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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Nonlinear control of the minimum safety factor in tokamaks by optimal allocation of spatially moving electron cyclotron current drive

The minimum value of the safety factor profile is related to the magnetohydrodynamic (MHD) stability of the plasma confined in a tokamak. Therefore, active control of the minimum safety factor may mitigate MHD instabilities that can degrade or even terminate plasma confinement. Typically, in most tokamak scenarios, the minimum safety factor evolves spatially with time, i.e., the location at which the safety factor achieves the minimum value changes with time. In addition to the inherent nonlinearities in the minimum safety factor evolution, its spatial variation makes the control design challenging. In particular, complexity in control design may arise from the need for time-dependent nonlinear models that account for spatial variation of the minimum safety factor. Furthermore, the minimum safety factor may drift to locations where the actuator authority is low. The problem of minimum safety factor control with target location tracking and moving electron cyclotron current drive (ECCD) is addressed in this work. A nonlinear time-dependent model that incorporates the spatial variation of the minimum safety factor is presented. A nonlinear controller based on optimal feedback linearization is developed to track a target minimum safety factor. The proposed controller treats the ECCD position as a controllable variable. In other words, the controller prescribes the ECCD position (in addition to the non-inductive powers) in real time based on an optimal criterion that is defined a priori. This work also presents the steps necessary to integrate the minimum safety factor controller with a total energy controller to achieve multiple control objectives simultaneously. In conclusion, the proposed integrated control algorithm is tested using nonlinear simulations in the Control Oriented Transport SIMulator (COTSIM) for a DIII-D tokamak scenario.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Simulating the effects of warm O + ions on the growth of electromagnetic ion cyclotron (EMIC) waves

Electromagnetic ion cyclotron (EMIC) waves are believed to play a crucial role in the dynamics of the Earth’s magnetosphere. It has been widely accepted that plasma compositions can influence the growth rate of EMIC waves in the inner magnetosphere, but how warm O + ions change the wave growth rate is not well known. In this study, we investigate the impact of ring current O + concentration on the EMIC growth rate during a specific storm when the O + ion flux significantly increases. We calculate the growth rate of EMIC waves by using physics-based ion distributions output from the Ring current–Atmosphere interactions Model with Self-Consistent magnetic (B) and Electric (E) fields (RAM-SCBE) model. The percentage of warm O + is parametrically varied to examine how the maximum EMIC growth rate changes over time and how the global distribution of the maximum EMIC growth rate is affected. We found that the maximum growth rate of H-band appears in the dusk-to-midnight sector near the plasmapause, while O-band is excited at a slightly outer region. The maximum growth rate of He-band is closely related to the cold plasma density. With the increase of warm O + density, the maximum growth rate of H-band and He-band EMIC wave is reduced, while that of O-band EMIC wave is increased, and the region with this wave excitation is widened. Furthermore, such variation in the maximum EMIC growth rate implies a potential impact on the associated wave–particle interactions and change of the decay rate in the ring current.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Modelling of the electron cyclotron emission burst from a laboratory tokamak plasma with loss-cone maser instability

The maser instability associated with the loss-cone distribution has been widely invoked to explain the radio bursts observed in the astrophysical plasma environment, such as aurora and corona. In the laboratory plasma of a tokamak, events reminiscent of these radio bursts have also been frequently observed as an electron cyclotron emission (ECE) burst in the microwave range (~2f ce near the last closed flux surface) during transient magnetohydrodynamic events. These bursts have a short duration of ~10 μs and display a radiation spectrum corresponding to a radiation temperature T e,rad of over 30 keV while the edge thermal electron temperature T e is only in the range of 1 keV. Suprathermal electrons can be generated through magnetic reconnection, and a loss-cone distribution can be generated through open stochastic field lines in the magnetic mirror of the near-edge region of a tokamak plasma. Radiation modelling shows that a sharp distribution gradient ∂f/∂v ⊥ > 0 at the loss-cone boundary can cause a negative absorption of ECE radiation through the maser instability. The negative absorption then amplifies the radiation so that the microwave intensity is significantly stronger than the thermal value. The significant T e,rad from the simulations suggests the potential role of the loss-cone maser instability in generating the ECE burst in a tokamak.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Drift-cyclotron loss-cone instability in 3-D simulations of a sloshing-ion simple mirror

