Development of a three-wave far-infrared laser interferometry and polarimetry diagnostic system for the C-2W field-reversed configuration plasmas

Deng, B. H.; Rouillard, M.; Feng, P.; Beall, M.; Armstrong, Seiji; Castellanos, Jorge; Kinley, John; Leinweber, H. K.; Ottaviano, Angelica; Settles, Greg; Snitchler, G.; Wells, J. S.; Ziaei, S.; Thompson, Matthew; Team, Tae

doi:10.1063/1.5036977

Cited by 13 publications

(6 citation statements)

References 9 publications

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“…The existence of this electrical field is observed in Q2D modelling [16]. The resultant E θ × B z force will lead to redistribution of radial equilibrium profiles, an effect that has been observed in density profile measurements [17].…”

Section: About the Dynamics Of Micro-burstsmentioning

confidence: 68%

First experimental measurements of a new fast ion driven micro-burst instability in a field-reversed configuration plasma

et al. 2018

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In modern field-reversed configuration (FRC) experiments (Binderbauer et al 2015 Phys. Plasmas 22 056110) at TAE Technologies, classical FRC instabilities are suppressed by advanced neutral beam injection and edge biasing methods, leading to high plasma confinement and fast ion pressure built-up which is comparable to the bulk plasma pressure. In some of these high performance FRC plasmas, a new macroscopically non-destructive fast ion driven micro-burst instability is observed as periodic small amplitude bursts with frequency down chirping in the diamagnetic drift frequency range, repeating about every 0.1 to 0.5 ms. The occurrence of these micro-bursts and burst-free operation can be controlled by changing the injected neutral beam energy. Major observed characteristics of this new instability are presented. Possible explanation of the phenomenon is suggested.

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Section: About the Dynamics Of Micro-burstsmentioning

confidence: 68%

First experimental measurements of a new fast ion driven micro-burst instability in a field-reversed configuration plasma

et al. 2018

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“…Under the C-2U-like machine configuration using only outer-divertor edge biasing/control, FRC plasma has successfully lived up to 8+ ms which is long enough to move on to the next operating phase (meaning that OP1.1 to OP1.2: edge biasing/control primarily from inner divertors with magnetic field flaring). In those long-lived FRC plasma discharges, a micro-burst type of weak/benign instability induced by injected fast ions has been observed [30], as previously seen in C-2U [46]. We have recently begun a new operating mode in OP1.2, in which extensive optimization processes have been executed both manually and with Google's optimization tool/algorithm [40] on many C-2W subsystems such as pulsed powers, magnets including fast-switching coils and formation DC coils, edge biasing/control systems and wall conditioning, which resulted in relatively good initial FRC plasma states with higher electron temperature as seen in figure 10 (shot #107322).…”

Section: Key Initial Results Of Collided/merged Frc Plasmas (In Opera...mentioning

confidence: 99%

“…Consequently, broad operating range and functionality for each diagnostic system is essential on C-2W. As shown in figure 3, plasma performance and parameters at different zones/areas are investigated and provided by a comprehensive suite of diagnostics that includes magnetic sensors [28], Langmuir probes [29], far-infrared interferometry/polarimetry [30], Thomson scattering [31], VUV/visible/IR spectroscopy, bolometry, reflectometry [32], energy analyzers [33], neutral particle analyzers, fusion product detectors, secondary electron emission detectors [34], and multiple fast imaging cameras [35]. In addition, extensive ongoing work focuses on advanced methods of measuring separatrix shape and plasma current profile that will facilitate equilibrium reconstruction and active control of FRCs [36].…”

Section: Plasma Diagnostic Suitementioning

confidence: 99%

Formation of hot, stable, long-lived field-reversed configuration plasmas on the C-2W device

