Experimental measurements of cross-field transport of test ions in a quiet plasma are reported. In a plasma with density fluctuations below 〈(δn/n0)2〉1/2≊0.002, the experimental results agree with simple predictions of test ion diffusion resulting from collisional processes for the range of parameters tested. The observed transport may be attributed to Coulomb collisions and the results disagree with predictions based solely on Bohm diffusion or turbulent processes.

Direct, experimental results show cross-field majority species ion transport which is linearly proportional to electrostatic fluctuation levels. Laser-induced fluorescence was used to tag ions within a plasma. The ion diffusive and convective motion could be observed. In a quiet plasma the ion cross-field diJfusion agreed with classical predictions. A controlled level of electrostatic turbulence was then introduced into the plasma. The resulting increase in cross-field diffusion was consistent with D 1 -:::::4(cT~/eB) (8n;lnKJ ).

By drawing an electron current through a plasma to a variably biased conducting button, the electrostatic ion cyclotron instability is excited, consistent with predictions of Drummond and Rosenbluth [Phys. Fluids 5, 1507 (1962)]. Recent results show that a nonuniform steady-state electric field reaches axially into the plasma. Our results indicate that electrons are accelerated along magnetic field lines and decelerated by collisions. The point in space where the electron drift speed exceeds a critical speed (vc∼0.2vte) determines the instability amplitude and frequency. This initiation point moved further into the plasma as the externally controlled electric field was raised. This experiment demonstrates the importance of applying biases so that eφ/T≲1, near threshold, to observe the linear electrostatic ion cyclotron instability.

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The coupling of increasing spatial intermittency with increasing attractor size, which occurs for D > 4, is perhaps counter-intuitive. It arises because the relation (4) between k 4 and k. is independent of D, while the rate of growth with k 4 of the total number of excited modes, at fixed 6, increases with D. There seems nothing internally inconsistent about the behavior for D > 4, at least at the primitive level of analysis employed above. Thus D = 4 may be a transition dimensionality for inertial-range behavior. Of course it could turn out that K41 is asymptotically exact for D>4. Whatever intermittency there actually is in the inertial range involves competition between cascade in scale size, which tends to increase intermittency, and mixing of spatial regions, which tends to obliterate intermittency. 6 Neither scaling analysis nor calculations based on low-order perturbation theory can settle this question. 11 ACKNOWLEDGMENTSI have enjoyed profitable conversations with C. Foias, 0. Manley, and R. Temam.