Search

International audience; We analyze data returned by the Magnetospheric Multiscale mission (MMS) constellation during a rapid (∼1.5 s) traversal of a flapping and reconnecting current sheet (CS) in the near Earth magnetotail (X ∼−20 RE). The CS was highly tilted, with its normal pointing strongly duskward. Its extreme thinness was confirmed by a curvature analysis of the magnetic field lines. The event was associated with a guide field of 8% of the reconnecting components. From the pitch angle distributions of low energy electrons we infer a crossing earthward of the X line. Traveling practically normal to the CS, MMS encountered an ion diffusion region (IDR) in which was embedded an electron diffusion region (EDR). IDR signatures included breaking of the ion frozen in condition in the presence of Hall B and E fields. EDR signatures included a strong out of plane current associated with a superAlfvénic electron jet, positive energy transfer, and a temperature anisotropy (Te∥ > Te⊥) which disappeared at the field reversal. Derived scale sizes normal to the CS are: ∼6.9 de (EDR) and ∼0.4 di (IDR; 40 and 100 km). We estimate the average dimensionless reconnection rate as 0.077 ± 0.050. The observations and inferences are supported by particle in cell (PIC) numerical simulations. We find very good agreement in the reconnection rates. We also discuss the effects of asymmetries in the density, temperature and magnetic field strength on the Hall fields and length of the outflow jets. The event is associated with a substorm onset which began 7 min after the MMS observations.

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.

Geomagnetically induced currents (GIC) can drive power outages and damage power grid components while also affecting pipelines and train systems. Developing the ability to predict local GICs is important to protecting infrastructure and limiting the impact of geomagnetic storms on public safety and the economy. While GIC data is not readily available, variations in the magnetic field, dB/dt, measured by ground magnetometers can be used as a proxy for GICs. We are developing a set of neural networks to predict the east and north components of the magnetic field, BE and BN, from which the horizontal component, BH, and its variation in time, dBH/dt, are calculated. We apply two techniques for time series analysis to study the connection of solar wind and interplanetary magnetic field properties obtained from the OMNI dataset to the ground magnetic field perturbations. The analysis techniques include a feed-forward artificial neural network (ANN) and a long-short term memory (LSTM) neural network. Here we present a comparison of both models' performance when predicting the BH component of the Ottawa (OTT) ground magnetometer for the year 2011 and 2015 and then when attempting to reconstruct the time series of BH for two geomagnetic storms that occurred on 5 August 2011 and 17 March 2015.

With the availability of data and computational technologies in the modern world, machine learning (ML) has emerged as a preferred methodology for data analysis and prediction. While ML holds great promise, the results from such models are not fully unreliable due to the challenges introduced by uncertainty. An ML model generates an optimal solution based on its training data. However, if the uncertainty in the data and the model parameters are not considered, such optimal solutions have a high risk of failure in actual world deployment. This paper surveys the different approaches used in ML to quantify uncertainty. The paper also exhibits the implications of quantifying uncertainty when using ML by performing two case studies with space physics in focus. The first case study consists of the classification of auroral images in predefined labels. In the second case study, the horizontal component of the perturbed magnetic field measured at the Earth’s surface was predicted for the study of Geomagnetically Induced Currents (GICs) by training the model using time series data. In both cases, a Bayesian Neural Network (BNN) was trained to generate predictions, along with epistemic and aleatoric uncertainties. Finally, the pros and cons of both Gaussian Process Regression (GPR) models and Bayesian Deep Learning (DL) are weighed. The paper also provides recommendations for the models that need exploration, focusing on space weather prediction.

Energy deposited in the magnetosphere during geomagnetic storms drives ion heating and convection. Ions are also heated and transported via internal processes throughout the magnetosphere. Injection of the plasma sheet ions to the inner magnetosphere drives the ring current and, thus, the storm intensity. Understanding the ion dynamics is important to improving our ability to predict storm evolution. In this study, we perform superposed epoch analyses of ion temperatures during storms, comparing ion temperature evolution by storm driver and storm intensity. The ion temperatures are calculated using energetic neutral atom measurements from the Two Wide-Angle Imaging Neutral-Atom Spectrometers (TWINS) mission. The global view of these measurements provide both spatial and temporal information. We find that storms driven by coronal mass ejections (CMEs) tend to have higher ion temperatures throughout the main phase than storms driven by corotating interaction regions (CIRs) but that the temperatures increase during the recovery phase of CIR-driven storms. Ion temperatures during intense CME-driven storms have brief intervals of higher ion temperatures than those during moderate CME-driven storms but have otherwise comparable ion temperatures. The highest temperatures during CIR-driven storms are centered at 18 magnetic local time and occur on the dayside for moderate CME-driven storms. During the second half of the main phase, ion temperatures tend to decrease in the postmidnight to dawn sector for CIR storms, but an increase is observed for CME storms. This increase begins with a sharp peak in ion temperatures for intense CME storms, likely a signature of substorm activity that drives the increased ring current.

