Author: Fredrik WisingPublisher:
ISBN:
Category :
Languages : en
Pages : 290
Book Description
Sawtooth Oscillations in Tokamak Plasmas
Author: Fredrik WisingSawtooth Oscillation in Tokamaks
Author: Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
A three-dimensional nonlinear toroidal full MHD code, MH3D, has been used to study sawtooth oscillations in tokamaks. The profile evolution during the sawtooth crash phase compares well with experiment, but only if neoclassical resistivity is used in the rise phase. (Classical resistivity has been used in most of the previous theoretical sawtooth studies.) With neoclassical resistivity, the q value at the axis drops from 1 to about 0.8 before the crash phase, and then resets to 1 through a Kadomtsev-type complete reconnection process. This .delta.q0 approx. = 0.2 is much larger than .delta.q/sub o/ approx. = 0.01, which is obtained if classical resistivity is used. The current profile is strongly peaked at the axis with a flat region around the singular surface, and is similar to the Textor profile. To understand this behavior, approximate formulas for the time behavior of current and q values are derived. A functional dependence of sawtooth period scaling is also derived. A semi-empirical scaling is found which fits the experimental data from various tokamaks. Some evidence is presented which indicates that the fast crash time is due to enhanced effective resistivity inside the singular current sheet, generated by, e.g., microinstability and electron parallel viscosity with stochastic fields at the x-point. 16 refs., 5 figs.
Q Measurements During Sawtooth Oscillations in a Low Q Tokamak
Author: Delaying Sawtooth Oscillations in the Compact Ignition Tokamak
Author: Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
A combination of pellets, off-axis heating, and current ramp is used to delay the onset of sawtooth oscillations for 3.4 seconds and achieve ignition with less than 0.2-second confinement time in a 1-1/2-D BALDUR simulation of the Compact Ignition Tokamak. Deuterium and tritium pellets are injected into an initially cold, relatively low density plasma, where they cool the center and produce a very centrally peaked density profile. A centrally peaked density profile (n/sub e0// = 4.0) is subsequently maintained by an inward particle pinch. Twenty megawatts of auxiliary heating is applied halfway between the magnetic axis and the edge of the plasma for 2 seconds after the pellets are injected. The plasma ignites and then burns from the time the auxiliary heating is turned off until the first large sawtooth crash occurs at 3.4 seconds. The burn would be expected to continue after that only if the sawtooth period is sufficiently long (roughly 0.3 seconds or longer).
Sawtooth Stabilization by Localized Electron Cyclotron Heating in a Tokamak Plasma
Author: K. HanadaDelaying Sawtooth Oscillations in the Compact Ignition Tokamak
Author: G. BatemanGiant Sawtooth Oscillation in Ohmically Heated Tokamak Plasma
Author: A. MontvaiPublisher:
ISBN: 9789633722329
Category :
Languages : en
Pages : 12
Book Description
Sawtooth Stabilization by Localized Electron Cyclotron Heating in a Tokamak Plasma
Author: Publisher:
ISBN:
Category :
Languages : en
Pages : 13
Book Description
Sawtooth oscillations (STO) in the ohmically heated WT-3 tokamak are strongly modified or suppressed by localized electron cyclotron resonance heating (ECH) near the q = 1 surface, where q refers to the safety factor. The effect of ECH is much stronger when it is applied on the high field side (the inner side of the tokamak) as compared to the low field side (outer side). Complete suppression of the STO is achieved for the duration of the ECH when it is applied on the high field side, in a low density plasma, provided the ECH power exceeds a thresholds value. The STO stabilization is attributed to a modification of the current density profile by hot electrons generated by ECH, which reduces the shear in the q = region. 14 refs., 5 figs.
Investigation of Magnetic Reconnection During a Sawtooth Crash in a High Temperature Tokamak
Author: R. V. BudnyAnalysis of Sawtooth Relaxation Oscillations in Tokamaks
Author: Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
Sawtooth relaxation oscillations are analyzed using the Kadomtsev's disruption model and a thermal relaxation model. The sawtooth period is found to be very sensitive to the thermal conduction loss. Qualitative agreement between these calculations and the sawtooth period observed in several tokamaks is demonstrated.