Emittance measurement of space charge dominated electron beam confined by a longitudinal magnetic field

Summary form only given, as follows. In microwave devices, the quality of electron beam is of considerable importance. For an axisymmetric beam in a uniform focusing channel, the emittance of the beam is related with the transverse electron temperature and the beam radius. While, the transverse electron temperature can be uniquely defined as a function of the electron density profile. Therefore, measuring the radial distribution of the electron density allows us a determination of the transverse electron temperature and thus the beam emittance. We present a method of measuring the beam emittance using a multi-layer Faraday cup. The experiment is done by directly measuring the beam current that flows into each layer of the Faraday cup, and these currents are then converted to the radial profile of the current density. The transverse temperature and emittance of the beam are calculated by fitting the current profile obtained from the measurement and that from the calculation. This method enables us to measure the emittance of a space charge dominated electron beam confined by a longitudinal magnetic field. The measurement is straightforward and it is possible to avoid the electron deflection and plasma generation due to the electron hitting the slits in a slit-slit method. The proposed method has been used to measure the emittance of a matched beam in a uniform compressing channel. The details of the method and experimental results are presented.