Nonlinear space-charge-limited ion currents in solid helium

Expressions are obtained for steady-state and transient space-charge-limited currents for a nonlinear velocity-field relation of the form nu(E)=(mu/gamma) x sinh(gamma E). Our experimental results are analyzed with these expressions. The positive-ion diffusion coefficient is a tensor with two activation energies associated with motion along c axis and in the basal plane. For bcc He-3 the dependence of negative-ion velocity on field is highly nonlinear and temperature dependent. Results ave compared with those of other authors and discussed in light of different models for ionic motion in solid helium. The diffusion coefficients for positive ions and isotopic impurities are compared and discussed.