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The University of Wisconsin-Madison has completed installation of a superconducting electron gun. Its concept was optimized to be the source for a CW free electron laser facility with multiple megahertz repetition rate end stations. This VHF superconducting configuration holds the promise of the highest performance for CW injectors. Initial commissioning efforts show that the cavity can achieve gradients of 35 MV/m at the cathode position. With the cathode inserted CW operation has been achieved at 20 MV/m with good control of microphonics, negligible dark current, and Q0 > 3×109 at 4 K. Bunch charges of ~100 pC have been delivered, and first simple beam measurements made. These preliminary results are very encouraging for production of 100s pC bunches with millimeter-milliradian or smaller normalized emittances. Plans are in place to carry out more definitive studies to establish the full capabilities. However, since the grant was not renewed, the electron gun is currently mothballed, and without supplemental fund the opportunity for further work will be lost.

Between sections of the vacuum chamber, bellows are needed to compensate for thermal expansion and transverse offsets. For beampipe made of stainless steel with a coefficient of linear expansion 19 x 10/sup -6///sup 0/C and a temperature variation of approx.316/sup 0/C, the allowance for bellows is approx.1.2% of the total length of the beampipe, if we assume that the bellows are 50% compressible. This implies 1.08 km of bellows for Design A of the SSC which has a circumference of 90 km. Such a length of bellows will certainly contribute to the longitudinal and transverse impedances of the accelerator and will therefore affect the stability of the beam. In the Reference Designs, the actual impedances of the bellows have not been calculated; only an allowance of Z/sub parallel//n = 0.05 ..cap omega.. and Z/sub perpendicular/ = 7 M..cap omega../m is made for miscellaneous discontinuities because all the bellows and pumping ports are assumed totally shielded. It is the purpose of this article to examine the actual contributions by the bellows to the longitudinal and transverse impedances assuming that they are not shielded.

A particle computer simulation code is presented, designed to describe the longitudinal motion of charged particles in a nonneutralized beam. The code is 1-d, electrostatic, and is capable of simulating coasting or bunched beams, cold or warm, with arbitrary wall impedance. External focusing forces are introduced in the bunched beam case. A variety of distribution functions can be represented. The code is self-consistent and it can follow both the linear and nonlinear evolution of a beam.