Search

The temporal evolution of parallel and perpendicular ion velocity distribution functions (ivdf ) in a pulsed, helicon-generated, expanding, argon plasma is presented. The ivdf’s temporal evolution during the pulse was determined with time resolved (1 ms resolution), laser induced fluorescence. The parallel ivdf measurements indicate that, in the expansion region of the plasma and for certain operational parameters, two ion populations exist: a population moving at supersonic speeds (1.1 Mach) resulting from acceleration in an electric double layer (EDL) and a slow moving population (0.7 Mach) generated by local ionization. After 100 ms, although present, the EDL is not fully developed and has not reached a steady-state. Measurements of the perpendicular ivdf indicate constant radial expansion, with ion speeds of ≈ 400 ms −1 , in the expansion region.

Amorphous fluorocarbon polymer films (a-C:F) have been grown by plasma enhanced chemical vapor deposition from a new precursor, namely perfluoro-octane (C8F18) vapor. The dielectric and insulating properties of the films have been assessed by means of capacitance–voltage and current–voltage characteristics, breakdown voltage measurements, scanning electron microscopy, and ellipsometric analyses. In the investigated frequency range, 120 Hz–1 MHz, the films have a low dielectric constant (≈2.4) and a low dielectric loss (⩽3×10−2). The electrical conduction mechanism is ohmic in the weak electric field regime, with a bulk resistivity of 4×1015 Ω cm, and a trap modulated space charge limited conduction in the strong electric field regime. For a film thickness between 1 and 12 μm, the dielectric strength varies with film thickness according to EB∼h−0.53. For a film thickness of 1 μm the film dielectric strength was 2.7 MV/cm while for 12 μm it decreased to 0.9 MV/cm. Measurements of the breakdown voltage in nitrogen gas in the low pressure regime between a-C:F coated cathode and copper anode showed an enhancement of the breakdown voltage by a factor of 2.5 with respect to the case of copper–copper electrodes.

The parallel ion flow in a high-density helicon source plasma expanding into a region of weaker magnetic field is measured as a function of neutral pressure, magnetic field strength, rf power and rf driving frequency. The dependence of the parallel ion flow and parallel ion temperature, measured by laser induced fluorescence, on the plasma density, electron temperature and floating potential, measured with an rf-compensated Langmuir probe, is also examined. At the end of the helicon plasma source, the ion velocity space distribution changes from a single subsonically drifting Maxwellian population to a supersonic ion beam (≈15 eV) plus a cold, subsonically drifting background ion population. At 38 cm into the expansion region beyond the end of the plasma source, the supersonic ion beam is not observed.

The method of obtaining amorphous fluorocarbon polymer (a-C:F) films by plasma enhanced chemical vapor deposition in a capacitively coupled, 13.56 MHz reactor, from a new monomer, namely perfluoro-octane (C8F18) vapor, is presented. For monomer pressure ranging from 0.2 to 1 Torr and input power density from 0.15 to 0.85 W/cm3, the maximum deposition rate reached 300 nm/min, while 10% monomer dilution with argon led to a deposition rate of 200 nm/min. The film surface and bulk morphologies, chemical and structural compositions were investigated using scanning electron microscopy, x-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. It was revealed that the films have a dense and compact structure. The fluorine to carbon ratio (F/C) of the films was between 1.57 and 1.75, and the degree of cross-linking was between 55% and 58%. The relative amount of perfluoroalkyl (CF2) groups in the films was 29%. The FTIR spectra showed absorption bands corresponding to the different vibrationa...

The titanium vapor plasma generated by a thermionic vacuum arc was spectroscopically investigated. The electronic temperature was obtained using the method of spectral lines intensity ratios. Three sets of spectral lines have been used, each set having the same energetic lower level namely: fundamental, 170.132 cm−1 and 386.874 cm−1 respectively. For an arc current Iarc=1 A and an arc voltage Uarc=670 V, an average electronic temperature of plasma Te=(2860±587) K was obtained. Moreover, spectroscopic investigations of the interelectrodic plasma show that the discharge is totally sustained by evaporated anode material.

