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The small signal-to-noise ratio (SNR) of conventional laser induced fluorescence (LIF) measurements using a continuous wave laser, either diode or dye, is typically overcome by amplitude modulating the laser at a specific frequency and then using lock-in amplification to extract the signal from measurement noise. Here, we present LIF measurements of the neutral helium velocity distribution function in an rf plasma using frequency modulated (FM) laser injection. A pulse train of 100% amplitude modulation is generated synthetically with a random sequence of pulse lengths. The FM signal then drives an acoustic optic modulator placed in the path of the injection beam in an LIF measurement. The signal from a fast photomultiplier tube is digitized and cross-correlated with the known modulation signal. The resultant FM-based LIF signal outperforms a conventional lock-in-based LIF measurement on the same plasma in terms of SNR and precision. [ABSTRACT FROM AUTHOR]

Laser induced fluorescence is used to measure argon ion heating during magnetic reconnection in the PHase Space MApping experiment (PHASMA). Sufficient signal-to-noise ratio (SNR) of the processed signal with pulsed laser injection is a delicate balance between saturation of the absorption line and injecting enough laser power to overcome the spontaneous emission of the plasma at the fluorescence wavelength. Averaging over many laser pulses and integrating over the fluorescence lifetime improves the SNR of the processed signal (processed SNR) when the SNR of the laser pulse time series is small (pulse SNR), but for laser powers small enough to avoid saturation, averaging over hundreds of pulses is needed to obtain an appreciable processed SNR over the entire Doppler-broadened absorption line. Here, we describe a matched filter processing method that significantly improves the SNR of the final measurement with fewer shots averaged. Investigation of simulated measurements validated by experimental results suggests that the matched filter method provides up to a 20% improvement in the processed SNR, resulting in less uncertainty in distribution function fits. [ABSTRACT FROM AUTHOR]

Development of new plasma instruments is needed to enable constellation‐ and small satellite‐based missions. Key steps in the development pathway of ultra‐compact plasma instruments employing lithographically patterned wafers are the implementation of layer‐to‐layer electrical interconnects and demonstration of massively parallel measurements, that is, simultaneous measurements through multiple identical plasma analyzer structures. Here we present energy resolved measurements of electron beams using a 5‐layer stack of wafer‐based, energy‐per‐charge, electrostatic analyzers. Each layer has eight distinct analyzer groups that are comprised of multiple micron scale energy‐per‐charge analyzers. The process of fabricating the electrical interconnects between the layers is described and the measured energy resolution and the angular resolution compared to theoretical predictions. The measurements demonstrate successful operation of 400 micron scale analyzers operating in parallel. Plain Language Summary: Spacecraft are expensive and difficult to build. CubeSats, a class of small, inexpensive spacecraft are being used for scientific missions. However, standard instruments to measure the local plasma environment cannot fit on such small spacecraft. Here we describe a new type of space plasma instrument that is manufactured with processes similar to how computer chips are made. These plasma instruments are made by stacking layers of micro‐scale plasma analyzers to create a larger instrument with a significant geometric factor. Each layer includes nearly one hundred small energy‐per‐charge plasma analyzers working in parallel. Initial measurements from a 5‐layer instrument along with the processes used to build the instrument are described in this work. Key Points: Microscale plasma energy analyzer demonstrated in laboratory testsLithographic fabrication process enables low voltage analysis of charged particles up to tens of keV/chargeMulti‐layer instrument required development of a novel fabrication process [ABSTRACT FROM AUTHOR]

Here, we present laser-induced fluorescence measurements of an ion beam extraction angle and speed through a plasma-vacuum boundary as a function of plasma source parameters and bias potential applied to a wafer simulacrum outside the plasma. Ion temperature, velocity, and relative density are calculated from the measured ion velocity distribution function and are compared to a particle-in-cell model of the system. The measurements demonstrate that beam steering is feasible by varying plasma source density and extraction bias voltage. The focal point of the extracted beam, resulting from the plasma meniscus at the plasma-vacuum interface, depends on source density and extraction bias in a manner consistent with computational predictions. [ABSTRACT FROM AUTHOR]

