Rolf M. Sinclair

A Unique Solar Marking Construct

An assembly of stone slabs on an isolated butte in New Mexico collimates sunlight onto spiral petroglyphs carved on a cliff face. The light illuminates the spirals in a changing pattern throughout the year and marks the solstices and equinoxes with particular images. The assembly can also be used to observe lunar phenomena. It is unique in archeoastronomy in utilizing the changing height of the midday sun throughout the year rather than its rising and setting points. The construct appears to be the result of deliberate work of the Anasazi Indians, the builders of the great pueblos in the area.

A Method for Mapping a Toroidal Magnetic Field by Storage of Phase Stabilized Electrons

We describe a method for measuring the shape of a toroidal magnetic field (such as in a stellarator) to demonstrate the existence and nature of magnetic surfaces. We detect the successive circuits of a pulse of low energy, phase stabilized electrons injected parallel to the field and stored for many thousands of circuits. We find that the cumulative effect of various field perturbations alters the parameters of the surfaces significantly, but does not destroy them. In certain special cases, there is excellent agreement between the measured and computed field shapes for our specific device. These results and methods are of immediate application to a broad class of magnetic (or other area preserving) mappings. The same experimental technique can also be used for the long term storage of low energy ions.

Ion Cyclotron Wave Generation in the Model C Stellarator

To permit quantitative comparisons between experiment and theory, ion cyclotron wave generation by the Stix coil system of the Model C stellarator is analyzed using a coil‐plasma model which closely approximates the physical system: filamentary currents at the coil loop positions induce plasma waves which propagate along the “cold” plasma column which is coaxial with a cylindrical waveguide. Most important in the analysis is the inclusion of finite electron inertia effects which cause the natural modes of the system to be characterized by two radial wavenumbers in place of one and which can seriously modify the properties of the ion cyclotron waves. Coil loading predictions are in good absolute agreement with experimental observations for wide ranges of plasma density and magnetic field, thus demonstrating the relevance of the cold theory to the laboratory plasma. However, magnetic field predictions are larger than the fields measured far from the Stix coil, suggesting wave attenuation by processes not co...

Ion Cyclotron Heating in the Model C Stellarator

A new ion cyclotron resonance heating system has been installed on the Model C stellarator. Use of low‐power rf during the entire Ohmic heating pulse shows that the density for optimum coupling is a factor of 1.5‐2 greater than that calculated from a simple theory. The variation of coupling with density and plasma radius is found to agree with theory. An anomalous second maximum in the coupling curve is found. At 1 MW power levels, little energy is transmitted around the ∪ bends by ion cyclotron waves, and it is necessary to have magnetic beaches adjacent to the Stix coil. Best heating is obtained with the least amount of magnetic beach. Use of a larger axial field gradient results in rapid loss of density under the Stix coil, with subsequent decrease in coupling and heating. The maximum ion temperature obtained in the ∪ bends is ∼ 550 eV, uniform to within 20%. A model is proposed in which cooling is dominated by particle losses and charge exchange, the particle loss rate being dependent on kTe.

Equilibrium of a Toroidal Plasma with a Conducting Aperture Limiter

A conducting limiter brings about equilibrium of a toroidal plasma by anchoring magnetic field lines. Charge separation arising from the curvature effect can be short circuited by the limiter. This way of achieving equilibrium is not possible if the charge separation current exceeds the maximum ion saturation current to the limiter. Experiments with the Model C stellarator are consistent with this model. An observed instability is related to the loss of equilibrium due to the excess charge separation current.

On Equilibrium of a Current‐Carrying Toroidal Plasma. II. Experiments with the Model C Stellarator

A series of experiments with the Model C stellarator showed that a previously detected asymmetry in the device could be removed by applying such a magnetic field BT, transverse to the main confining magnetic field, that an inherent lack of closure of the flux lines of the confining field was removed. The symmetrized stellarator was then used to demonstrate that an equilibrium (discussed theoretically elsewhere) could be achieved in the plasma by applying a uniform magnetic field transverse to the plane of the stellarator. With current IOH flowing toroidally in the plasma, the tendency for the toroid to expand, due to the hoop force and the U‐bend drift, is counterbalanced by the IOH × BT force. The observed transverse field required for equilibrium is in good agreement with the value predicted theoretically. Improvement at equilibrium of such plasma parameters as electron temperature, particle confinement time, and energy replacement time is demonstrated.

Equilibrium of a Current‐Carrying Toroidal Plasma

A current‐carrying plasma confined in a smooth toroidal magnetic field tends to expand due to the nonuniformity of the field and the self‐interaction of the current. This expansion can be nullified, in the absence of externally imposed rotational transform, by means of a vertical magnetic field (perpendicular to the plane of the toroid). Macroscopically considered, such a vertical magnetic field interacts with the Ohmic heating current to supply an inward ponderomotive force. This paper derives the magnitude of the plasma expansion tendency and of the vertical field required to achieve steady state conditions. It is also demonstrated that if the plasma configuration is determined by an aperture limiter, helical fields are equivalent to an applied vertical field, insofar as the plasma equilibrium is concerned.

Properties of magnetic surfaces in the Model C stellarator

The authors have mapped the magnetic field of the Model C stellarator by a new technique using the long-term storage of low-energy electrons. They correlate the properties of the field (such as the existence of surfaces, and realistic values of their average radius and transform) with the behavior of plasma in the device.

OPTIMUM GENERATION OF ION-CYCLOTRON WAVES IN A CYLINDRICAL TWO-ION PLASMA

Ion‐cyclotron waves have been generated in a hydrogen‐deuterium plasma (previously formed by Ohmic heating) contained in the Model C stellarator, using an induction coil of finite wavelength. The conditions for optimum generation of waves, found experimentally, were in good agreement with theoretical predictions.

Ion Cyclotron Instability of Energetic Plasma Confined in Magnetic Mirrors in the Model C Stellarator

A portion of the plasma in the Model C stellarator is heated by ion cyclotron resonance heating and contained within magnetic mirrors (1.02 ≤ R ≤ 1.3, B0 ≈ 35 kG). The plasma so formed (ne ≈ 1012‐1013 cm−3) has little interaction with the main body of toroidal plasma, and has perpendicular ion temperature up to 4 keV while the electron temperature remains at less than 100 eV. New results show that the cooling of this energetic plasma, lasting several milliseconds, is accompanied by emission of radiation at frequencies close to the local ion cyclotron frequency and its harmonics. Experimental results are presented of observations of this rf activity, and related to theoretically predicted instabilities of the ion cyclotron type. It is concluded that the observed behavior can be satisfactorily explained by the presence of an electrostatic, temperature‐anisotropy‐driven instability. There is no correlation between the rf activity and the cooling time of the mirror‐contained plasma; the containment time still...