An internal scanning probe capable of spatially resolved measurements throughout a horizontal (r,z) cross section of the expansion region between a helicon plasma source and an expansion chamber is described. For complete diagnosis of the expanding magnetoplasma, the probe is designed to simultaneously measure the electron temperature, the electron density, the plasma potential, the magnetic fluctuation spectrum in three dimensions, and the two-dimensional ion velocity distribution function (through a tomographic inversion method). The probe design and operational characteristics as well as representative measurements are presented.

The breakdown voltage (Vs) of nitrogen gas between aluminum (Al) sphere-sphere electrodes, which were coated with thin fluorocarbon polymer (FCP) films in a C8F18 vapor RF plasma, at a gas pressure (p) times gap length (d) between 0.6 Torrcm and 20 Torrcm was studied. The Vs in this electrode system was enhanced threefold at pd=1 Torrcm and twofold at 20 Torrcm compared with Vs between the Al electrodes. The Vs enhancement mechanism was examined with respect to film insulation properties and secondary-electron emission from FCP film.

High levels of ion production (~1013 cm-3 plasma density) by helicon plasma sources and supersonic ion exit speeds (between 8 and 15 km/s) have generated considerable interest in the possibility of a helicon source electric double layer thruster. Pulsing the helicon discharge might solve important thruster issues such as plasma detachment, turbulent cross-field diffusion, and antenna heating. Therefore, for thruster applications, an understanding of the temporal evolution of the ion velocity distribution function (ivdf) downstream of an expanding helicon source is needed to choose the optimal operational parameters (duty cycle, pulse length, input power, driving frequency, etc.) to obtain the desired specific impulse along the expansion direction while minimizing the ion energy in the perpendicular direction. We report on laser induced fluorescence measurements of the temporal evolution of the argon-ion velocity distribution function in the expansion region of a pulsed helicon plasma. The measurements were taken in the expansion region, 19 cm downstream of the helicon source. Temporal resolution of 1 ms allowed investigations of different plasma pulse lengths and duty cycles. It was revealed that below a threshold pressure of ~2 mTorr, the ivdfs show a bimodal structure comprised of a slow ion population that appears simultaneously with the inception of the rf pulse and a fast ion population (~7-8 km/s axial flow speed) that appears few tens of ms later.

Summary form only given. There is a need for moderate energy fluxes of metastable nitrogen molecules in the growth of thin films of GaN, a wide band gap semiconductor. A laser induced fluorescence technique (LIF) has been developed for the measurement of N2 (A3 u + S , v=4) relative population density and flow speed in a steady state, helicon discharge at a pressure of 20 mtorr. This particular transition is part of the first positive system of N2 (3 3 A B u g + S reg P ). A coherent 899 tunable ring dye laser is scanned in the range 596.5-597.0 nm to pump the P12(9) rotational line of the (8,4) band of the A + Su 3 state to J=8 of the B3 g P state which then fluoresces by emitting a photon at 645.96 nm (the Q11(8) line of the (8,5) band). A Stanford Research SR830 lock-in amplifier and a 1 nm band pass interference filter in conjunction with optical chopping of the laser are used to distinguish fluorescent emission from spontaneously emitted background light at the same wavelength. A small portion of the laser light is passed through an iodine cell for a consistent zero-velocity reference measurement. With a calibration obtained by previous optical emission spectroscopy measurements and a model to account for reaction pathways in generation and destruction of 3 u A + S , it is possible to infer the density of this state. From the full width at half maximum (FWHM) of the Doppler broadened fluorescence line, the temperature of N2 molecules can be also inferred and compared with values of the gas temperature obtained by rotational analysis of ro-vibrational emission spectra of 1-0 an d 2-0 bands

