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Acceleration Overview. J. Scott Berg Brookhaven National Laboratory January 8, 2014. Acceleration Goals. Accelerate rapidly to avoid decays High average RF gradient: ≈5 MV/m for 70% transmission Control costs and power use Make many passes through RF

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Acceleration overview

Acceleration Overview

J. Scott Berg

Brookhaven National Laboratory

January 8, 2014

Acceleration goals
Acceleration Goals

  • Accelerate rapidly to avoid decays

    • High average RF gradient: ≈5 MV/m for 70% transmission

  • Control costs and power use

    • Make many passes through RF

    • To simultaneously maintain high average RF gradient: high average dipole field

  • Handle large emittance beams

Beam properties
Beam Properties

  • Wide variety of emittances to accelerate

  • Biggest challenge is the large longitudinal emittance for the higher energy colliders

  • Higgs factory beam is more reasonable size

    • But still need to accelerate large longitudinal emittance through that energy range

  • Neutrino factory beam has very large transverse emittance

    • Specific solution for neutrino factory discussed earlier

Accelerator types linac
Accelerator Types: Linac

  • Best for low energies, large beams

  • Large longitudinal emittance

    • 325 MHz SCRF not possible for low energies (until about 700 MeV)

  • Use technologies from final cooling for acceleration (expensive)

    • Induction linacs: low gradient

    • Low frequency RF: low gradient

    • Cooling RF: high gradient, longitudinal acceptance

  • No re-use of RF

Accelerator types rla
Accelerator Types: RLA

  • Recirculating linear accelerator

  • Multiple passes through RF

  • Large longitudinal acceptances possible

  • Can’t put too many beamlines in switchyard

    • Large emittance beam

    • Limits number of passes

  • Dogbone geometry

    • Maximizes separation for given number of passes

    • Gives very high average accelerating gradient

  • Start these right after cooling RF

Accelerator types ffag
Accelerator Types: FFAG

  • Fixed field alternating gradient accelerator

  • Single beamline with wide energy range

    • No switchyard limiting number of passes

  • Trade single beamline with large magnets for many beamlines with smaller magnets in RLA

  • Passes limited by tolerable longitudinal emittance distortion

    • Worse with large longitudinal emittance

    • Do not appear to be cost-effective with 70 mm longitudinal emittance

Accelerator types synchrotron
Accelerator Types: Synchrotron

  • Synchrotron with very fast ramping time

    • 1.5 T maximum fields

      • Low average bend field: low RF efficiency

    • Pulse times: 63–375 GeV, 200 µs for 5 MV/m

    • Beam moves in aperture to correct time of flight

    • Pulse times too short at low energies

  • Hybrid synchrotron

    • Alternate fixed-field high-field dipoles and low-field bipolar pulsed dipoles to get large average dipole field

    • More passes through RF, but faster ramp times

    • Ideal solution at high energies

Acceleration scenario2
Acceleration Scenario

  • Linac with cooling technologies to ≈700 MeV

  • RLA to 63 GeV

    • Compatible with 70 mm longitudinal emittance

  • Acceleration to ≈375 GeV

    • RLA or non-hybrid synchrotron

      • Appear to have comparable costs

      • Synchrotron could share tunnel with next stage

      • Relatively safe technologies

    • Hybrid synchrotron (two stages)

      • Appears better for cost/efficiency

      • Short pulse times a challenge (70 µs for 5 MV/m)

Acceleration scenario3
Acceleration Scenario

  • Hybrid synchrotron above ≈375 GeV

    • Gets easier as energies increase

    • 10 T SC dipoles, 1.5 T ramped dipoles, looks like could accelerate to 3 TeV on Fermilab site

Design challenges
Design Challenges

RLA switchyard layout


Time of flight correction

Collective effects

Showstoppers unlikely, but cost escalation an issue


  • NuMAX concept in place

  • Concept for 63 GeV acceleration in place

    • May need modifications for 70 mm longitudinal emittance

  • Hybrid synchrotron design exists

    • Needs modification for current magnet parameters

    • Needs time of flight correction

    • Should look at chromaticity correction

    • Needs to be scaled to other energies

Key technologies
Key Technologies

  • RF

    • High-gradient SCRF: higher helps efficiency & decays

    • High gradients for cooling RF systems used for early acceleration

  • Superconducting magnets: higher fields help efficiency and decays

  • Kickers for injection/extraction

Key technologies pulsed magnets
Key Technologies: Pulsed Magnets

  • Workable designs for 1.5 T

    • 1.8 T with grain oriented steel, but

      • Field line pinning makes this sensitive to construction tolerances

      • Not possible to model accurately with existing codes

    • FeCo could achieve 2.2 T

      • But need shielding solution for Co activation, unlikely

  • Quadrupole design

  • Better understand steel behavior with short pulse times, high fields, thin laminates

    • Pushing limits on existing measurements

    • Consequences of short pulse times

  • Power supplies: controlled ramp