  We present design and simulation results on the electron source for 2856 MHz
technological electron linac. This device is a combination of an RF gun and a
DC diode gun. The designed gun consists of a thermionic cathode, which is
mounted on the wall of the TM010 cavity that is under negative high voltage
potential relatively to an anode. The use of such an electron source makes it
possible to exclude the high-voltage gun modulator and resonator for beam
prebunching from the accelerator circuit. Duration and position of an electron
beam pulse within a RF power supply pulse of the accelerating section can be
adjusted with tailoring of RF pulse feeding the cavity. The paper describes the
design and electrodynamics characteristics of the gun cavity and a filter,
which allows to transfer microwave power to that cavity. The particles dynamics
has been studied by simulation. It is shown that the beam parameters at the gun
exit satisfy the stated requirements. At an average particle energy of 95 keV,
the beam pulse current is 0.44 A, the emittance does not exceed 4.8 mm mrad,
and 70% of all electrons are concentrated in the 72 deg phase range.
