Bunching of an Intense Electron-Beam Extracted from a Triode Gun Modulated at 1 Ghz

We present measurements of the bunch length and emittance of a high-current electron beam, which is extracted from a triode modulated at 1 GHz and subsequently compressed by means of velocity modulation in a prebuncher cavity. The prebuncher is detuned by about 1 MHz in order to ensure that the total field, which is the sum of the field from an external generator and the beam-induced field, has the correct phase and amplitude. The bunch length is measured by means of a capacitive pick-up probe and a 20 GHz sampling oscilloscope. A bunch length of 40 ps, at a charge of 220 pC, has been obtained at the end of the drift space behind the prebuncher, which has a length of 200 mm. The normalized emittance is 36-pi mm mrad.