INITIAL STUDIES OF ELECTROMAGNETIC SHOWER ENERGY DEPOSITION IN SMALL-BORE SUPERCONDUCTING UNDULATOR STRUCTURES IN LINAC ENVIRONMENTS

One of the more promising technologies for developing minimal-length i nsertion devices for linac-driven, single-pass free electron lasers (F ELs) operating in the X-ray range is based on the use of superconducti ng (SC) materials. Despite its advantage of minimal length, however, S C technology can present difficulties for insertion device design and operation. One critical problem, as observed, e.g., by Madey and co-wo rkers in their initial (25 MeV) FEL experiments, was the frequent quen ching induced by scattered electrons upstream of their (bifilar helica l) SC device. In view of the short-term stability required of undulato rs for user facilities, we have initiated a systematic investigation o f these earlier results to determine whether quenching could become si milarly probable in SLACs (10-15 GeV) linac coherent light source (LCL S), a 1.5 Angstrom FEL. Postulating that the onset and spread of norma l zones are precipitated by directly-scattered or bremsstrahlung-propa gated particle energy deposited into the SC material or into material contiguous with it, we have used the EGS4 particle-tracking code devel oped at SLAC to perform studies of scattered-particle energy depositio n into SC structures with geometries comparable to a small-bore bifila r helical undulator. Preliminary numerical results for both the Madey and SLAC LCLS cases have been obtained.