In this work, we provide experimental measurements of the E × B flow above a non-magnetic, absorbing boundary in a magnetized plasma. Measurements are taken as a function of the angle between the background magnetic field and the boundary normal. The measurements are compared to computational predictions for oblique magnetic fields based on Chodura's model. Ion flow measurements were obtained with laser induced fluorescence and the presheath potential structure was measured with an emissive probe. The ions were found to accelerate to nearly 30% of the sound speed parallel to the boundary at oblique angles of the magnetic field (∼80°) and the ion speed at the electrostatic sheath edge was found to decrease with angle. The edge of the magnetic presheath has been experimentally determined based on the appearance of the E × B drift and is found to be independent of the angle of the magnetic field. We also demonstrate that laser induced fluorescence is suitable as a non-perturbative diagnostic to measure the electric field in a magnetized sheath. [ABSTRACT FROM AUTHOR]

Radio frequency (RF) driven helicon plasma sources are commonly used for their ability to produce high-density argon plasmas (n > 1019 m−3) at relatively moderate powers (typical RF power < 2 kW). Typical electron temperatures are <10 eV and typical ion temperatures are <0.6 eV. A newly designed helicon antenna assembly (with concentric, double-layered, fully liquid-cooled RF-transparent windows) operates in steady-state at RF powers up to 10 kW. We report on the dependence of argon plasma density, electron temperature and ion temperature on RF power. At 10 kW, ion temperatures >2 eV in argon plasmas are measured with laser induced fluorescence, which is consistent with a simple volume averaged 0D power balance model. 1D Monte Carlo simulations of the neutral density profile for these plasma conditions show strong neutral depletion near the core and predict neutral temperatures well above room temperatures. The plasmas created in this high-power helicon source (when light ions are employed) are ideally suited for fusion divertor plasma-material interaction studies and negative ion production for neutral beams. [ABSTRACT FROM AUTHOR]

In laboratory plasmas, arrays of probes have typically been used to measure the evolution of the magnetic field topology. Here, we present initial image-based measurements of the magnetic topology in a low-temperature plasma using a purely optical diagnostic. Laser induced fluorescence measurements of neutral velocity distribution functions are made using a fast camera, imaging the Zeeman splitting of σ-peaks in neutral argon. The separation of σ-peaks provides spatially resolved magnetic field magnitude measurements with a detection threshold on the order of 10 G. [ABSTRACT FROM AUTHOR]

We present planar, laser induced fluorescence (PLIF) measurements of the velocity-resolved distribution function of ions in a plasma using a modulated, narrow linewidth, continuous-wave laser. Plasma emission is acquired with a high frame rate camera, and the laser light is spread into a thin sheet so that an entire plane of the plasma is imaged at each interrogation wavelength. Fourier analysis is conducted on each pixel of the images to separate the modulated fluorescent emission from the background light. Argon ion temperatures and bulk flow maps are reported in a helicon plasma source, and standard single-point LIF measurements provide validation of the PLIF measurement. [ABSTRACT FROM AUTHOR]

Mesoscale structures in Earth's magnetotail are a primary feature of particle transport to the inner magnetosphere during storms and substorms. We demonstrate that such structures can be observed in energetic neutral atom (ENA) data which can provide remote, global images of the magnetosphere. In particular, we present localized regions of increased ion temperatures that appear in equatorial ion temperature maps calculated from Two Wide‐angle Imaging Neutral‐atom Spectrometers (TWINS) ENA data. These regions are associated with a dipolarization front with bursty ion flows measured by Magnetospheric MultiScale (MMS) and are concurrent with substorm features observed in field aligned currents (FAC) from Active Magnetosphere and Planetary Electrodynamics Response Experiment measurements. We conduct a magnetohydrodynamics simulation of the same event and show simulated ion temperatures, ion flows, and FACs that agree with the measurements. However, the observed plasma heating is less intense in the simulated results than in the TWINS and MMS data, indicating that some heating processes may be missing from the model. Plain Language Summary: Large chunks of energetic particles and enhanced magnetic field from the Sun can cause geomagnetic storms and substorms in the space surrounding Earth. During these active times, the energy from the Sun can get dumped into the nightside where ions and electrons are heated and propelled toward the Earth like from a slingshot. When these energetic particles get closer to the Earth, they can disrupt satellites and cause power outages, so scientists hope to improve our understanding and develop forecasting tools for these storms and substorms. Scientists have shown that the particles move toward the Earth in narrow channels. We demonstrate that these channels are heated and can be seen in temperature maps created from the NASA TWINS mission. To support our findings, we also compare the results to measurements from other satellites and computer simulations. This means that we can use such maps for more research and to improve forecasting models. For example, we found that the measured temperatures are higher than the simulated temperatures, indicating that more is needed in the models. We could also use a satellite like TWINS to act as a warning system for storms and substorms. Key Points: An interval of bursty flows during a magnetospheric substorm expansion phase is observed by Two Wide‐angle Imaging Neutral‐atom Spectrometers (TWINS), Magnetospheric MultiScale (MMS), and Active Magnetosphere and Planetary Electrodyamics Response Experiment and simulated using the Space Weather Modeling FrameworkThe localized regions of ion heating observed by TWINS are directly related to the bursty plasma flow channel and substorm developmentThe observed heating is less intense in the simulations than the TWINS and MMS data; additional heating processes are needed in the model [ABSTRACT FROM AUTHOR]