The kinetic stability of collisionless, sloshing beam-ion (45° pitch angle) plasma is studied in a three-dimensional (3-D) simple magnetic mirror, mimicking the Wisconsin high-temperature superconductor axisymmetric mirror experiment. The collisional Fokker–Planck code CQL3D-m provides a slowing-down beam-ion distribution to initialize the kinetic-ion/fluid-electron code Hybrid-VPIC, which then simulates free plasma decay without external heating or fuelling. Over 1 – 10 μs, drift-cyclotron loss-cone (DCLC) modes grow and saturate in amplitude. The DCLC scatters ions to a marginally stable distribution with gas-dynamic rather than classical-mirror confinement. Sloshing ions can trap cool (low-energy) ions in an electrostatic potential well to stabilize DCLC, but DCLC itself does not scatter sloshing beam-ions into the said well. Instead, cool ions must come from external sources such as charge-exchange collisions with a low-density neutral population. Manually adding cool ∼1keV ions improves beam-ion confinement several-fold in Hybrid-VPIC simulations, which qualitatively corroborates prior measurements from real mirror devices with sloshing ions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Molecular Characterization of Organophosphorus Compounds in Wildfire Smoke Using 21-T Fourier Transform-Ion Cyclotron Resonance Mass Spectrometry

Here, we present a detailed molecular characterization of organophosphorus compounds in ambient organic aerosol influenced by wildfire smoke. Biomass burning organic aerosol (BBOA) is an important source of phosphorus (P) to surface waters, where even a small imbalance in the P flux can lead to substantial effects on water quality, such as eutrophication, algal blooms, and oxygen depletion. We aimed to exploit the ultrahigh resolving power, mass accuracy, and sensitivity of Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) to explore the molecular composition of an ambient BBOA sample collected downwind of Pacific Northwest wildfires. The 21-T FT-ICR MS yielded 10533 distinct formulae, which included molecular species comprising C, H, O, and P with or without N, i.e., organophosphorus compounds that have long been quantified in wildfire smoke but have not yet been characterized at the molecular level. The lack of detailed molecular characterization of organophosphorus compounds in BBOA is primarily due to their inherently low concentrations in aerosols and poor ionization efficiency in complex mixtures. We demonstrate that the exceptional sensitivity of the 21-T FT-ICR MS allows qualitative analysis of a previously uncharacterized fraction of BBOA without its selective concentration from the organic matrix, exemplifying the need for ultrahigh-resolution tools for a more detailed and accurate molecular depiction of such complex mixtures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Global Simulation of Electron Cyclotron Harmonic Wave Instability in a Storm-Time Magnetosphere

Electron cyclotron harmonic (ECH) waves are electrostatic emissions between the ECHs and play a dominant role for precipitating energetic electrons in the magnetotail. Statistically, the ECH wave intensity is stronger at nightside and dawnside than at dayside and duskside. In this study, we, for the first time, simulate the global ECH wave evolution during a geomagnetic storm event using Ring current Atmosphere interactions Model with Self-Consistent Magnetic field (RAM-SCB) combined with a linear growth rate solver.We find that the simulation results are generally consistent with the statistical and real-time observations. The ECH wave instability is much stronger at nightside and dawnside, compared to the instability at dayside and duskside. Before a geomagnetic storm (quiet time), the unstable regions of the ECH waves lie beyond $5R_E$ with a weak instability level. During the main phase of a geomagnetic storm, the unstable regions can extend to a lower altitude $(3R_E)$ with a strong instability level. Finally, during the recovery phase, the unstable regions return to $5$ ~ $6R_E$. We also find that the inner boundary of unstable ECH wave regions is coincident with the plasmapause location during the whole geomagnetic storm event.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Simultaneous Observations of Electromagnetic Ion Cyclotron (EMIC) Waves and Pitch Angle Scattering During a Van Allen Probes Conjunction

