Fermilab Run 2 Accelerator Status and Upgrades

1
Fermilab Run 2 Accelerator Status and Upgrades

• Keith Gollwitzer
• Antiproton Source
• Beams Division
• Fermi National Accelerator Laboratory
• October 8, 2003

2
Outline

• Overview of the Fermilab Accelerator Complex
• Status of Run 2
• Comparison to Run 1
• The last year of running
• Overview of Upgrades for Run 2

3
Fermilab Overview
Proton source
CDF
Tevatron
Main Injector\ Recycler
D0
Antiproton source
4
Schematic of Accelerator Complex
5
Protons to the Tevatron

• Protons
• 750keV Cockcroft-Walton
• 2 stage H- LINAC to 400MeV
• Booster to 8GeV
• Main Injector to 150GeV
• Also 120GeV protons to pbar production target

6
Antiprotons to the Tevatron

• Antiprotons
• 120 GeV protons on Nickel target
• Pulsed Lithium lens to focus secondaries beam
• 8GeV pbars collected in Debuncher
• Transfer to Accumulator to further decrease phase
  space and accumulation of pbars
• Transfer to Main Injector ramped to 150GeV

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Tevatron Beams

• Inject 36 bunches of 150 GeV protons onto central
  orbit
• Open helix using Electrostatic Separators
• Inject 36 bunches of 150 GeV pbars onto second
  helical orbit
• Accelerate beams to 980 GeV
• Bring beam into collisions by modifying helices
  at detectors

8
Run II Milestones

• September 1998 - Main Injector commissioning
  begins
• May 2000 first attempts to unstack Pbars from
  the Accumulator
• June 2000 pbars extracted from Accumulator,
  accelerated to 150 GeV in the Main Injector
• August 2000 - 980 GeV protons in the Tevatron
  re-established
• August 2000 Pbars in the Tevatron
• October 2000 36 x 36 collisions achieved at 980
  GeV
• March 2001 - Run II officially begins
• August 2002 - Initial luminosity 2.6 x 1031
  cm-2s-1
• Exceeds best of Run I
• August 2003
• 4.88 x 1031 cm-2s-1 initial luminosity achieved
• 330 pb-1 integrated since Run II began

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Peak Luminosity
10
Integrated Luminosity
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Parameter List
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What could be Better Fixes

• Tevatron Performance
• Coupling of transverse motion is large
• Major source identified in dipoles (see slides)
• Stability control
• Removal of unused Lambertson decreased machine
  impedance
• Adding vacuum liner to remaining Lambertsons
• Cu-Be bronze high electrical thermal
  conductivities
• Limited orbit control
• Vertical correctors running near maximum due to
  roll of dipoles
• Resetting many magnets during current shutdown

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Tevatron Coupling
Data shows in-plane and out-of-plane difference
orbits after single horizontal kick. Data is for
1st 5 turns in Tevatron.
Coupling in Tevatron is uniform around the ring
and is consistent with 1.5 units of a1 per
dipole. This is compensated by a distributed
skew quad circuit of 42 elements.
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Tevatron Coupling (continued)
Tevatron coil and cryostat assembly is held
within the iron by 4 supports at 9 locations
along the length of the magnet. Recent
measurements of the smart bolts (upper
supports) on magnets in the tunnel, indicate that
the coil assembly has sagged by 2 mils from
original. This is enough to produce 1 unit of
a1 per dipole. In 1984, compensating skew quad
circuit was running at 2A. From 1995
compensating skew quad circuit has been running
at 24A (_at_ 800 GeV).
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What could be Better Fixes

• More particles to collisions
• Overall transmission efficiency 55-65
• N stages each 90
• Work to increase each stage to 95 efficiency
  ?70-80
• More Antiprotons
• Longer stores -- accumulation of more pbars
• Tevatron stores ending unintentionally
• Want to increase stacking rate (see slides)
• Improve phase space compression in Antiproton
  Source
• More protons on target
• Better collection of antiprotons.

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Antiproton Stacking
20 Antiproton produced per 10e6 on
target Stacking Rate (mA/hr) 10 Largest
Stack to Date 236mA 0
0 50 100 150
200 250
Stack Size (mA)
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Antiproton Stack Process

• Accumulator Stacktail Cooling
• Process
• Debuncher beam is transferred to the Injection
  Orbit
• Bunched with RF
• Moved with RF to Deposition Orbit
• Stacktail pushes and compresses beam from the
  Deposition Orbit to the Core
• Core Momentum systems gather and further
  compresses
• Transverse systems also compress phase space of
  beam
• The Problem
• Pulse rate determined by speed Stacktail can move
  beam off Deposition Orbit
• Amount needed to move dependent upon incoming
  longitudinal width
• Debuncher needs to compress the beam smaller
  before transfers

