The Heidelberg 3MV-CW Heavy Ion Postaccelerator Section Using Independently Phased Spiral Resonators

The Heidelberg 3MV heavy ion postaccelerator section based on independently phased normal conducting spiral resonators working at 108 MHz is described. The design veloctity of the spiral resonators is ?? = 0.10. The peak voltage drop is 0.37 MV at 20 kW CW input power (0.74 MV at 80 kW, duty factor 0.25) corresponding to a peak accelerating field of 1.7MV/m (3,4MV/m) averaged over the external length of the resonator. Using a synchronous phase of ??S = -20?? gives a maximum effective voltage of 0.35 MV (0.7 MV). The resonators are stacked in modules of four with one external quadrupole doublet. The total effective voltage of this first test section of the Heidelberg postaccelerator under construction is 3 MV-CW (6 MV d. f. 0,25) providing ion energies up to 6 MeV/ nucleon at mass A=40. The postaccelerator will be integrated into the existing experimental area. Beam matching to the longitudinal acceptance of the postaccelerator is done by a separate spiral resonator as rebuncher. The high quality of the tandem beam with respect to longitudinal and transverse phase space is maintained in the designed postaccelerator.