Progress in experiments towards increasing of confinement time of dense plasma in long open trap GOL-3-II is presented.1 This facility is an open trap with total length of magnetic system of 17 m. The main part of the facility is 12-meter-long solenoid with 4.7 T in homogeneous part and 9 T field in mirrors. The plasma heating is provided by a high-power electron beam with the total energy content of up to 200 kJ. The former phase of the GOL-3-II activity was completed with the achievement of high efficiency of collective relaxation of the beam in the plasma. Electron temperature of the plasma is up to 2-3 keV at 1015 cm−3 density. Energy confinement time is mainly determined by longitudinal thermal conductivity. The main aim of the recent activity on the GOL-3-II facility is to research the possibility of improvement of confinement of the dense plasma after its heating. The GOL-3-II facility was essentially modified for this purpose. The 12-meter plasma column was separated from entrance solid electrode and an exit beam receiver by vacuum sections and expanders for decreasing of the longitudinal electron thermal conductivity. In addition, the magnetic field on a part of solenoid was transformed into multimirror (corrugated) configuration with the ratio Hmax/Hmin ~1.5 and 22 cm cell length. The problem of macroscopically stable transportation of the beam through the whole system was solved by creation of an artificial return current. As a result of the experiments at modified facility the energy confinement time for the plasma with density of 5·1014÷2·1015 cm−3 range and with sub-keV temperature is increased at an order of magnitude.