Hydrogen Arc Research Articles

Plasma application in the steel industry in Japan

Abstract

Expansion of hydrogen arcs driven by oscillating currents

Calculations of the arc channel radius using the arc current as the independent variable are presented and discussed. Previously reported experimental results for the expansion of approximately 300-A to approximately 3000-A discharges in 460-torr hydrogen are compared with the theoretical radius calculations presented. Errors introduced in the calculated channel radius are investigated by first assuming the channel conductivity to vary according to the Spitzer conductivity, and then assuming the channel conductivity to be constant and comparing the numerical results of these two methods with the experimentally measured values of channel radius. It is shown that according to Hugoniot adiabatics, the apparent relationship between the arc channel pressure and the directed energy of the shock front is given by the pressure-velocity relationship of the gas leaving the shock front instead of the more commonly used pressure-velocity relationship for the gas entering the shock front. >

Radiometric calibrations of portable sources in the vacuum ultraviolet

The radiometric calibration program carried out by the vacuum ultraviolet radiometry group in the Atomic and Plasma Radiation Division of the National Bureau of Standards is presented in brief. Descriptions are given of the primary standards, which are the hydrogen arc and the blackbody line arc, and the secondary standards, which are the argon mini- and maxi-arcs and the deuterium arc lamp. The calibration methods involving both spectral radiance and irradiance are then discussed along with their uncertainties. Finally, the calibration services are delineated in an appendix.

Stabilization of a high-pressure arc in hydrogen

The authors describe hydrogen plasma sources with densities of approx. 10/sup 18/ cm/sup -3/ for investigating spectral optical characteristics. The plasma is created using a gas vortex-stabilized arc at high atmospheric pressures. A system is described that includes an electrical discharge high-pressure chamber and an arc feed source, and the arc characteristics for a large current i = 2-8 A at a pressure of p = (1-30) x 10/sup 5/ Pa and the hydrogen plasma parameters are given.

Arc discharge conditioning test on the oak ridge 25URC accelerator

A hydrogen arc discharge has been run in the top five units (fifteen 20 cm tube sections) of the ORNL tandem accelerator to test the effectiveness of this method of cleaning the high voltage electrodes. The discharge was maintained in both the high- and low-energy tubes for a period of six hours. The arc current in each tube was 4.0 A and the hydrogen pressure was nominally 100 mTorr. The arc discharge does not appear to have significantly affected the operating voltage of the top five units of the accelerator. However, the voltage conditioning behavior of the tested units is markedly different.

Hydrogen arc discharge cleaning of accelerator tubes

Accelerator tubes manufactured by NEC were cleaned by the hydrogen arc discharge method and tested on the NEC 3 MV test accelerator. We will discuss the results of this testing program. Generally, we confirm the favorable experience previously obtained by Korschinek et al. [1]. The familiar microdischarges exhibited by normal tubes are largely eliminated in arc discharge cleaned tubes. Thus, the arc discharge process has the same observable effect as voltage conditioning. This result suggests that the hydrogen discharge is effective in removing carbon and hydrocarbons from the surface of the accelerator tube.

Hydrogen arc discharge in magnetic multipole plasma generator with La2O3 doped Mo bulk cathodes.

Bulk cathodes with a large emission area are proposed for use in a magnetic multipole ion source of a neutral beam injector. Compared to designs with tungsten (W) filaments, this design simplifies the thermionic cathode replacement procedure. The cathode was tested by causing a hydrogen arc discharge in a rectangular shaped plasma generator (18 X 39 X 20 cm3). The generator had two La2O3 doped Mo (LM) cathodes of disk shape with 10 cm diameter, which were operated in the emission limited region to find the electron emission current density of LM as a function of its temperature. An arc efficiency of the generator estimated from the present data was 1/3 of that typically achieved in ion sources with the W filaments. In the experiment, a few improvements were also made for flattening the distributions of ion saturation current density near a plasma grid of generator and of the cathode temperature.

Contribution of excited atoms to the index of refraction of a plasma

The influence of excited atoms on the plasma refractive index is calculated for typical hydrogen arc plasma conditions. It is shown that the excited atoms contribution is, in many cases of interest, dominant in comparison with that of the ground state atoms, which is usually the only one taken into account. The effect on the total refractive index, including electrons and ions, strongly depends on the physical conditions and on the probe wavelength. At short wavelength and high pressures, the excited atoms can have a considerable influence.

The development and laboratory testing of low [formula omitted] refractory coatings for fusion reactor limiters

A materials development program for low Z ( Z < 24) coated tokamak limiters is described. A variety of refractory coatings applied by chemical vapor deposition, plasma spraying, and chemical conversion to graphite and copper substrates have been evaluated. The results of laboratory testing for low energy hydrogen ion erosion, arc erosion, and thermal fatigue by pulsed electron beam heating are reported. The 250-V hydrogen ion erosion data, analysed in terms of the effect on plasma radiation losses from resultant contaminants, indicates near equivalence of the very low Z (B and B 4C, for example) and the moderate Z (e.g. TiB 2) coatings. Thermal fatigue testing has identified several candidate materials which can survive 1000, 3 kJ/cm 2 pulses of electron beam heating. The development of prototype limiters of TiB 2, TiC, and B coated graphite for testing in the ORNL ISX-B tokamak is described.

