Johnson, James C. | Engineering Papers

NASA NTRS1998

Effects of Single-Task Interference on Dual-Task Interference

Van Sergi, Ruthruff and Johnston found that dual-task practice can markedly reduce interference in the Psychological Refractory Period paradigm. Their results are consistent with a bottleneck model in which practice serves primarily to reduce stage durations. This model predicts that single-task practice on Task 1 alone should produce marked reductions in interference, whereas single-task practice on Task 2 should not. New experiments test these predictions. Alternative theoretical accounts are also considered.

Johnson, James C.↗

NASA NTRS1988

Ion-beam focusing in a double-plasma device

The authors studied the propagation of a low-energy charge-neutralized ion beam injected into the target region of a long double-plasma device. A magnetic field of up to about 180 G may be applied along the axis of the device. As a result of charge exchange collisions, the ion beam is attenuated as it propagates into the target region. However, under certain conditions of magnetic field strength and neutral gas pressure, the authors have observed a `reemergence' of the beam on axis far downstream in the target. This reemergence of the ion beam is attributed to a focusing of the ions by a self-consistently produced radial ambipolar electric field. The effect may be expected to occur in other types of plasma devices as well, whenever a sufficiently large radially inward electric field is present.

Johnson, James C.↗