Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Plasma dynamic and confinement characteristics were investigated with magnetic probes in a theta pinch operating with oscillatory current waveform and hydrogen gas at pressure between 45 and 150 mtorr. Current-sheath implosion was evident after the third half cycle until sixth half cycle when the external current has practically decayed. Each cycle starts with a trapped reversed magnetic field residual from the previous half cycle. Probe-signal fluctuations due to radial hydromagnetic oscillations were also observed. A modified snowplow model including an initial bias field and a flux-loss term gives a reasonable description of the experimental results for plasma radial dynamic and internal trapped field. Typical equilibrium-density profiles are of a hollow type with maximum density around one-third of the discharge-tube radius. Estimations from these profiles show small variation of temperature and density among half cycles in discharges at low pressure. At high-pressure regime, the temperature strongly drops in subsequent half cycles, while the density increases.371121862190Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)