1Jefferson Lab

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A Medium Energy Collider at JLab
Alex Bogacz1, Tanja Horn1, Franz Klein2, Pawel
Nadel-Turonski2

• 1Jefferson Lab
• 2Catholic University of America

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High vs. Medium Energy Colliders
Concepts are mutually exclusive

• High energy colliders can only operate close to
  maximum energy
• Widening the energy range reduces the luminosity
• Only weak focusing (ß) possible to accommodate
  quadrupole strengths at high energy and aperture
  sizes (smax) at low energy.
• Detector must fit in the interaction region (f)

thin lens limit

• Multi-purpose design cannot compete with an
  optimized one
• Physics Options
• Inclusive at high energies
• Exclusive at medium energies

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Figure of Merit
Luminosity x Acceptance x Polarization2
ion side is the key
The Pelican provides an optimized solution.
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Physics at a Medium Energy Collider
Physics opportunities and requirements

• Exclusive processes at high Q2 or low x
• resolution
• Compton Scattering (DVCS, double DVCS)
• Meson production
• Charmed baryons (Lattice QCD)
• Hybrid baryons?
• (Semi-) Inclusive measurements
• kinematic reach and flavor tagging
• Down to x10-3 at vs similar to COMPASS
• Charge symmetry violation?

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Symmetric Collider
Max fixed target equivalent energy of 170 GeV

• Compared with fixed targets, colliders have the
  advantage of
• Small backgrounds (no Mollers)
• Good figure of merit, in particular with
  transverse polarization
• Symmetric colliders also offer
• Lowest lab momenta for a given vs
• Optimal momentum resolution
• Good particle identification
• Improved acceptance

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Example Angular Resolutions in (e,ep)
4 on 4
4 on 4

• Outgoing electron and meson cover nearly 4p
• Provides best angular resolution

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Pelican Detector Concept
10m

• Detector tailored for specific needs of the
  various physics processes
• Solenoid-Torus combination suitable
• As guideline for space needed consider a large
  torus like CLAS

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EIC Emerging detector concept
8 meters (for scale)
140 degrees
Offset IP
T. Horn and R. Ent
TOF
HCAL
PbWO4 ECAL
Tracking
dipole
RICH
HCAL
Needed?
solenoid
Issues 1) would need to change (E)TOF with HTCC
if 500 MHz operation 2) need addl Particle Id.
(RICH/DIRC) for large angle p/K/p? 3) conflict
with charm measurements that require low central
field?
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Similar to PANDA Detector Concept
T. Horn and R. Ent
10m
See PANDA Technical Progress Report also here
discussions of solenoid vs. solenoid dipole vs.
solenoid toroid.
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Accelerator Design
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Contributions to Luminosity
Luminosity per IR 2 1033 cm-2 s-1 in 4 on 4
GeV/c kinematics.
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Collider Performance Summary cont.

• Electromagnetic beam-beam forces between
  colliding bunches, may
• cause emittance growth
• induce coherent instabilities
• decrease luminosity and its lifetime

• Severity of the effect is measured by the
  beam-beam interaction parameter, ?

• Acceptable values for ?

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ProjectX style ion injector
Accumulator/electron cooling ring
SRF linac
ProjectX-like linac
polarized ion source

• IUCF style polarized ion source (p, d, He-3,
  He-4, Li-7)
• polarized ion gun (RFQs) 25 mAmp
• SRF linac HINS-like (300 MeV/u pulsed)
• Accumulator/Electron cooling ring cooling with
  200 keV DC electrons (0.01 sec) - 80 mA
• SRF linac based on CW Project X (2 GeV)
• 0.5 MW average power

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ProjectX style ion injector

• Stacking/Accumulation/Bunching Booster Ring
• Multi-turn (10 15) injection from 2 GeV SRF
  linac to the Stacking Ring
• Electron stripping and phase space painting
• Accumulation of 0.8 A un-bunched beam at space
  charge limited emittance
• Stochastic cooling down to the equilibrium
  emittance eN 0. 210-6 m rad
• RF bunching (1.5 GHz) with tunable RF (500-1500
  MHz)
• Further acceleration and ramping

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Collider Rings
Pair of Figure-8 Rings (900 m circumference)
ProjectX style ion injector
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Interaction Region design
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Interaction Region design - ions

• Triplet based low beta Optics
• larger distance IP - first quad
• larger crossing angle 50-100 mrad
• 5 Tesla/m FF gradients - no need for SC quads
• Reasonable longitudinal acceptance Dp/p 10-4
• effective chromatic compensation with sextupoles

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Interaction Region design - electrons

• Relaxed Triplet based IR Optics (electrons) with
  large b 18 cm
• first FF quad far from the IP (8-10 m)
• no need for chromatic compensation

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Storage Ring - COSY vs Pelican

• Pelican Two figure-8 storage rings with four
  interaction points would be built. No
  acceleration would be performed in the storage
  ring.
• COSY The storage ring for the ions would be
  COSY itself. A second ring would be built for
  electrons. There would only be one interaction
  region.

