Results of experimental work on annular plasma columns are presented. The plasma density was determined by measuring the dipole resonance using a section of a stripline. Results of the stripline measurement were used to locate the passband of the backward surface wave. The theoretically predicted forward and backward surface waves were measured. Agreement between the theory and the experiment is excellent. Theoretical consideration is given to a possible spurious oscillation resulting from electron beam interaction with the plasma body wave and a criterion for the existence of backward wave in a plasma column. Experimental results are presented of the measurement of the conductivity of pyrolytic graphiteBN layered material. The real part of the effective conductivity measured for one sample was 0.006 mhometer. This value of the conductivity represents a possible improvement of 100000 in the loss characteristics of microwave slow-wave circuits built with this material over the pyrolytic graphite structures previouly discussed.