Helicon plasma generated at very high radio frequency has almost the same properties as common high frequency helicon plasmas. By measurements of wave number and plasma potential, additional mode changes inside the helicon plasma were observed with increasing magnetic field. It was also observed that the wavelength of the helicon wave changes discretely with respect to the plasma length indicating strong restriction of the parallel wavelength to the plasma dimension. The dependence of plasma potential on magnetic field indicates that its change is not entirely due to capacitive coupling. The corresponding mode transition is related to the cavity modes driven by a helicon wave.