The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform
Osamu Mitarai - One of the best experts on this subject based on the ideXlab platform.
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Plasma Current Start-up in a Spherical Tokamak
Ieej Transactions on Fundamentals and Materials, 2020Co-Authors: Osamu Mitarai, Charles Kessel, Akira HiroseAbstract:The various Plasma Current start-up techniques and related topics in a spherical tokamak (ST) device are described. The Ohmic heating coil Current clamp experiments in NSTX are described and discussed, and the Plasma Current start-up experiments in the STOR-M tokamak with iron core and the outer vertical field coil is presented as one of technique for a Plasma Current start-up in a ST.
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Plasma Current Rampup by the Outer Vertical Field Coils in a Spherical Tokamak Reactor
Fusion Science and Technology, 2017Co-Authors: Osamu Mitarai, Yuichi TakaseAbstract:To find a solution of the Plasma Current rampup problem in a low aspect ratio spherical tokamak (ST) reactor, the effect of the outer vertical field coils on Plasma Current rampup is studied with n...
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Plasma Current start-up experiments without a central solenoid in the iron core STOR-M tokamak
Nuclear Fusion, 2015Co-Authors: Osamu Mitarai, David Mccoll, C Xiao, G. Tomney, A. Rohollohi, E. Lewis, Akira HiroseAbstract:Reproducible Plasma Current start-up without a central solenoid (CS) has been demonstrated using the outer ohmic heating (OH) coils in the iron core STOR-M tokamak (Mitarai et al 2014 Fusion Eng. Des. 89 2467–71). Although the outer OH coil Current saturates the iron core eventually, it has been demonstrated that the Plasma Current can be maintained during the iron core saturation phase. In this work, further studies have been conducted to investigate the effects of the turn number of the outer OH coils (N = 4 or N = 6) in the CS-less discharges and to evaluate the Plasma stability with respect to the n-decay index of the vertical magnetic field. For the loose coupling of the iron core with N = 4 turns, the Plasma Current can be sustained after the additional third capacitor bank is applied near the iron core saturation phase, showing the slow transition from the unsaturated to the partially saturated phase. For the case of stronger coupling of N = 6 turns, the Plasma Current is increased at the same fast bank voltage, but the main discharge is shortened from 35 to 20 ms. As the magnetizing Current is smaller due to stronger coupling between the OH coils and the Plasma Current, the transition from the unsaturated to the saturated phase is slightly difficult at present. The present experimental results suggest a feasible operation scenario in a future spherical tokamak (ST) at least using loose iron core coupling for smoother transition from the unsaturated to the saturated iron core phase. Thus, a reliable Plasma Current start-up by the outer OH coils and the Current ramp-up to a steady state by additional heating power and vertical field coils could be considered as an operation scenario for future ST reactors with an iron core transformer.
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Plasma Current sustainment after iron core saturation in the stor m tokamak
Fusion Engineering and Design, 2014Co-Authors: Osamu Mitarai, M Hubeny, Takumi Onchi, David Mccoll, Y. Ding, C Xiao, Y. Lu, Akira HiroseAbstract:Abstract We propose to use of a small iron core transformer to start up the Plasma Current in a spherical tokamak (ST) reactor without central solenoid (CS). Taking advantage of the high aspect ratio of the STOR-M iron core tokamak, we have demonstrated that the Plasma Current up to 10–15 kA can be started up using the outer Ohmic heating (OH) coils without CS, and that the Plasma Current can be maintained further by increasing the outer OH coil Current during iron core saturation phase. When the magnetizing Current reaches 1.2 kA and the iron core becomes saturated, the third capacitor bank connected to the outer OH coils is discharged to maintain the Plasma Current. The Plasma Current is slightly increased and maintained for additional 5 ms as expected from numerical calculations. Core saturation has been clearly observed on the hysteresis curve. This is the first experimental demonstration of the feasibility of slow transition from the iron core to air core transformer phase without CS. The results implies that a Plasma Current can be initiated by a small iron core and could be ramped up by additional heating and vertical field after iron core saturation in future STs without CS.
