[en] The expansion of the l=2 stellarator magnetohydrostatic equilibrium around its circular magnetic axis is reconsidered. All parameters occurring up to third order in the distance from the magnetic axis are kept finite. Equilibrium and stability plasma β estimates are calculated in connection with a discussion of stagnation points occurring in the third-order flux surfaces. Results for the case without toroidal current are: irrespective of the five parameters describing this type of stellarator, there are universal bounds for the β estimates of 0.66% and 0.22% for the necessary and the sufficient stability criterion, respectively. (author)

No abstract available

No abstract available

[en] In a previous paper it was shown that the β limit in ASDEX follows a law βsub(max) = C . I/(a . B) (%,MA,m,T) wich Capprox.=3.5 for βsup(equ) (β from equilibrium measurements) and Capprox.=2.8 for βsup(dia) (β from a diamagnetic loop), in agreement with theoretical predictions. It was also pointed out that β - at constant neutral beam power - cannot be kept at the maximum value but decreases to a lower value. It was speculated that this decay in β corresponds to a resistive adjustment of the current density distribution to the less favourable broad H-mode temperature profiles. This contribution discusses the transient behaviour of the β limit and shows that in ASDEX H-discharges the stationary β limit (for βsup(dia)) lies about 20-30% below the maximum value. (orig./GG)

[en] Existance of asymmetric magnetic configurations without a toroidal field in particular adiabatic traps of an open type, where integral U=∫B^-1dl reaches the final maximum on a certain drift surface is shown. The plasma of isotopic pressure with β<<1 occupying the layer, which includes this surface (with maximum pressure over it), MHD is stable according to the principle of a magnetic well

[en] Stability of tandem mirrors to rigid-displacement ballooning modes is studied using vacuum field geometry. Results show substantial improvement in values of beta over those predicted by ''infinite-m'' theory. Previous work has shown that kinetic effects stabilize these latter short-wavelength modes, suggesting that only the rigid mode survives

[en] Measurements from the Tokamak Fusion Test Reactor (TFTR) of the q-profile using motional Stark effect (MSE) polarimetry and the pressure profiles have allowed detailed comparison of both supershots and L-mode discharges to theoretical models describing the stability of sawteeth. In TFTR supershots sawteeth are usually absent, whereas in L-mode discharges they are generally present, and in both cases q(O) is less than one. It has been found that the ω*-stabilization criterion of the two-fluid collisionless m=l reconnection mode agrees very well with the presence or absence of sawteeth in TFTR and no beta limits to the sawtooth stabilization have been observed

[en] A study was made on small-scale, quasiflute perturbations in tokamak with finite plasma pressure and shear. A special attention is paid to consideration of finite plasma pressure. It is shown that shear in this case produces a stabilizing effect on studied perturbations

No abstract available

No abstract available