Discharge Section Research Articles

Compact high-efficiency carbon monoxide laser at 1 kW

A fast-axial-flow, cryogenically cooled, carbon monoxide laser has been operated at 28% efficiency producing a continuous wave output power of 1.08 kW. The laser uses two cylindrical discharge sections, each 225 mm in length, which are excited by transverse radio-frequency fields at 27 MHz in a linear stable optical resonator. A specific power output of 2.41 kW m−1 and an extraction power density of 9.41 W cm−3 have been attained by optimization of the transverse and longitudinal electrode configuration.

Analysis of plasma critical flow in a combined discharge capillary ablative pipe system

The system of a high pressure discharge capillary connected to an ablative pipe is shown here to be an efficient and convenient plasma source. The characteristics of the source (mass and energy fluxes) are determined by the joule energy supplied to the discharge section as well as by the wall material and geometrical parameters of the discharge capillary and the ablative pipe. For a given wall material and fixed geometrical characteristics of the capillary, a large range of exit plasma parameters values can be obtained by varying either the length of the ablative pipe or the electrical current carried by the discharge. Useful information for the design of the proposed plasma source is given. It is based on consistent numerical solution of the quasi one-dimensional continuity momentum and energy equations with non-ideal state equation and non-uniform ionization degree for the combined discharge unit and ablative pipe.

Planar waveguide, 1 kW cw, carbon dioxide laser excited by a single transverse rf discharge

A transverse radio frequency discharge excited, carbon dioxide slab laser has been operated cw with a hybrid waveguide / confocal unstable resonator to produce an output power of 1.06 kW at 12% efficiency. The active volume of 770×95×2 mm3 consists of a single discharge section with one cable feed.

Double XeCl laser with lateral UV preionization

We present a very compact and very reliable laser system formed of two discharge sections both with lateral UV preionization. The discharge electrodes are contained in a single vessel and form an oscillator-amplifier system. A single spark gap switches on both circuits. By applying a generalized self-filtering unstable resonator to the oscillator and injecting the laser beam into the single pass amplifier, an output beam of 105 mJ, with a brightness of 5.5×1013 W cm−2Sr−1 has been obtained. Moreover, by applying a pulse-forming network in one discharging circuit, the duration of the discharge breakdown has been increased and output laser pulses of 40 ns FWHM, and 80 ns base width duration (at 10% points) and of energy 100 mJ are obtained.

High homogeneity gain distribution in a cross flow AC excited CO/sub 2/ laser

Gain measurements at 10.6 mu m, performed on an alternating-current-excited CO/sub 2/ laser discharge, are presented. The discharge occurred between individually ballasted p-i-n electrodes. The values of the ballast capacitors were arranged in order to obtain a stable discharge as well as an almost uniform gain distribution through all of the discharge section. The results show that an appropriate distribution of the specific power density into the active medium volume can produce a stable discharge as well as good uniformity of the small-signal gain in the discharge cross section. The downstream small-signal gain, however, decreases slightly, despite a higher excitation rate, due to a higher temperature and an increased thermal population of the lower laser level. The rather high values of the small signal gain, even in the high excitation region, offer promise of good beam quality and high efficiency. >

A104 エキシマレーザの放電部衝撃波の可視化

Experimental study on shock waves in a high repitation rate excimer laser has been carried out. In a high repitation rate excimer laser. shock waves in subsonic loop are induced by the active medium excitation by means of pulse discharge. Shock waves in He gas by a pulse discharge are visualized by schlieren method using a scale discharge section model, CCD camera, stroboscope, and digital image memory which used to take photographer. Shock waves from anode surface, cathode surface. discharge region, and pin sparks for preionization are observed. Shock waves reflect at anode and cathode surfaces alternately for several times. Shock waves from dischrage region travel through channel.

Life test of a sealed‐off CO2laser with SnO2coated cathodes

Abstract A sealed‐off CO2 laser with an intracavity structure and dual discharge sections has been built to test its lifetime under different treatments of cathodes. The output characteristics of this laser system, under different discharge conditions, have also been investigated. Several techniques, such as the sealing of optical components on a laser tube, the coating of tin‐oxide (SnO2) on stainless steel cathodes, and the making of a discharge tube of three layers, are established to construct this tube. By using SnO2 coated SUS 304 cathodes and a gas mixture of CO2:N2:He:Xe:H2= 15:14:65:4:2 in this laser tube, an operational lifetime in excess of 1,800 hours and an output power up to 52W/m are obtained.

