As particles travel down the NSRL beamline, magnetic lenses steer and shape them before they exit the vacuum window and enter the target room. These magnets effectively distribute the particles into a particular pattern of high intensity and low intensity regions across the plane perpendicular to the particles’ axis of travel. This distribution is referred to as the “beam shape”, “beam spot”, or “beam profile”. An image depicting one such beam profile as captured by the NSRL digital beam imager is shown below.
The areas corresponding to higher intensity appear as a lighter color, and those with lower intensity appear as a darker color, corresponding to the color scale on the right. The intensity is given in arbitrary units. 8 fiducial corner marks can be seen. The inner 4 represent a square with 10 cm (3.9 inch) sides, and the outer 4 represent a square with 20 cm (7.9 inch) sides.
The NSRL beamline’s magnetic optics allow a fairly unique beam shape to be produced. Two octupole magnets can bend the tails of a gaussian-profile beam in towards the center. The resultant profile has a large rectangular uniform region, surrounded by high intensity “ears” at the edges.
Square Beam
Although the beam profile at NSRL can be tuned to a variety of shapes and sizes, the most common profiles used in physics or electronics testing experiments are “square” beams with a uniform center of 20×20 cm2 or 7×7 cm2. Other arbitrary rectangular shapes are most often achieved by collimating the beam with an adjustable tungsten collimator rather than tuning it, which allows NSRL to maintain a smaller set of well tuned and accurately calibrated beams while still permitting the beam spot to be adjusted.
Specially tuned beams can be developed upon request if they are necessary for a test.
Other Beam Shapes
In addition to the larger “square” beam spots, small beam spots can be achieved for physics experiments. Although the size of the final focus depends on beam energy and ion species, typical spot sizes of 1 cm RMS can be achieved. Small spots or other beam shapes can be produced through the use of collimators. If you have any special demands, contact the NSRL PI while you are planning your experiment to ensure that the beam conditions you need will be available.
While not typically used for physics or electronics testing experiments, the NSRL beamline is capable of producing an overfocused beam with a larger uniform area of up to 60×60 cm2. These beams are not recommended for electronics testing work due to their comparatively low flux, divergent geometry, and difficulty of setup.
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