intro-Beam Scattering(IBS) process;RF phase noise;Other noise sources;

• Deleterious Effects of the Uncaptured Beam: Increasing HEP detector background;Quenching;Damaging detector components;Compromising detector efficiency;Shorten detector lifetime;

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Uncaptured Beam & RF Trip Off

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Abort Gap Cleaning

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• Protons leak out of main bunches to the gaps.Tevatron is sensitive to few x 109 particles in the abort gaps (total beam ~ 1013) as they lead to quench on beam abort (kicker sprays them)

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Cleaning Uncaptured P-beam

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Beam in Abort Gap

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0 200 400 600 800-0.01

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

Time (ns)

Inte

nsity

(Arb

itrar

y U

nits

)

DataRF Bucket Structure

End of Abort Gap

Bunch 1

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ELECTRON COLUMNPreliminary Studies:

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Electron Column Generator

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Concept Design by V.Shiltsev

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Electrodes in TELs

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Tune Shifts Due to Trapped Electrons

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Summary• TELs were successfully commissioned and operating daily @Tevatron.• The most important role for TEL in Tevatron operation is uncaptured

beam cleaning.• In a series of stores, TEL2 acted on a single proton bunch and

DOUBLED its lifetime shown suppressions of the pbar emittance growth.• BB Compensation helps for ~10 hrs in store.• Wire beam-beam compensation studied at RHIC and SPS, DAΦNE.• R&D of the electron lens are progressing for RHIC and LHC.• Electron beam collimation system which utilize hollow electron beam was

proposed for LHC.• With the new Gaussian electron gun installed, the further studies for the

nonlinear BBC will be carried out soon and will benefit LHC.• Further understand the electron column and stabilities needed for the

space charge compensation.• TEL can also be used as Beam Tickler, Controlled Scraper, etc.

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The End