In present tokamaks the density limit (DL) is observed to coincide with complete divertor detachment. A scrape-off layer (SOL) based model is presented for this `detachment limit'. Emphasis is placed on understanding the power independent, 1/q-type scaling (Hugill-Greenwald type scaling) observed in many divertor machines. A simple analytical model for the SOL, complemented by dimensional considerations on gas targets, is used to describe the underlying mechanism and derive scalings for the critical density. Physically, the power independent regime is associated with an intermediate transverse neutral collisionality in the divertor. Extensive B2-EIRENE studies were conducted to verify the analytical considerations. Computational results are compared with experimental findings on JET. Possible ways to access the power dependent regime are discussed
The integral equation technique previously developed for electrostatic drift waves to study low-frequency electromagnetic perturbation is extended. When σe≫σi (as is the case for tearing modes) the problem can be reduced to the simultaneous solution of an integral and a differential equation. Using a Fourier representation for φ̃(x), a differential equation is derived from Ampere’s law for a modified Green’s function that contains the magnetic effects. This equation is solved simultaneously with an integral equation (corresponding to the quasineutrality condition in k space) to obtain the eigenvalues and corresponding eigenfunctions. When applied to the study of microtearing modes this method gave, for the same values of the parameters, larger growth rates than those of the usual differential approximation.
A Monte Carlo code is employed to study
the interaction of neutral
beams with a field reversed configuration (FRC). The code
follows the exact particle trajectories in the
self-consistent equilibrium calculated
including the beam and plasma currents. For
high enough beam currents, a
self-consistent confining effect is observed which
prevents expansion
of the beam along the FRC axis. The beam
current drive and the power
and momentum transferred are calculated for a variety
of beam parameters.
The results are slightly affected by the details
of the injection geometry.
The dependence on the neutral current IN and beam
energy EN is influenced
by several factors, such as particle losses through
the ends, the density
increase around the injection region and the
finite Larmor radius effect.
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