Arc Operation Research Articles

Practical factors affecting cathode performance in ion sources of the Nier-Bernas type

To understand the influence of cathode design on the characteristics of the source arc, the intensity distribution of the arc, generated by a simple cathode, was observed under different conditions of source parameters, by scanning across the arc column with probes inside the ionization chamber. Two main phenomena were observed: 1. a) a deflection of the arc column in the beam direction due to the magnetic field of the cathode heating current, 2. b) a lateral asymmetry in the arc density due to the ohmic voltage drop on the cathode, especially in the pressure-limited mode of arc operation. As a consequence of these results, a short-legged helical cathode was designed which produces a dense symmetric plasma column with stable location relative to the emission slit. Thus, the two disturbing effects mentioned above were eliminated and, at the same time, the cathode efficiency was enhanced. Preliminary observations with the helical cathode at low hash conditions have shown that the source efficiency was increased by a factor of 1.8 for beam currents of 20 and 30 mA. Further, the life of the helical cathode is estimated to be at least twice that of a standard U-type cathode for the same output.

A high performance HV power supply and an ion source automatic control system

Two electronic systems which were developed for the MEIRA E.M.I. separator are described. 1. a) A 50 kV, 100 mA, hv power supply which achieves a long-term stability of ±15 ppm. Special methods were used to protect the sensitive solid state circuits, extensively used in the regulation system, from hv breakdown transients. 2. b) An automatic control system which regulates the ion source parameters in order to maintain the selected operating conditions without frequent intervention of the operator. The system has two alternative operational modes compatible with the pressure-limited or cathode-limited regimes of arc operation. Within the practical ranges of 1–15 A and 30–120 V, arc regulation varies between 0.5 and 2%.

Flowfield Characteristics and Perf ormance Limitations of Quasi-Steady Magnetoplasmadynamic Accelerators

Measurements of terminal voltage, exhaust velocity, current and potential distributions in a quasi-steady MPD arc operating over a range of currents from 3 to 25 kA countervene previous indications of basic limitations on MPD performance. Terminal voltage fluctuations, previously used as an indicator of a unique limiting value of the parameter current squared over mass flow, are shown to be related to cathode surface area rather than to interelectrode plasma phenomena. With improved electrodes and insulators, satisfactory arc operation at specific impulses somewhat beyond previously proposed limits has been demonstrated, and the significant thrust producing mechanisms in such arcs have been identified.

Control of the Output from a High-Intensity Xenon Arc Lamp

The emission spectrum of a xenon high-pressure arc lamp provides a reasonable approximation to the ultraviolet-visible region of terrestrial sunlight. This lamp has therefore been employed in a variety of laboratory testing equipment designed to predict the useful outdoor lifetime of plastics, textiles, dyes, asphalt, etc. Several methods of operation (ASTM and Atlas) of an Atlas 6000W xenon arc Weather-Ometer have been examined, and the necessity of monitoring intensities at both ultraviolet (at 340 nm) and visible (at 420 nm) wavelengths is illustrated. Lamp aging has been found to be the main factor in decreasing lamp intensity. Xenon lamp control at intensities similar to noon summer sunlight at 340 nm gives short lamp lifetimes of approximately 400 h. Operation of the arc at lower wattages (3500–5000W) has been found to provide a stable lamp intensity for much longer periods—approximately 2000 h.

超大型鋼塊の製造における保持炉の操業と鋼塊内偏析

超大型鋼塊の製造における保持炉の操業と鋼塊内偏析

Laser-Initiated Vacuum ARC for Heavy Ion Sources

Laser-triggered discharges have been considered for some time both for electron[1] and ion[2] sources. It has been recently shown that conventionally triggered metal-vapor vacuum arcs[3] can sustain even higher ion currents. In this paper, we point out that laser initiation permits arc operation in a high-current regime, and with geometry attractive for heavy ion sources. We present preliminary data on laser-initiated vacuum arcs [4] using carbon, copper, and tungsten cathode electrodes. Discharge current pulses of over 104 amperes with durations of up to 1 msec were employed to yield fully ionized source plasmas of liters volume with ion densities greater than 1013 cm-3. Electrode erosion rates were in the range of 10-4gm/C (the same order as in vacuum arcs) corresponding to ion injection currents in the range of 103 amperes.