Summary form only given. We report preliminary results on the development of a helicon plasma source with variable activated nitrogen composition for plasma assisted molecular beam epitaxy of III/V-nitrides. The main idea is to alter the population of specific reactive nitrogen species in a helicon plasma source by modifying the electron energy distribution function through the resonant wave-particle interaction arising from electrons traveling at same velocity as the phase velocity of the helicon wave. The high plasma density and high ion exit flow speed (ne = 1013 cm-3 and v i = 8,000 m/s for argon) should yield significantly higher fluxes at the substrate surface and consequently an improved deposition rate over existing MBE plasma sources. Epilayer quality could also be improved by lowering kinetic energy of reactive species. The active nitrogen source is a steady state, high density, helicon plasma source CHEWIE (Compact HElicon Waves and Instabilities Experiment). The helicon vacuum chamber is a 12 cm long, Pyrex tube, 6 cm in diameter, connected to a stainless steel diffusion chamber, 30 cm long, 15 cm in diameter. Three magnetic field coils surround the source and are capable of generating an axial magnetic field up to 1200 G in the source and about 100 G at the end of the expansion chamber. A 7 cm long, water cooled, Boswell saddle type antenna couples the RF energy into the plasma. RF power of up to 600 W over a frequency range of 3-28 MHz is used to create the steady state plasma in the source which expands away into a region of decreasing magnetic field. Optical emission spectroscopy investigations in the plasma source show that under certain working conditions, the N2 first positive system (B3Pi g rarr A3 Sigmau +) are the dominant transitions in nitrogen, helicon-generated plasma. From band head intensities a Boltzmann relative vibrational population distribution is obtained. From the fit of the Deltav=+1 (at 891.24 nm), Deltav=+2 (at 891.24 nm) and Deltav=+3 (at 687.50 nm) bands, a gas temperature of ~350 K for an input power of 300 W, a magnetic field of 800 G and N2 gas pressure of 20 mtorr is inferred

Summary form only given. Using the compact helicon waves and instabilities experiment (CHEWIE) device we present a method of calculation of nitrogen dissociation degree in a helicon generated plasma by microwave interferometry and Langmuir probe measurements. The dependencies of nitrogen dissociation degree on external source parameters: input power, gas pressure and magnetic field strength are also presented. The nitrogen plasma is generated in CHEWIE helicon plasma source, which consists of a 12 cm long, 6 cm diameter Pyrex tube concentrically connected to a stainless steel expansion chamber, 30 cm long, 15 cm in diameter. The helicon antenna is a water cooled, 7 cm long Boswell saddle antenna that can handle up to 600 W of RF power over the frequency range 3 to 28 MHz. Helicon waves are generated with the help of an external magnetic field (up to 1200 G) from three electromagnets that surround the Pyrex tube. The radially averaged electron plasma density is determined by the phase shift of a 94 GHz microwave signal passing through the bulk plasma with respect to "plasma off" signal. The magnitude of total phase shift is a fraction of the wavelength. Instead of counting fringes we use the phase lock-loop functionality of the millimeter wave source to actively change the frequency during the "plasma on" time to match the interference signal of the "plasma off" time. With sufficient bandwidth in the feedback circuit this allows us to monitor any afterglow effects in the plasma in pulsed operating mode. Complementary measurements of the plasma density are accomplished with a RF compensated, cylindrical Langmuir probe. The probe consists of 0.5-mm-diam graphite rod shielded by an alumina tube. The effective collecting length of the tip is 3 mm. A series of RF filters are used to suppress interference from the helicon source in the 3-28 MHz range. Magnetic field effects on the probe characteristic are accounted by probe calibration through comparisons with microwave measurements in argon plasma

