| 1. |
- Chapman, I. T., et al.
(författare)
-
Three-dimensional distortions of the tokamak plasma boundary: boundary displacements in the presence of resonant magnetic perturbations
- 2014
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 54:8, s. Article no. 083006-
-
Tidskriftsartikel (refereegranskat)abstract
- The three-dimensional plasma boundary displacements induced by applied non-axisymmetric magnetic perturbations have been measured in ASDEX Upgrade, DIII-D, JET, MAST and NSTX. The displacements arising from applied resonant magnetic perturbations (RMPs) are measured up to +/- 5% of the minor radius in present-day machines. Good agreement can be found between different experimental measurements and a range of models-be it vacuum field line tracing, ideal three-dimensional MHD equilibrium modelling, or nonlinear plasma amplification. The agreement of the various experimental measurements with the different predictions from these models is presented, and the regions of applicability of each discussed. The measured displacement of the outboard boundary from various machines is found to correlate approximately linearly with the applied resonant field predicted by vacuum modelling (though it should be emphasized that one should not infer that vacuum modelling accurately predicts the displacement inside the plasma). The RMP-induced displacements foreseen in ITER are expected to lie within the range of those predicted by the different models, meaning less than +/- 1.75% (+/- 3.5 cm) of the minor radius in the H-mode baseline and less than +/- 2.5% (+/- 5 cm) in a 9MA plasma. Whilst a displacement of 7 cm peak-to-peak in the baseline scenario is marginally acceptable from both a plasma control and heat loading perspective, it is important that ITER adopts a plasma control system which can account for a three-dimensional boundary corrugation to avoid an n = 0 correction which would otherwise locally exacerbate the displacement caused by the applied fields.
|
|
| 2. |
- Liu, Yueqiang, 1971, et al.
(författare)
-
Feedback and rotational stabilization of resistive wall modes in ITER
- 2004
-
Ingår i: 20th IAEA Fusion Energy Conference,Vilamoura, Portugal, 1-6 November 2004. ; TH, s. 2-1
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Different models have been introduced in the stability code MARS-F in order tostudy the damping effect of resistive wall modes (RWM) in rotating plasmas. Benchmarkof MARS-F calculations with RWM experiments on JET and D3D indicates thatthe semi-kinetic damping model is a good candidate for explaining the dampingmechanisms. Based on these results, the critical rotation speeds required forRWM stabilization in an advanced ITER scenario are predicted. Active feedbackcontrol of the $n=1$ RWM in ITER is also studied using the MARS-F code.
|
|
| 3. |
- Liu, Yueqiang, 1971, et al.
(författare)
-
Modelling toroidal rotation damping in ITER due to external 3D fields
- 2015
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 55:6
-
Tidskriftsartikel (refereegranskat)abstract
- The linear and quasi-linear plasma response to the n = 3 and n = 4 (n is the toroidal mode number) resonant magnetic perturbation (RMP) fields, produced by the in-vessel edge localized mode control coils, is numerically studied for an ITER 15MA H-mode baseline scenario. Both single fluid and fluid-kinetic hybrid models are used. The inclusion of drift kinetic effects does not strongly alter the plasma response compared to the fluid approximation for this ITER plasma. The full toroidal drift kinetic model is also used to compute the neoclassical toroidal viscous (NTV) torque, yielding results close to that of an analytic model based on geometric simplifications. The computed NTV torque from low-n RMP fields is generally smaller than the resonant electromagnetic torque for this ITER plasma. The linear response computations show a weak core kink response, contrary to a strong kink response often computed for plasmas from present day tokamak devices. Initial value quasi-linear simulations, including various torque models, show a localized damping of the plasma toroidal flow near the edge, as a result of the applied RMP fields. This localized rotation damping can be weak or strong depending on whether a weakly unstable edge localized peeling mode is present. No qualitative difference is found between the n = 3 and n = 4 RMP field configurations, in both the linear and non-linear response results.
|
|
| 4. |
|
|
| 5. |
|
|
| 6. |
|
|
| 7. |
- Chu, M.S., et al.
(författare)
-
Response of a resistive and rotating tokamak to external magnetic perturbations below the Alfven frequency
- 2011
-
Ingår i: Nuclear Fusion. - 1741-4326 .- 0029-5515. ; 51, s. 073036-
-
Tidskriftsartikel (refereegranskat)abstract
- Motivated by the recent experimental observation that plasma stability can be improved by external magnetic perturbations, the general problem of plasma response to external magnetic perturbations is investigated. Different (vacuum, ideal and resistive) plasma response models are considered and compared. Plasma response, in experiments where stabilization was achieved, is obtained through computation using the MARS-F code, with a plasma model that includes both plasma resistivity and rotation. The resultant magnetic field line stochasticity is much reduced from that obtained formerly using the vacuum plasma model. This reduced stochasticity is more consistent with the favourable experimental observation of enhanced stability. Examples are given for the response of an ITER plasma to perturbations generated by the correction coils; and the response of a plasma to external coils (antenna) up to the Alfvén frequency.
|
|
| 8. |
|
|
| 9. |
|
|
| 10. |
- Liu, Yueqiang, 1971, et al.