This AGU section formed a task force to make visible underrepresented scientists deserving of recognition for their work.

The role of Universal Time (UT) dependence on storm-time development has remained an unresolved question in geospace research. This study presents new insight into storm progression in terms of the UT of the storm peak. We present a superposed epoch analysis of solar wind drivers and geomagnetic index responses during magnetic storms, categorized as a function of UT of the storm peak, to investigate the dependency of storm intensity on UT. Storms with Dst minimum less than - 100 nT were identified in the 1970 - 2012 era (305 events), covering four solar cycles. The storms were classified into 6 groups based on the UT of the minimum Dst (40 to 61 events per bin), then each grouping was superposed on a timeline that aligns the time of the minimum Dst. Fifteen different quantities were considered, seven solar wind parameters and eight activity indices derived from ground-based magnetometer data. Statistical analyses of the superposed means against each other (between the different UT groupings) were conducted to determine the mathematical significance of similarities and differences in the time series plots. It was found that the solar wind parameters have no significant difference between the UT groupings, as expected. The geomagnetic activity indices, however, all show statistically significant differences with UT during the main phase and/or early recovery phase. Specifically, the 02:00 UT groupings are stronger storms than those in the other UT bins. That is, storms are stronger when the Asian sector is on the nightside (American sector on the dayside) during the main phase.

Over the past two decades, instruments designed to image plasmas in energetic neutral atom (ENA) emission have flown in space. In contrast to typical satellite-based in situ instruments, ENA imagers provide a global view of the magnetosphere because they remotely measure ion distributions via neutrals that are not tied to the magnetic field. An intrinsic challenge that arises during analysis of magnetospheric ENA images is that the ENA fluxes are integrated along the line-of-sight of the instrument. We propose a method of enhancing ENA emission from a localized region in space, thereby enabling spatially resolved measurements of ENA emission in a remotely obtained ENA image. Here we show that releases of modest volumes (~ 1.4 m3) of liquid hydrogen in space are sufficient to accomplish the ENA localization.

Taking advantage of technological developments in wafer-scale processing over the past two decades, such as deep etching, 3-D chip stacking, and double-sided lithography, we have designed and fabricated the key elements of an ultracompact 1.5cm (exp 3)plasma spectrometer that requires only low-voltage power supplies, has no microchannel plates, and has a high aperture area to instrument volume ratio. The initial design of the instrument targets the measurement of charged particles in the 3-20keV range with a highly directional field of view and a 100 duty cycle; i.e., the entire energy range Is continuously measured. In addition to reducing mass, size, and voltage requirements, the new design will affect the manufacturing process of plasma spectrometers, enabling large quantities of identical instruments to be manufactured at low individual unit cost. Such a plasma spectrometer is ideal for heliophysics plasma investigations, particularly for small satellite and multispacecraft missions. Two key elements of the instrument have been fabricated: the collimator and the energy analyzer. An initial collimator transparency of 20 with 3deg x 3deg angular resolution was achieved. The targeted 40 collimator transparency appears readily achievable. The targeted energy analyzer scaling factor of 1875 was achieved; i.e.20 keV electrons were selected for only a 10.7V bias voltage in the energy analyzer.

The location of the outer edge of the plasmasphere (the plasmapause) as a function of geomagnetic storm time is identified and investigated statistically in regard to the solar wind driver. Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) extreme ultraviolet (EUV) data are used to create an automated method that locates and extracts the plasmapause. The plasmapause extraction technique searches a set range of possible plasmasphere densities for a maximum gradient. The magnetic local time (MLT)-dependent plasmapause results are compared to manual extraction results. The plasmapause results from 39 intense storms are examined along a normalized epoch storm timeline to determine the average plasmapause L shell as a function of MLT and storm time. The average extracted plasmapause L shell follows the expected storm time plasmapause behavior. The results show that during the main phase, the plasmapause moves earthward and a plasmaspheric drainage plume forms near dusk and across the dayside during strong convection. During the recovery phase, the plume rejoins the corotationally driven plasma while the average plasmapause location moves farther from the Earth. The results are also examined in terms of the solar wind driver. We find evidence that shows that the different categories of solar wind drivers result in different plasmaspheric configurations. During magnetic cloud-driven events the plasmaspheric drainage plume appears at the start of the main phase. During sheath-driven events the plume forms later but typically extends further in MLT.