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Inductive Plasma Current start-up by the outer vertical field coil in a spherical tokamak
Plasma Physics and Controlled Fusion, 1999Co-Authors: Osamu MitaraiAbstract:Plasma Current-start up induced by an outer vertical field coil is studied during the ignition access phase in a spherical tokamak reactor. We have illustrated the concept that the Plasma Current of ~50 MA could be induced by the outer vertical field coil in the proposed spherical tokamak with the help of the small central solenoid flux of ±5 V s and the strong heating power less than 100 MW for the internal inductance of i~0.4-0.8 without the help of bootstrap Current and non-inductive Current drive power. The required condition to achieve this operation scenario is that the flux produced by the equilibrium vertical field is larger than the inductive flux. Current start-up operation is achieved by adding the small ohmic heating solenoid flux for the flux waveform adjustment because the flux from the outer vertical field coil cannot solely induce the desired Plasma Current waveform in the case of the preprogramming of the heating power.
Marc Wuilpart - One of the best experts on this subject based on the ideXlab platform.
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Theoretical Assessment of Plasma Current Measurement in Tokamaks in Relation with the OTDR Detector Noise
2019 PhotonIcs & Electromagnetics Research Symposium - Spring (PIERS-Spring), 2019Co-Authors: Rastislav Motuz, Andrei Gusarov, Willem Leysen, Eva Gescheidtova, P. J. Moreau, Petr Drexler, Marc WuilpartAbstract:In this paper, we present a theoretical analysis of the Plasma Current measurement in tokamak-type fusion reactors using a Polarization Optical Time-Domain Reflectometer (POTDR) setup, where the general case of non-uniform distribution of a magnetic field along the sensing fibre is analyzed. A low birefringent fibre has been considered as the sensing fibre. The numerical simulations were based on the Jones formalism and take into account the OTDR detector noise reflecting the measurement error as a function of the Plasma Current. The measurement performance was evaluated for an ITER (International Thermonuclear Experimental Reactor)-relevant sensor configuration. Based on the simulation results we demonstrate that for Plasma Currents in the range of 0 to 1 MA, the signal-to-noise ratio (SNR) of 6 dB, achievable in modern POTDRs, complies with the ITER requirements. Subsequently, the SNR level of 4 dB satisfies the Plasma Current range of 1 to 20 MA.
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Theoretical assessment of the OTDR detector noise on Plasma Current measurement in tokamaks.
Applied Optics, 2019Co-Authors: Rastislav Motuz, Andrei Gusarov, Philippe Moreau, Willem Leysen, Petr Drexler, Marc WuilpartAbstract:In this paper, we propose a theoretical study dedicated to the assessment of Plasma Current measurement in magnetic confinement fusion reactors using a polarization optical time-domain reflectometer (POTDR) setup with a low-birefringence fiber used as the sensing fiber. We consider the general case of a non-uniform magnetic-field distribution along the sensing fiber. The numerical simulations, based on Jones formalism taking into account the OTDR noise, provide the measurement error as a function of the Plasma Current. The measurement performance is evaluated for an ITER-relevant sensor configuration. We demonstrate that a signal-to-noise ratio of 6 dB, achievable in modern POTDRs, allows us to comply with the ITER requirements for Plasma Currents from 0 to 1 MA, while for the 1 to 20 MA range, the level is relaxed to 4 dB.
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Measurement of Plasma Current in Tokamaks using an optical fibre reflectometry technique
EPJ Web of Conferences, 2018Co-Authors: Marc Wuilpart, Andrei Gusarov, Philippe Moreau, Willem Leysen, Patrice MégretAbstract:An optical time-domain reflectometer sensitive to the polarization of light is proposed for the measurement of Plasma Current in the Tore Supra fusion reactor. The measurement principle relies on the Faraday effect i.e. on the generation of a circular birefringence along an optical fiber subject to an axial magnetic field. The circular birefringence induces a polarization rotation that can be mapped along the fiber thanks to an opticaltime domain reflectometer followed by an linear polarizer. A proper fitting of the measurement trace then allows determining the applied Plasma Current. The sensor has been experimentally validated on the Tore Supra tokamak fusion reactor for a Plasma Current range going from 0.6 to 1.5 MA. A maximum error of 13.50% has been observed for the lowest Current.
