Ion Optics

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Students interested in Ion Optics should consider taking Phy 684 which is often a course in Accelerator Physics taught by CASE faculty.

A nice primer oriented to low energy facilities was posted to the web by Dr. Berg of Notre Dame University at Intro to Ion Optics


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, matching 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


Estimates for the beamline optics settings are made with this online Optics Calculator

Glossary of Ion Transport Terms

Here is a link to a glossary of terms used in beam transport at facilities such as the CASE Tandem Van de Graaff IonTransportGlossary

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