Summary form only given. Plasma assisted molecular beam epitaxy (PAMBE) of III/V-group nitrides is a potential alternative to metal-organic chemical vapor deposition (MOCVD) for fabrication of high quality wide band gap semiconductor devices. The main advantage of PAMBE over MOCVD is the use of solid gallium evaporated in a Knudsen cell in conjunction with a pure nitrogen plasma source to generate the reactive nitrogen species. Consequently, elevated substrate temperatures are not needed and low temperature nitridation dramatically improves the optical and structural qualities of the GaN epitaxial layers. A helicon discharge could be an attractive alternative plasma source for reactive nitrogen species creation since it allows control of the population of specific reactive N2 species by modifying the electron energy distribution function through the resonant wave-particle interaction arising from electrons traveling at same velocity as the phase velocity of the helicon wave. The high plasma density (Gt1013 cm-3) and high ion exit flow speed (Mach 2.5 for argon) would yield significantly higher fluxes at the substrate surface and consequently an improved deposition rate over existing MBE plasma sources. Epilayer quality could also be improved by lowering kinetic energy of reactive species. The helicon source will also be less contaminating since, unlike conventional RF or other plasma sources, it does not require an antenna, a plasma filtering aperture or a nozzle inside the chamber. We report on control of nitrogen dissociation degree in a compact helicon plasma source by adjustment of the external working parameters such as the source magnetic field, gas pressure, driving frequency, and input power. The dissociation degree has been inferred from the ratio of nitrogen atomic line (746.8 nm) and the molecular transition (B3Pg, v'=4 fi A3Su +, v"=2 at 750.4 nm) by taking into account electron impact excitation rate coefficients

Summary form only given. Current-free plasma expansion in a divergent magnetic field is surprisingly common and is found on a variety of spatial scales and in a variety of applications. Plasma expansion is essentially equivalent to a pressure gradient arising from a change in the plasma density. The density gradient can give rise to a potential gradient that retards motion of the lighter plasma electrons but accelerates the more massive ions downstream. The solar wind expansion and corresponding creation of the interplanetary electric field is a classic example of this process. Also, there is strong experimental evidence in support of Alfven's hypothesis that the aurora results from energetic electrons precipitating onto the upper atmosphere and that the electrons in space could be accelerated by double layer (DL) electric fields with components parallel to the terrestrial magnetic field. Under certain external conditions, theoretical simulations and experimental observations showed that in a helicon plasma expanding into a weaker magnetic field, a DL with a width of a few tens of Debye lengths can form at the end of helicon plasma. The DL accelerates ions to Mach numbers of order 2. In this work, we present the temporal evolution of both parallel and perpendicular to the magnetic field argon ion velocity distribution functions (IVDFs) in pulsed helicon plasmas obtained by using a time resolved laser induced fluorescence technique with 1 ms resolution. At 600 W of RF power and 1 mtorr pressure, for pulses of 200 ms at a duty cycle of 0.5, the DL forms in the first 40 ms of the discharge. The parallel argon ion flow speed rises from 400-500 m/s at the beginning of the pulse to 3000-3500 m/s at the end of the pulse. Perpendicular measurements showed no change in the perpendicular flow speed, consistent with a DL electric field parallel to the background magnetic field

With nonperturbative laser-induced fluorescence measurements of ion flow, we confirm numerical simulations of spontaneous electric double-layer (DL) formation in a current-free expanding plasma. Measurements in two different experiments confirm that the DL is localized to the region of rapidly diverging magnetic field. The measurements indicate that the trapped ion population is a single Maxwellian, that the spatial gradient of the energy of ions accelerated through the DL matches the magnetic field gradient, and that DL formation is triggered when the ion-neutral collisional mean-free path exceeds the magnetic field gradient scale length.