Here, we report on modifications to the electron energy distribution function during X-mode microwave injection in argon and helium helicon plasmas. No electron heating is observed in argon helicon plasmas. Significant electron heating, Δ T e ∼ 1 eV, is observed in helium plasmas. The heating is spatially localized to the upper hybrid resonance layer. Previously absent helium ion emission lines, from states over 50 eV above the helium ion ground state, are observed with the injection of X-mode microwaves. [ABSTRACT FROM AUTHOR]

As diagnostic groups are increasingly called upon to participate in experimental campaigns at remote facilities, there is a need to develop portable versions of plasma diagnostic systems. One such diagnostic is laser induced fluorescence (LIF). Here, we describe a portable LIF apparatus that eliminates the need for an optical table, beam splitters, and an optical chopper. All of the light exiting the laser system is coupled through optical fibers to the experiment and housekeeping diagnostics. The collected light is coupled through an optical fiber as well. A key feature is modulation of the tapered amplifier current instead of physical modulation of the laser output. Using this portable LIF system, measurements of ion temperature, ion flow, and relative metastable ion density are reported for two different remote experiments. [ABSTRACT FROM AUTHOR]

We report experiments conducted in an expanding argon plasma generated in the inductive mode of a helicon source in the Hot hELIcon eXperiment–Large Experiment on Instabilities and Anisotropies facility. As the neutral gas pressure increases, the supersonic ion acceleration weakens. Increasing neutral pressure also alters the radial profile of electron temperature, density, and plasma potential upstream of the plasma expansion region. Langmuir probe measurements of the electron energy probability function (EEPF) show that heating of electrons at the plasma edge by RF fields diminishes with increasing gas pressure, yielding a plasma with a centrally peaked electron temperature, and flat potential profiles at higher neutral pressures. For neutral pressures at which ion acceleration regions develop in the expanding plasma plume, EEPFs reveal electrons with two temperature components. [ABSTRACT FROM AUTHOR]

Ion temperature anisotropy in an expanding magnetized plasma is investigated using laser induced fluorescence. Parallel and perpendicular ion velocity distribution functions (IVDFs) were measured simultaneously with high spatial resolution in the expanding plasma. Large ion temperature anisotropies ( T ⊥ i / T ∥ i ∼ 10) are observed in a conical region at the periphery of the expanding plasma plume. A simple 2D Boris stepper model that incorporates the measured electric field structure is able to reproduce the gross features of the measured perpendicular IVDFs. A Nyquist stability analysis of the measured IVDFs suggests that multiple instabilities with k ⊥ ρ i ∼ 1 and k | | ρ i ∼ 0.2 are likely to be excited in these plasmas. [ABSTRACT FROM AUTHOR]

