Control of emittance growth in PPM focussed TWT´s

Last year at this conference, tunnel emittance growth was identified as a real effect observed in periodically focussed TWT\´s. Note that growth in T-emittance reflects a progressive increase in beam disorder and/or beam size with distance caused by a) initial beam homogenization (scallop decorrelation), and b) conversion of potential energy (space charge depression) into kinetic energy (transverse velocity). This paper describes further work aimed at control or reduction of this growth. This past year, explicit relationships were developed to enable accelerator beam theory on emittance growth to be recast into more familiar terms. The paper identifies how T-emittance relates to "standard" emittance, and defines the concept of tune depression via the K-V (Kapchinskij-Vladimirskij) equation. Next, the paper presents a spent beam model for depressed collector calculations (based on T-emittance). The paper closes with a discussion of how downstream T-emittance affects performance in TWT\´s and other devices.