Gota¹,

Binderbauer²,

Tajima³

et al. 2019

Nucl. Fusion

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TAE Technologies' research is devoted to producing high temperature, stable, long-lived field-reversed configuration (FRC) plasmas by neutral-beam injection (NBI) and edge biasing/control. The newly constructed C-2W experimental device (also called "Norman") is the world's largest compact-toroid (CT) device, which has several key upgrades from the preceding C-2U device such as higher input power and longer pulse duration of the NBI system as well as installation of inner divertors with upgraded electrode biasing systems. Initial C-2W experiments have successfully demonstrated a robust FRC formation as well as its translation into the confinement vessel through the newly installed inner divertor with adequate guide magnetic field. They also produced dramatically improved initial FRC parameters with higher plasma temperatures (Te up to 300 eV; total electron and ion temperature >1.5 keV) and more trapped flux (up to ~15 mWb, based on rigid-rotor model) inside the FRC immediately after the merger of collided two CTs in the confinement section. As for effective edge biasing/control on FRC stabilization, a number of edge biasing schemes have been tried via open-fieldlines, in which concentric electrodes located in both inner and outer divertors as well as end-on plasma guns are electrically biased independently. As a result of effective outer-divertor electrode biasing alone, FRC plasma diamagnetism duration has reached up to ~9 ms which is equivalent to C-2U plasma duration. Magnetic field flaring/expansion in both inner and outer divertors plays an important role in creating a thermal insulation on open-field-lines to reduce a loss rate of electrons, which leads to improvement of the edge as well as core FRC confinement properties.

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“…The diagnostics deployed on C-2W are required to provide data for a very wide range of plasma parameters to follow the discharge evolution from a seed FRC to a much hotter and higher energy state. Plasma performance and various other parameters are discerned using this comprehensive suite of diagnostics that includes: a variety of magnetic probes [29]; several iterations of bolometers; multiple interferometers including a far-infrared (FIR) interferometer/polarimeter [30], millimeter-wave interferometer [31], dispersion interferometer [32], and micrometer-wave interferometer [33]; core and jet region Thomson scattering systems [34,35]; spectroscopy of many varieties including impurity-and main-ion chargeexchange recombination spectroscopy (ChERS) [36,37], a combination doppler backscattering/cross-polarization scattering reflectometer [38], fast-ion D α spectrometer [39],…”

Section: Plasma Diagnostic Suitementioning

confidence: 99%

Overview of C-2W: high temperature, steady-state beam-driven field-reversed configuration plasmas

Gota¹,

Binderbauer²,

Tajima³

et al. 2021

Nucl. Fusion

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TAE Technologies, Inc. (TAE) is pursuing an alternative approach to magnetically confined fusion, which relies on field-reversed configuration (FRC) plasmas composed of mostly energetic and well-confined particles by means of a state-of-the-art tunable energy neutral-beam (NB) injector system. TAE’s current experimental device, C-2W (also called ‘Norman’), is the world’s largest compact-toroid device and has made significant progress in FRC performance, producing record breaking, high temperature (electron temperature, T e > 500 eV; total electron and ion temperature, T tot > 3 keV) advanced beam-driven FRC plasmas, dominated by injected fast particles and sustained in steady-state for up to 30 ms, which is limited by NB pulse duration. C-2W produces significantly better FRC performance than the preceding C-2U experiment, in part due to Google’s machine-learning framework for experimental optimization, which has contributed to the discovery of a new operational regime where novel settings for the formation section and the confinement region yield consistently reproducible, hot, and stable plasmas. An active plasma control system has been developed and utilized in C-2W to produce consistent FRC performance as well as for reliable machine operations using magnets, electrodes, gas injection, and tunable NBs. The active control system has demonstrated stabilization of FRC axial instability. Overall FRC performance is well correlated with NBs and edge-biasing system, where higher total plasma energy is obtained by increasing both NB injection power and applied-voltage on biasing electrodes. C-2W divertors have demonstrated a good electron heat confinement on open-field-lines using strong magnetic mirror fields as well as expanding the magnetic field in the divertors (expansion ratio > 30); the energy lost per electron ion pair, η e ∼ 6–8, is achieved, which is close to the ideal theoretical minimum.

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Development of a three-wave far-infrared laser interferometry and polarimetry diagnostic system for the C-2W field-reversed configuration plasmas

Cited by 13 publications

References 9 publications

First experimental measurements of a new fast ion driven micro-burst instability in a field-reversed configuration plasma

First experimental measurements of a new fast ion driven micro-burst instability in a field-reversed configuration plasma

Formation of hot, stable, long-lived field-reversed configuration plasmas on the C-2W device

Overview of C-2W: high temperature, steady-state beam-driven field-reversed configuration plasmas

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