High Charge State Heavy Ion Production from a PIG Source

The comparison of pulsed vs. dc arc operation for nitrogen and argon shows a shift in charge distribution toward the higher charge states for the pulsed case. Tests with various magnetic field shapes along the arc column show a significant increase in high charge state output for a uniform field compared to the case with a field low at the cathodes.

Dynamic equation and characteristics of a short arc moving in a transverse magnetic field

The dynamic behaviour of a d.c. arc in a metalplate quenching chamber is discussed. The arc, burning in air at 1 atm, is propelled laterally by an applied external magnetic field. The dynamic-arc equation describing the time development of the current and voltage is derived from the heat-transfer equation formulated semiempirically. The assumption of forced convection, based on a fraction of the mainstream flowing through the arc body, leads to characteristics consistent with experiment. The computed voltage characteristics under conditions of unstable arc operation predict, in agreement with experiment, an almost steady behaviour of arc voltage throughout the period when the currents falls to zero. These characteristics are favourable for application to d.c.-circuit interruption. Measurements of the current/voltage characteristics of the arcs have been performed for currents between 1 and 6 kA. The arc length has been varied from 1.5 to 17.4 mm, giving information on the electric field. Typical values were 70 V/cm for a wide range of initial currents at B = 2.0 T and for an arc length l of 3.2 mm. It was also shown how the ‘switching off’ time depends on the time constant of the external circuit, the magnetic field and the initial current.

Anode Heat Transfer in a DC Electric ARC with Superimposed Axial Flow

A DC electric arc is operated in argon at pressures between 100 and 760 mm Hg, axial flow velocities from 0 to 100 m/sec, and currents from 50 to 200 amps to assess the influence of these parameters on anode heat transfer using a double-anode configuration consisting of two plane, parallel anodes. Since the anode arc attachment size is appreciably smaller than the anode surface area in these experiments, a method is developed using an optical and/or floating potential probes for measuring the size of the near-anode arc column. The relative variation of two perpendicular dimensions of the near-anode arc column for variation in the arc operating parameters (pressure, flow velocity, current, anode separation) are measured. The results reveal that the cross section of the nearanode column is not circular and the average local heat fluxes show a strong dependence on the gas pressure.

Pressure and Current Effects on the Thermal Efficiency of an MPD Arc Used as a Plasma Source

Measurements of arc voltage and energy loss to the cooled electrodes of a magnetoplasmadynamic (MPD) arc, operating without an applied magnetic field, were made at chamber pressures of 26 to 950 torr, argon mass flow rates of 0.08 to 44 g/s and current of 200 to 2000 A. The resulting arc thermal efficiency varied from 22% at a chamber pressure of 26 torr to 88% at 950 torr. Thermal efficiency was only weakly dependent on arc current. It is concluded that the MPD arc operating without an applied magnetic field and at higher pressure than normally used in thruster applications is a reliable and efficient steady-state plasma source.

State of the art in microwave sensors for measuring non-electrical quantities†

Use of microwave sensors for measuring non-electrical quantities in laboratory, industrial and field environments is outlined along with salient, specifications imposed by diversification of modern technology. The basic principles of operation and typical applications of common microwave sensors arc presented and new concepts for possible future implementation are suggested.

Modulated Spectra of ac Arc Lamps

Light emanating from ac arcs operating on 60-Hz power exhibits a 120-Hz modulation of intensity. Although time-averaged spectra of such arcs are usually reported, the instantaneous light spectrum and its dependence on the oscillating plasma temperature is a more valuable source of spectroscopic information. An experimental technique is described for scanning the spectrum of an ac discharge at any fixed phase in the arc operating cycle. Spectra were recorded at phases corresponding to maximum and minimum light output for a pure Hg arc, a Hg–Na, Sc, Th metal-iodide arc, a Hg high-pressure Na arc, and a Hg–SnI2 arc. Intensity ratios Imax/Imin of spectral lines generally increased with increasing upper-state energy. Many of the dominant lines also exhibited sizable changes of line profile with variations of phase. In the Hg–Na, Sc, Th metal-iodide arc, the intensity variations of optically thin lines were used to obtain estimates of upper-state energies and relative gA values of some Th lines for which these quantities were previously unknown.