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Plan for Higher Luminosity

• Luminosity Formula
• Dominant Terms
• Number of pbars
• Proton Brightness
• The other terms we have little ability to change
• Essentially at limit of number of protons/bunch
• Strategy is to increase the number of pbars
• Increase protons on target production
  efficiency
• Increase capability to handle pbar flux
• Need to control Tevatron Beam-Beam effects

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More Protons on Production Target

• Quantity
• Slip Stacking will nearly double beam on target
• Quality
• Bunch length is passed on to the pbars
• Smaller helps in RF capture of pbars
• Smaller emittance helps collection
• Target
• Increase of energy deposited in target
• Investigating new target materials
• Beam sweeping to move beam spot during spill

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Slip Stacking Cartoon
(1)
(2)
(3)
(1) Booster batch 1. (2) Batch 1 in MI. (3)
RF system A accelerates beam while Booster batch
2 is prepared. (4) Inject batch 2 into MI.
(5) Decelerate batch 2 with RF system B. (6)
Allow batches to slip until lined up capture
both batches with RF system C while turning off
RF systems AB.
(4)
(5)
(6)
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Collect More Antiprotons

• Increase pbar yield
• Increase gradient of collection lens
• Increase the admittance of the transfer line and
  Debuncher ring

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Higher Gradient Lithium Lens

• Trade off between gradient and lens lifetime
• Nearly same design with improvements
• Cooling, Diffusion bonded, new Titanium Alloy

23
Increase Antiproton Acceptance

• Most elements in 300m beam line and 500m
  Debuncher ring should handle 40? mm-mrad
• Identifying and taking corrective action
• Beam-based alignment
• Adding corrector elements to current limit set
• Improving diagnostics and procedures

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How to handle the increased pbar flux

• Optimize Debuncher cooling systems
• Change Accumulator Stacktail system to push more
  flux
• Consequence smaller core
• Hence need another place to accumulate pbars
• Recycler Ring in Main Injector tunnel
• Stochastic cooling will not be sufficient
• Electron cooling at 8GeV

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Recycler Ring Status

• Slowly being commissioned over the last few years
  while operating Run 2
• Little tunnel access time
• Main magnets are permanent magnets
• Recent addition of surplus LEP correctors
• Better orbit control particularly when the Main
  Injector ramps
• Current shutdown will finish all vacuum work
• Stacking is done using barrier RF buckets
• Electron cooling will be main cooling system
• Installation next Spring/Summer
• Final commissioning and integration into
  operations over the next 1.5 year

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Overview of Electron Cooling

• Co-moving low emittance electron beam cools pbars
• First use at medium energy
• High current with strict electron beam
  requirements for the 20m cooling section

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Electron Cooling Parameters

• Emphasis on longitudinal cooling transverse
  free assume incoming 3? mm-mrad (normalized)
  and 10 eV-sec

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Beam-Beam Interactions

• Near misses mainly,on each side of the
  interaction region
• Effect of beams on each other is a series of
  focusing events causing the tune to change
• Current Nproton 10Npbar Future Nproton 2Npbar

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Beam-Beam Issues

• What to do about spread in tunes due to Beam-Beam
  Interactions
• Increase Electrostatic Separator strength to
  increase orbit separation
• Beam-Beam Compensation
• Electron Lens
• High Current Wires

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Tevatron Electron Lens

• Can modulate electron beam for each pbar bunch (
  abort gap)
• Installed in TeV
• Used mainly for keeping abort gap clear by
  driving particles to a strong resonance
• Have demonstrated decrease rate of emittance
  blow-up for single pbar bunch
• A second lens is needed for full BBC

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Wires Beam-Beam Compensation

• An RD project
• Current thought is to have 4 stations
• At each station, 4 wires
• Each wire with 200A
• Prototype later this fall
• Prototype station ready for 2004 summer shutdown
  installation

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Draft Run 2 Schedule
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Parameters of Upgrade
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Tevatron Reliability

• Analysis of number of store hours between
  Tevatron failures
• Failures occur randomly
• Rarely are failures correlated
• For any hour of store failure probability is
  2.5
• Many possible components can fail implies the
  mean lifetime of Tevatron components is 5yr

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Summary

• Fermilab Run 2 Progresses
• Accelerator complex in 2 years has delivered
  twice as much integrated luminosity as Run 1
• Still work to be done in improving operations and
  understanding the accelerator complex
• Run 2 Upgrades to be done over the next 3yr
• Increase weekly integrated luminosity factor 5.5
• Mostly comes from increased number of Antiprotons
• Increased stacking rate requires the Recycler
  Ring with Electron Cooling
• Will require understanding and mitigating
  Beam-Beam effects