Ion temperature is a key parameter that influences dynamics in the magnetosphere, such as particle transport and wave-particle interactions. Measurements of ion heating and energization yield information about phenomena such as magnetic reconnection, bursty bulk flows, and ion injections. Taking advantage of the global view provided by energetic neutral atom imaging, a database of ion temperature maps during geomagnetic storms occurring throughout the National Aeronautics and Space Administration (NASA) Two Wide-angle Imaging Neutral atom Spectrometers (TWINS) mission has been created. These ion temperature maps and relevant metadata are publicly available on CDAWeb to facilitate comparison to in situ measurements and model output, for use as boundary conditions for simulations, and for other relevant studies. A preliminary study of average plasma sheet ion temperatures calculated from these maps has revealed a common occurrence of decreasing ion temperature, and a case study for one storm is presented. [ABSTRACT FROM AUTHOR]

Argon and xenon ion velocity distribution functions are measured in Ar-He, Ar-Xe, and Xe-He expanding helicon plasmas to determine if ion beam velocity is enhanced by the presence of lighter ions. Contrary to observations in mixed gas sheath experiments, we find that adding a lighter ion does not increase the ion beam speed. The predominant effect is a reduction of ion beam velocity consistent with increased drag arising from increased gas pressure under all conditions: constant total gas pressure, equal plasma densities of different ions, and very different plasma densities of different ions. These results suggest that the physics responsible for the acceleration of multiple ion species in simple sheaths is not responsible for the ion acceleration observed in expanding helicon plasmas. [ABSTRACT FROM AUTHOR]

We report spatially resolved perpendicular and parallel, to the magnetic field, ion velocity distribution function (IVDF) measurements in an expanding argon helicon plasma. The parallel IVDFs, obtained through laser induced fluorescence (LIF), show an ion beam with v ≈ 8000 m/s flowing downstream and confined to the center of the discharge. The ion beam is measurable for tens of centimeters along the expansion axis before the LIF signal fades, likely a result of metastable quenching of the beam ions. The parallel ion beam velocity slows in agreement with expectations for the measured parallel electric field. The perpendicular IVDFs show an ion population with a radially outward flow that increases with distance from the plasma axis. Structures aligned to the expanding magnetic field appear in the DC electric field, the electron temperature, and the plasma density in the plasma plume. These measurements demonstrate that at least two-dimensional and perhaps fully three-dimensional models are needed to accurately describe the spontaneous acceleration of ion beams in expanding plasmas. [ABSTRACT FROM AUTHOR]

A plasma spectrometer design based on advances in lithography and microchip stacking technologies is described. A series of curved plate energy analyzers, with an integrated collimator, is etched into a silicon wafer. Tests of spectrometer elements, the energy analyzer and collimator, were performed with a 5 keV electron beam. The measured collimator transmission and energy selectivity were in good agreement with design targets. A single wafer element could be used as a plasma processing or fusion first wall diagnostic. [ABSTRACT FROM AUTHOR]

We have developed a new diagnostic based on two-photon absorption laser induced fluorescence (TALIF). We use a high intensity (5 MW/cm2), narrow bandwidth (0.1 cm-1) laser to probe the ground state of neutral hydrogen, deuterium and krypton with spatial resolution better than 0.2 cm, a time resolution of 10 ns, and a measurement cadence of 20 Hz. Here, we describe proof-of-principle measurements in a helicon plasma source that demonstrate the TALIF diagnostic is capable of measuring neutral densities spanning four orders of magnitude; comparable to the edge neutral gradients predicted in the DIII-D tokamak pedestal. The measurements are performed in hydrogen and deuterium plasmas and absolute calibration is accomplished through TALIF measurements in neutral krypton. The optical configuration employed is confocal, i.e., both light injection and collection are accomplished with a single lens through a single optical port in the vacuum vessel. The wavelength resolution of the diagnostic is sufficient to separate hydrogen and deuterium spectra and we present measurements from mixed hydrogen and deuterium plasmas that demonstrate isotopic abundance measurements are feasible. Time resolved measurements also allow us to explore the evolution of the neutral hydrogen density and temperature and effects of wall recycling. We find that the atomic neutral density grows rapidly at the initiation of the discharge, reaching the steady-state value within 1 ms. Additionally, we find that neutral hydrogen atoms are born with 0.08 eV temperatures, not 2 eV as is typically assumed. [ABSTRACT FROM AUTHOR]

