Average Ion Mass Research Articles

Field line distribution of density at <I>L</I>=4.8 inferred from observations by CLUSTER

Abstract. For two events observed by the CLUSTER spacecraft, the field line distribution of mass density ρ was inferred from Alfvén wave harmonic frequencies and compared to the electron density ne from plasma wave data and the oxygen density nO+ from the ion composition experiment. In one case, the average ion mass M≈ρ/ne was about 5 amu (28 October 2002), while in the other it was about 3 amu (10 September 2002). Both events occurred when the CLUSTER 1 (C1) spacecraft was in the plasmatrough. Nevertheless, the electron density ne was significantly lower for the first event (ne=8 cm−3) than for the second event (ne=22 cm−3), and this seems to be the main difference leading to a different value of M. For the first event (28 October 2002), we were able to measure the Alfvén wave frequencies for eight harmonics with unprecedented precision, so that the error in the inferred mass density is probably dominated by factors other than the uncertainty in frequency (e.g., magnetic field model and theoretical wave equation). This field line distribution (at L=4.8) was very flat for magnetic latitude |MLAT|≲20° but very steeply increasing with respect to |MLAT| for |MLAT|≳40°. The total variation in ρ was about four orders of magnitude, with values at large |MLAT| roughly consistent with ionospheric values. For the second event (10 September 2002), there was a small local maximum in mass density near the magnetic equator. The inferred mass density decreases to a minimum 23% lower than the equatorial value at |MLAT|=15.5°, and then steeply increases as one moves along the field line toward the ionosphere. For this event we were also able to examine the spatial dependence of the electron density using measurements of ne from all four CLUSTER spacecraft. Our analysis indicates that the density varies with L at L~5 roughly like L−4, and that ne is also locally peaked at the magnetic equator, but with a smaller peak. The value of ne reaches a density minimum about 6% lower than the equatorial value at |MLAT|=12.5°, and then increases steeply at larger values of |MLAT|. This is to our knowledge the first evidence for a local peak in bulk electron density at the magnetic equator. Our results show that magnetoseismology can be a useful technique to determine the field line distribution of the mass density for CLUSTER at perigee and that the distribution of electron density can also be inferred from measurements by multiple spacecraft.

Pulsed and Continuous Wave Acrylic Acid Radio Frequency Plasma Deposits: Plasma and Surface Chemistry

Plasma polymers have been formed from acrylic acid using a pulsed power source. An on-pulse duration of 100 micros was used with a range of discharge off-times between 0 (continuous wave) and 20,000 micros. X-ray photoelectron spectroscopy (XPS) has been used in combination with trifluoroethanol (TFE) derivatization to quantify the surface concentration of the carboxylic acid functionality in the deposit. Retention of this functionality from the monomer varied from 2% to 65%. When input power was expressed as the time-averaged energy per monomer molecule, E(mean), the deposit chemistry achieved could be described using a single relationship for all deposition conditions. Deposition rates were monitored using a quartz crystal microbalance, which revealed a range from 20 to 200 microg m(-2) s(-1), and these fell as COOH functional retention increased. The flow rate was found to be the major determinant of the deposition rate, rather than being uniquely defined by E(mean), connected to the rate at which fresh monomer enters the system in the monomer deficient regime. The neutral species were collected in a time-averaged manner. As the energy delivered per molecule in the system (E(mean)) decreased, the amount of intact monomer increased, with the average neutral mass approaching 72 amu as E(mean) tends to zero. No neutral oligomeric species were detected. Langmuir probes have been used to determine the temporal evolution of the density and temperature of the electrons in the plasma and the plasma potential adjacent to the depositing film. It has been found that even 500 micros into the afterglow period that ionic densities are still significant, 5-10% of the on-time density, and that ion accelerating sheath potentials fall from 40 V in the on-time to a few volts in the off-time. We have made the first detailed, time- and energy-resolved mass spectrometry measurements in depositing acrylic acid plasma. These have allowed us to identify and quantify the positive ion species in the acrylic acid plasma during both the on- and the off- periods. The relative intensities of oligomeric species of the type [nM + H]+ as large as n = 3 were observed to increase in the off-time suggesting vapor phase polymerization after power input to the plasma was ceased. The energy distribution functions of these ions demonstrated that they were produced in the plasma in both the on- and the off-times. This remarkable observation contradicts the assumptions usually made when speculating on pulsed plasma that ions have very short lifetimes, although it is anticipated that radicals still have significantly longer lifetimes, estimated from calculation to be in excess of 1 ms. The increase in average positive ion mass during the off-period can be related to the lower mobility of the heavier components, reducing their relative loss to surfaces, and the polymer chain growth in the gas phase due to the ion-neutral collisions. The implications of these observations are discussed in light of polymerization mechanisms proposed from continuous acrylic acid and millisecond pulsing plasmas.