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Electron Injector - COSY vs Pelican

• Pelican An accumulator ring would be used to
  increase number of electrons per bunch from
  millions in CEBAF to 10.8 billion (at 4 GeV)
  before injecting into the storage ring. The
  weaker electron focusing allows larger emittances
  than in a collider with high ion momenta, but no
  detailed study has been made as to how far one
  can push the limit.
• COSY Bunches of 45 billion electrons were
  assumed at 5 GeV. The CEBAF side could be made
  identical for both solutions!

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Interaction Regions - COSY vs Pelican

• Pelican IR uses asymmetric focusing, based on
  triplet optics with b of 5 mm for the ions
  allowing 8 m of magnet free space for detectors.
  As the ion energy gets lower, the strong focusing
  makes the beam sizes at FF quads quite large.
• COSY A "traveling focusing" scheme with
  non-linear elements is suggested, which would
  enable short electron bunches to collide with
  different slices of long ion bunches. A b of 2.5
  mm is proposed. The magnet aperture problem is
  addressed by reducing the magnet-free space for
  detectors

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Ion Injector - COSY vs Pelican

• Pelican The injector consists of several stages
• initial 0.3 GeV linac (0.25 mA of polarized beam)
  
• injects into a small (10 m) accumulator ring,
  which performs electron cooling (at low energy
  range where it is efficient).
• 80 mA beam is then accelerated in a 1.7 GeV
  linac, providing very little emittance growth
• injected into an accumulator/booster ring at an
  energy suitable for stochastic cooling applied to
  un bunched beam.
• The beam would then be bunched to acquire the
  appropriate time structure, and be accelerated to
  the desired energy.
• stochastic cooling with bunched beams (final
  round of cooling) will be applied before
  injection into the collider ring.
• it would give 800 mA (3.33 billion ions per
  bunch) with normalized emittance of 2 x 10-7 m
  rad at 4 GeV222

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Ion Injector - COSY vs Pelican

• COSY The injector consists of fewer stages
• The ions are accelerated by a 0.2 GeV linac
• Then injected directly into COSY, where electron
  cooling is applied.
• The beam is then bunched and accelerated up to
  3.7 GeV.
• Here it is suggested that electron cooling is
  applied again.
• It is estimated that one can have 1.5 billion
  ions per bunch and a normalized emittance of 2.75
  x 10-7 m rad at 5 GeV.

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Staging for ELIC - COSY vs Pelican

• Pelican Is independent of ELIC. High-energy
  booster and storage rings can, however, be added
  without changes to the pelican. The injectors
  could be shared.
• COSY Both COSY and the electron storage ring
  will be dismounted before building ELIC. It is
  intended to use the COSY parts as an ion
  accumulator.

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Backup Material
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The Next JLab Upgrade
A strategic choice has to be made

• Fixed target experiments
• Increase CEBAF energy beyond 12 GeV
• Beam emittance will deteriorate
• Collider experiments
• Use CEBAF as part of injector
• Further energy upgrades are detrimental for
  luminosity
• Design criteria for high and low energy colliders
  are very different

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Staged Construction Plan

• Proton Linac and Fixed Target Area
• Ion Linac providing 80mA of 2 GeV/c protons (50
  M)
• Unpolarized high-current ion source (5 M)
• Beamline and fixed target areas for both basic
  and applied research
• Collider with Unpolarized Ions
• Intersecting storage rings (20 M)
• Accumulator ring for lepton injector (10 M)
• Simple detector for storage ring
• High-Luminosity Collider with Polarized Ions
• Polarized ion source (10 M)
• Small ring for electron cooling (2 M)
• Booster ring (40 M)
• Detector(s) for storage ring

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Add COSY to CEBAF?
May not be as simple as one may think

• Limitations of a COSY collider
• Lacks the polarization advantage of a Figure-8
  design
• Luminosity at least an order of magnitude lower
• Proton energy limited to 3.7 GeV
• Upgrade potential limited
• Cost benefits are limited extensive
  modifications required
• Individual COSY components can be a valuable
  addition
• Experiments (e.g. WASA, ANKE)
• Ring could be used as ion accumulator (no RF)
  NOT needed here
• Beam pipes, diagnostics, ion sources, and parts
  of the cooling system

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Fixed Target Physics
WASA detector

• Physics opportunities without additional
  investment
• Good way of expanding the user community
• High quality low-energy nuclear physics
• Will attract a new hadronic user community
• Fills an important void

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Accelerator Applications
Transmutation of Nuclear Waste

• Challenge Energy Independence and global warming
• Nuclear energy will be part of the solution
• Fast reactors may be perceived as unsafe
• No passive safeguards (void, Doppler)
• A sub-critical system with accelerator driven
  spallation source could be easier to accept
• Requires reliable high-current proton linac
  technology (Ep gt 1 GeV)

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Neutron Spallation Source
Research into atomic structure and dynamics of
materials

• Oak Ridge 1.4 MW short-pulsed SNS
• European Spallation Source (ESS) planned 5 MW
  long-pulsed
• Large user community
• Unlikely to materialize due to high cost and lack
  of political support.
• With all infrastructure in place, JLab could
  provide ESS performance at a fraction of the cost