Efflux of Atoms From Cathode Spots of Low-Pressure Mercury Arc

A novel measuring technique was devised for the determination of the rate at which particles are ejected from the cathode spots of a low-pressure arc. The measurements were performed with anchored spots in a low-pressure steady-state mercury discharge. During arc operation, the total efflux of mercury from the cathode is composed of (i) the atoms which evaporate from the spot-free mercury surface and (ii) the particles which are ejected in connection with the cathode spots. The method applied permits a separation of these two contributions, thus yielding more accurate results than reported in the literature so far. From these measurements an electron -to-atom emission ratio of 208±12 was derived for the contribution from the cathode spots, corresponding to a ratio of emitted mass to emitted charge of (9.99±0.06)×10−6 g/C.

Modulated mercury arc excitation sources in luminescence spectroscopy

The operation of HBO series mercury arcs from an unsmoothed, full wave rectified 50 Hz supply is described. The light output which is a 100 Hz sine curve provides a convenient excitation source for the measurement of luminescence by the lock-in technique.

A Spectroscopic Source with Improved Analytical Properties and Remote Sampling Capability

A direct current capillary arc operating in argon at atmospheric pressure has been combined with a device which produces fine particles directly from the surface of a solid metal sample. The aerosol generator is a simple device in which the sample acts as the cathode of a dc arc discharge. Rapid movement of the cathode spot produces uniform sampling over a well-defined area. A flowing gas stream transports the aerosol particles to the capillary arc discharge. Reproducibility and analytical curves are shown for ten elements in low alloy, stainless, and tool steel samples, for total analytical times of 10 sec.

Partial Equilibrium in an Arc Spectrum

Time resolved spectra have been taken of a pulsed arc operating in 2 Torr of helium, C${\mathrm{O}}_{2}$, air, or argon. Wall confinement aided by close-fitting return conductors produce a 3.5-eV arc plasma in local thermodynamic equilibirum (LTE) during the first 10 \ensuremath{\mu}sec. The electron density is ${10}^{17}$ ${\mathrm{cm}}^{\ensuremath{-}3}$. Thereafter, the plasma cools and the silicon impurity rises. The arc temperature is limited by radiation losses. LTE is found among eight species, as expected at these values of ${N}_{e}$; but neutral helium is found to be about 1.5 eV cooler than the rest of the plasma. Such a result could cause large temperature errors in plasma diagnostics using He II/I line ratios.

Transition Probabilities for the Prominent Red Lines of Ne I

Relative transition probabilities of all 30 lines belonging to the prominent $3s\ensuremath{-}3p$ transition array of Ne I have been measured in emission with a wall-stabilized arc operating in an argonneon mixture at atmospheric pressure. The data have been normalized to an absolute scale provided by recent lifetime measurements of the $3p$ levels. Our results, as well as the data from other emission measurements, have been subjected to extensive comparisons and tests, including a check for fulfillment of the $J$-file sum rule. It is found that our data exhibit a much better consistency than any other set of individual values. On the basis of this analysis as well as our uncertainty estimates, we estimate that the accuracy of our individual transition probabilities for this transition array, except for a few weak lines, is of the order of 10% on an absolute basis.

A hot Cathode Magnetron Discharge for Hollow Cathode Arc Ignition

AbstractAn E X B discharge has been used to ignite a hollow cathode arc in a convenient and reliable manner.Voltage‐current characteristics of this auxiliary high pressure magnetron discharge in argon have been measured in the pressure and magnetic field ranges of our usual hollow cathode arc operation parameters. Two stable branches of the characteristics can be distinguished, resembling arc and abnormal glow discharges. In both regimes measurements of heat generation at the electrodes show that about 75% of the generator power is transferred to the cathode by the ion current. When cathode temperatures above 1300 K are reached, the main hollow cathode discharge can be started easily.

Transition Probabilities for Prominent Ar i Lines in the Near Infrared*

Relative transition probabilities of 81 infrared Ar i lines in the wavelength range from 9000–24 000 Å have been measured with a wall-stabilized arc operating in argon at atmospheric pressure. The large majority of the lines from the 4p–5s and 4p–3d transition arrays has been observed and the measurements are consistent with the J-file-sum rule. The data have been normalized to an absolute scale by utilizing the results of other recent arc and lifetime experiments.

Preliminary investigation of arc stabilization with a forced vortex

The stabilization of an arc using a forced vortex was studied experimentally. Measurements on the arc characteristics were made as a function of the stabilizing flow parameters. It was found that the behaviour of the arc may be understood in terms of measurements made on the stabilizing flow without the arc. It is concluded that stable arc operation may be achieved using forced vortex stabilization, but that in open-ended systems end effects on the vortex are likely to cause severe convective losses in the arc.