Improved Validation of Peptide MS/MS Assignments Using Spectral Intensity Prediction

A major limitation in identifying peptides from complex mixtures by shotgun proteomics is the ability of search programs to accurately assign peptide sequences using mass spectrometric fragmentation spectra (MS/MS spectra). Manual analysis is used to assess borderline identifications; however, it is error-prone and time-consuming, and criteria for acceptance or rejection are not well defined. Here we report a Manual Analysis Emulator (MAE) program that evaluates results from search programs by implementing two commonly used criteria: 1) consistency of fragment ion intensities with predicted gas phase chemistry and 2) whether a high proportion of the ion intensity (proportion of ion current (PIC)) in the MS/MS spectra can be derived from the peptide sequence. To evaluate chemical plausibility, MAE utilizes similarity (Sim) scoring against theoretical spectra simulated by MassAnalyzer software (Zhang, Z. (2004) Prediction of low-energy collision-induced dissociation spectra of peptides. Anal. Chem. 76, 3908-3922) using known gas phase chemical mechanisms. The results show that Sim scores provide significantly greater discrimination between correct and incorrect search results than achieved by Sequest XCorr scoring or Mascot Mowse scoring, allowing reliable automated validation of borderline cases. To evaluate PIC, MAE simplifies the DTA text files summarizing the MS/MS spectra and applies heuristic rules to classify the fragment ions. MAE output also provides data mining functions, which are illustrated by using PIC to identify spectral chimeras, where two or more peptide ions were sequenced together, as well as cases where fragmentation chemistry is not well predicted.

Mass density inferred from toroidal wave frequencies and its comparison to electron density

We have estimated the magnetospheric local mass density using the frequency of the toroidal standing Alfvén waves detected with the magnetic (B) and electric (E) field experiments on the Combined Release and Radiation Effects Satellite (CRRES), which had a low‐latitude elliptical orbit (6.3 RE apogee and 18° inclination). A 73‐day period in 1991, which included several geomagnetic storms, was chosen for analysis because the spacecraft was located on the afternoon sector where toroidal waves are routinely excited. Dynamic spectra of the B and E fields were generated for each CRRES orbit for visual identification of toroidal mode ULF waves excited at a number of harmonics. The fundamental mode is the most persistent feature in the spectra, and this mode appears more clearly in the electric field than in the magnetic field. For statistical analysis we determined the fundamental frequency f1 from a separate set of electric field spectra that were computed in a moving 20‐min time window with 10‐min overlap. The frequency is in the range of 1.7–14.2 mHz. The local mass density consistent with f1 was obtained by numerically solving a magnetohydrodynamic wave equation that incorporated the Tsyganenko magnetic field model and an analytical form of field‐line mass density variation that was derived from a recent study of toroidal harmonics. We combined the estimated mass density with the local electron number density ne derived from the plasma wave spectra at CRRES to obtain the local average ion mass M (=ρ/ne). A total of 1094 M samples were obtained, with the majority (95%) coming from the plasmatrough region (ne < 100 cm−3). Our technique for the mass density is confirmed to be reliable because only 3.5% of the M samples lie outside the physically plausible range of 1 amu (all‐H+ plasma) to 16 amu (all‐O+ plasma). The average ion mass has a median value of 3.0 amu and depends on geomagnetic activity. For example, M is 2.5 amu for Dst = 0 and 4.1 amu for Dst = −60 nT. There is a similar dependence of M on Kp, but only when the Kp values are averaged over a few days. There is no strong dependence of M on the magnetic field L shell in the range L = 4 to L = 8 covered by the f1 samples, although M is significantly low (<2 amu) for the plasmaspheric regime (ne > 100 cm−3).