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Plasma Current Measurement in Thermonuclear Fusion Reactors Using a Photon-Counting POTDR
IEEE Photonics Technology Letters, 2017Co-Authors: Marc Wuilpart, Andrei Gusarov, Philippe Moreau, Matthieu Aerssens, Patrice MégretAbstract:In this letter, we present a fiber-optic Current sensor for the measurement of Plasma Current in thermonuclear fusion reactors. The sensor includes a low-birefringence optical fiber placed around a section of the vacuum vessel that hosts the fusion reaction. The interrogating unit consists of a polarization-sensitive photon-counting optical time domain reflectometer that enables to determine the light polarization rotation induced by the Plasma Current. The measurement principle is demonstrated by means of the Jones formalism. The sensor has been experimentally validated on the Tore Supra tokamak fusion reactor for a Plasma Current range going from 0.6 to 1.5 MA. A maximum error of 13.50% has been observed for the lowest Current.
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Effect of vibration-induced perturbations in Plasma Current measurement using a fiber optic Current sensor
2014Co-Authors: Frédéric Descamps, Matthieu Aerssens, Andrei Gusarov, Patrice Mégret, Marc WuilpartAbstract:The measurement of the Plasma Current is of paramount importance for controlling the Plasma in tokamak discharges. FOCS (fibre optic Current sensor) technology has already been proposed to perform such a measurement. During ITER operation, the vessel and the sensing fibre will be subject to vibrations and therefore to time varying extra parasitic birefringence. In this paper we propose to simulate the effects of vibrations on the measurement of the Plasma Current using the FOCS approach in ITER environment and to quantify the resulting inaccuracy.
David A. Humphreys - One of the best experts on this subject based on the ideXlab platform.
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Backstepping Control of the Toroidal Plasma Current Profile in the DIII-D Tokamak
IEEE Transactions on Control Systems Technology, 2014Co-Authors: Mark D. Boyer, Eugenio Schuster, T.c. Luce, J.r. Ferron, Justin Barton, Michael L. Walker, Ben G. Penaflor, Robert D. Johnson, David A. HumphreysAbstract:One of the most promising devices for realizing power production through nuclear fusion is the tokamak. To maximize performance, it is preferable that tokamak reactors achieve advanced operating scenarios characterized by good Plasma confinement, improved magnetohydrodynamic stability, and a largely noninductively driven Plasma Current. Such scenarios could enable steady-state reactor operation with high fusion gain, the ratio of produced fusion power to the external power provided through the Plasma boundary. For certain advanced scenarios, control of the spatial profile of the Plasma Current will be essential. The complexity of the Current profile dynamics, arising due to nonlinearities and couplings with many other Plasma parameters, motivates the use of model-based control algorithms that can account for the system dynamics. A first-principles-driven, control-oriented model of the Current profile evolution in low-confinement mode (L-mode) discharges in the DIII-D tokamak is employed to address the problem of regulating the Current profile evolution around desired trajectories. In the primarily inductive L-mode discharges considered in this paper, the boundary condition, which is dependent on the total Plasma Current, has the largest influence on the Current profile dynamics, motivating the design of a boundary feedback control law to improve the system performance. The backstepping control design technique provides a systematic method to obtain a boundary feedback law through the transformation of a spatially discretized version of the original system into an asymptotically stable target system with desirable properties. Through a nonlinear transformation of the available physical actuators, the resulting control scheme produces references for the total Plasma Current, total power, and line averaged density, which are tracked by existing dedicated control loops. Adaptiveness is added to the control scheme to improve upon the backstepping controller's disturbance rejection and tracking capability. Prior to experimental testing, a Simserver simulation was carried out to study the controller's performance and ensure proper implementation in the DIII-D Plasma Control System. An experimental test was performed on DIII-D to test the ability of the controller to reject input disturbances and perturbations in initial conditions and to demonstrate the feasibility of the proposed control approach.