(författare)
-
Feedback Control of Resistive Wall Modes in Toroidal Devices
- 2004
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 44:1, s. 77-86
-
Tidskriftsartikel (refereegranskat)abstract
- Feedback control of nonaxisymmetric resistive wall modes is studied analytically for cylindrical plasmas and computationally for high beta tokamaks. Internal poloidal sensors give superior performance to radial sensors, for instance in terms of the highest achievable plasma pressure. A single poloidal array of feedback coils allows robust control with respect to variations in plasma pressure, current and rotation velocity. The control analysis is applied to advanced scenarios for ITER. Configurations with multiple poloidal coils and feedback systems for nonresonant MHD instabilities in reversed field pinches are also studied. The control study was carried out using the assumption of ideal amplifiers.
|
|
| 11. |
- Liu, Yueqiang, 1971, et al.
(författare)
-
Modeling of resistive wall mode and its control in experiments and ITER
- 2006
-
Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 13:5
-
Tidskriftsartikel (refereegranskat)abstract
- Active control of the resistive wall mode (RWM) for DIII-D [Luxon and Davis, Fusion Technol. 8, 441 (1985)] plasmas is studied using the MARS-F code [Y. Q. Liu, Phys. Plasmas 7, 3681 (2000)]. Control optimization shows that the mode can be stabilized up to the ideal wall beta limit, using the internal control coils (I-coils) and poloidal sensors located at the outboard midplane, in combination with an ideal amplifier. With the present DIII-D power supply model, the stabilization is achieved up to 70% of the range between no-wall and ideal-wall limits. Reasonably good quantitative agreement is achieved between MARS-F simulations and experiments on DIII-D and JET (Joint European Torus) [P. H. Rebut, Nucl. Fusion 25, 1011 (1985)] on critical rotation for the mode stabilization. Dynamics of rotationally stabilized plasmas is well described by a single mode approximation; whilst a strongly unstable plasma requires a multiple mode description. For ITER [R. Aymar, P. Barabaschi, and Y. Shimomura, Plasma Phys. Controlled Fusion 44, 519 (2002)], the MARS-F simulations show the plasma rotation may not provide a robust mechanism for the RWM stabilization in the advanced scenario. With the assumption of ideal amplifiers, and using optimally tuned controllers and sensor signals, the present feedback coil design in ITER allows stabilization of the n=1 RWM for plasma pressures up to 80% of the range between the no-wall and ideal-wall limits.
|
|
| 12. |
- Liu, Yueqiang, 1971, et al.
(författare)
-
Modelling of plasma response to RMP fields in MAST and ITER
- 2011
-
Ingår i: Nuclear Fusion. - 1741-4326 .- 0029-5515. ; 51, s. 083002-
-
Tidskriftsartikel (refereegranskat)abstract
- The resonant magnetic perturbation (RMP) fields, including the plasma response, are computed within a linear, full toroidal, single-fluid resistive magnetohydrodynamic (MHD) model, and under realistic plasma conditions for MAST and ITER. The response field is found to be considerably reduced, compared with the vacuum field produced by the magnetic perturbation coils. This field reduction relies strongly on the screening effect from the toroidal plasma rotation. Computations also quantify three-dimensional (3D) distortions of the plasma surface, caused by RMP fields. A correlation is found between the computed mode structures, the plasma surface displacement and the observed density pump-out effect in MAST experiments. Generally, the density pump-out tends to occur when the surface displacement peaks near the X-points.
|
|
| 13. |
- Liu, Yueqiang, 1971, et al.
(författare)
-
Multimachine Data-Based Prediction of High-Frequency Sensor Signal Noise for Resistive Wall Mode Control in ITER
- 2016
-
Ingår i: Fusion Science and Technology. - : Informa UK Limited. - 1536-1055 .- 1943-7641. ; 70:3, s. 387-405
-
Tidskriftsartikel (refereegranskat)abstract
- The high-frequency noise measured by magnetic sensors, at levels above the typical frequency of resistive wall modes, is analyzed across a range of present tokamak devices including DIII-D, JET, MAST, ASDEX Upgrade, JT-60U, and NSTX. A high-pass filter enables identification of the noise component with Gaussian-like statistics that shares certain common characteristics in all devices considered. A conservative prediction is made for ITER plasma operation of the high-frequency noise component of the sensor signals, to be used for resistive wall mode feedback stabilization, based on the multimachine database. The predicted root-mean-square n = 1 (n is the toroidal mode number) noise level is 10(4) to 10(5) G/s for the voltage signal, and 0.1 to 1 G for the perturbed magnetic field signal. The lower cutoff frequency of the Gaussian pickup noise scales linearly with the sampling frequency, with a scaling coefficient of about 0.1. These basic noise characteristics should be useful for the modeling-based design of the feedback control system for the resistive wall mode in ITER.
|
|
| 14. |
- Liu, Yueqiang, 1971, et al.
(författare)
-
Stabilization of Resistive Wall Modes in ITER by Active Feedback and Toroidal Rotation
- 2004
-
Ingår i: Nuclear Fusion. - 1741-4326 .- 0029-5515. ; 44, s. 232-
-
Tidskriftsartikel (refereegranskat)abstract
- Two approaches are examined for stabilization of the resistive wall mode (RWM) of toroidal mode number n = 1 in an advanced ITER scenario. Active feedback control, with the present coil design and poloidal sensors placed just inside the inner wall, can be very efficient in stabilizing the RWM. Within the voltage limit of the present design for the feedback coils and conservative constraints on performance, the plasma pressure can be increased up to at least 70% between the no-wall and ideal-wall beta limits. Stabilization of the RWM by toroidal plasma rotation depends on the rotation profile as well as on the model for ion Landau damping. Feedback control of rotating plasmas for the advanced scenario is considered. The effect of the blanket is also studied using a simplified model.
|
|