A plasmaspheric mass density model and constraints on its heavy ion concentration

The first empirical model of the equatorial mass density of the plasmasphere is constructed using ground‐based ULF wave diagnostics. Plasmaspheric mass density between L = 1.7 and L = 3.2 has been determined using over 5200 hours of data from pairs of stations in the MEASURE array of ground magnetometers. The least squares fit to the data as a function of L shows that mass density falls logarithmically with L. Average ion mass as a function of L is also estimated by combining the mass density model with plasmaspheric electron density profiles determined from the IMAGE Radio Plasma Imager (RPI). Additionally, we use the RPI electron density database to examine how the average ion mass changes under different levels of geomagnetic activity. We find that average ion mass is greatest under the most disturbed conditions. This result indicates that heavy ion concentrations (percent by number) are enhanced during large geomagnetic disturbances. We also find that the average ion mass increases with increasing L (below L = 3.2), indicating the presence of a heavy ion torus during disturbed times. Heavy ions must play an important role in storm‐time plasmaspheric dynamics. The average ion mass is also used to constrain the concentrations of He+ and O+. Estimates of the He+ concentration determined this way may be useful for interpreting IMAGE Extreme Ultraviolet Imager (EUV) images.

Electron capture dissociation Fourier transform ion cyclotron resonance mass spectrometry in the electron energy range 0-50 eV.

Electron capture dissociation (ECD) of polypeptide cations was obtained with pencil and hollow electron beams for both sidekick and gas-assisted dynamic ion trapping (GADT) using Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) with an electrostatic ion transfer line. Increasing the number of trapped ions by multiple ICR trap loads using GADT improved the ECD sensitivity in comparison with sidekick ion trapping and ECD efficiency in comparison with single ion trap load by GADT. Furthermore, enhanced sensitivity made it possible to observe ECD in a wide range of electron energies (0-50 eV). The degree, rate and fragmentation characteristics of ECD FTICR-MS were investigated as functions of electron energy, electron irradiation time, electron flux and ion trapping parameters for this broad energy range. The results obtained show that the rate of ECD is higher for more energetic (>1 eV) electrons. Long electron irradiation time with energetic electrons reduces average fragment ion mass and decreases efficiency of formation of c- and z-type ions. The obtained dependencies suggest that the average fragment ion mass and the ECD efficiency are functions of the total fluence of the electron beam (electron energy multiplied by irradiation time). The measured electron energy distributions in low-energy ECD and hot ECD regimes are about 1 eV at full width half maximum in employed experimental configurations.

The Role of Ions in the Plasma Polymerization of Allylamine

The radio-frequency-induced plasma polymerization of allylamine has been investigated in the plasma-gas phase by mass spectrometry and at the plasma−solid interface by means of an ion flux probe and a quartz mass balance. The surface chemistry of the deposits has been determined by X-ray photoelectron spectroscopy. The objective of this study was to unravel the mechanism(s) by which allylamine plasma polymers form. The results are compared with those obtained in an earlier investigation of the plasma polymerization of acrylic acid. In the plasma-gas phase, evidence is provided for reactions between cations and intact neutral monomers (allylamine). These oligomerization reactions were found to be relatively power-insensitive compared with those seen in plasmas of acrylic acid, as was the gas-phase concentration of the intact neutral monomer. At the polymer surface, ion fluxes were found to increase with plasma input power (P) from 6.6 × 1016 ions m-2 s-1 at 1 W to 1.4 × 1018 ions m-2 s-1 at 14 W. The ionic mass transport to the polymer surface (ion mass flux) was calculated by multiplying the measured ion flux by the average ion mass (determined by mass spectrometry). At P = 1 W, the ion mass flux was 11.7 μm m-2 s-1, and at 14 W, the ion mass flux was 226.6 μm m-2 s-1. These values differed from the total mass deposition rates measured by the quartz mass balance, which were 18.7 and 127.1 μm m-2 s-1, respectively. However, the relationship found between the ion mass flux, the mass deposition rate, and P was complex, and it is shown that, at very low P (<1 W), the ion mass flux is sufficient to account for all of the deposit.

Optical Measurements of Aerosol Size Distributions in Great Smoky Mountains National Park: Dry Aerosol Characterization

ABSTRACT Aerosol size distributions were measured during the summertime 1995 Southeastern Aerosol and Visibility Study (SEAVS) in Great Smoky Mountains National Park using an Active Scattering Aerosol Spectrometer (ASASP-X) optical particle counter. We present an overview of the experimental method, our data inversion technique, timelines of the size distribution parameters, and calculations of dry accumulation mode aerosol density and refractive index. Aerosol size distributions were recorded during daylight hours for aerosol in the size range 0.1 < Dp < 2.5 u,m. The particle refractive index used for the data inversion was calculated with the partial molar refractive index approach using 12-hr measured aerosol chemical composition. Aerosol accumulation mode volume concentrations ranging from 1 to 26 u,m3 cm-3 were observed, with an average of 7 ± 5 u,m3 cm-3. The study average dry accumulation mode geometric volume median diameter was 0.27 ± 0.03 u,m, and the mean geometric standard deviation was 1.45 ± 0.06. Using an internally mixed aerosol model, and assuming chemical homogeneity across the measured particle distribution, an average accumulation mode dry sulfate ion mass scattering efficiency of 3.8 ± 0.6 m2 g-1 was calculated.