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Backstepping control of the Plasma Current profile in the DIII-D tokamak
2012 American Control Conference (ACC), 2012Co-Authors: Mark D. Boyer, Eugenio Schuster, T.c. Luce, J.r. Ferron, Justin Barton, Michael L. Walker, Ben G. Penaflor, David A. Humphreys, Robert D. JohnsonAbstract:Control of the spatial profile of Plasma Current in tokamak Plasmas has been demonstrated to be a key condition for achieving advanced scenarios with improved confinement and possible steady-state operation. The dynamics of the Current profile are nonlinear and coupled with several other Plasma parameters, motivating the design of model-based controllers that can account for these complexities. In this work, we consider a control-oriented model of the Current profile evolution in DIII-D and the problem of regulating the Current profile around a desired feed-forward trajectory. In open-loop, the response of the system to disturbances and perturbed initial conditions may be undesirable. To improve the performance of the system, the PDE model is discretized in space using a finite difference method and a backstepping design is applied to obtain a discrete transformation from the original system into an asymptotically stable target system with desirable properties. Through a nonlinear transformation, the resulting boundary control law utilizes the total Plasma Current, total power, and line averaged density as actuators. A Simserver simulation study is done to test the controller's performance and its implementation in the DIII-D Plasma control system. Finally, experimental results showing the ability of the controller to reject input disturbances and perturbations in initial conditions are presented.
Yuichi Takase - One of the best experts on this subject based on the ideXlab platform.
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Plasma Current Ramp-Up in the Component Test Facility (CTF)
2020Co-Authors: O. Mitarai, Yueng Kay Martin Peng, Yuichi TakaseAbstract:Plasma Current ramp-up in CTF has been studied by the heating power and vertical field without a central solenoid in the case of equal electron and ion temperature. For the fusion power of 150 MW, the Plasma Current up to 12.8 MA has been obtained by the 40 MW heating/Current drive power. To maintain the steady state the more power of 64 MW is required because of no additional Current drive capability supplied by the vertical field as in the transient phase. Steady state operation with the maximum neutron wall loading of 2 MW/m'2', much lower density than the Greenwald limit, and lower beta of 24 % than the present experimental value in CTF are attractive for developing ignition physics and fusion technology.
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Plasma Current Rampup by the Outer Vertical Field Coils in a Spherical Tokamak Reactor
Fusion Science and Technology, 2017Co-Authors: Osamu Mitarai, Yuichi TakaseAbstract:To find a solution of the Plasma Current rampup problem in a low aspect ratio spherical tokamak (ST) reactor, the effect of the outer vertical field coils on Plasma Current rampup is studied with n...
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Plasma Current start-up using the lower hybrid wave on the TST-2 spherical tokamak
2015Co-Authors: Yuichi Takase, Akira Ejiri, T. Inada, Charles P. Moeller, T. Shinya, Naoto Tsujii, S. Yajima, H. Furui, H. Homma, K. ImamuraAbstract:Non-inductive Plasma Current start-up, ramp-up and sustainment by waves in the lower hybrid wave (LHW) frequency range at 200 MHz were investigated on the TST-2 spherical tokamak (R0 ≤ 0.38 m, a ≤ 0.25 m, Bt0 ≤ 0.3T, Ip ≤ 0.14 MA). Experimental results obtained using three types of antenna were compared. Both the highest Plasma Current (Ip = 18 kA) and the highest Current drive figure of merit ηCD≡n¯eIpR0/PRF=1.4×1017 A/W/m2 were achieved using the capacitively-coupled combline (CCC) antenna, designed to excite the LHW with a sharp and highly directional wavenumber spectrum. For Ip greater than about 5 kA, high energy electrons accelerated by the LHW become the dominant carrier of Plasma Current. The low value of ηCD observed so far are believed to be caused by a rapid loss of energetic electrons and parasitic losses of the LHW energy in the Plasma periphery. ηCD is expected to improve by an order of magnitude by increasing the Plasma Current to improve energetic electron confinement. In addition, edge po...