We investigate the effects of different ionospheric conductance and electron loss models on ring current dynamics during the large magnetic storm of 5–7 April 2010 using the magnetically and electrically self-consistent Rice Convection Model–Equilibrium (RCM-E). The time-varying RCM-E proton distribution boundary conditions are specified using a combination of TWINS 1 and 2 ion temperature maps and in situ THEMIS and GOES spectral measurements in the plasma sheet. With strong electron pitch-angle diffusion, the simulated equatorial ring current electron pressure is weak with (1) uniform conductance or (2) conductance based on parameters from the International Reference Ionosphere 2007 and the feedback of simulated precipitating electrons. With the Chen and Schulz electron loss model that includes strong diffusion in the plasma sheet and weak diffusion in the plasmasphere, the stormtime equatorial RCM-E electron pressure is enhanced in the inner magnetosphere from midnight through dawn to the dayside. The enhancement extends to lower geocentric distance with uniform conductance than with the more realistic ionospheric conductance model due to electric field shielding effects. Electron losses affect not only the simulated electron pressures, but through magnetospheric-ionospheric coupling, the redistributed electric and magnetic fields affect the ring current proton transport. The simulations reproduced features observed by in situ magnetic field and proton flux data, and TWINS global ENA observations. The simulated stormtime ring current energization can vary significantly depending on the ionospheric conductance and electron loss model used. Thus, it is important to incorporate realistic descriptions of ionospheric conductance and electron losses in inner magnetospheric models.

Ions in the plasma sheet are measured by the energetic neutral atom imagers on the Two Wide-Angle Imaging Neutral-Atom Spectrometers (TWINS) spacecraft. A line of sight (LOS) projection is used to determine the location of the ions that dominate the measured spectrum, assuming that the equatorial plane is the hottest region along the LOS. We verify reasonable agreement between ion spectral shapes measured using this remote measurement technique and in situ measurements from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft during two moderate geomagnetic storms. Conditions for reliable use of this technique to determine ion spectra and effective ion temperatures are identified. The technique is applied to the substorm interval associated with the loss of communication with the Galaxy-15 satellite. During this interval, localized and broad regions of ion energization are observed, demonstrating that magnetic reconnection and current disruption may have played a role during this very extreme event. These observations demonstrate the ability of this technique to cast local ion spectra measurements in a global context.

Coronal mass ejections (CMEs) and corotating interaction regions associated with high speed solar wind streams (CIR/HSSs) drive geomagnetic storms in the terrestrial magnetosphere. Each type of storm driver yields different dynamics of storm evolution. We present results from comparative superposed epoch analyses of global ion temperatures calculated from TWINS energetic neutral atom (ENA) data and simulations using the comprehensive ring current model (CRCM). During the June 2008–April 2012 timeframe, 48 geomagnetic storms (minimum Dst≤−40 nT) occurred. Of these, 21 storms were CME-driven and 15 were driven by CIR/HSSs. Superposed epoch analysis results demonstrate that ion temperatures increase during the recovery phase of CIR/HSS-driven storms, while ions are rapidly heated at the commencement of CME-driven storms then cool over the main phase, particularly for intense (minimum Dst≤−78 nT) CME-driven storms. Higher energy ions are convected to lower L-shells during CME-driven storms, while CIR/HSS-driven storms tend to have average ion temperatures that are higher on the dayside than nightside.