Development, Installation, and Operating Results of a Steam Injection System (STIG™) in a General Electric LM5000 Gas Generator

This paper describes the first full-scale field test of a steam injection system for a natural-gas-fired G.E. LM5000 gas generator for the purpose of: (a) decreased exhaust emissions, (b) increased power output, and (c) improved efficiency. It discusses the steam supply system, engine features, test results, and plant economics for steam injection into the combustor and compressor discharge sections of the LM5000 at rates up to 65,000 lb/hr (29,510 kg/hr).

Longitudinal mode selection in hybrid CO2 laser for subthreshold operation of cw discharge section

The relative mode intensities in the hybrid CO2 laser output are investigated for subthreshold operation of cw gain section. The rate equation model developed for the purpose provides estimates in very satisfactory agreement with experimental results. The model also predicts the existence of an optimum pressure and length for the cw discharge section and shows that very good longitudinal mode discrimination is possible even when cw discharge section gain is only a tenth of that required for oscillation.

大出力ＣＯ２レーザ放電部流れの可視化

In a high power CO 2 laser, laser gas is electrically excited by glow discharge and the quantum energy is utilized as laser beam. The gas in the discharge area is cooled by convection. However, the glow discharge phenomena are strongly related to the laser gas flow characteristics within the discharge section. Consequently, the power of CO 2 laser device is influenced by the gas flow pattern. In order to understand the flow characteristics within the discharge section, a scale model adopting water flow is used here. A beam scan type laser light sheet and fine Al powder are adopted as the light source and particle tracer respectively. The results are as follows. (1) It is possible to take photograph which clarify the velocity of the particle with a beam scan type LLS. (2) It is possible to visualize the flow pattern within the discharge section in case without discharge.

Theoretical investigation of the traveling wave excitation in a TE N2 laser

Theoretical investigation of traveling wave excitation using the property of photon addition has been carried out in a 50-cm-long TE N2 laser tube with ten separated discharge sections. The laser power outputs under traveling wave excitation have been calculated numerically with varying gas pressures from 30 to 85 Torr and applied voltages from 14 to 21 kV, and compared with those of simultaneous excitation. Theoretical results show that the laser peak power increases with increasing applied voltage, and has a maximum value at gas pressure P≂60 Torr. The laser pulse width is narrowed and the laser power is doubled under the traveling wave excitation, compared with simultaneous excitation. Experimental confirmation also has been conducted. Experimentally observed gas presssure dependence of output power agrees qualitatively well with theoretical results. The maximum discrepancy in the absolute values between theory and experiment is approximately 50%.

H− ion density measurement in a tandem multicusp discharge

The H− ion density is measured by photodetachment in the source and target sections of a tandem multicusp discharge containing a ‘‘magnetic filter.’’ The results confirm previous observations based on the measurement of extracted currents, that a magnetic filter, together with a small positive bias on the plasma grid, produce a significant increase in the H− ion density and a reduction in the electron density in the target section.

Winter-Regime Thermal Response of Heated Streams

The increase in water temperature in natural streams due to waste heat disposal from thermal power plants leads to extensive ice-free reaches during winter periods. It is shown that the surface heat exchange between water and the atmosphere can be expressed, for most practical purposes, as a linear function of the water temperature. Using this approximation, a closed-form solution of the one-dimensional unsteady convection-diffusion equation is developed to predict temperature distributions in streams and the lengths of ice-free reaches downstream from the thermal discharge sections.

Analysis of Thermal Induction Plasmas Dominated by Radial Conduction Losses

The energy balance equation is applied to induction plasmas in thermal equilibrium. Approximate, iteration-type, solutions are obtained for cases where heat losses by radiation, axial conduction, and convection can be disregarded. It is assumed that the electric conductivity rises in proportion to the heat conduction potential and that the radial distribution of the induced electric field can be represented by a power law. Under these conditions, the equation can be transformed into Bessel's equation and solved for the heat conduction potential. With a uniform field, the solution reduces to that for a dc arc. The condition of vanishing temperature at the enclosing wall establishes an eigenvalue for the induced electric field at the circumference. Absolute temperature distributions can be calculated as a function of gas properties and applied conditions. It is shown that the latter are given by the time rate of change of primary magnetic flux through the discharge section. The method is applied to argon plasmas at atmospheric pressure. For these plasmas, optimum conversion of magnetic energy into heat should occur at a primary flux rate of 48 V. This value is lowered by the secondary current in the plasma to an actual burning voltage of 32 V. Both values are independent of driving frequency and plasma radius. Skin depth ratio and conversion efficiency at the optimum point agree closely with the values known from induction heating of metals. Experimental data indicate that the discharge has a tendency to operate near this point. Comparison of temperature distributions obtained by this method with exact computer solutions show that the axis temperature is over-estimated by about 15%, but the general shape of the profile is well approximated.

