EMMA: A Recoil Mass Spectrometer for ISAC-II

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EMMA A Recoil Mass Spectrometer for ISAC-II

• Barry Davids

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Workshop 11-12 Dec 2003

• 30 participants included both prospective
  ISAC-II users and spectrometer experts from
  Canada, USA, UK, France, and Italy
• Goal identify scientific aims that will drive
  design, survey existing designs
• Recoil mass spectrometer needed to separate
  recoils from beam, identify (A,Z), and localize
  them for subsequent decay studies
• Must be well-integrated with detector systems for
  light charged particles (silicon array) and gamma
  rays (TIGRESS)
• Reactions of interest fusion-evaporation and
  transfer, particularly (d,p)

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Workshop Conclusions

• High beam (background) rejection is essential
• Good energy resolution is not helpful
• Energy and angular resolution of detected heavy
  recoils insufficient to resolve states for A gt 30
  beams
• Large angular, mass/charge, and energy
  acceptances desired for high collection
  efficiency
• All discussed reactions are strongly
  forward-peaked
• Angular acceptance should be close to symmetric
• Angular and energy spreads largest for
  fusion-evaporation reactions (10-15 msr, DE/E
  10-20)
• At least 3 charge states should be collected
• Mass resolution requirement set by single-nucleon
  transfer reactions must have M/DM 400

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Design Implications

• Velocity filter no mass resolution
• Large acceptance magnetic spectrometer ray
  tracing required, M/DM lt 150, no physical
  separation of adjacent masses with finite beam
  emittance
• Gas-filled separators poor mass resolution (50)
• Hybrid devices (e.g. VAMOS magnetic spectrometer
  Wien filter) M/DM lt 125
• EDE RMS design best choice, virtues include
• Excellent beam suppression, typically 107- 1011
• High mass resolution, physical separation of
  masses
• Large energy acceptance
• Versatile good performance for both transfer and
  fusion-evaporation

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EMMA Design
Length 9.1 m Solid angle 60 mrad by 54
mrad 13 msr M/q acceptance 4 Energy
acceptance 20 1st order mass resolution
505 M/DM for 3 deg by 3 deg (11msr), DE/E
10 360
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Simulated Focal Plane Image
d(132Sn,p)133Sn at 6 MeV/u
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Comparison EMMA vs. FMA
Maximum electric rigidity 25 greater
Mass acceptance 14 greater
Energy acceptance Equal
Solid angle 60 greater, and more symmetric
Size of dominant aberration, (xq2) 25 smaller
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Future Plans

• Expert Design Review 11 June 2004
• Purpose verify ion optics, suitability for users
  
• 3 internal panelists
• Rick Baartman (accelerator physics)
• Dave Hutcheon (DRAGON)
• Andy Miller (high energy)
• 2 external panelists
• Cary Davids (RMS expert)
• Carl Svensson (ISAC-II user)
• RTI application September 2004

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