Summary form only given. Recent models for ion heating in the fast solar wind region of the Sun predicts the heating is due to MHD turbulence driven by counter propagating, low-frequency Alfven waves. Experiments to test this theory is conducted in the West Virginia University HELIX (Hot Helicon Experiment) device in helium plasma. Densities in HELIX are on the order of 10/sup 13/ cm/sup -3/ with ion temperatures of about 0.3 eV. To create counter propagating Alfven waves one of two techniques are employed. We first attempt to launch the Alfven waves from the helicon source region and generate a reflection due to an Alfven speed gradient. The HELIX device has an Alfven speed profile similar to the solar corona, a short region of increased Alfven speed followed by a rapid decrease in speed as the magnetic field expands. Should the first method prove to be unsuccessful, two waves are launched at each other from different antennas. This method has the added advantage of allowing the relative intensities of the counter-propagating waves to be varied. Temperatures of helium ions are measured using a RF compensated energy analyzer. We present information on the experimental apparatus as well as preliminary data.

A high-uniformity inductively coupled plasma source is presented. The plasma uniformity is improved with a magnetic multicusp structure that surrounds the plasma chamber. A picture showing the alternating bright and dark plasma regions along the perimeter of the plasma chamber-an effect of the magnetic confinement-is presented as well.

This work concerns with the excitation and ionization processes in the cathode region of the hollow cathode abnormal glow discharge, like in a genetically abnormal glow discharge in mixture of noble gases and metal vapors. The proposed model takes into account the ionic and atomic population of metal vapors, the metastables population of predominant buffer gas and of the ion population of the gas mixture, while the other models, reported in the literature don't take into account the last two populations. This model is qualitatively experimentally attested.

The molecular vibration temperature of the plasma from an interrupt arc discharge in air at atmospheric pressure and at current intensities in the range of 2 divided by 8 Amperes, using electronic and vibration bands of violet [B 2 (Sigma) + - X 2 (Sigma) + ] and red [A 2 (Pi) - X 2 (Sigma) + ] systems of the CN molecule was determined. At the equilibrium temperature of 6400 K, 27 lines of Ti, contained as impurity in coal electrode were found. These spectral lines were found in the 247 divided by 340 nm spectral range, having the upper levels of the excitation energies in the 3.60 divided by 5.69 eV range, in the neighborhood of the energy of dissociation of the CN molecule on the fundamental electronic state. Some considerations about the vibrational states populations are also made.

University ofBucharest, Spi. Independentei 3 13, 772O6Bucharest, RomaniaABSTRACTThe paper presents a data processing algorithm, based on a deconvolution technique that enables the recovery of thelow intensity spectral lines, in connection with the analysis of the radiative mechanisms from the non isothermal plasma ofa hollow cathode discharge. This method represents a useful tool in the study of the radiative competitive processesinvolved in the selective excitation mechanisms for ISV and visible spectral line's emission. It permits the evaluation of thesecond kind collision's weight in conjunction with the concentration of the plasma ions for different discharge parameters.Keywords: hollow cathode discharge. deconvolution methods, second kind collisions, selective excitations1. DTRODUCTIONIn the hollow cathode discharges the occurrence of second kind collisions processes could induce selective excitationsof the plasma atoms and ions. Of practical interest for spectral sources and lasers active media are the line's intensityincreasing by selective excitation of the Copper vapor atoms obtained by cathode sputtering under ionic bombardment inpulsed hollow cathode discharge in noble gases' mixtures '

Observations in steady-state plasmas confirm predictions that formation of a current-free double layer in a plasma expanding into a chamber of larger diameter is accompanied by an increase in ionization upstream of the double layer. The upstream plasma density increases sharply at the same driving frequency at which a double layer appears. For driving frequencies at which no double layer appears, large electrostatic instabilities are observed. Time-resolved measurements in pulsed discharges indicate that the double layer initially forms for all driving frequencies. However, for particularly strong double layers, instabilities appear early in the discharge and the double layer collapses.

The diagnostic technique of laser induced fluorescence (LIF), generalized to the case of oblique laser injection angle relative to the local magnetic field direction, is employed for studies of the ion velocity distribution function (IVDF) in the magnetic expansion region of a helicon plasma source. One-dimensional LIF measurements reveal key characteristics of the acceleration mechanism responsible for creation of an ion beam in the expansion regions: a bimodal IVDF comprising a slowly drifting (~150?m?s?1) ion population and a fast ion beam (~10.7?km?s?1). Two-dimensional LIF, LIF tomography, provides additional insight regarding the origins of the two ion populations: the nearly isotropic slow population is a locally created background population whereas the distorted velocity distribution of the fast population is consistent with an origin upstream of the measurement location.

