The results of experiments on high-temperature plasma confinement in a quasi-stationary fusion facility are presented. The results were obtained on the L-2M stellarator in which superposition of magnetic fields with three-dimensional spatial symmetry is created with the help of external windings. The plasma was created and heated using microwave pulses with a record specific power of 2 to 4 MW/m3. Under these conditions, spontaneous transition processes were observed in a plasma stable with respect to large-scale instabilities, leading to an abrupt increase in energy. High thermal loads on the wall of the vacuum chamber are observed in the area of the helical separatrix, which leads to an increase in the penetration of impurities into the plasma. Plasma energy and confinement time correspond to L-2M single-machine scaling at lower powers while at specific powers above 3 MW/m3, confinement time decreases due to the accumulation of impurities. The research results can be used to develop fusion energy facilities or to simulate astrophysical phenomena.