The mechanism of sawtooth precursors and sawtooth relaxations

Journal Article · Tue May 01 04:00:00 EDT 1990 · Physics of Fluids B; (USA)

DOI:https://doi.org/10.1063/1.859242· OSTI ID:6999926

Rogister, A; Kaleck, A; Psimopoulos, M; Hasselberg, G ^[1]

---

1. Institut fuer Plasmaphysik der Forschungszentrum, Juelich, GmbH, Juelich (DE) Association EURATOM-KFA, Postfach 1913, 5170 Juelich, Federal Republic of Germany (DE)

It is shown that certain specific properties are requested from the current density profile in order to arrive at a coherent theoretical explanation of the sawtooth phenomenon in tokamaks: (1) the shear {ital {cflx s}} must be small at the {ital q}=1 surface (hence the current density profile has a plateau or shoulder in the neighborhood of {ital q}=1); (2) {ital J}{prime} varies abruptly not far away from {ital q}=1 (in particular, the outer edge of the plateau is close to {ital q}=1). Indeed, when these conditions are satisfied, the contribution to the jump of the derivative of the magnetohydrodynamic (MHD) solution (({Psi}{prime}){sub {ital r}{sub 1}}) from those terms that are proportional to {epsilon}{sup 2} ({epsilon} is the inverse aspect ratio) is not negligible. It is, moreover, opposite in sign to the usual contribution (({Psi}{sup (0){prime}}){sub {ital r}{sub 1}}{proportional to}{ital {cflx s}}{sub 1}) so that the inverse of the logarithmic jump 1/{Delta}{prime}{proportional to}{Psi}{sub {ital r}{sub 1}}/({Psi}{prime}){sub {ital r}{sub 1}} can now take on either positive values ({ital {cflx s}}{sub 1}{gt}{ital {cflx s}}{sub 1,{ital c}}), or negative ones ({ital {cflx s}}{sub 1}{lt}{ital {cflx s}}{sub 1,{ital c}}), or can diverge'' (1/{Delta}{prime}{r arrow}{plus minus}{infinity} for {ital {cflx s}}{sub 1}{r arrow}{ital {cflx s}}{sub 1,{ital c}}).

• OSTI ID: 6999926
• Journal Information: Physics of Fluids B; (USA), Journal Name: Physics of Fluids B; (USA) Vol. 2:5; ISSN 0899-8221; ISSN PFBPE
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
700107* -- Fusion Energy-- Plasma Research-- Instabilities
700108 -- Fusion Energy-- Plasma Research-- Wave Phenomena
CLOSED PLASMA DEVICES
DISPERSION RELATIONS
ELECTRON TEMPERATURE
FLUID MECHANICS
HYDRODYNAMICS
INSTABILITY
INSTABILITY GROWTH RATES
MAGNETIC FIELD CONFIGURATIONS
MAGNETIC SURFACES
MAGNETOHYDRODYNAMICS
MECHANICS
OSCILLATIONS
PLASMA
PLASMA INSTABILITY
PLASMA MACROINSTABILITIES
PRECURSOR
RELAXATION
SAWTOOTH OSCILLATIONS
THERMONUCLEAR DEVICES
TOKAMAK DEVICES
TRAJECTORIES
TRAPPING