The University of Washington Sixty-Inch Cyclotron

Abstract

The new constant frequency 60-inch cyclotron at the University of Washington is described. Its principle mechanical features are the following: (1) A 20-inch diffusion pump is placed close to the vacuum chamber in order to provide high pumping speed; (2) The rf conductors are almost free of unsoldered joints in order to provide a high ``Q'' circuit; (3) The positions of the shorting ``spiders'' can be readily changed without breaking the vacuum; (4) The dees and dee stems are removable as one unit from the vacuum envelope; (5) The cyclotron vacuum chamber is constructed of welded aluminum alloy in order to reduce accumulated radioactivity; (6) A unique side-loading target chamber can be used for ordinary bombardments without disturbing apparatus more remote from the cyclotron; (7) The exit strip and other parts of the dee system subject to beam erosion are made of graphite. The oscillator uses a single ML-5681 tube in a grounded-grid self-excited circuit. A 2-kw frequency-modulated booster oscillator drives the main oscillator above the ``multipactoring'' threshold. A cathode bias resistor is used in place of the familiar constant-current network. Ions are drawn out of the dees by means of a dc-biased rf deflector. Four degrees of freedom of the deflector are adjustable from the console. An account is given of the major troubles encountered and the steps taken to achieve satisfactory operation. The cyclotron produces external beams of 125 to 200 μa at a nominal deuteron energy of 21 Mev with an oscillator power input of 100–125 kw.