It is straightforward to create fully ionized plasmas with modest rf power in a helicon. It is difficult, however, to create plasmas with density >1020 m-3, because neutral depletion leads to a lack of fuel. In order to address this density limit, we present fast (1 MHz), time-resolved measurements of the neutral density at and downstream from the rf antenna in krypton helicon plasmas. At the start of the discharge, the neutral density underneath the antenna is reduced to 1% of its initial value in 15 μs. The ionization rate inferred from these data implies that the electron temperature near the antenna is much higher than the electron temperature measured downstream. Neutral density measurements made downstream from the antenna show much slower depletion, requiring 14 ms to decrease by a factor of 1/e. Furthermore, the downstream depletion appears to be due to neutral pumping rather than ionization. [ABSTRACT FROM AUTHOR]

We present time-resolved measurements that demonstrate that large amplitude electrostatic instabilities appear in pulsed, expanding helicon plasmas at the same time as particularly strong double layers appear in the expansion region. A significant cross-correlation between the electrostatic fluctuations and fluctuations in the number of ions accelerated by the double layer electric field is observed. No correlation is observed between the electrostatic fluctuations and ions that have not passed through the double layer. These measurements confirm that the simultaneous appearance of the electrostatic fluctuations and the double layer is not simple coincidence. In fact, the accelerated ion population is responsible for the growth of the instability. The double layer strength, and therefore, the velocity of the accelerated ions, is limited by the appearance of the electrostatic instability. [ABSTRACT FROM AUTHOR]

Helicons are efficient plasma sources, capable of producing plasma densities of 1019 m-3 with only 100 s W of input rf power. There are often steep density gradients in both the neutral density and plasma density, resulting in a fully ionized core a few cm wide surrounded by a weakly ionized plasma. The ionization profile is usually not well known because the neutral density is typically inferred from indirect spectroscopic measurements or from edge pressure gauge measurements. We have developed a two photon absorption laser induced fluorescence (TALIF) diagnostic capable of directly measuring the neutral density profile. We use TALIF in conjunction with a Langmuir probe to measure the ionization fraction profile as a function of driving frequency, magnetic field, and input power. It is found that when the frequency of the driving wave is greater than a critical frequency, fc≈3flh, where flh is the lower hybrid frequency at the antenna, the ionization fraction is small (0.1%) and the plasma density low (1017 m-3). As the axial magnetic field is increased, or, equivalently, the driving frequency decreased, a transition is observed. The plasma density increases by a factor of 10 or more, the plasma density profile becomes strongly peaked, the neutral density profile becomes strongly hollow, and the ionization fraction in the core approaches 100%. Neutral depletion in the core can be caused by a number of mechanisms. We find that in these experiments the depletion is due primarily to plasma pressure and neutral pumping. [ABSTRACT FROM AUTHOR]

Using laser induced fluorescence (LIF), radial profiles of azimuthal ion fluid velocity and ion temperature are measured in the controlled shear de-correlation experiment (CSDX) linear helicon plasma device. Ion velocities and temperatures are derived from the measured Doppler broadened velocity distribution functions of argon ions. The LIF system employs a portable, high power (>300 mW), narrowband (∼1 MHz) tunable diode laser-based system operating at 668.614 nm. Previous studies in CSDX have shown the existence of a radially sheared azimuthal flow as measured with time delay estimation methods and Mach probes. Here, we report the first LIF measurements of sheared plasma fluid flow in CSDX. Above a critical magnetic field, the ion fluid flow profile evolves from radially uniform to peaked on axis with a distinct reversed flow region at the boundary, indicating the development of a sheared azimuthal flow. Simultaneously, the ion temperature also evolves from a radially uniform profile to a profile with a gradient. Measurements in turbulent and coherent drift wave mode dominated plasmas are compared. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We report experimental measurements of the axial plasma flow and the parallel ion temperature in a magnetized linear plasma device. We used laser induced fluorescence to measure Doppler resolved ion velocity distribution functions in argon plasma to obtain spatially resolved axial velocities and parallel ion temperatures. We also show changes in the parallel velocity profiles during the transition from resistive drift wave dominated plasma to a state of weak turbulence driven by multiple plasma instabilities. [ABSTRACT FROM AUTHOR]

