A sharp transport barrier, accompanied by a bifurcated poloidal rotation and a radial electric field, is formed at the plasma edge by driving a radial current across the outer magnetic surfaces of a tokamak. A decrease in particle transport is observed for negative radial E fields. When the radial current is turned off, the E field and the rotation damp on a time scale comparable with the ion-ion collision time.PACS numbers: 52.25.Fi, 52.55.Pi, 52.70.Ds An intensive effort is in progress, worldwide, to correlate the large and growing data base of experimental observations on plasma transport in magnetic fusion containment devices with theoretical models. In particular, the so-called "//^-mode" regimes in tokamaks have attracted strong interest due to their enhanced particle and energy confinement properties. ^""^ The transition of a plasma into the H mode is marked by a sudden decrease in the hydrogenic light emission from the plasma edge, followed by a prolonged increase in the plasma density. The reduction of hydrogen light (H^ or H^) indicates that the incoming neutral particle flux is reduced, presumably because of a decrease of the outgoing plasma flux, leading to a reduction in "recycling." The improvement in the energy confinement is generally less than the increase in particle confinement, ^-mode measurements also reveal the formation of sharp density and temperature gradients inside the last closed magnetic surfaces, which represents a transport barrier. Despite the magnitude of the effort aimed at modeling the H mode, no clear mechanism has been identified, although radial electric fields are thought to play a role."*'^ In this Letter, experimental observations confirming the importance of the radial E field and the associated plasma rotation for 7/-mode confinement are presented.In 1979, electron injection was used to modify the edge potentials in order to reduce ion sputtering in the Macrotor tokamak.^ Subsequently, improved particle confinement and a concomitant impurity accumulation were observed,^ apparently giving rise to an H mode. These effects were attributed to the creation of edge radial electric fields and associated negative plasma potentials much larger in magnitude than Tgia), where a is the plasma radius. Recently we have extended this earlier work using the new, titanium-gettered. Continuous Current Tokamak (CCT) at the University of California, Los Angeles. The recent experiments clearly show the //-mode signatures found in other tokamaks in various limiter, divertor, and auxiliary-heating configurations. The previously seen impurity limitations^ have also been eased by new electrode designs. ^ For the //-mode-regime studies, CCT was operated in the pulsed neo-Alcator regime, with central parameters R^l.5 m, a =0,4 m, Bt=3 kG, /p=50 kA, ne=5 xlO*Vcm^ Kioop<1.5 V, Te>l50 eV, and T/> 100 e = 180 INSULATOR ELECTRODE = 0" C/2 Q 1.5 1.8 MAJOR RADIUS (M) FIG. 1. (a) Cross section of tokamak, a ^40 cm, showing the location of the exciting electrode, re ^25 cm, and the "rake" probe arrays used...

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In 1991 a manuscript describing an instrument for studying magnetized plasmas was published in this journal. The Large Plasma Device (LAPD) was upgraded in 2001 and has become a national user facility for the study of basic plasma physics. The upgrade as well as diagnostics introduced since then has significantly changed the capabilities of the device. All references to the machine still quote the original RSI paper, which at this time is not appropriate. In this work, the properties of the updated LAPD are presented. The strategy of the machine construction, the available diagnostics, the parameters available for experiments, as well as illustrations of several experiments are presented here.