Excitation of a Canonical RF Shelter with Relativistic Electrons and with Enhanced Risetime Bremsstrahlung

In two tests at the Aurora flash x-ray machine, a cavity (canonical rf shelter) was excited in two ways: (1) with relativistic electrons, and (2) with enhanced-risetime bremsstrahlung. Differences in cavity excitation resulting from the two types of sources are explored. The relativistic electrons excite the cavity producing large electric fields (>80 kV/m), but are not expected to produce much of a SGEMP response in individual cables and electronic boxes inside the shelter, because the electrons are easily shielded by such enclosures. The relativistic electron current density in the case of direct e-beam injection is about two orders of magnitude greater than the Compton electron current density produced by enhanced risetime bremsstrahlung. The direct e-beam currents, therefore, excite significantly larger electromagnetic fields than the bremsstrahlung produced Compton currents. The greater penetrating power of the bremsstrahlung radiation, on the other hand, excites both the larger cavity and smaller interior sub-cavities and cables. The two methods thus provide a possible means of distinguishing between different types of SGEMP excitation. Conclusions are drawn from the results concerning the feasibility of using relativistic electrons in SREMP simulation schemes.