Comments on "Plasma current drive by injection of photons with helicity" [Comm. Plasma Phys. Controlled Fusion 12, 165 (1989)]

Ohkawa has proposed a tokamak current-drive scheme [Comm. Plasma Phys. Controlled Fusion 12, 165 (1989)], which relies on the injection of circularly polarized magnetohydrodynamic waves. It is shown here that the favorable current-drive efficiency predicted by Ohkawa is not attained because excessive power is dissipated by the fluctuating fields. The ratio of power absorbed by the plasma to the dc Ohmic power required to drive the same current is Pabsorbed/POhmic[approximately-equal-to]4(Ba/b)^2, where Ba is the static toroidal field strength and b is the strength of the fluctuating field

Can useful toroidal current be driven by classical viscoresistive Alfvén waves?

Simple, yet exact, analytic solutions for the shear and compressional Alfvén wave are obtained for helical magnetohydrodynamic (MHD) waves in cylindrical geometry with both resistivity and viscosity included. The current driven by all possible combinations of these waves is examined in the quasilinear regime (i.e., where the magnetic field produced by the driven current is not self-consistently included in the equilibrium where the wave equations are derived). It is found in all cases that it is not possible to drive significant bulk axial current with small amplitude wave fields. Thus, any useful low-frequency current drive scheme will have to be based on phenomena more complicated than those discussed here

Single beam, single detector diagnostic for plasma density profiles across a magnetic field gradient

A scheme is proposed whereby the density profile of a tokamak or mirror plasma is mapped to nonlinear sidebands of a diagnostic wave, so that the sideband frequency spectrum is an image of the density profile traversed by the wave. The diagnostic relies on a monochromatic, high-frequency (omega>~omegace), pulsed wave source to determine the density profile across a magnetic field gradient. In principle, the technique offers time-dependent direct density profiles having high spatial resolution. However, the feasibility of the diagnostic is limited by the intense power and the rapid rise time required of the pulsed diagnostic wave. For parameters relevant to fusion plasmas, and for the particular scattering geometry suggested here, the technique requires, roughly, 30 mJ pulses of 2 nsec duration. The required power can be reduced by a factor of roughly 10^4 by applying signal averaging techniques. The rise time of the pulsed source must be short in comparison to one period of the diagnostic wave

Notes towards autonomous geographies: creation, resistance and self management as survival tactics

This paper’s focus is what we call 'autonomous geographies' – spaces where there is a desire to constitute non-capitalist, collective forms of politics, identity and citizenship. These are created through a combination of resistance and creation, and a questioning and challenging of dominant laws and social norms. The concept of autonomy permits a better understanding of activists’ aims, practices and achievements in alter-globalisation movements. We explore how autonomous geographies are multi-scalar strategies that weave together spaces and times, constituting in-between and overlapping spaces, blending resistance and creation, and combining theory and practice. We flesh out two examples of how autonomous geographies are made through collective decision-making and autonomous social centres. Autonomous geographies provide a useful toolkit for understanding how spectacular protest and everyday life are combined to brew workable alternatives to life beyond capitalism