We have integrated dynamic, spatiotemporally resolved ion temperature boundary conditions into the Comprehensive Ring Current Model (CRCM), which are based on 2-D equatorial maps derived from the Two Wide-Angle Imaging Neutral-Atom Spectrometers (TWINS) energetic neutral atom (ENA) data. The high-speed stream-driven event on 22 July 2009 is simulated and compared against an identical simulation using a statistically derived boundary condition model. ENA-derived temperatures allow users to include event-specific observations associated with a dynamic plasma sheet. This method also provides temperatures in the important region between geosynchronous orbit and the plasma sheet, a region which existing empirical models exclude. We find that the spatial and energy distributions of ring current flux and pressure have sensitive dependence on boundary conditions during this event. The coupling of boundary conditions to the time history of the convection field strength also plays an important role by throttling the influence of the boundary plasma on the inner magnetosphere. Simulated moments and spectra from our simulations are compared with remotely imaged ion temperatures from TWINS and also in situ energy spectra and temperature moments from Time History of Events and Macroscale Interactions during Substorms-D. Storm time dusk-dawn asymmetries consistent with observational data, such as Zhang et al. (2006), are reproduced well when CRCM is provided with the event-specific boundary model. A hot localized structure observed by TWINS at geosynchronous midnight during a strong northward interplanetary magnetic field interval is also reproduced with this boundary model, whereas the empirical boundary model fails to yield this feature.

We compare three laser induced fluorescence schemes for measuring velocity distributions of Ar-I 1s 5 metastables in the presence of a magnetic field. In these three-level schemes, the 1s 5 state is optically pumped to 2p 2, 2p 3, or 2p 4 by sweeping the frequency of a tuneable CW laser over transitions in the visible range at 696.7352 nm, 706.9167 nm, and 714.9012 nm, respectively. Broadening in the fluorescence spectra is attributed to Zeeman splitting and saturation effects. We present measurements of spectral broadening dependence on injected laser intensity and describe spectral reconstructions that account for Zeeman splitting. For laser injection parallel to a background magnetic field, the separation of the Zeeman-split σ ± clusters is an effective, non-perturbative localized magnetic field diagnostic. We discuss the advantages of the three transition schemes and present the optimal transition for several applications.

The CubeSat for GNSS Sounding of Ionosphere-Plasmasphere Electron Density (CuSPED) is a 3U CubeSat mission concept that has been developed in response to the NASA Heliophysics program's decadal science goal of the determining of the dynamics and coupling of the Earth's magnetosphere, ionosphere, and atmosphere and their response to solar and terrestrial inputs. The mission was formulated through a collaboration between West Virginia University, Georgia Tech, NASA GSFC and NASA JPL, and features a 3U CubeSat that hosts both a miniaturized space capable Global Navigation Satellite System (GNSS) receiver for topside atmospheric sounding, along with a Thermal Electron Capped Hemispherical Spectrometer (TECHS) for the purpose of in situ electron precipitation measurements. These two complimentary measurement techniques will provide data for the purpose of constraining ionosphere-magnetosphere coupling models and will also enable studies of the local plasma environment and spacecraft charging; a phenomenon which is known to lead to significant errors in the measurement of low-energy, charged species from instruments aboard spacecraft traversing the ionosphere. This paper will provide an overview of the concept including its science motivation and implementation.

We present an analysis of laser-induced fluorescence and emission spectroscopy profile measurements of the excited states of neutral argon for two different helicon source pressures. Through use of a collisional–radiative model that calculates excited state profiles based on measured electron densities, electron temperatures, and the measured edge neutral pressure, the ground state neutral density profile is determined for each pressure case. The results demonstrate that it is possible to extract the ground state neutral density profile from such measurements and that the degree of ionization at the center (r = 0) of a helicon source plasma can vary significantly for a small change in source pressure.

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.

Ion temperatures as a function of the x and y axes in the geocentric solar magnetospheric (GSM) coordinate system and time are available for 76 geomagnetic storms that occurred during the period July 2008 to December 2013 on CDAWeb. The method for mapping energetic neutral atom data from the Two Wide‐angle Imaging Spectrometers (TWINS) mission to the GSM equatorial plane and subsequent ion temperature calculation are described here. The ion temperatures are a measure of the average thermal energy of the bulk ion population in the 1–40 keV energy range. These temperatures are useful for studies of ion dynamics, for placing in situ measurements in a global context, and for establishing boundary conditions for models of the inner magnetosphere and the plasma sheet., Key Points Ion temperatures are calculated from TWINS energetic neutral atom dataMaps of ion temperatures during geomagnetic storms are available on CDAWeb

