Summary of the magnetic confinement theory and modelling

Krasheninnikov, S. I.

doi:10.1088/0029-5515/47/10/s04

Cited by 3 publications

(3 citation statements)

References 63 publications

(67 reference statements)

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“…In fact, whereas no reliable measurement of particle recycling is available, the rate at which particles enter the vacuum chamber through the gas valves is nonetheless known and given by G puf . In any case, such has been essentially a modeller's option (deemed to be the best suited to minimize the arbitrariness in the choice of free parameters one is allowed to play with) and, in essence, no physical meaning should be attached to the values of R cyc and G puf taken individually (except when the latter becomes nil before the end of the current ramp, as discussed later in section 4.8), but rather to their relative variation (which has to 8 Basically, in a deuterium plasma with carbon impurity, a good guess is…”

Section: On the Benchmarking Methodologymentioning

confidence: 99%

“…Plasma transport simulation and modelling has always been a major activity in magnetic fusion research and one which, particularly in view of ITER, has seen a significant increase in the latter years and has become mostly focused on integrated tokamak modelling . This effort has comprised studies devoted essentially to understand, validate and extrapolate transport models [1-7, 9, 11, 12, 18-21, 25, 26, 28, 34-37], has also been very much goal-oriented towards ITER scenario development [10, 13-15, 21, 23, 24, 27, 28, 31, 38], having made the fusion community aware of the need to develop powerful tools for integrated tokamak modelling [8,16,17,22,29,30,32,33], and has very much relied on JET as a unique machine on which to test, benchmark and validate transport codes and models [1-7, 9, 11, 12, 16, 18, 20, 21, 25, 28, 33-35, 37]. For their most part, tokamak modelling activities have addressed the so-called ramp-up and flat-top phases of tokamak pulses, and less attention has been paid to the termination of tokamak discharges (when the plasma current is ramped down to zero), even knowing that pulses should always be safely terminated and so appropriate ramp-down modelling must become available, inasmuch as additional concerns arise for ITER and demand reliable ramp-down procedures that must account for things such as disruption, plasma shape and stability, and volt-second saving [14,15,19,21,28,31,37,[39][40][41][42][43].…”

Section: Introductionmentioning

confidence: 99%

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Modelling the Ohmic L-mode ramp-down phase of JET hybrid pulses using JETTO with Bohm–gyro-Bohm transport

Bizarro

Köchl

Voitsekhovitch

et al. 2016

Plasma Phys. Control. Fusion

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The empirical Bohm-gyro-Bohm (BgB) transport model implemented in the JETTO code is used to predictively simulate the purely Ohmic (OH), L-mode current-ramp-down phase of three JET hybrid pulses, which combine two different ramp rates with two different electron densities (at the beginning of the ramp). The modelling is discussed, namely the strategy to reduce as much as possible the number of free parameters used to benchmark the model predictions against the experimental results. Hence, keeping the gas puffing rate as measured whilst controlling the line-averaged electron density via the recycling coefficient (which in the modelling is taken at the separatrix instead of the wall), one of the many possible ways to fix the total particle source, it is shown that the BgB model reproduces well the experimental data, as far as both average quantities (plasma internal inductance and volume-averaged electron temperature) and profiles (electron density and temperature) are concerned, with relative errors remaining mostly below 20%. The sensitivenesses with respect to the recycling coefficient, the ion effective charge, the energy of neutrals entering the plasma through the separatrix and the need to introduce a particle pinch are assessed; the necessity for a proper sawtooth model if experimental results are to be reproduced is also shown. The strong non-linear coupling in a OH plasma between density, temperature and current (essentially via interplay between the powerbalance equation, Joule's heating with a temperature-dependent resistivity and the dependence of BgB transport coefficients on profile gradients) is put in evidence and analyzed in light of modelling results. It is still inferred from the modelling that the real value of the recycling coefficient at the separatrix (basically, the so-called fuelling efficiency times the actual recycling coefficient at the wall) must become close to one in the final stages of the discharges, when the gas puffing is switched off and so recycling comes to be the only source of particles. If the wall recycling remains close to one (as standard for tokamaks), this may indicate that the fuelling efficiency also approaches unity, apparently consistent with the observed fact that the plasma is pushed towards the machine wall at the end of the current ramps.

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Section: On the Benchmarking Methodologymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Modelling the Ohmic L-mode ramp-down phase of JET hybrid pulses using JETTO with Bohm–gyro-Bohm transport

Bizarro

Köchl

Voitsekhovitch

et al. 2016

Plasma Phys. Control. Fusion

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“…The experimental and theoretical studies of anomalous processes of transfer in the SOL plasma have been underway for several decades. Extensive literature is devoted to these processes, which is reviewed, for example, in [15][16][17][18]. Some part is further played in the energy balance in the SOL by the Pfirsch-Schlüter convection, in the case of which the motion of plasma to the central core is possible on the inner contour, which is accompanied by compression due to the energy of expansion on the outer contour.…”

Section: Basic Processes Of Energy Conversion In the Solmentioning

confidence: 99%

The conversion of the thermal energy of plasma in the SOL of tokamaks

Nedospasov¹,

Nenova²

2008

Nucl. Fusion

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When the plasma expands across the confining magnetic field, a part of its thermal energy is converted to electrical energy. In the SOL of tokamaks, the motion of the plasma across the field due to turbulent processes is accompanied by its departure along the open lines of the magnetic field. The conversion of thermal energy is taken into account in theoretical studies devoted to the physics of plasma in the SOL; however, this conversion is ignored in numerical models, for example, in B2–SOLPS4.0. This paper deals with thermal-to-electrical energy conversion in the SOL of tokamaks. It is demonstrated that the part of the thermal energy subjected to conversion to electrical energy forms an appreciable part of the total energy flowing in the SOL. In ITER, this fraction may be as high as 20–25%. The electrical energy generated in the SOL volume is liberated in the form of Joule heat in a relatively cold plasma in the vicinity of diverter plates or directly on these plates.

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Stability threshold of ion temperature gradient driven mode in reversed field pinch plasmas

Guo

2008

Physics of Plasmas

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For the first time in the reversed field pinch (RFP) configuration, the stability threshold of the ion temperature gradient driven (ITG) mode is studied by linear gyrokinetic theory. In comparison with tokamaks, the RFP configuration has a shorter connection length and stronger magnetic curvature drift. These effects result in a stronger instability driving mechanism and a larger growth rate in the fluid limit. However, the kinetic theory shows that the temperature slopes required for the excitation of ITG instability are much steeper than the tokamak ones. This is because the effect of Landau damping also becomes stronger due to the shorter connection length, which is dominant and ultimately determines the stability threshold. The required temperature slope for the instability may only be found in the very edge of the plasma and/or near the border of the dominant magnetic island during the quasi-single helicity state of discharge

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Summary of the magnetic confinement theory and modelling

Abstract: Summary of the papers presented at the 21st IAEA Fusion Energy Conference (Chengdu, October 2006) and devoted to magnetic confinement theory and modelling.

Cited by 3 publications

References 63 publications

Modelling the Ohmic L-mode ramp-down phase of JET hybrid pulses using JETTO with Bohm–gyro-Bohm transport

Modelling the Ohmic L-mode ramp-down phase of JET hybrid pulses using JETTO with Bohm–gyro-Bohm transport

The conversion of the thermal energy of plasma in the SOL of tokamaks

Stability threshold of ion temperature gradient driven mode in reversed field pinch plasmas

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