The Extraction System of the Nevis Synchrocyclotron

Abstract

The improved Nevis Synchrocyclotron is a sector focused machine which accelerates protons to 555 MeV and operates at a cycle rate of 300 Hz. At the end of the accelerating part of each cycle, the 555 MeV proton beam is shifted into a region of radial instability by a time-varying field distortion over a period of up to 2.2 ms, resulting in duty cycles of up to 67%. The radial instability is due to a conventional peeler-regenerator field distortion. Large radial oscillations induced in the instability result in a maximum radial gain per turn at the radius of the extraction channel of about 1.6 in. The 0.28 in. extraction channel septum intercepts about 35% of the beam; this is essentially the extraction inefficiency. The extracted beam suffers some moderate vertical expansion on the last turn prior to extraction. It is transported through the extraction channel, passes through a horizontally focusing field distortion (the iron channel) and a horizontal steering magnet (the iron current channel), and enters the primary proton beam transport system at the exit of the cyclotron vacuum system. At this point, the extracted beam has a horizontal width of about 1 in. (fwhm) and a vertical width ofmore » about 1.5 in (fwhm).« less