Circulation and dynamics in the jovian magnetosphere

Io continually adds mass to the Io torus and this density builds up until centrifugal force is sufficient to overcome the line tying of the jovian ionosphere. The magnetic flux is carried outward with this slow radial convection. Under the assumption that 1 ton per second is added to the torus at Io and that the Voyager observed densities and average ion mass are pertinent for the Pioneer and Galileo epochs, a consistent flow pattern arises. The outward flow near Io is a few meters per second. Near Europa the velocity, based on the observations of a Europa plume, rises to about 400 m/s. Beyond 24 R J in the magnetodisk it is possible to again estimate the velocity. It is about 20 km/s at 25 R J and about 50 km/sec at 40 R J consistent with the Voyager LECP measurements. This outflow of magnetic flux is replenished by reconnection of magnetic flux in the near tail and the subsequent inward convection of empty flux tubes into the inner magnetosphere. These flux tubes are seen in the middle magnetosphere and the Io torus. Their scarcity as judged by the fact that they constitute only about 0.4% of the observing time indicates that they are moving inward at a much higher rate than the mass-loaded magnetospheric plasma moves outward. In the neighborhood of the magnetodisk the outflow appears not to be steady as the magnetic flux crossing the current sheet varies greatly from orbit to orbit. This unsteadiness may lead the occasional auroral storms seen in the ionosphere at the feet of these field lines.

Probing Ganymede's magnetosphere with field line resonances

We report on the spectrum of field line resonances identified in data acquired by the Galileo spacecraft within Ganymede's magnetosphere on a relatively low latitude pass. We infer properties of the plasma distribution and its transport from the observed spectrum. The harmonic structure in the spectrum of the magnetometer data agrees very well with the frequencies predicted for resonances of a dipole field. The spectrum implies a density of 2 amu cm−3 near the equator on closed field lines of Ganymede's magnetic field inside of 2 RG (Ganymede radii). This density is significantly reduced relative to the local density of the Jovian plasma sheet near Ganymede (≤ 8 electrons cm−3, or ∼100 amu cm−3 for an average ion mass per charge of 20 amu and average charge of 1.5 electron charges). A shadowing effect of Ganymede for the flow of particles injected at a reconnection layer on the side of the moon downstream relative to the direction of torus plasma flow accounts for the marked density depletion. Implications for conducting paths near Ganymede's surface are considered.

Negative ions in the auroral mesosphere during a PCA event around sunset

Abstract. This is a study of the negative ion chemistry in the mesosphere above Tromsø using a number of EISCAT observations of high energy proton precipitation events during the last solar maximum, and in particular around sunset on 23 October, 1989. In these conditions it is possible to look at the relative importance of the various photodetachment and photodissociation processes controlling the concentration of negative ions. The data analysed are from several UHF GEN11 determinations of the ion-plasma ACF together with the pseudo zero-lag estimate of the `raw' electron density, at heights between 55 km and 85 km, at less than 1 km resolution. The power profiles from the UHF are combined with the 55-ion Sodankylä model to obtain consistent estimates of the electron density, the negative ion concentrations, and the average ion mass with height. The neutral concentrations and ion temperature are given by the MSIS90 model. These parameters are then used to compare the calculated widths of the ion-line with the GEN11 determinations. The ion-line spectrum gives information on the effects of negative ions below 70 km where they are dominant; the spectral width is almost a direct measure of the relative abundance of negative ions.Key words. Ionosphere (auroral ionosphere; ion chemistry and composition; particle precipitation).

Thermochemical processes and ion transport in inductively coupled plasma mass spectrometry: theoretical description and experimental confirmation

