Experimental measurements taken in a large magnetoplasma show that a simple double half-turn antenna will excite mϭ1 helicon waves with wavelengths from 10-60 cm. Increased ionization in the center of the downstream plasma is measured when the axial wavelength of the helicon wave becomes less than the characteristic length of the system, typically 50-100 cm. A sharp maximum in the plasma density downstream from the source is measured for a magnetic field of 50 G, where the helicon wave phase velocity is about 3ϫ10 8 cm s Ϫ1 . Transport of energy away from the source to the downstream region must occur to create the hot electrons needed for the increased ionization. A simple model shows that electrons in a Maxwellian distribution most likely to ionize for these experimental conditions also have a velocity of around 3ϫ10 8 cm s Ϫ1 . This strong correlation suggests that the helicon wave is trapping electrons in the Maxwellian distribution with velocities somewhat slower than the wave and accelerating them into a quasibeam with velocity somewhat faster than the wave. The nonlinear increase in central density downstream as the power is increased for helicon waves with phase velocities close to the optimum electron velocity for ionization lends support to this idea.

Experiments on the TCV tokamak have shown that rapid vertical movement of diverted ELMy H-mode plasmas can affect the time sequence of Edge Localised Modes. The effect is attributed to the induction of an edge current during the movement of the plasma column in the spatially inhomogeneous vacuum field of a single null configuration. In TCV the fast vertical movement is provoked by the positional control coils inside the vacuum vessel, however it is argued that a similar effect might be produced in larger devices only using poloidal field coils external to the vessel. A simple model, which includes plausible elements of the dynamical behaviour of the edge pressure gradient and edge current, which together dictate the MHD stability of the discharge against edge-localised, current-driven modes, is used to reproduce some of the features seen in these experiments.

Although the Earth's Van Allen radiation belts were discovered over 50 years ago, the dominant processes responsible for relativistic electron acceleration, transport and loss remain poorly understood. Here we show evidence for the action of coherent acceleration due to resonance with ultra-low frequency waves on a planetary scale. Data from the CRRES probe, and from the recently launched multi-satellite NASA Van Allen Probes mission, with supporting modelling, collectively show coherent ultra-low frequency interactions which high energy resolution data reveals are far more common than either previously thought or observed. The observed modulations and energy-dependent spatial structure indicate a mode of action analogous to a geophysical synchrotron; this new mode of response represents a significant shift in known Van Allen radiation belt dynamics and structure. These periodic collisionless betatron acceleration processes also have applications in understanding the dynamics of, and periodic electromagnetic emissions from, distant plasma-astrophysical systems.

[1] The adiabatic drift-resonant interaction between relativistic, equatorially mirroring electrons and narrowband, Pc 5 ultra low frequency (ULF) waves in the magnetosphere is investigated using a time-dependent magnetohydrodynamic (MHD) wave model. Attention is focused on the effect of a ULF wave packet with finite duration on the equatorially mirroring, relativistic electron phase space density (PSD) profile. It is demonstrated that a burst of narrow band ULF waves can give rise to the growth of strong localized peaks in PSD with L-shell by nondiffusive radial transport. This contrasts with the diffusive ''external source acceleration mechanism'' described by Green and Kivelson (2004), a radial transport mechanism often attributed to ULF waves, which cannot produce peaks in PSD that increase with time. On the basis of this paradigm, observations of locally growing PSD peaks are usually attributed to very low frequency (VLF) wave acceleration by resonant interactions with lower-band chorus (e.g., Horne et al., 2005). However, we show that in situations where large amplitude, narrow bandwidth ULF waves are also observed, these time-limited coherent ULF waves can also generate growing PSD peaks and under such circumstances may offer an alternative explanation.

We present simulations of the outer electron radiation belt using a new ULF wave-driven radial diffusion model, including empirical representations of loss due to chorus and plasmaspheric hiss. With an outer boundary condition constrained by in situ electron flux observations, we focus on the impacts of magnetopause shadowing and outward radial diffusion in the heart of the radiation belt. Third invariant conserving solutions are combined to simulate the L shell and time dependence of the differential flux at a fixed energy. Results for the geomagnetically quiet year of 2008 demonstrate not only remarkable cross L shell impacts from magnetopause shadowing but also excellent agreement with the in situ observations even though no internal acceleration source is included in the model. Our model demonstrates powerful utility for capturing the cross-L impacts of magnetopause shadowing with significant prospects for improved space weather forecasting. The potential role of the plasmasphere in creating a third belt is also discussed.