Experimental studies and sheet beam transport for low-voltage, grating TWT amplifiers

Abstract

Summary form only given, as follows. Spontaneous emission and linear gain measurements for a low-voltage sheet-beam-compatible, grating TWT amplifier are presented. Results of analyses of a sheet beam formation by magnetic quadrupoles from a round beam and staple transport in a periodic cusp magnetic field are also discussed. A round "probe" beam from a 10 kV, 0.25 A Pierce gun electron source is utilized for 14 GHz amplifier experiments. The spontaneous emission measurements provide (a) measurement of the grating-induced spontaneous emission spectrum which can be correlated with the theoretically predicted linear gain curves, (b) measurements of broad-band noise emission, and (c) measurement of spontaneous emission in the backward-wave regime to correlate with start oscillation predictions. The noise emission spectra have been correlated with experimental factors including the guide magnetic field intensity and body current. Measurements of linear gain are also compared with the theoretical prediction in both forward and backward-wave regimes. A sheet beam can be formed by the use of magnetic quadrupoles to transform an initially round beam from a conventional Pierce gun into a highly eccentric elliptical beam. Results of a 3-D PIC simulation of the beam will be discussed.