Results from a proof-of-principle experiment are presented that demonstrate it is possible to construct a completely optical, robust, and compact probe capable of spatially resolved measurements of magnetic field fluctuations smaller than 1 G over a frequency range of 1 Hz–8 MHz in a plasma. In contrast to conventional coil probes, the signal strength is independent of fluctuation frequency and the measurement technique is immune to electrostatic pickup. The probe consists of a high Verdet constant crystal, two polarizers, optical fibers, and a photodetector. [ABSTRACT FROM AUTHOR]

The first two sessions of this mini-conference focused attention on two areas of helicon source research: The conditions for optimal helicon source performance and the origins of energetic electrons and ions in helicon source plasmas. The final mini-conference session reviewed novel applications of helicon sources, such as mixed plasma source systems and toroidal helicon sources. The session format was designed to stimulate debate and discussion, with considerable time available for extended discussion. [ABSTRACT FROM AUTHOR]

The effect of parametric ion cyclotron turbulence on the heating of cold and suprathermal ions in the edge of a tokamak plasma during injection of high radio frequency (rf) power in the ion cyclotron resonance frequency range is studied. The maximum turbulent heating rates for cold edge ions and suprathermal edge ions are calculated analytically for ion cyclotron turbulence driven by rf heating at the plasma edge. It is demonstrated that the maximum turbulent ion-heating rate for suprathermal ions is insufficient to explain the observed heating of edge ions. Therefore, the excitation of ion cyclotron turbulence by rf heating systems in the plasma edge is unlikely to be responsible for the experimentally observed large population of suprathermal ions in the edge of tokamak plasmas. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Experimentally observed anisotropic ion heating in helicon plasma sources may result from the interaction of ions with ion-sound turbulence. The ion-sound turbulence develops due to excitation of the short scale, kinetic, parametric ion-sound instability. From the quasilinear equation for the ion distribution function, which includes the induced scattering of ion-sound waves by ions, the turbulent heating rate is determined. This anomalous ion heating is predominantly across the magnetic field and can lead to strong turbulence effects, such as the collective statistical effect of ion-sound turbulence on individual ion orbits (resonance broadening). Resonance broadening is a strong turbulence saturation mechanism for ion-sound turbulence. The energy density of the ion-sound turbulence in the saturated state, the ion and electron heating rates, as well as the effective collision frequency arising from the anomalous absorption of the helicon wave, are estimated and compared to experimental data. [ABSTRACT FROM AUTHOR]

Using laser-induced fluorescence, measurements have been made of metastable argon-ion, Ar[SUP+]*(3d[SUP4]F[SUB&frac72;], velocity distributions on the major axis of an axisymmetric magnetic-mirror device whose plasma is sustained by helicon wave absorption. Within the mirror, these ions have sub-eV temperature and, at most, a subthermal axial drift. In the region outside the mirror coils, conditions are found where these ions have a field-parallel velocity above the acoustic speed, to an axial energy of ∼30 eV, while the field-parallel ion temperature remains low. The supersonic Ar[SUP+]*(3d[SUP4]F[SUB&frac72;] are accelerated to one-third of their final energy within a short region in the plasma column, &les;1 cm, and continue to accelerate over the next 5 cm. Neutral-gas density strongly affects the supersonic Ar[SUP+]*(3d[SUP4]F[SUB&frac72;] density. [ABSTRACT FROM AUTHOR]

Recent experiments have demonstrated that phenomena associated with ion dynamics, such as the lower hybrid resonance, play an important role in helicon source operation. In this work, a review of recent ion heating measurements and the role of the slow wave in heating ions at the edge of helicon sources is presented. The relationship between parametrically driven waves and ion heating near the rf antenna in helicon sources is also discussed. Recent measurements of parallel and rotational ion flows in helicon sources are presented and the implications for particle confinement, instability growth, and helicon source operation are reviewed. [ABSTRACT FROM AUTHOR]

Parametric decay of the electromagnetic helicon pump wave into two electrostatic waves, thought to be a lower hybrid wave and an ion acoustic wave, is observed. The parametric excitation of the electrostatic waves is strongest near the axis of the helicon source. The parametrically excited wave amplitudes can be as large as 8% of the pump wave amplitude. Thus, efficient coupling between the parametrically excited waves and plasma particles (ions and electrons) can lead to enhanced plasma densities, electron temperatures, and ion temperatures. A correlation between the lower hybrid wave and electron temperatures and a correlation between the ion acoustic wave and ion temperatures near the antenna are observed. [ABSTRACT FROM AUTHOR]