On 22 December 2015, the two Van Allen Probes observed two sets of electromagnetic ion cyclotron (EMIC) wave bursts during a close conjunction when both Probe A and Probe B were separated by 0.57 to 0.68 R E . Here, the EMIC waves occurred during an active period in the recovery phase of a coronal mass ejection-driven geomagnetic storm. Both spacecraft observed EMIC wave bursts that had similar spatial structure within a 1–2 min time delay. The EMIC waves occurred outside the plasmasphere, within ΔL ≈ 1–2 of the plasmapause and within a few degrees in magnetic latitude of the equatorial plane. The spatial structure of the EMIC wave bursts may have been related to the proton drift paths outside the plasmasphere and influenced by total magnetic field strength variations associated with solar wind pressure enhancements. The EMIC waves were observed in a narrow L shell region from L ≈ 4.55–5.32 between 10 and 11 magnetic local time (MLT) on the outbound halves of the spacecraft orbits and from L ≈ 4.82–5.51 between 13 and 14 MLT on the inbound halves of the spacecraft orbits. However, Pc1 pulsations were observed on the ground over a broad range of local times. The anisotropy of the proton pitch angle distributions was enhanced when the EMIC waves were observed. Although the overall radiation belt response during this storm was dominated by acceleration and transport processes, the EMIC waves produced local pitch angle scattering of 13–15 keV protons and 2.1–2.6 MeV electrons, consistent with calculations of the expected resonant energies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Magnetic Tilt Effect on Externally Driven Electromagnetic Ion Cyclotron (EMIC) Waves

Abstract We examine coupling of fluctuations in the solar wind with electromagnetic ion cyclotron (EMIC) waves in the magnetosphere using an advanced full‐wave simulation code, Petra‐M. Dipole tilt dramatically affects the coupling process. While very little wave power can reach the inner magnetosphere without tilt effects, a tilted dipole field dramatically increases the efficiency of the coupling process. Solar wind fluctuations incident at high magnetic latitude effectively reaches the ground along the field line and mode‐convert to linearly polarized field‐aligned propagating waves at the Alfvén and IIH resonances. Therefore, solar wind compressions efficiently drive linearly polarized EMIC waves when the dipole angle is tilted toward or away from the Sun‐Earth direction.

58 GEOSCIENCES↗
DOE OSTI2023

Hybrid Simulation of Proton Cyclotron Waves Upstream of Mars Generated by Pickup Ion Beam Distribution

Linear instability analysis as well as a corresponding two‐dimensional hybrid simulation are performed to examine the excitation of the proton cyclotron waves observed upstream of Mars. The waves are believed to be excited by the pickup ions produced from the ionization of the Martian hydrogen exosphere. And previous statistical analysis of wave observations suggested that the waves are mostly related to pickup ion beam velocity distributions. While earlier linear instability analysis of pickup ion beam distributions has mainly been focused on the parallel unstable modes, our analysis reveals that the maximum growth rate occurs at very oblique propagation. The corresponding hybrid simulation confirms the linear analysis results and further demonstrates that the pickup ions are scattered toward an isotropic shell velocity distribution by the waves excited. Interestingly, the waves at oblique propagation gradually damp out and the system is eventually dominated by waves of quasi‐parallel propagation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Analysis of neoclassical tearing mode stabilization experiment by electron cyclotron injection in KSTAR

We report the neoclassical tearing mode (NTM) stabilization experimental results by injection of the electron cyclotron (EC) beam in KSTAR, and its analysis with integrated modelling. In the KSTAR experiment, NTM was intentionally induced and the EC beam was injected by the plasma control system (PCS) to stabilize it. Here, the EC angle was controlled based on the minimum seeking algorithm for the island growth rate. Although the EC angle was not changed significantly, the island width significantly decreased towards the end of the experiment followed by the recovery of plasma performance. To assess the NTM stabilization experiment from a stability perspective, we performed integrated modelling with TRIASSIC utilizing the reconstructed equilibrium with magnetic diagnostics and motional stark effect diagnostics. As a result, we observed that the NTM is stabilized by EC.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Overview of recent turbulence studies across multiple confinement modes at the ASDEX Upgrade tokamak using the Correlation Electron Cyclotron Emission diagnostic

