In the recent experiments, on-axis transverse beta exceeding 0.4 in the fast ion turning points near the end mirrors has been achieved in the GDT experiment with 4 MW injection of 15-17 keV deuterium neutral beams at the center of the device. Neither enhanced transverse losses of the plasma nor anomalies in the fast ion scattering and slowing down were observed. The measured beta value is close to that needed in the versions of the GDT-based 14 MeV neutron source. At the same time, the electron temperature for given injection power and pulse duration is limited to 100-130eV. Its further increase is planned after upgrade of the injection system and increase of the magnetic field at the center of device up to 0.3T. Upgrade of the injection system assumes that neutral beam power incident on to the plasma will be increased up to 9-10 MW and pulse duration is extended from 1.2 to 5 ms. According to the results of numerical simulations, for the extended pulse duration a plasma steady state will be achieved with electron temperature of 250-320 eV, depending upon the assumptions on the transverse energy loss rate. Future experiments on the GDT-upgrade are discussed in the paper.