The scattering of low energy electrons from nitrogen has been investigated for a range of impact energies (1.5, 2.1, 3.0 and 5.0 eV) which encompass the 2 Pi g resonance. Measured differential and integral cross sections for both elastic scattering and rovibrational excitation (v=0-1, 2, 3) of the ground electronic state are compared with results from previous experimental and theoretical investigations. In some cases, particularly at 1.5 eV, significant discrepancies are found between the present and previous experiments.

By adding a current-carrying central rod to the basic rotamak apparatus, a magnetic configuration has been produced which is that of a spherical tokamak (ST) maintained in steady state by the application of a rotating magnetic field. The noteworthy reproducibility of the rotamak-ST discharges has facilitated the measurement of the time-averaged magnetic field components throughout a poloidal plane. These measurements, together with an assumption of axisymmetry, have enabled the field lines of an ST to be directly reconstructed from experimental data for the first time. [S0031-9007(98)07036-7] PACS numbers: 52.55.Fa, 52.55.HcThe investigation of plasma/field configurations of the compact torus variety is of current interest in the field of fusion research. Two configurations of this genre are the field reversed configuration (FRC) which does not have an externally applied toroidal magnetic field and the spherical tokamak (ST) which possesses such a field.The rotamak [1] is a compact torus configuration having the unique and distinctive feature that the steady toroidal plasma current is driven in a steady-state, noninductive fashion by means of the application of a rotating magnetic field (RMF) [2]. The toroidal current ring is kept in horizontal and vertical equilibrium by an externally applied magnetic field and, if conditions are appropriate, it can reverse this equilibrium field thus generating a compact torus configuration of the FRC type. Some of the latest results describing the operation of the rotamak as an FRC can be found in [3].The ST is the low aspect ratio limit of the tokamak. It has the advantages of simple construction, lower magnetic fields, and improved stability over the conventional tokamak. Interest in this particular compact torus concept is growing apace, supported in part by a favorable report [4] which highlights its potential as an economic fusion power plant. FIG. 1. The Flinders Rotamak-ST. By means of a simple modification, a steady toroidal magnetic field can be added to the basic rotamak apparatus and the configuration then becomes that of an ST maintained in steady state by means of the application of the RMF. Such a modified rotamak apparatus was indeed the first spherical tokamak experiment [5]. FIG. 2. Time history of (a) the rod current, ( b) the vertical field, and (c) the driven toroidal plasma current. The RMF was applied during the period 30 -70 ms. 2072 0031-9007͞98͞81(10)͞2072(4)$15.00

In the rotamak concept, a rotating magnetic field is used to drive toroidal plasma current in a compact torus device in a non-inductive manner. The latest results from a 0.5 m diameter rotamak apparatus are presented. These show that, for a given filling pressure of hydrogen, it is possible to drive more current, whilst simultaneously preserving the compact torus configuration, by increasing the amount of RF power transferred to the plasma. Attention is drawn to the fact that a fair evaluation of the rotamak concept requires experimentation at higher RF power levels than are presently available

A new high power helicon (HPH) plasma system has been designed to provide input powers of several tens of kilowatts to produce a large area (0.5 m 2 ) of uniform high-density, of at least 5 × 10 17 m −3 , plasma downstream from the helicon coil. Axial and radial plasma characteristics show that the plasma is to a lesser extent created in and near the helicon coil and then is accelerated into the axial and equatorial regions. The bulk acceleration of the plasma is believed to be due to a coupling of the bulk of the electrons to the helicon field, which in turn transfers energy to the ions via ambipolar diffusion. The plasma beta is near unity a few centimetres away from the HPH system and Bdot measurements show B perturbations in the order of the vacuum magnetic field magnitude. In the equatorial region, a magnetic separatrix is seen to develop roughly at the mid-point between the helicon and chamber wall. The magnetic perturbation develops on the time scale of the plasma flow speed and upon the plasma reaching the chamber wall decays to the vacuum magnetic field configuration within 200 µs.

Mini-Magnetospheric Plasma Propulsion (M2P2) seeks the creation of a magnetic wall or bubble (i.e. a magnetosphere) attached to a spacecraft that will intercept the solar wind and thereby provide high-speed propulsion with little expenditure of propellant. Results from a laboratory prototype that demonstrate the basic formation and expansion of a mini-magnetosphere are presented. The prototype uses a helicon source embedded asymmetrically in a dipole-like magnetic field. Breakdown of the plasma can be produced at neutral pressures of between about 0.25 to 1 mTorr to produce plasma densities of the order of 10 11-10 12 cm-3 with a temperature of a few eV. The plasma pressure is sufficient to cause the outward expansion or inflation of the mini-magnetosphere. The motion of both open and closed field lines within the vacuum chamber is demonstrated through the optical emissions from the helicon plasma. Inflation of the magnetosphere to several feet away from the magnetic coil and the equatorial confinement of the plasma are demonstrated. In space, inflation to about 15-20 km would be expected for the same configuration, which would potentially lead to the acceleration a 70-140 kg payload to speeds of about 50-80 km/s over a 3-month acceleration period. At this speed, missions to the heliopause and beyond can be achieved in under 10 yrs.