An analysis of spontaneous impulse activity of units in the striate cortex of unrestrained cats.

1. Recordings were made from sixty-five cells in the visual cortex of unanaesthetized, dark-adapted cats and transferred automatically to computer input paper tape.2. The activity of each cell was measured as a function of time (the running mean). The unit of time used was inversely proportional to the mean firing rate, in order to give comparable results for different cells.3. For sixty-nine sections of discharge from fifty-two cells, the length of time recorded was sufficient to test for the long-term stability of the running mean. In twenty-six sections, various kinds of trend and long-term irregularity were found.4. The interspike interval histogram was computed for the forty-one sections (from thirty-one cells) in which there were more than 2000 discharges. Only eight histograms approximated closely to the exponential form. A test was also made of the distribution of the longer intervals alone and in twenty-five sections they did not deviate significantly from the exponential form.5. There was no significant correlation between the behaviour of the longer interspike intervals and the long-term stability or otherwise of the running mean.

Magnetic and Ionic Structure of An Electromagnetically Produced Shock

The structure of the gas behind a strong shock generated by an electromagnetic shock tube has been investigated using magnetic pickup loops, an asymmetrical ion probe, an image-converter camera, and a piezoelectric pressure probe. The shock tube consists of a 15-cm-i.d. Pyrex tube of adjustable length connected to a conical discharge section. Four 7.5-μF capacitors were charged to 12 kV and fired into the tube at a pressure of 30 μHg. The azimuthal magnetic field generated by the electrical discharge is ``frozen'' into the gas behind the shock because of the high magnetic Reynolds number (Rm∼2). Its transverse distribution is shown to be consistent with a toroidal current hypothesis. The peak magnetic field strength measured was 5000 G at 10 cm from the discharge section and 20 G at 40 cm. The peak ion concentration was observed to be 8 × 1014 cm−3 at 50 cm and 3×1014 cm−3 at 190 cm from the discharge section. A precursor ion density three orders of magnitude below the shock maximum is also observed 6 cm in front of the shock at a position 70 cm from the discharge section.

The effect of radiative losses on the attenuation of electromagnetically driven shock waves

The approximate, one dimensional blast wave theory of Harris is modified to take into consideration the effect of radiation losses from plasmas behind strong shock waves produced in electromagnetic shock tubes. The semi-empirical radiation theory of Kivel is used in evaluating the resulting modified shock expansion equation. The influence of various shock tube operating parameters such as energy input and ambient density on the shock wave velocity attenuation via radiation is examined. The predictions suggested by the proposed theory are confirmed by means of experimental data obtained in a conical discharge section electro-magnetic shock tube. It is seen that the most severe effect due to radiative losses occurs near the gaseous discharge. Radiation losses are found to be unimportant at distances downstream of the electrical discharge when the gas density is low.

Theory of Electron Driven Shock Waves

Previous calculations of the time required for ion heating in the discharge or driver section of an electrical shock tube yielded values much greater than that in which formation and acceleration of the first luminous front is observed to occur. The model of an electron driven shock presented here shows that the relation between shock velocity V and electron temperature Te, which has been established experimentally over a wide range of parameters, remains valid even though the conventional picture of a shock driven by hot ions must be abandoned. Thermal expansion of the hot electron gas accelerates the cold ions, resulting in a shock front or moving electrostatic double layer. Assuming conditions behind the shock to be coupled to those in the discharge region through a simple rarefaction wave, it is found that MV2/kTe is a universal function of W/MV2, where W is the effective ionization potential. This is shown to be in excellent agreement with a wide variety of experimental data.

XI.Negative sections of the cold-cathode glow discharge in helium

Abstract An outline is presented of the results of the first part of an investigation of a cold-cathode low-voltage glow discharge in He at about 1 mm. pressure made chiefly by collector methods supplemented optically. Data so obtained are less exact than with discharge forms passing heavier currents, but represent an advance on older methods in enabling outstanding problems to be defined more precisely even when not yet solved. Neglecting the negative glow and Faraday dark-space plasmas, analysis of which is being continued, attention is particularly directly to (1) the collector evidence for emission of fast electrons from the cathode (this illustrates the difficulty of deciding between macroscopic and atomic effects in a discharge); (2) the uncertainty as to the electrical conditions in the gas close to the cathode in the primary dark-space and cathode glow; (3) the fact that analysis of cathode dark-space collector characteristics would possibly yield data for a region of space-charge similar to data ...