The West Virginia University Hot hELIcon eXperiment (HELIX) provides variable density and ion temperature plasmas, with controllable levels of thermal anisotropy, for space relevant laboratory experiments in the Large Experiment on Instabilities and Anisotropy (LEIA) as well as fundamental studies of helicon source physics in HELIX. Through auxiliary ion heating, the ion temperature anisotropy (T⊥/T∥) is variable from 1 to 20 for parallel plasma beta (β = 8πnkTi∥/B2) values that span the range of 0.0001 to 0.01 in LEIA. The ion velocity distribution function is measured throughout the discharge volume in steady-state and pulsed plasmas with laser induced fluorescence (LIF). The wavelengths of very short wavelength electrostatic fluctuations are measured with a coherent microwave scattering system. Operating at low neutral pressures triggers spontaneous formation of a current-free electric double layer. Ion acceleration through the double layer is detected through LIF. LIF-based velocity space tomography of the accelerated beam provides a two-dimensional mapping of the bulk and beam ion distribution functions. The driving frequency for the m = 1 helical antenna is continuously variable from 8.5 to 16 MHz and frequency dependent variations of the RF coupling to the plasma allow the spontaneously appearing double layers to be turned on and off without modifying the plasma collisionality or magnetic field geometry. Single and multi-species plasmas are created with argon, helium, nitrogen, krypton, and xenon. The noble gas plasmas have steep neutral density gradients, with ionization levels reaching 100% in the core of the plasma source. The large plasma density in the source enables the study of Aflvén waves in the HELIX device.

Recently, we demonstrated that a single, tunable, low-power, diode laser can be used for laser-induced fluorescence (LIF) measurements of both argon ions and helium neutrals. We have now identified a third fluorescence scheme, for neutral argon atoms, accessible with the same tunable diode laser. Fluorescence measurements of a heated iodine cell are used to monitor the wavelength of the laser during the LIF measurement.

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.

[1] The remotely measured increase in plasma sheet ion temperatures during high speed stream-driven storms is greater than that of ICME-driven storms. These hot ions are convected to the inner magnetosphere where they drive the ring current. On 22 July 2009, a high speed stream yielded a moderate (minimum Dst of −79 nT) storm, one of the largest that occurred during the extended solar minimum between January 2007 and September 2010. We present measurements obtained with an energetic neutral atom (ENA) imager of the TWINS mission during the main phase of the storm. Ion temperatures calculated from the ENA measurements show storm-time increase in ion temperature and a subsequent convection of hot ions into the inner magnetosphere. In the magnetotail, a region of hot ions near local midnight is observed that may be associated with substorm-related bursty bulk flows.

Inclusion of thermal anisotropy effects is shown to be required to describe recently reported experimental measurements as shear-modified, ion acoustic instabilities. For the reported experimental conditions, isotropic theory yields no instability growth that depends on the magnitude of the shear in the parallel flow.

Ion temperature analysis of the first energetic neutral atom images of the quiet -time, extended magnetosphere provides evidence of multiple regions of ion heating. This study confirms the existence of a dawn -dusk asymmetry in ion temperature predicted for quiescent magnetospheric conditions by Spence and Kivelson (1993) and demonstrates that it is an inherent magnetospheric feature.

We present a method to infer the electron temperature in argon plasmas using a collisional-radiative model for argon ions and measurements of electron density to interpret absolutely calibrated spectroscopic measurements of argon ion (Ar II) line intensities. The neutral density, and hence the degree of ionization of this plasma, can then be estimated using argon atom (Ar I) line intensities and a collisional-radiative model for argon atoms. This method has been tested for plasmas generated on two different devices at the University of Texas at Austin: the helicon experiment and the helimak experiment. We present results that show good correlation with other measurements in the plasma.

[1] Time-resolved remote ion temperature measurements of the magnetosphere from 10 R E to ―60 R E are presented for the first 48 h of the storm of 4―7 October 2000. Ion temperatures are calculated from Maxwellian fits to data from the Medium Energetic Neutral Atom instrument aboard the Imager for Magnetopause-to-Aurora Global Exploration spacecraft. The calculated ion temperatures in the magnetotail are consistent with in situ measurements from multiple geosynchronous spacecraft and Geotail at x = -9 R E . The measurements indicate two separate instances of an earthward propagating increase in ion temperature during the storm. Ion heating is observed coincident with substorm injections at 0600 UT and 1720 UT on 4 October. At -12 R E , the remotely measured ion temperatures are consistent with predictions of a solar wind velocity correlation equation only when the solar wind-magnetospheric coupling is strong. At other times, the measured ion temperature is 2-3 times larger than the predicted value.

