Ion Optics

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Herein should be a general intro to ion optics. A set of links should include one to courses taught by CASE faculty.

The NSL Facility

  • Negative ions sputter from the source sample holder (often called "cone" locally). Details of the electric field lines, production of a conical divot and material all contribute to the emittance of the ions as they leave the sample holder. Typical units are tens of MeV-mm/mradian
  • The electric field created by the extraction electrode "extracts" the negative ions.
  • A gridded Einzel Lens focuses the beam to the object point of the inflection magnet. An aperture is placed where the beam is large to allow for reduced currents.
  • The 90 degree inflection magnet has a natural focal length of R (radius= ?? meters). This matched in the vertical plane by shaped pole pieces.
  • An aperture at the entrance to the injector accelerator tube reduces the electron load to the tube and provides an image to the lens of the tube. This lens is weak.
  • An electrostatic triplet and electrostatic steerer at Ground Station create a beam waist just in front of the Tandem, amtching to the bulge lens effect of the Tandem accelerator tubes.
  • The first 20 planes of the Low Energy column have reduced value (gradually decreasing from full to half value) to weaken the bulge lens effect.
  • There are no active optical elements in the Tandem Van de Graaff, only gently focusing via the spiral inclined electrodes in the tubes
  • The High Energy AG Lens is the first magnetic focusing element. It works with the HE Magnetic Steerer to create a beam waist at the object point of the Analyzing Magnet. We create this with a circular aperture ~ 1.5 meters in front of the magnet.
  • Image #2 is the image point of the Analyzer. It is closer to the magnet than the object point, therefore we have magnification of less than one.
  • The Tunnel Triplet has its object point at Image 2. Along with the Tunnel vertical steerer and the Switching Magnet is creates an image on whatever beamline is selected.
  • The Beamline Quadrupole creates a focus at the target. If steering is required there are horizontal and vertical steerers on each beamline


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