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The beam energy obtained with an Alvarez linac is normally determined within narrow limits by the design energy of the synchronous -particle. In the SuperHilac poststripper the tank is divided into several separately excited sections. In each section varying .the electric field from zero to maximum causes the energy increment of that section to vary from zero to the maximum (synchronous value). By so adjusting each of 5 seconds, the output energy can be varied continuously from 2.6 to 8.5 MeV/N. Some aspects of the expected behavior of the partial energy beams are discussed-particularly the energy spread. A formula is suggested whereby results obtained for the heavy ion linac can be scaled to predict variable energy performance of other linacs. Introduction Methods which have been used to obtain beams of less than maximum energy from a linac are a) the use of a movable rf diaphragm, 1 b) decreasing the electric field strength along the cavity so that at some point accelerating buckets cease to exist, c) use of degrading foils. Method a) gives beams of full intensity and good quality, but c.hanging energy requires going up to air, followed by a lengthy pumpdown, in order to move the diaphragm. Method c) increases energy spread and foil life imposes intensity limitatipns. Method b) has been used for a number of years at the HILAC to obtain partial energy beams. 2 Careful tuning of the electric field tilt, of the relative phase between prestripper and poststripper, and of the poststripper quadrupole currents is necessary in order to get good results. Continuous energy variation is not possible and full intensity is not always obtainable at a given energy. A chainof independently driven single cell resonatora has been proposed for the Unilac heavy ion accelerator. 3 By adjusting voltage and phase of the resonators so as to produce appropriate synchronous acceleration (or deceleration) a wide range of final energies can be achieved. In planning the SuperHilac, a method was desired which easily permitted contimuous variation of energy, and which did not add very much to the cost; The method adopted is to insert a number of fixed rf diaphragms into the poststripper, dividing it into separately excited resonant cavities. The length of these sections is chosen so that they can be economically driven by one power tube. (See Fig. 1)

METHOD FOR OBTAINING LINAC BEAMS OF CONTINUOUSLY VARIABLE ENERGY.