11 Overview of the Tevatron Collider V.S. Morozov Old Dominion University Muons, Inc. Collider Review Retreat, Jefferson Lab, February 24, 2010

11

Overview of the Tevatron Collider

V.S. MorozovOld Dominion University

Muons, Inc.

Collider Review Retreat, Jefferson Lab, February 24, 2010

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Outline

• Accelerator Complex Overview• Tevatron• Low- insertion• Electrostatic p/p beam separators• 1st- and 2nd-order chromaticity control• Beam-beam effects• Instabilities

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04/20/23 Elvin Harms - HCP 2002 3

fAccelerator Complex Overview

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– Proton source• Cockroft-Walton preaccelerator 750 keV

5


– Proton source• Drift tube Linac

116 MeV

– Proton source• Side-coupled

cavity Linac 400 MeV

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– Proton source• Rapid-cycling Booster synchrotron 8 GeV

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• Main Injector/Recycler 8 to 150 GeV

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• Antiproton source– Antiproton production target station 120 GeV– Debuncher 8 GeV– Accumulator 8 GeV

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• Tevatron– Superconducting synchrotron 980

GeV

Elvin Harms 10

fTevatron Loading scheme

• Protons are loaded first - 1 bunch at a time and spaced in 3 groups of 12 (20 empty buckets between bunches, 139 empty buckets between trains)

• Antiprotons are loaded four bunches at a time for a total of 9 transfers from the Accumulator to MI to the Tevatron

• The 36 bunches of Pbars are equally spaced in 3 groups of 12 around the Tevatron

04/20/23November 8, 2002

Fermilab Snapback WorkshopMike Martens

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Tevatron ParametersSynchrotron with superconducting magnets.Collide 36 proton bunches on 36 pbar bunches.Radius 1 kmEnergy 150 Gev to 980 GevLattice 6 identical 60º arcs with 15 FODO cells/arcFODO cellmin = 30 m, max = 100 m, ~60º betatron phase

advance in both planesRun with tunes at 20.575 (vertical) and 20.585 (horizontal).h 1113RF frequency 53.14 MHzBucket spacing 18.8 nsecLow Beta regions at B0 and D0. * is 35 cmElectrostatic separators to separate the proton and antiproton orbits.772 dipole magnets with B = 4.4 Tesla @ 1000 GeV.

04/20/23 Elvin Harms - HCP 2002 12

fParameter List

RUN Ib (1993-95)

6 x 6

Run IIa

(36 x 36)

Current best

Protons/bunch 2.3 x 1011 2.7 2.1 x 1011

Antiprotons/bunch 0.55 x 1011 0.3 0.17 x 1011

Total Antiprotons 3.3 x 1011 11 6.1

Pbar Production Rate 6.0 x 1010/hour 20 12.4

Proton Emittance 23 mm-mrad 20 20 mm-mrad

Antiproton Emittance 13 mm-mrad 15 20mm-mrad

* 35 cm 35 35 cm

Energy 900 GeV 1000 980

Bunch Length (rms) 0.60 meter 0.37 ~0.60 m

Crossing Angle 0 rad 0 0

Typical Luminosity 1.6 x 1031cm-2s-1 8.6 3.0

best-to-date

Integrated Luminosity 3.2 pb-1/week 17.3 4.3

Bunch spacing ~3500 nsec 396 396

Interactions/Crossing 2.5 2.3 2.3

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Ingredients of Tevatron Luminosity

• Low- insertions

• Reduction of beam-beam tune shift by separation of p and p beams on helical orbits

• Control of 1st and 2nd-order chromaticities

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Retrospective ViewTalk by R. Johnson, ~1986

04/20/23November 8, 2002


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Standard Cell in the Tevatron Lattice

F D

Tevatron Dipole

F Tevatron Quadrupole

Tevatron Quad corrector

Tevatron Sextupole corrector

Tevatron Beam Position Monitor

T:QF

T:SF

HorzBPM

T:QD

T:SD

VertBPM

(There are 772 Tevatron dipoles)

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Low- Insertion

• Two low- insertions at B0 and D0

• 18 cold-iron quads arranged as a triplet and 6 “trims” on each side of interaction region

• Fully matched to lattice by “trims”

• Approximately symmetric around interaction point

• Magnetic gradients antisymmetric

• Each insertion’s * independently adjustable within 0.25-1.7 m range

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Low- Insertion

• Each insertion adds half unit to betatron tunes

• Horizontal dispersion zero at interaction point * limited by max, magnet’s bore tube and field errors

• Inner quads specially designed to fit detector clearance

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Low- Insertion * of 35 cm prior to 2005

• New optics with * of 28 cm implemented in July 2005 based on precise knowledge of lattice details obtained using Orbit Response Matrix (ORM) and Linear Optics from Closed Orbit (LOCO) methods

• Gain in luminosity of ~10%

• Further reduction of * undesirable because of 2nd-order chromaticity and hour-glass effect

04/20/23November 8, 2002


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Tevatron Ramp Cycle

Time

Tev

En

ergy

980 Gevflattop

150 GevFront Porch

90 GevReset

Low

bet

aSq

ueez

e

150 GevBack porch

Typical times for Tevatron store• 150 Gev Front porch: ~2 hours• 980 Gev Flattop: ~12-24 hours• 150 Gev Back Porch: ~1 minute• 90 Gev Reset: ~20 seconds

