Jerry W. Hughes

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In Alcator C-Mod discharges lower hybrid waves have been shown to induce a countercurrent change in toroidal rotation of up to 60 km/s in the central region of the plasma (r/a approximately <0.4). This modification of the toroidal rotation profile develops on a time scale comparable to the current redistribution time (approximately 100 ms) but longer than(More)
The sources of neutrals at the outer midplane of the plasma are discussed. We find that both the flux of neutrals escaping the divertor through leaks and ion recycling at main chamber surfaces appear to contribute. The ion flux to the walls is larger than the flux entering the divertor and comparable to recycling at the divertor plate. The cause of these(More)
High resolution measurements on the Alcator C-Mod tokamak [I.H. Hutchinson et al, of the transport barrier in the " Enhanced D α " (EDA) regime, which has increased particle transport without large edge localized modes, show steep density and temperature gradients over a region of 2-5 mm, with peak pressure gradients up to 12 MPa/m. Evolution of the(More)
Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. The goal of the Lower Hybrid Current Drive ͑LHCD͒ system on the Alcator C-Mod(More)
The time evolution of toroidal rotation velocity profiles has been measured in Alcator C-Mod [I.mas using a tangentially viewing x-ray spectrometer array. The strong co-current toroidal rotation in enhanced D α (EDA) high confinement mode (H-mode) plasmas is observed to propagate in from the edge on a time scale similar to the energy confinement time. The(More)
An improved energy confinement regime, I-mode is studied in Alcator C-Mod, a compact high-field divertor tokamak using Ion Cyclotron Range of Frequencies (ICRF) auxiliary heating. I-mode features an edge energy transport barrier without an accompanying particle barrier, leading to several performance benefits. H-mode energy confinement is obtained without(More)
A high resolution Thomson scattering diagnostic is in operation on the Alcator C-Mod tokamak, measuring radial profiles of electron temperature and density at the plasma edge. Photons are scattered from an Nd-YAG laser beam pulsed at 30 Hz (1.3-J, 8-ns pulse), and are measured by a filter polychromator with four spectral channels. The polychromator measures(More)
The recently upgraded phase-contrast imaging (PCI) diagnostic is used to characterize the transition from the low (L) to the enhanced D α (EDA) high (H) confinement mode in Alcator C-Mod integrated density fluctuations along vertical chords. The number of channels has been increased from 12 to 32, the sampling rate from 1 MHz to 10 MHz. This expansion of(More)