The Michigan Mark I <a href="https://en.wikipedia.org/wiki/FFAG_accelerator" class="extiw" title="w:FFAG accelerator">FFAG accelerator</a> (fixed field alternating gradient accelerator), as erected at the <a href="https://en.wikipedia.org/wiki/University_of_Michigan" class="extiw" title="w:University of Michigan">University of Michigan</a> before it was moved to the <a href="https://en.wikipedia.org/wiki/Midwestern_Universities_Research_Association" class="extiw" title="w:Midwestern Universities Research Association">Midwestern Universities Research Association</a> lab in <a href="https://en.wikipedia.org/wiki/Madison,_Wisconsin" class="extiw" title="w:Madison, Wisconsin">Madison, Wisconsin</a>.  This 400KeV electron accelerator was the first operational FFAG accelerator.  As shown here, it used <a href="https://en.wikipedia.org/wiki/betatron" class="extiw" title="w:betatron">betatron</a> acceleration; after the move to Madison, it was reconfigured as a 500KeV electron <a href="https://en.wikipedia.org/wiki/synchrotron" class="extiw" title="w:synchrotron">synchrotron</a>.
<p>The horizontal ring centered in the photo was composed of alternating positive (big) and negative (small) bending magnets.  These enclosed the vacuum chamber that accommodated particle orbits between 0.7 and 1.0m diameter.  Magnet power was provided by one of the two <a href="https://en.wikipedia.org/wiki/motor-generator" class="extiw" title="w:motor-generator">motor-generator</a> sets partially visible in the upper left.  The large rectangular yoke on the right of the photo is the water-cooled <a href="https://en.wikipedia.org/wiki/betatron" class="extiw" title="w:betatron">betatron</a> core, a <a href="https://en.wikipedia.org/wiki/transformer" class="extiw" title="w:transformer">transformer</a> core where the secondary winding was the <a href="https://en.wikipedia.org/wiki/particle_beam" class="extiw" title="w:particle beam">particle beam</a> being accelerated.  The primary winding on the betatron core was excited by 500Hz AC provided by the other motor generator set.  A bank of large <a href="https://en.wikipedia.org/wiki/capacitor" class="extiw" title="w:capacitor">capacitors</a>, not visible, was wired across the betatron primary winding improve the <a href="https://en.wikipedia.org/wiki/power_factor" class="extiw" title="w:power factor">power factor</a>.
</p>
The <a href="https://en.wikipedia.org/wiki/vacuum_pump" class="extiw" title="w:vacuum pump">vacuum pump</a> for the accelerator filled most of the under-table space visible in the photo.  The large rectangular box in the upper left was an <a href="https://en.wikipedia.org/wiki/19-inch_rack" class="extiw" title="w:19-inch rack">electronics rack</a>, partially obscuring the view of the motor generator sets and an <a href="https://en.wikipedia.org/wiki/oscilloscope" class="extiw" title="w:oscilloscope">oscilloscope</a>.
Lawrence W. Jones
CC BY-SA 3.0 us
Published as <a rel="nofollow" class="external text" href="http://inspirehep.net/record/38999/files/MURA-104.pdf">A Small Model Fixed Field Alternating Gradient Radial Sector Accelerator</a>, MURA technical report LWJ/KMT-5 (report 104), April 3, 1956; Figure 4, unnumbered page 20.  The version of the photo shown here has been re-scanned from a vintage 9.5x13 inch black-and-white print.  3 separate scans were made and pieced together to deal with streaks created by bad pixels in the scanner, and numerous dust flecks and scratches on the print were edited out.