Amanda Hubbard

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The Thomson scattering (TS) diagnostics set [Rev.] has been upgraded to deliver measurements of electron temperature (T e) and density (n e) with improved temporal and spatial resolution. Two 30 Hz, 1.3 J Nd-doped yttrium aluminum garnet (Nd:YAG) lasers share a vertical beam path through the tokamak plasma and are fired in alternating fashion, allowing(More)
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)
Citation McDermott, R. M. et al. " Edge radial electric field structure and its connections to H-mode confinement in Alcator C-Mod plasmas. 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.(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)
An overview of the diagnostics installed on the Alcator C-Mod tokamak [I.] is presented. Approximately twenty-five diagnostic systems are being operated on C-Mod. The compact design of the machine and the cryostat enclosing the vacuum vessel and magnetic field coils make access challenging. Diagnostics are used to study four focus areas: Transport, plasma(More)
Early operation of the Alcator C-MOD tokamak is surveyed. Reliable operation, with plasma current up to 1 MA, has been obtained, despite the massive conducting superstructure and the associated error fields. However, vertical disruptions are not slowed by the long vessel time-constant. With pellet fueling, peak densities up to 9 x 1020 m-3 have been(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)
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)
At modest 3 He levels (n 3He /n e ~ 8-12%), in relatively low density D(3 He) plasmas, e n ≤ 1.3×10 20 m-3 , heated with 50 MHz rf power at B t0 ~ 5.1 T, strong (up to 90 km/s) toroidal rotation (V φ) in the co-current direction has been observed by high-resolution x-ray spectroscopy on Alcator C-Mod. The change of central V φ scales with the applied rf(More)
Trace non-recycling impurities (Sc and CaF 2) have been injected into Alcator C-Mod plasmas in order to determine impurity transport coefficient profiles in a number of operating regimes. Recycling Ar has also been injected to characterize steady state impurity density profiles. Subsequent impurity emission has been observed with spatially scanning x-ray(More)