ENERGY EXCHANGE IN THE HIGH-INTENSITY ARC PLASMA. TECHNICAL NOTE NO. 1. EFFECT OF FLUID TRANSPIRATION THROUGH THE ANODIC ARC BOUNDARY
A basic discussion of arc phenomena is presented for the purposes of orientation and definition. Emphasis is placed on the distinction between low- intensity and high-intensity modes of arc operation. Following the preliminary discussion, the fundamental prenmises for the concept of a "fluid transpiration" arc are laid down. This concept relates to an arc discharge subject to the forced convection of a fluid medium, but differentiated from other systems of this type by the fact that the fluid is injected into the arc conduction zone via the anodic terminus through a porous anode structure. The postulated effectiveness criteria for this technique of arc heating require that the average pore size be less than the anode fall space thickness, that the transpiration surface be integrally congruent with the anodic discharge boundary, and that the injected gas particle flux density have the same order of magnitude as the opposing drift electron flux density within the anode sheath region. A two-phase experimental program is described, the first being concerned with the validation of the basic concept and the second with a study of intrinsic characteristics. The first group of experiments established the feasibility of fluid transpiration through the anodic arc boundary as a practical method of arc heating. Transition to a new mode of arc operation at a specific rate of fluid flow was demonstrated. The new mode exhibited general features similar to a Benck type high-intensity arc, but in some respects it is shown to be different. The second group of experiments detailed a number of unique properties for the technique of fluid transpiration through the anoden. Some evidence was obtained for an abnormally high degree of ionization in the plasma jet. Erosion tests on both porous graphite and tungsten demonstrated that steady state anode consumption as low as 10/sup, -6/ gms/sec are achievablen in an argon medium. The major cause of anode wear was found to be spalling of surface fragments due to arc ignition stresses. A very pure plasma jet, essentially free of electrode vapor, was generated for a wide range of gas flow ratens. Anode erosion using helium gas was found to be higher than that for argon, other things being equal. This is tentatively explained as an effect of relative atom-electron collision cross-sections ink. the anode sheath. Normalized specific enthalpiens between 1.0 and 5.0 k-cal/gm mole-kw at transfer efficiencies between 70 and 88.5% are reported. Probe experiments revealed an apparent smoothing effect for gas transpiration through the anode on the flow regime in the effiuent plasma. In addition an apprecnkable fraction (1/2 to 3/4) of the anode fall voltage was found to be detached from the anode surface by the gas flow, effectively dividing the fall space into two separate zones. These two zones are separated by an "anode dark space," characterized by the absence of Iuminosity and essentially zero voltage gradient. Finally, a new geometry, involving a truncated conical shell for the porous anode and a conical gas conduction zone, is shown to generate a region of exceptionally high energy density and provide a higher power input capability. (auth)
- Research Organization:
- Vitro Labs., West Orange, N.J.
- DOE Contract Number:
- AF49(648)-477
- NSA Number:
- NSA-16-003528
- OSTI ID:
- 4816820
- Report Number(s):
- AFOSR-860; VL-2143-10-0
- Resource Relation:
- Other Information: Orig. Receipt Date: 31-DEC-62
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ANODES
ARGON
ATOMS
BEAMS
COATING
CROSS SECTIONS
DIFFUSION
EFFICIENCY
ELECTRIC ARCS
ELECTRODES
ELECTRONS
ENERGY
ENTHALPY
EROSION
EVAPORATION
FLUID FLOW
FLUIDS
GAS FLOW
GASES
GRAPHITE
HELIUM
IMPURITIES
INTERACTIONS
IONIZATION
MEASURED VALUES
PLASMA
POROSITY
SPUTTERING
STRESSES
SURFACES
TESTING
THERMODYNAMICS
TUNGSTEN
WEAR