• J. Popielarski, T. L. Grimm, W. Hartung, R. C. York
  NSCL, East Lansing, Michigan

The Spallation Neutron Source (Oak Ridge), the proposed 8 GeV Proton Driver (Fermilab), and the proposed Rare Isotope Accelerator use multicell elliptical SRF cavities to provide much of the accelerating voltage. This makes the elliptical cavity segment the most expensive part of the linac. A new type of accelerating structure called a half-reentrant elliptical cavity can potentially improve upon existing elliptical designs by reducing the cryogenic load by as much as 30% for the same accelerating voltage. Alternatively, with the same peak surface magnetic field as traditional elliptical cavities, it is anticipated that half-reentrant designs could operate at up to 25% higher accelerating gradient. With a half-reentrant shape, liquids can drain easily during chemical etching and high pressure rinsing, which allows standard multicell processing techniques to be used. A half-reentrant cavity for β = v/c = 1, suitable for the proposed ILC, has been designed and fabricated, with RF tests in progress*. In this paper, we present electromagnetic designs for three half-reentrant cell shapes suitable for an ion or proton linac (β = 0.47, 0.61 and 0.81, f = 805 or 1300 MHz).

* M. Meidlinger et al., in Proc. XXIII Int. Linac Conf., Knoxville, TN, Aug 2006