Electron temperature measurements in helicon plasmas are difficult. The presence of intense rf fields in the plasma complicates the interpretation of Langmuir probe measurements. Furthermore, the non-negligible ion temperature in the plasma considerably shortens the lifetime of conventional Langmuir probes. A spectroscopic technique based on the relative intensities of neutral helium lines is used to measure the electron temperature in the HELIX (Hot hELicon eXperiment) plasma [P. A. Keiter et al., Phys. Plasmas 4, 2741 (1997)]. This nonintrusive diagnostic is based on the fact that electron impact excitation rate coefficients for helium singlet and triplet states differ as a function of the electron temperature. The different aspects related to the validity of this technique to measure the electron temperature in rf generated plasmas are discussed in this paper. At low plasma density this diagnostic is believed to be very reliable since the population of the emitting level can be easily estimated with reasonable accuracy by assuming that all excitation originates from the ground state (steady-state corona model). At higher density, (ne≤10111m-3secondary processes (excitation transfer, excitation from metastable, cascading) become more important and a more complex collisional radiative model must be used to predict the electron temperature. In this work, different helium transitions are examined and a suitable transition pair is identified. For an electron temperature of 10 eV, the line ratio is measured as a function of plasma density and compared to values predicted by models. The measured line ratio function is in good agreement with theory and the data suggest that the excitation transfer is the dominant secondary process in high-density plasmas. [ABSTRACT FROM AUTHOR]

Focuses on efficient heating in a steady-state helicon plasma source with two external loop antennae just above the ion cyclotron frequency. Measurement of the ion velocity space distribution; Laser induced fluorescence in an argon plasma; How the measured bulk ion heating is highly anisotropic even though the plasma is moderately collisional; Suggestion that an electrostatic ion cyclotron wave is launched.

Describes a Thomson parabola spectrograph that utilizes an electric field parallel to a magnetic field and a two-dimensional imaging detector to uniquely identify the energy-per-charge and mass-per-charge distributions of plasma ions. Characteristics of the spectrograph; Removal of deviations of observed spectra; Applicability of the spectrograph for neutral atom identification.

Recent laser upgrades on the Hot Helicon Experiment at West Virginia University have enabled multiplexed simultaneous measurements of the ion velocity distribution function at a single location, expanding our capabilities in laser-induced fluorescence diagnostics. The laser output is split into two beams, each modulated with an optical chopper and injected perpendicular and parallel to the magnetic field. Light from the crossing point of the beams is transported to a narrow-band photomultiplier tube filtered at the fluorescence wavelength and monitored by two lock-in amplifiers, each referenced to one of the two chopper frequencies. [ABSTRACT FROM AUTHOR]

We present ion velocity distribution function (IVDF) measurements obtained with a five grid retarding field energy analyzer (RFEA) and IVDF measurements obtained with laser induced fluorescence (LIF) for an expanding helicon plasma. The ion population consists of a background population and an energetic ion beam. When the RFEA measurements are corrected for acceleration due to the electric potential difference across the plasma sheath, we find that the RFEA measurements indicate a smaller background to beam density ratio and a much larger parallel ion temperature than the LIF. The energy of the ion beam is the same in both measurements. These results suggest that ion heating occurs during the transit of the background ions through the sheath and that LIF cannot detect the fraction of the ion beam whose metastable population has been eliminated by collisions. [ABSTRACT FROM AUTHOR]

We describe a three-dimensional (3D) laser-induced fluorescence (LIF) diagnostic for argon ions in a helicon plasma source. With three different laser injection orientations at a single spatial location, LIF measurements are performed to determine the 3D ion temperature and the 3D ion flow vector. The measurement process is then repeated at multiple locations in a cross section of the plasma column to create a two-dimensional (2D) map of the 3D ion flow, the ion temperature, and metastable ion density. Scanning in the 2D plane is accomplished by mounting the injection and collection optics on stepping motor driven stages. [ABSTRACT FROM AUTHOR]