Akira Hirose - One of the best experts on this subject based on the ideXlab platform.
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Plasma Current Start-up in a Spherical Tokamak
Ieej Transactions on Fundamentals and Materials, 2020Co-Authors: Osamu Mitarai, Charles Kessel, Akira HiroseAbstract:The various Plasma Current start-up techniques and related topics in a spherical tokamak (ST) device are described. The Ohmic heating coil Current clamp experiments in NSTX are described and discussed, and the Plasma Current start-up experiments in the STOR-M tokamak with iron core and the outer vertical field coil is presented as one of technique for a Plasma Current start-up in a ST.
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Plasma Current start-up experiments without a central solenoid in the iron core STOR-M tokamak
Nuclear Fusion, 2015Co-Authors: Osamu Mitarai, David Mccoll, C Xiao, G. Tomney, A. Rohollohi, E. Lewis, Akira HiroseAbstract:Reproducible Plasma Current start-up without a central solenoid (CS) has been demonstrated using the outer ohmic heating (OH) coils in the iron core STOR-M tokamak (Mitarai et al 2014 Fusion Eng. Des. 89 2467–71). Although the outer OH coil Current saturates the iron core eventually, it has been demonstrated that the Plasma Current can be maintained during the iron core saturation phase. In this work, further studies have been conducted to investigate the effects of the turn number of the outer OH coils (N = 4 or N = 6) in the CS-less discharges and to evaluate the Plasma stability with respect to the n-decay index of the vertical magnetic field. For the loose coupling of the iron core with N = 4 turns, the Plasma Current can be sustained after the additional third capacitor bank is applied near the iron core saturation phase, showing the slow transition from the unsaturated to the partially saturated phase. For the case of stronger coupling of N = 6 turns, the Plasma Current is increased at the same fast bank voltage, but the main discharge is shortened from 35 to 20 ms. As the magnetizing Current is smaller due to stronger coupling between the OH coils and the Plasma Current, the transition from the unsaturated to the saturated phase is slightly difficult at present. The present experimental results suggest a feasible operation scenario in a future spherical tokamak (ST) at least using loose iron core coupling for smoother transition from the unsaturated to the saturated iron core phase. Thus, a reliable Plasma Current start-up by the outer OH coils and the Current ramp-up to a steady state by additional heating power and vertical field coils could be considered as an operation scenario for future ST reactors with an iron core transformer.
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Plasma Current sustainment after iron core saturation in the stor m tokamak
Fusion Engineering and Design, 2014Co-Authors: Osamu Mitarai, M Hubeny, Takumi Onchi, David Mccoll, Y. Ding, C Xiao, Y. Lu, Akira HiroseAbstract:Abstract We propose to use of a small iron core transformer to start up the Plasma Current in a spherical tokamak (ST) reactor without central solenoid (CS). Taking advantage of the high aspect ratio of the STOR-M iron core tokamak, we have demonstrated that the Plasma Current up to 10–15 kA can be started up using the outer Ohmic heating (OH) coils without CS, and that the Plasma Current can be maintained further by increasing the outer OH coil Current during iron core saturation phase. When the magnetizing Current reaches 1.2 kA and the iron core becomes saturated, the third capacitor bank connected to the outer OH coils is discharged to maintain the Plasma Current. The Plasma Current is slightly increased and maintained for additional 5 ms as expected from numerical calculations. Core saturation has been clearly observed on the hysteresis curve. This is the first experimental demonstration of the feasibility of slow transition from the iron core to air core transformer phase without CS. The results implies that a Plasma Current can be initiated by a small iron core and could be ramped up by additional heating and vertical field after iron core saturation in future STs without CS.