This work presents an overview of recent and ongoing experimental measurements of core and edge turbulence across multiple confinement regimes using the Correlation Electron Cyclotron Emission (CECE) diagnostic at the ASDEX Upgrade (AUG) tokamak. A common goal among these investigations is to identify how the properties of the turbulent electron temperature fluctuations measured by CECE influence and regulate the unique transport characteristics of each confinement regime, including L-mode, I-mode, ELMy H-mode, and ELM-free H-mode. Optics and signal processing methods to aid in the analysis and interpretation of experimental turbulence results are also presented. These methods, and particularly the down-sampling and ensemble averaging method, are relevant to a wide variety of fusion and non-fusion applications.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2026

Initial electron cyclotron heating/current drive scoping study for the SMall Aspect Ratio Tokamak (SMART)

In this work an initial electron cyclotron heating/current drive (EC H&CD) scoping study is presented for the SMall Aspect Ratio Tokamak (SMART), constructed and operated by the Plasma Science and Fusion Technology (PSFT) Laboratory of the University of Seville. We consider two planned phases of operation with different magnitude of magnetic field (B 0.4, and 1 T). This EC H&CD scoping study is carried out by using the ray tracing code TRAVIS, which allows to quickly perform a series of scans on the main SMART plasma scenarios. A scan in the poloidal and toroidal launching angles is performed for the B 0.4 T plasma scenario assuming three launching locations (mid-plane, off-mid-plane, and top-launcher) and the extraordinary (X-) mode polarization. The absorption occurs at the second harmonic and, overall, the highest power absorption is obtained launching the EC beam from the top of the machine. A numerical analysis of the fundamental X-mode EC H&CD start-up regime for the B 1.0 T plasma scenario with two different wave frequencies (28 and 35 GHz) is presented showing a very high current drive efficiency.

Bertelli, Nicola [Princeton Plasma Physics Laborat↗
DOE OSTI2020

Electron cyclotron resonance (ECR) magnetometry with a plasma reservoir

The local magnetic field in a Penning–Malmberg trap is found by measuring the temperatures that result when electron plasmas are illuminated by microwave pulses. Multiple heating resonances are observed as the pulse frequencies are swept. The many resonances are due to electron bounce and plasma rotation sidebands. The heating peak corresponding to the cyclotron frequency resonance is identified to determine the magnetic field. A new method for quickly preparing low density electron plasmas for destructive temperature measurements enables a rapid and automated scan of microwave frequencies. This technique can determine the magnetic field to high precision, obtaining an absolute accuracy better than 1 ppm and a relative precision of 26 ppb. One important application is in situ magnetometry for antihydrogen-based tests of charge-parity-time symmetry and of the weak equivalence principle.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