Low

bet

aU

n-sq

ueez

eTypical times for dry squeeze • 150 Gev Front porch: ~10 minutes• 980 Gev Flattop: ~15 minutes• 150 Gev Back Porch: ~1 minute• 90 Gev Reset: ~20 seconds

Inje

ct p

orot

ns &

pba

rs

• During injection and acceleration * kept at 1.7 m then “squeezed” to 0.28 m by ramping trim magnets while triplet elements remain unchanged

• In fixed target runs low- insertions approximate “normal-” straight sections

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Separation of Proton and Antiproton Orbits

• Tevatron’s betatron tune working point between 4/7 and 3/5 resonance lines leaving 0.028 tune space available

• Beam-beam tune shift 0.025 for antiprotons and 0.02 for protons

• Unseparated beams multiple crossing locations each contributing to beam-beam tune shift limited number of bunches and beam intensity

• Keep beams separate everywhere except interaction regions with electro-static separators

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Electro-Static Separators

• Function as “3-bumps” in vertical and horizontal planes

• Bunches go in helical orbits around unseparated orbit

• Orbits remain separated during injection and acceleration

• Separators adjusted to bring beams into collision at interaction regions

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Electrostatic Separators1986 talk by R. Johnson 1991 paper by D. Herrup et al.

04/20/23November 8, 2002


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Chromaticity in the Tevatron

• High chromaticity - large betatron tune spread - some beam loss on ramp (~15%).

• Reducing chromaticity ma cause transverse instabilities

• Keep chromaticities at 8 units (horz and vert) on front porchIncrease chromaticites to 12 units just before ramp.Keep chromaticity at 15 to 20 units on the ramp.

• Chromaticity drifts are created by drifting b2 (sextupole) fields in dipoles.

• b2 compensation scheme keeps chromaticity constant at 150 Gev and on the snapback (sort of.)

04/20/23November 8, 2002


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Chromaticity in the Tevatron

• The total chromaticity has several components

Total = Natural + Dipoles + Sext corr

Natural = -29 units (from optics calculations)

Dipoles = b2 drift + b2 geometric

Sext corr = T:SF + T:SD + C:SFB2 + T:SDB2

• 176 chromaticity correction sextupolesOriginally combined into two families, SF and SD88 elements in each family powered in seriesSextupoles located next to quadrupoles of regular FODO lattice

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Transverse Dampers• Lower chromaticity by 4-6 units thus reducing betatron tune

spread and improving beam lifetime

• Use transverse dampers to keep beam stable

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2nd-Order Chromaticity Correction• Needed to move betatron tune

working point to new place near 1/2 resonance where there is more tune space available

• Elimination of chromatic dependence of beta function at IP should improve beam lifetime

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2nd-Order Chromaticity Correction

• Sextupoles with or /2 betatron phase advance with respect to final focus quads were identified

• 22 sextupoles were taken out from each of SF and SD families

• They were grouped into 4 families

• New groups allow one to change 2nd-order chromaticity while keeping linear chromaticity constant

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2nd-Order Chromaticity Correction• 2nd-order chromaticity reduced from

-15000 to -3000 units

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fBeam-Beam Effects – 150 GeV

Issue Solution Impact on Luminosity Schedule

Increased Proton Intensity Transverse Dampers 30% to L0 Horizontal commissioning in progress, vertical to follow (this month)

Improve injection aperture and emittance growth

Improved MI to Tevatron transfer line match

6% to L0 Matching in progress


Turn-by-turn position diagnostics and orbit closure algorithm

6% to L0 Pbar system in operation


Fast injection dampers 5-10% to L0 Early 2003

Limited aperture and separation at 150 GeV

Replace C0 Lambertson magnets with larger aperture dipoles (double the vertical aperture)

10% to L0 Next extended shutdown

Limited aperture and separation at 150 GeV

Improved optics across A0 straight section

5-10% to L0 Early 2003

Time-dependent tune and coupling drift at 150 GeV

Tune drift compensation 2-5% on integrated L Put into operation last week

04/20/23 30

fBeam-Beam Effects – 980 GeV


Drifting tunes during store On-line tune stabilization 4-10% in integrated Luminosity

Long-term

Low lifetime – restore to Run I values (>15 hours)

Explore larger helix separation

10-30% in integrated Luminosity

Long-term

Low lifetime – restore to Run I values (>15 hours)

Optimize tunes for most bunches

up to 30% in integrated Luminosity

Long-term

Pbar tune shift by protons Beam-beam compensation with electron lens

10% in integrated Luminosity

Long-term

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fInstabilities


Coherent transverse beam blow-up at all beam energies

Transverse dampers, additional investigation

see above Damper commissioning in progress

Coherent longitudinal bunch by bunch beam blow-up

Longitudinal bunch-bunch dampers, additional investigation

better understanding Longitudinal damper in operation at 150 and 980 GeV

Coherent ‘dancing bunches’ Observed, under study better understanding December 2002

Incoherent bunch length growth

Observed, under study better understanding early 2003

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1986 talk by R. Johnson 2006 paper by A. Valishev

Documents

11 Overview of the Tevatron Collider V.S. Morozov Old Dominion University Muons, Inc. Collider Review Retreat, Jefferson Lab, February 24, 2010