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1. Absolute electron density fluctuation reconstruction for two-dimensional Hydrogen beam emission spectroscopy

Author(s):
Lampert, Mate
Abstract:
Scrape-off layer (SOL) and edge plasma turbulence contribute significantly to the radial particle and heat transport lowering plasma confinement and increasing heat load on the plasma facing components. SOL turbulence is predominantly intermittent which manifest in the occurrence of isolated density filaments or blobs. Filaments propagate radially outwards towards plasma facing components limiting their lifetime by erosion and sputtering. To characterize this phenomenon in detail few diagnostic techniques are available. Beam emission spectroscopy is a diagnostic capable of measuring plasma turbulence in both SOL and edge plasmas. Due to the finite lifetime of the excitation states during the beam - plasma interaction, and the misalignment between the optics and the magnetic field, spatial smearing is introduced in the measurement. In this paper a novel method is introduced to overcome this hindering effect by inverting the fluctuation response matrix on an optimally smoothed signal. We show that this method is fast and provides significantly more accurate absolute density fluctuation reconstruction than the direct inversion technique. The presented method is usable for all types of beam emission diagnostics where the spatial resolution is higher than the combined smearing of the atomic physics and the observation.
Type:
Dataset
Issue Date:
November 2023

2. Density Limits as Disruption Forecasters for Spherical Tokamaks

Author(s):
Berkery, John
Abstract:
Fusion power output from spherical tokamaks would benefit from increased confined plasma density, but there exists a limit on the density before confinement is lost and the plasma current is disrupted. This density limit has long been characterized by a simple, global Greenwald limit proportional to the plasma current and inversely proportional to the cross sectional area of the plasma. It is shown that in the database of discharges from the NSTX and MAST spherical tokamaks, the likelihood of disruption does increase above the Greenwald limit, and especially in the plasma current rampdown phase. The physics of the density limit has been recently theoretically explored through local criteria. Several of these are tested using the disruption event characterization and forecasting (DECAFTM) code for their potential effectiveness as disruption warning signals. For a limited set of NSTX discharges, a local island power balance criteria was found to be less reliable, presently, than the Greenwald limit. An empirical critical edge line density and a boundary turbulent transport limit were both tested for MAST-U, which has an electron density profile measurement with high spatial resolution in the outer part of the plasma. Both were found to have similar dependencies on key plasma parameters. In a limited set of MAST-U discharges that appear to disrupt due to rising density at values under the Greenwald limit, crossing of the boundary turbulent transport limit occurred close to the time of disruption. Finally, these limits were evaluated for their potential use in real-time, and it was found that with the necessary real-time inputs and with refinement through further testing, these limits could be implemented in a real-time disruption forecasting system.
Type:
Dataset
Issue Date:
30 June 2023

3. Operational Space and Performance Limiting Events in the First Physics Campaign of MAST-U

Author(s):
Berkery, John
Abstract:
The MAST-U fusion plasma research device, the upgrade to the Mega Amp Spherical Tokamak, has recently completed its first campaign of physics operation. MAST-U operated with Ohmic, or one or two neutral beams for heating, at 400-800 kA plasma current, in conventional or “SuperX” divertor configurations. Equilibrium reconstructions provide key plasma physics parameters vs. time for each discharge, and diagrams are produced which show where the prevalence of operation occurred as well as the limits in various operational spaces. When compared to stability limits, the operation of MAST-U so far has generally stayed out of the low q, low density instability region, and below the high density Greenwald limit, high beta global stability limits, and high elongation vertical stability limit. MAST-U still has the potential to reach higher elongation, which could benefit the plasma performance. Despite the majority of operation happening below established stability limits, disruptions did occur in the flat-top phase of MAST-U plasmas. The reasons for these disruptions are highlighted, and possible strategies to avoid them and to extend the operational space of MAST-U in future campaigns are discussed.
Type:
Dataset
Issue Date:
18 January 2023

5. Reduced Physics Model of the Tokamak Scrape-off-Layer for Pulse Design

Author(s):
Zhang, Xin
Abstract:
The dynamic interplay between the core and the edge plasma has important consequences in the confinement and heating of fusion plasma. The transport of the Scrape-Off-Layer (SOL) plasma imposes boundary conditions on the core plasma, and neutral transport through the SOL influences the core plasma sourcing. In order to better study these effects in a self-consistent, time-dependent fashion with reasonable turn-around time, a reduced model is needed. In this paper we introduce the SOL Box Model, a reduced SOL model that calculates the plasma temperature and density in the SOL given the core-to-edge particle and power fluxes and recycling coefficients. The analytic nature of the Box Model allows one to readily incorporate SOL physics in time-dependent transport solvers for pulse design applications in the control room. Here we demonstrate such a coupling with the core transport solver TRANSP and compare the results with density and temperature measurements, obtained through Thomson scattering and Langmuir probes, of an NSTX discharge. Implications for future interpretive and predictive simulations are discussed.
Type:
Dataset
Issue Date:
January 2023

8. Thermal ion kinetic effects and Landau damping in fishbone modes

Author(s):
Liu, Chang; Jardin, Stephen; Bao, Jian; Gorelenkov, Nikolai; Brennan, Dylan; Yang, James
Abstract:
The data set consists of the figures in a manuscript titled Thermal ion kinetic effects and Landau damping in fishbone modes, and plotting script used for figure generation. There are 16 figures with captions.
Type:
Dataset
Issue Date:
22 November 2022

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