W-band system-on-chip electron cyclotron emission imaging system on DIII-D

Monolithic, millimeter wave “system-on-chip” (SoC) technology has been employed in heterodyne receiver integrated circuit radiometers in a newly developed Electron Cyclotron Emission Imaging (ECEI) system on the DIII-D tokamak for 2D electron temperature profile and fluctuation evolution diagnostics. Here, a prototype module operating in E-band (72-80 GHz) was first employed in a 2 x 10 element array that demonstrated significant improvements over the previous quasi-optical Schottky diode mixer arrays during the 2018 operational campaign of the DIII-D tokamak. For compatibility with International Thermonuclear Experimental Reactor (ITER) relevant scenarios on DIII-D, the SoC ECEI system was upgraded with 20 horn-waveguide receiver modules. Each individual module contains a University of California at Davis designed W-band (75 -110 GHz) receiver die that integrates a broadband low noise amplifier (LNA), a double balanced down-converting mixer, and a x4 multiplier on the local oscillator (LO) chain. A x2 multiplier and two IF amplifiers are packaged and selected to further boost the signal strength as well as downconvert the signal frequency. The upgraded W-band array exhibits > 30 dB additional gain and 20x improvement in noise temperature comparing with the previous Schottky diode radio frequency (RF) mixer input systems; an internal 8 times multiplier chain is used to bring down the LO frequency below 12 GHz, thereby obviating the need for a large aperture for quasi-optical LO coupling and replacing it with coaxial connectors. The horn-waveguide shielding housing avoids out-of-band noise interference on each individual module. The upgraded ECEI system plays an important role for absolute electron temperature evolution and fluctuation measurements for edge and core region transport physics studies.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Upgrades to the ion cyclotron emission diagnostic on the DIII-D tokamak

The ion cyclotron emission diagnostic on the DIII-D tokamak comprises seven single-turn loops that measure high-frequency (1–100 MHz) magnetic field fluctuations that are often excited by energetic particles in the plasma. The raw voltage signals induced in the loops in response to these fluctuations travel through a series of cables, isolation transformer DC blocks, low-pass filters, and finally a digitizer before being analyzed in frequency space. The diagnostic has been recently upgraded, most notably to include four additional graphite tile loops and a new eight-channel digitizer. The previous three loops are all on the low-field side of the tokamak. The measurement capabilities of the system have been expanded by the addition of a new horizontally oriented loop on the low-field side, an additional toroidal loop on the low-field side, and two toroidal loops on the high-field side. These loops will be used to provide approximate mode polarization, improved toroidal mode number calculations, and information on modes in inward-shifted plasmas, respectively.

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

Diagnosing the pedestal magnetic field and magnetohydrodynamics radial structure with pedestal–scrape of layer electron cyclotron emission radiation inversion in H-mode plasma (invited)

Forward modeling is used to interpret inversion patterns of the pedestal–Scrape of Layer (SOL) Electron Cyclotron Emission (ECE) in DIII-D H-mode experiments. The modeling not only significantly improves the ECE data interpretation quality but also leads to the potential measurements of (1) the magnetic field strength |B| at the separatrix, (2) the pedestal |B| evolution during an inter-Edge Localized Mode (ELM) period, and (3) the pedestal Magnetohydrodynamics (MHD) radial structure. The ECE shine-through effect leads to three types of pedestal–SOL radiation inversions that are discussed in this paper. The first type of inversion is the non-monotonic T e,rad profile with respect to the major radius. Using the ECE frequency at the minimum T e,rad , the inversion can be applied to measure the magnetic field |B| at the separatrix and calibrate the mapping of the ECE channels with respect to the separatrix. The second type of inversion refers to the opposite phase between the radiation fluctuations δT e,rad at the pedestal and SOL. This δT e,rad phase inversion is sensitive to density and temperature fluctuations at the pedestal foot and, thus, can be used to qualitatively measure the MHD radial structure. The third type of inversion appears when the pedestal and SOL T e,rad evolve in an opposite trend, which can be used to infer the pedestal |B| field change during an inter-ELM period. Finally, the bandwidth effect on measuring δT e,rad due to pedestal MHD is also investigated in the radiation modeling.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

A Pockels cell enabled heterodyne phase contrast imaging diagnostic for detection of ion cyclotron emission

This work describes a novel optical heterodyne detection scheme that significantly extends the frequency response of the phase contrast imaging method to detect electron density fluctuations in tens of megahertz frequency range. The system employs a variable frequency electro-optic modulator to allow operation at any frequency in the range 10–40 MHz without the need to realign the system. The frequency coverage of the system makes it suitable to measure the radial structure of the electron density component of ion cyclotron emission on devices having confining magnetic field of a few tesla, thus extending the purely temporal measurements provided so far by magnetic probes.

47 OTHER INSTRUMENTATION↗