Cathodes are electron sources used for gas ionization and ion beam neutralization in Hall thrusters. A laboratory model of a 5 A-class cathode has been experimentally studied in the so-called diode configuration with a flat metal anode. The cathode design is based on the direct heating of a flat disk lanthanum hexaboride (LaB 6) insert to emit electrons. The paper presents the characterization of the LaB 6 cathode operated at xenon mass flow rates between 0.2 and 0.6 mg:s À1 with discharge currents ranging from 2 A to 19 A. Electrical parameters and temperature of several parts, including the LaB 6 insert, were collected and analyzed in order to investigate the possibility of operating the cathode in an extended range of discharge current with respect to its nominal condition (5 A at 0.4 mg:s À1). Particular attention was paid to the identification of the discharge mode (spot versus plume) through spectral analysis of discharge current waveforms. Temperature measurements performed with thermocouples reveal that the LaB 6 insert is moderately heated during the cathode operation (about 1600 C at 19 A), except for the lowest mass flow rate.