Ion Optics

Background

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

Particulars

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

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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