Two-dimensional argon ion velocity distribution functions (IVDFs) in the expansion region of a helicon plasma source have been measured by laser-induced-fluorescence tomography. Below a threshold value of the magnetic field in the expansion region, the IVDFs show a bimodal structure comprised of a supersonic ion population axially moving away from the source and an isotropic, slow, background, ion population. Increasing the magnetic field divergence leads to an increase in the axial speed of the supersonic component. A maximum axial speed of ∼2.9cs was obtained for a source/expansion magnetic field ratio of 43.

Estimates of the dissociation degree in the diffusion region of a nitrogen helicon plasma source based on optical emission spectroscopy and Langmuir probe measurements are presented. The estimation procedure relies on measurements of the ratios of the intensities of the atomic triplet 3pS04→3sP4 (742.36, 744.23, and 746.83nm) to the intensity of the 4-2 band of the first positive system (AΣu+3→BΠg3) at 750.39nm and the measured relative vibrational distribution of the BΠg3 state. The electron energy distribution function, obtained from the second derivative of the Langmuir probe characteristic, and published excitation cross sections are used to calculate the electron-impact excitation rate coefficients—which are then compared to the atomic line and molecular band intensities to calculate the dissociation degree. For two distinct operating regimes, capacitively and inductively coupled, dissociation fractions of 5% and 13% are obtained in the expansion region of a 10mTorr, 500W, 10.74MHz helicon generated ...

A method of gas temperature determination in nitrogen or nitrogen doped discharges is presented. The method employs fits of numerically generated spectra of the 0-0, 1-0, and 2-0 bands of the first positive system (B Π3g→A Σ3u+) of nitrogen to experimental measurements. Excellent agreement between gas temperature values inferred by using this method and by using the 3-0 band peak ratio method [M. Simek and S. De Benedictis, Plasma Chem. Plasma Proc. 15, 451 (1995)] is demonstrated for a helicon plasma. The spectral model is available for use by the plasma spectroscopy community. The model, along with user instructions, can be downloaded from Electronic Physics Auxiliary Publication Service of American Institute of Physics. The model includes the line positions, Honl-London factors, and provides rapid determination of gas temperature if one or more of the aforementioned emission rovibrational band spectra are available.

Measurements of the three-dimensional ion flow field and the ion temperature in a cross section of a cylindrical, argon, helicon plasma are presented. When these measurements are combined with radially resolved measurements of the plasma density, electron temperature, neutral density, and neutral temperature, the radial profiles of the ion viscosity and ion-neutral momentum transfer rate can be calculated. The ion viscosity and ion-neutral momentum transfer rate profiles are important input parameters for theoretical models of azimuthal flows arising from the nonlinear interaction of drift waves in helicon sources. The experimentally determined magnitudes and radial profiles reported in this work are significantly different than those used in recent theoretical studies. Measurements of the radial flow of argon neutrals and helium neutrals are also presented for a helicon plasma.

We present a method of rotational and vibrational temperature estimation in nitrogen plasma by simulation of the emission spectrum of the first positive system (BΠg3→AΣu+3) of nitrogen. The gas kinetic temperature, assumed to be in equilibrium with the rotational temperature, was obtained from a fit to the experimentally obtained 0→0 at 1051nm, 1→0 at 872.23nm, and 2→0 at 775.32nm rovibrational band spectra. Excellent agreement between values inferred from each band [(499±29)K] as well as inferred by using the 3→0 band peak ratio method [(473±25)K] was obtained for a 600W, 850G, and 10mTorr helicon N2 plasma. The vibrational temperature was determined from a Boltzmann plot of the integrated band intensities [(6040±225)K] and by numerical fit to the Δv=+1, +2, and +3 sequences after accounting for Franck-Condon factors and electronic-vibrational transition moments [(6200±400)K].