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. Ion-neutral and electron-neutral collisions can be important mechanisms for Alfven wave damping, ion cyclotron wave damping, and flow thermalization in helicon sources. The phenomenon of neutral pumping, leading to reduced neutral pressures on axis, has been suggested to play an important role in the physics of cylindrically symmetric helicon sources. However, the spatial distribution, temperature, and flow of neutral atoms in helicon sources are poorly understood quantities. We have obtained laser induced fluorescence (LIF) measurements of argon neutrals, helium neutrals, and argon ions as a function of radial position with a low power, tunable diode laser in the Hot hELIcon eXperiment (HELIX) at West Virginia University. Using radial profile measurements of electron density and electron temperature, the neutral (or ion) density profile can be extracted from spatially resolved LIF measurements of the interrogated species. LIF neutral density profiles are compared to neutral density profile measurements obtained through spatially resolved, passive emission spectroscopy measurements.

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.

Summary form only given, as follows. Initial ion temperature measurements in The Hot hELIcon eXperiment (HELIX) helicon source showed that the ion temperature is non-negligible and can be as high as 1 eV. The measurements also showed that the ion temperature scales with magnetic field strength and that the ion temperature is anisotropic with respect to the magnetic field. The perpendicular ion temperature increases with increasing magnetic field strength while the parallel ion temperatures remain the same. Further investigation by Balkey et al. [Plasma Sources Sci. and Tech., 10, 284(2001)] showed that the increase in ion temperature and the electron density are correlated with the lower hybrid frequency. Recent experimental data will be presented that are consistent with hypothesis that the anomalous rf absorption in helicon sources is due to electron scattering arising from parametrically driven ion-acoustic waves downstream from the antenna. Theory predicts that the scattering should be largest near the lower hybrid frequency. We will also present ion temperature measurements that demonstrate anisotropic heating (T/sub /spl perp//>T/sub /spl par//) at the edge of the discharge when the rf frequency equals the lower hybrid frequency at the edge of the plasma. The most likely explanation is ion Landau damping of electrostatic slow waves at a local lower hybrid frequency resonance.

Experimental data are presented that are consistent with the hypothesis that anomalous rf absorption in helicon sources is due to electron scattering arising from parametrically driven ion-acoustic waves downstream from the antenna. Also presented are ion temperature measurements demonstrating anisotropic heating (T( perpendicular)>T(parallel)) at the edge of the discharge. The most likely explanation is ion-Landau damping of electrostatic slow waves at a local lower-hybrid-frequency resonance.

We present experimental evidence for the spontaneous formation of multiple double layers within a single divergent magnetic field structure. Downstream of the divergent magnetic field, multiple accelerated ion populations are observed. The similarity of the accelerated ion populations observed in these laboratory experiments to ion populations observed in the magnetosphere and in numerical simulations suggests that the observation of a complex ion velocity distribution alone is insufficient to distinguish between simple plasma expansion and magnetic reconnection. Further, the effective temperature of the aggregate ion population is significantly larger than the temperatures of the individual ion population components, suggesting that insufficiently resolved measurements could misidentify multiple beam creation as ion heating. Ions accelerated in randomly oriented electric fields that mimic heating would have an ion heating rate dependent on the ion charge and mass that is qualitatively consistent with recent experimental observations of ion heating during magnetic reconnection.

[1] Energy spectra of ENA images obtained with the MENA imager on the IMAGE observatory are used to construct remote images of the plasma ion temperature. The remotely measured ion temperatures are consistent with in-situ ion temperature measurements. During the storm of August 12, 2000, the ion temperatures on the dawn side of the magnetosphere are significantly lower than the dusk side ion temperatures. Similar observations of ion temperature asymmetry are presented for three other storm periods.

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 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.

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.

Neutral atoms play important roles in non-fully-ionized plasmas. In helicon sources, neutral pumping and neutral damping of waves are poorly understood. Measurement of the spatial distribution of neutral atoms is possible with spectroscopic diagnostics such as laser-induced fluorescence (LIF) and passive emission spectroscopy. However, these measurements typically apply to an excited neutral atom state, rather than the entire neutral population. With a collisional-radiative (CR) model employing Langmuir probe measured electron parameters in argon helicon source plasmas, we have reproduced LIF and emission spectroscopy measured radial profiles for three excited neutral states. The CR model indicates a neutral depletion on axis of at least 60%. Simple calculations based on measured edge neutral pressures and peak plasma densities significantly underestimate the degree of ionization in the core of the helicon plasma.