Cold Halo Research Articles

ROSAT PSPC observations of the remnant of SN 1006

We report soft X-ray observations ( ∼0.1–2.4 keV) of the remnant of the AD 1006 supernova, obtained with the ROSAT PSPC in 1993 January. These data provide the best spectrally resolved X-ray images of the whole remnant yet recorded. The hard and soft components of the remnant known from previous observations are now very clearly defined. Analysis of the radial surface-brightness profiles demonstrates that the hard flux is confined to thin sheets located in two ‘aegis’ which cap the sides of the remnant at the north-east and south-west limbs. The interior flux is softer and is located in a shell which extends inwards to about 0.6 of the shock radius. The spectral analysis is characterized by two components, a thermal plasma and a power-law continuum. The power-law component is associated with the thin sheets which dominate in the aegis, and the thermal component comes from the interior. Apart from the aegis, the spatial distribution of X-ray-emitting material is approximately as expected from an isothermal Sedov model. We conclude that the remnant is at a distance of 0.7 ± 0.1 kpc, that the mass is 1.7 ± 0.7 M⊙, and that the thermal energy of the observed plasma is (2.4± 1.0)× 1049 erg. The ambient density is 0.40±0.06 cm−3, the mean shock radius is 3.6±0.5 pc, and the present shock velocity is (1.4 ± 0.2) × 103 km s−1. The column density to the remnant is (3.9–5.7) × 1020 cm−2, yielding a mean density along the line of sight of 0.19–0.28 cm−3. It is likely that the thermal plasma is not in ionization equilibrium. We suggest that the aegis are formed by relativistic electrons, beamed from an otherwise unseen central object, interacting with the wound-up magnetic field in the post-shock region. The luminosity required from the central source is > 1.2 × 1034 erg s−1. The high velocity dispersion of the cold iron seen in absorption in the UV spectrum of the sbOB star (the so-called S-M star) near the centre of the remnant indicates that the bulk of this material must be outside the shock radius. The estimated kinetic energy in this cold halo is 2 × 1049 erg, so the total initial energy of the supernova was > 4.4 × 1049 erg.

Interchange, rotational, and ballooning stability of long-thin axisymmetric systems with finite-orbit effects

The stability of axisymmetric tandem mirror plasmas with respect to interchange, rotational, and ballooning modes is investigated in the paraxial approximation. The stabilizing effects of finite orbits, rigid energetic fast-drifting electrons, nearby conducting walls, and line-tying by a cold plasma halo are incorporated. Numerical calculations are performed to construct equilibria with finite plasma pressure and to determine linear stability by integrating a two-dimensional, initial-value equation. These numerical calculations support and extend analytical results. Analytical and numerical stability criteria are obtained.

Operation of cold‐cathode magnetron gauges in high magnetic fields

The Mirror Fusion Test Facility (MFTF‐B), under construction at LLNL, requires measurement of the neutral gas density in high magnetic fields near the plasma at several axial regions. This background gas pressure (BGP) diagnostic will help us understand the role of background neutrals in particle and power balance, particularly in the maintenance of the cold halo plasma that shields the hot core plasma from the returning neutrals. The BGP consists of several cold‐cathode, magnetron‐type gauges stripped of their permanent magnets, and utilizes the MFTF‐B ambient B‐field in strengths of 5–25 kG. Similar gauges have operated in TMX‐U in B‐fields up to 3 kG. To determine how well the gauges will perform, we assembled a test stand which operated magnetron gauges in an external, uniform magnetic field of up to 30 kG, over a pressure range of 10−8–10−5 Torr, at several cathode voltages. This paper describes the test stand and presents the results of the tests.

Combined confinement system applied to tokamaks.

From particle orbit point of view, a tokamak is a combined confinement configuration where a closed toroidal volume is surrounded by an open confinement system like a magnetic mirror. By eliminating a cold halo plasma, the energy loss from the plasma becomes convective. The H-mode in diverted tokamaks is an example. Because of the favorable scaling of the energy confinement time with temperature, the performance of the tokamak may be significantly improved by taking advantage of this effect.