A low-frequency, transverse electromagnetic wave is observed in a magnetized helicon plasma with 1⪢β>νe∕Ωe. The wave is localized to the vicinity of the largest plasma density gradient and appears only at a low neutral pressure. Based on the scaling of the wave frequency and amplitude with magnetic field strength, the wave is identified as the resistive drift Alfven wave.

A time-resolved laser induced fluorescence (LIF) technique for pulsed argon plasmas is described. A low power, tunable diode laser pumps a three level Ar II transition sequence at a wavelength of 668.6138 nm. With a standard LIF system designed for steady-state plasmas (e.g., 4 kHz optical chopper, 20 kHz band-width detector, and a lock-in amplifier), we demonstrate that the evolution of the ion velocity distribution can be resolved with a time resolution of 1 ms through a combination of time-series averaging and post-acquisition digital signal processing.

Summary form only given. Molecular beam epitaxy of III-N materials is potential alternative to MOVPE for fabrication of high quality wide band gap semiconductor devices. However, during the MBE film growth enhancement of nitrogen accommodation and sputtering damage minimization remain as technological hurdles. We report preliminary results on control of reactive nitrogen species performed in a steady state, high density, helicon plasma source CHEWIE (Compact HElicon Waves and Instabilities Experiment). The helicon vacuum chamber is a 12 cm long, Pyrex tube, 6 cm in diameter, connected to a stainless steel diffusion chamber. RF power of up to 1.0 kW over a frequency range of 6-18 MHz is used to create the steady state plasma. A 7 cm long, half wave, m=+1, helical antenna couples the rf energy into the plasma. By a proper selection of the helicon wave phase velocity and input power it is possible to modify the electron velocity distribution function. Thereby increasing the production of molecular excited species, which are favorable to the growth process, and decreasing the production of ionic species, which are detrimental to the epilayer. Further, the expansion of the helicon plasma into the diffusion chamber should permit, through spontaneous radiative relaxation, the different N/sub 2/ triplet excited states to cascade down to the metastable A/sup 3//spl Sigma//sub u//sup +/ state. With a sufficiently long transit time to the expansion chamber, the long lived A/sup 3//spl Sigma//sub u//sup +/ state will become the dominant reactive nitrogen specie in the plasma. Previous optical emission spectroscopy investigations have demonstrated that the N/sub 2/ (B/sup 3//spl Pi//sub g/, v'=11 /spl rarr/A/sup 3//spl Sigma//sub u//sup +/, v"=7 at 580.4 nm) transition, which is a part of the 1st positive system, is the dominant transition in nitrogen helicon generated plasma.

Summary form only given. A possible explanation for the high RF absorption efficiency of helicon sources is the damping of the slow wave, the so called "Trivelpiece-Gould" wave, at the plasma edge in a helicon discharge. Because of the extremely short wavelength of the slow wave (less than 1 mm) direct measurements of the slow wave are not possible with standard electrostatic probes. We report on the development of a simple, portable diagnostic capable of directly measuring sub-millimeter wavelength fluctuations in helicon sources. The technique is based on collective scattering principles in which a plane polarized electromagnetic wave scatters off an electron density fluctuation in the plasma with a fraction of scattered light being detected at an angle /spl theta/ relative to the direction of the incident wave. Similar measurements are routinely performed in fusion plasmas. Our quasi-optical diagnostic, operating at 288 GHz, will be capable of measuring fluctuation wavelengths from .63 to 6.3 mm (k/sub /spl perp//=100-10 cm/sup -1/). As shown by Kline et al., waves with k/sub /spl perp///spl sim/10 cm/sup -1/ are routinely observed in HELIX. The scattered signal is measured with a homodyne detector with sufficient time resolution to detect waves in the frequency range of 1 kHz to 50 MHz.