Measurement of hydrogen transport functions by means of precision arc experiments

Motivated by discrepancies of measured and calculated hydrogen transport coefficients, pure hydrogen arc plasmas have been investigated again in the wide temperature range from 5000 to 27,000 K. The plasmas are generated in cascaded arc chambers with 2, 3, and 5 mm channel diam. Temperature diagnostics are performed by side-on spectroscopy in the Balmer region, using an automatic data acquisition system and computer processing. The immediate results are in excellent agreement with precision measurements by other authors. The electricalE—I characteristics are recorded using cascade plates as probes. These characteristics and the temperature measurements together yield the transport coefficients as a function ofT. The present results for the electrical conductivity are in very good agreement with theory. As for the heat conductivity, some improvements could be achieved in the relative dependence, but the experimental values are still above the theoretical ones. In the region of low ionization this discrepancy is explained by deviations from LTE in the arc plasma. Here, a rigid PLTE analysis is presented.

Interferometric determination of electron density in a high pressure hydrogen arc. I. Calculation of refraction index

The refraction index of a hydrogen plasma in LTE was calculated as a function of the wavelength of observation, temperature and pressure, taking into account bound-bound and bound-free transitions of the neutral atom. According to the author's calculations, the influence of excited states at higher temperatures is smaller than indicated by Baum and co-workers (1975) for argon. Using the calculations presented here, the interferometric investigation of a high pressure hydrogen arc should allow the determination of the electron density with an accuracy of the order of 1%.

VUV radiometry below 100 nm: the high-power hydrogen arc as a standard source of continuum radiation between 53 and 92 nm. (USA)

VUV radiometry below 100 nm: the high-power hydrogen arc as a standard source of continuum radiation between 53 and 92 nm. (USA)

Measurement of atom and molecule number densities in hydrogen arcs by means of VUV spectroscopy

The number density of ground state atoms in the 2mm hydrogen arc (T≈20000 K) and the number density of molecules in the 5 mm hydrogen arc (T≈12000 K) have been measured by means of vuv spectroscopy. These species' are particularly likely to deviate from the equilibrium population and may therefore falsify the hydrogen transport coefficients measured in arc experiments. In the present investigation the optically thick line wings of Ly-α and the H2 molecular spectrum around 1600 A have been analyzed. The results demonstrate that the former assumptions of LTE and PLTE, respectively, are completely justified on and near the arc axis. However, in the outer zones of these arcs a considerable overpopulation of the molecules must be expected as a consequence of radial diffusion.

VUV radiometry below 100 nm: the high-power hydrogen arc as a standard source of continuum radiation between 53 nm and 92 nm

A stationary hydrogen arc discharge may be used as a standard source of radiation in the VUV below 100 nm. The Lyman resonance continuum is used, the cross sections of which are theoretically well known. The method described is based on optically thin radiation, requiring high plasma temperatures and an effective helium gas separation in the arc. The investigations demonstrate that, in appropriate experimental conditions, the plasma is indeed transparent down to the onset of the He ground-state absorption. Above that, the VUV spectral radiance can be predicted within less than 15% uncertainty from conventional plasma diagnostics. For a first application, the He continuum has been measured between 65 nm and 92 nm. The consistency of these results with theoretical calculations confirms the validity of the concept presented.

Co2 Laser Thomson Scattering from a Pulsed Hydrogen Arc

Thermal level Thomson scattering of a pulsed 70 MW C02 laser from a hydrogen arc plasma (ηe = 1015 - 1016 cm-3, Te ≈ Ti ≈ 5 eV) has been observed using video detection. Spectral resolution of the ion feature has been achieved thus demonstrating the feasibility of this method for determining ion temperatures in a wide variety of laboratory and fusion plasmas.

Highly regulated power supply for hydrogen or deuterium arc lamps used in ultraviolet spectrometry

Highly regulated power supply for hydrogen or deuterium arc lamps used in ultraviolet spectrometry

High-resolution emission spectra of MgH and MgD in the 600 to 850 nm wavelength region

The emission spectra from a magnesium dc arc in hydrogen or deuterium have been photographed at high resolution from 600 to 850 nm. Thirteen new bands of MgH and 18 of MgD in the B′2Σ+–X2Σ+ system have been identified and complete rotational analyses have been performed. Term values have been obtained for all bound ground state rotational levels of MgH for ν = 4–9 and MgD for ν = 6–13 and limiting curves of dissociation have been used to determine the dissociation energy of MgH. The experimental value, D00″(MgH) = 1.27 ± 0.03 eV is in excellent agreement with theory. The ground state RKR potential curve and Franck–Condon factors for the B′–X system are reported. Data on the isotopic molecules 25MgH, 26MgH, 25MgD, and 26MgD have also been obtained.

Plasma scattering experiments with a periodic Nd:YAG laser at 1.06μm and A Si-avalanche detector

First spectra obtained by scattering from a hydrogen arc plasma using a periodically pulsed cw-pumped Nd:YAG laser are presented. Because of its high quantum efficiency at 1.06 μm a large-area Si-avalanche diode followed by a capacitance-compensating amplifier is used as detector.

Forward scattering at 10.6 μ using light mixing to measure the ion temperature in a hydrogen arc plasma

Light mixing techniques were used to scatter at small forward angles with a hybrid CO 2-laser from a thermal plasma. The ion temperature and the enhancement of ion-acoustic resonances by ion-ion collisions were obtained from the scattered spectrum recorded in one shot.

Spectrally resolved measurements of collective scattering from thermal plasma fluctuations using a CW-CO2 laser

CO 2 laser scattering is applied to a magnetically stabilized hydrogen arc. The ion feature is resolved by means of a Fabry-Perot interferometer. The radiation power in the resolved spectral interval is typically 10 -12 W. The technique of measurement is described and results are given.