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Start Over Community Princeton Plasma Physics Laboratory

1. Exploration of the parameter space of quasisymmetric stellarator vacuum fields through adjoint optimisation

Author(s):
Nies, Richard; Paul, Elizabeth J.; Panici, Dario; Hudson, Stuart R.; Bhattacharjee, Amitava
Abstract:
Optimising stellarators for quasisymmetry leads to strongly reduced collisional transport and energetic particle losses compared to unoptimised configurations. Though stellarators with precise quasisymmetry have been obtained in the past, it remains unclear how broad the parameter space is where good quasisymmetry may be achieved. We here study the range of aspect ratio and rotational transform values for which stellarators with excellent quasisymmetry on the boundary can be obtained. A large number of Fourier harmonics is included in the boundary representation, which is made computationally tractable by the use of adjoint methods to enable fast gradient-based optimisation, and by the direct optimisation of vacuum magnetic fields, which converge more robustly compared to solutions from magnetohydrostatics. Several novel configurations are presented, including stellarators with record levels of quasisymmetry on a surface, three field period quasi- axisymmetric stellarators with substantial magnetic shear, and compact quasisymmetric stellarators at low aspect ratios similar to tokamaks.
Type:
Dataset
Issue Date:
2024

2. Sam Cohen's ginormous data

Author(s):
Cohen, Samuel A.; Swanson, Charles; Jandovitz, Peter; Vinoth, Sangeeta; David, Liam; Berlinger, Bruce
Type:
Dataset
Issue Date:
2023

3. 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

4. Test NSTX-U

Author(s):
Cole, Carolyn
Type:
Dataset
Issue Date:
2023

5. Test v0.79.0

Author(s):
Cole, Carolyn
Type:
Dataset
Issue Date:
2023

7. 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

8. A reduced-turbulence regime in the Large Helical Device upon injection of low-Z materials powders

Author(s):
Nespoli, Federico; Tanaka, Kenji; Masuzaki, Suguru; Ashikawa, Naoko; Shoji, Mamoru; Gilson, Erik; Lunsford, Robert; Oishi, Tetsutarou; Ida, Katsumi; Yoshinuma, Mikirou; Takemura, Yuki; Kinoshita, Toshiki; Motojima, Gen; Osakabe, Masaki; Kenmochi, Naoki; Kawamura, Gakushi; Suzuki, Chihiro; Nagy, Alex; Bortolon, Alessandro; Pablant, Novimir; Mollen, Albert; Tamura, Naoki; Gates, David; Morisaki, Tomohiro
Abstract:
Recently an improved confinement regime, characterized by reduced turbulent fluctuations has been observed in the Large Helical Device upon the injection of boron powder into the plasma (Nespoli et al 2022 Nat. Phys.18 350–56). In this article, we report in more detail the experimental observations of increased plasma temperature and the decrease of turbulent fluctuations across the plasma cross section, on an extended database. In particular, we compare powders of different materials (B, C, BN), finding similar temperature improvement and turbulence response for the three cases. Modeling of the powder penetration into the plasma and of neoclassical electric field and fluxes support the interpretation of the experimental results. Additionally, we report evidence of the temperature improvement increasing with powder injection rates and decreasing for both increasing density and heating power. Though, plasma turbulence response varies depending on the initial conditions of the plasma, making it difficult to draw an inclusive description of the phenomenon.
Type:
Dataset
Issue Date:
19 May 2023

9. 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

10. Alfvén waves at the interface of solar wind and magnetosphere

Author(s):
Kim, Eun-Hwa; Johnson, Jay R.; Damiano, Peter A.
Abstract:
This includes data for Chapter 11 Alfvén waves at the interface of solar wind and magnetosphere in Book "AGU Monograph. Alfvén Waves across Heliophysics: Progress, Challenges, and Opportunities." It includes Matlab data and files for figures 2, 3, 4, 6, 7, 11 and 12 shown in the forthcoming book chapter.
Type:
Dataset
Issue Date:
2023

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