Some preliminary experimental results on the acceleration of plasma in circular waveguides are reported. The experiments were carried out in the 10-cm region with H₀₁ and H₁₁ waves and with various plasma injectors. Plasma bunches with an initial particle concentration of 10¹² cm^-3 and higher were injected with an initial velocity of 5 × 10⁶ cm/sec from a spark source or formed directly on the axis of the waveguide with the help of a pressure differential plasma source ensuring a vacuum in the accelerator corresponding to pressures in the range 10^-7 to 10^-6 mm Hg. Electric probes, super high-frequency methods and an electrostatic particle energy analyser were employed for diagnostic purposes. Plasma confinement was accomplished by the use of auxiliary external magnetic fields having various configurations. Accelerated ions with energies exceeding 10 keV were obtained.