J. R. Walk

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Non-local heat transport experiments were performed in Alcator C-Mod Ohmic L-mode plasmas by inducing edge cooling with laser blow-off impurity (CaF2) injection. The non-local effect, a cooling of the edge electron temperature with a rapid rise of the central electron temperature, which contradicts the assumption of “local” transport, was observed in low(More)
The need to fit smooth temperature and density profiles to discrete observations is ubiquitous in plasma physics, but the prevailing techniques for this have many shortcomings that cast doubt on the statistical validity of the results. This issue is amplified in the context of validation of gyrokinetic transport models (Holland et al. 2009, Phys. Plasmas(More)
The first measurements of long wavelength (kyρs < 0.3) electron temperature fluctuations in Alcator C-Mod made with a new Correlation Electron Cyclotron Emission (CECE) diagnostic support a long-standing hypothesis regarding the confinement transition from Linear Ohmic Confinement (LOC) to Saturated Ohmic Confinement (SOC). Electron temperature fluctuations(More)
A dedicated series of ELMing H-Mode discharges on Alcator C-Mod spanning a broad range of plasma parameters, including plasma current (400-1000kA), magnetic field (3.5-8T), and plasma shaping, are presented with experimental scalings of the plasma pedestal with bulk plasma and engineering parameters. The H-modes presented achieve pedestals with densities(More)
With fusion device performance hinging on the edge pedestal pressure, it is imperative to experimentally understand the physical mechanism dictating the pedestal characteristics and to validate and improve pedestal predictive models. This Letter reports direct evidence of density and magnetic fluctuations showing the stiff onset of an edge instability(More)
Developing a validated predictive capability is critical to the design, optimization and successful operation of fusion experiments. However, in part because of the coupled, multi-physics nature of tokamak plasmas, it can be challenging to isolate physics and control an experiment sufficiently to precisely test predictions. Here we report on experience with(More)
We present inboard (HFS) and outboard (LFS) radial electric field (Er) and impurity temperature (Tz) measurements in the I-mode and H-mode pedestal of Alcator C-Mod. These measurements reveal strong Er wells at the HFS and the LFS midplane in both regimes and clear pedestals in Tz, which are of similar shape and height for the HFS and LFS. While the H-mode(More)
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