No abstract

In the course of developing new high peak power klystrons at SLAC, high electric fields in several regions of these devices have become an important source of vacuum breakdown phenomena. In addition, a. renewed interest in breakdown phenomena for nanosecond pulse, multi-megavoll per centimeter fields has been sparked by recent R&D work in the area of gigawalt RF sourcesThe most important regions of electrical breakdown are in the output c*vjiy gap area, the RF ceramic windows, and the gun ceramic insulator.The details of the observed breakdown in these regions, ex periments performed to understand the phenomena arid solu tions found to alleviate the problems will be discussed.Recently experiments have been performed on a new proto type R&D klystron. Peak electric fields across the output cavity gaps of this klystron exceed 2 MV/cm. The effect of peak field duration (i,e> pulse width) on the onset of breakdown havt-been measured. The pulse widths varied from tens of nanoseconds to microseconds. Results from these experiments will be presented.

Secondary electron yield measurements before and after Ar ion sputter cleaning were made on Nb and Nb compounds of interest for rf superconducting cavities. Total secondary electron yields (σ) for primary energies 20–1500 eV were measured for solid Nb (σmax=1.3 at 300 eV), anodized Nb2O5 (σmax=1.2 at 300 eV), and powders of Nb(σmax=1.0 at 400 eV), NbO (σmax=0.9 at 400 eV), NbO2 (σmax=1.0 at 400 eV), Nb2O5 (σmax=0.95 at 400 eV), NbC(σmax=0.8 at 400 eV), and NbN (σmax=0.8 at 500 eV). Determinations were made for Auger elemental sensitivities, and the relationship between Auger peak heights and oxide stoichiometry is discussed. The sputter etch rate of anodized Nb2O5 was measured by depth profiling anodic coatings of known thickness.