Equilibrium thermodynamic modeling has been used to study thermochemical processes in the inductively coupled plasma (ICP). A thermodynamic model for the central ICP channel has been developed, which takes into account all realistic initial plasma compositions and all possible components at the equilibrium. The accuracy of the model was confirmed by a good agreement between the experimental and calculated values for the electron concentrations in the ICP analytical zone. Degrees of ionization for 75 elements in the temperature range from 6000 to 9000 K were calculated at each 1000 K. A relation has been developed for describing the mass discrimination function of registered ions in a mass spectrometer with the ICP (ICP-MS). Using the experimental detection limits of elements in the ICP-MS and calculated partial pressures of their ions in the ICP, similar well-defined discrimination functions were obtained for many Ar ICP-MS spectrometers of different producers and for He ICP-MS. This confirms the accuracy and validity of using the equilibrium model in the central ICP channel and allows the adjustment of the calibration of ICP-MS spectrometers in multi-component semi-quantitative analysis. The series of calculations have shown significant matrix ion contributions in the total ion current in the ICP. This has been confirmed by the experimental data and indicates that the temperature in the central ICP channel is usually less than 7000 K. The new model can be used to determine the total ion current and average ion mass at the interface entrance. This is necessary for quantitatively analyzing the processes of ion loss during their transport in the ion beam.

Ion-line in the D- and E-regions from EISCAT observations and the Lancaster-Sodankyla model

Results are presented from runs of the Lancaster-Sodankylä model compared to EISCAT observations of the lower ionosphere during evening to early morning. The data are from several multibeam experiments (using both UHF and VHF radars) covering heights from 70 to 120 km. The VHF radar measured the plasma autocorrelation function using a multipulse scheme at two different time-lags, while the tristatic UHF system provided power profile and electric field information. The UHF power profiles are input to the model to obtain consistent estimates of electron density, negative ion concentrations, and average ion mass with height. The neutral concentrations and ion temperature are given by the MSIS model. These parameters are then used to compare the calculated widths of the ion-line with the VHF determinations.

Ion composition and effective ion recombination rate in the nighttime auroral lower ionosphere

Abstract We present the results of a combined study applying the Lancaster-Sodankyla model and EISCAT radar observations of the lower ionosphere during evening to early morning hours. The purpose is to derive the spectrum of incoming energetic electrons which produce the ionisation, and to determine the effective recombination coefficient and the concentrations of the positive and negative ions over the height range 70 to 120 km. This was done by combining a semiempirical “profile-inversion” technique to estimate the spectrum of the precipitating electrons from the electron density profiles measured by the EISCAT radars, and the 35-ion Sodankyla model of the chemistry of the D and E regions. Both procedures assume chemical equilibrium conditions. It is found that, below 85 km, precipitation reduces the average ion mass at a given height by changing the relative proportions of the various ions, with the simpler molecular ions becoming dominant over the complex and hydrated ions. The same reactions occur as in the undisturbed nighttime mesosphere, and the concentrations of most cluster ions as well as most negative ions are increased by precipitation, though by less than those of the molecular ions. The effective electronion recombination rate is very sensitive to the energetic charged particle spectrum, and is strongly reduced by any increase of the precipitation flux at the higher energies. Above a certain threshold flux of harder precipitation (exceeding 120–150keV), the profile of the effective recombination coefficient appears to change very little with flux, reaching values comparable to that for daytime conditions.

Tokamak Fusion Test Reactor D-T results

Abstract Temperatures, densities and confinement of deuterium plasmas confined in tokamaks have been achieved within the last decade that are approaching those required for a D-T reactor. As a result, the unique phenomena present in a D-T reactor plasma (D-T plasma confinement, α confinement, α heating and possible α-driven instabilities) can now be studied in the laboratory. Recent experiments on the Tokamak Fusion Test Reactor (TFTR) have been the first magnetic fusion experiments to study plasmas with reactor fuel concentrations of tritium. The injection of about 20 MW of tritium and 14 MW of deuterium neutral beams into the TFTR produced a plasma with a T-to-D density ratio of about 1 and yielding a maximum fusion power of about 9.2 MW. The fusion power density in the core of the plasma was about 1.8 MWm−3, approximating that expected in a D-T fusion reactor. A TFTR plasma with a T-to-D density ratio of about 1 was found to have about 20% higher energy confinement time than a comparable D plasma, indicating a confinement scaling with average ion mass A of τE ∁ A0.6. The core ion temperature increased from 30 to 37 keV owing to a 35% improvement of ion thermal conductivity. Using the electron thermal conductivity from a comparable deuterium plasma, about 50% of the electron temperature increase from 9 to 10.6 keV can be attributed to electron heating by the α particles. The approximately 5% loss of α particles, as observed on detectors near the bottom edge of the plasma, was consistent with classical first orbit loss without anomalous effects. Initial measurements have been made of the confined high energy α particles and the resultant α ash density. At fusion power levels of 7.5 MW, fluctuations at the toroidal Alfven eigen-mode frequency were observed by the fluctuation diagnostics. However, no additional α loss due to the fluctuations was observed. These D-T experiments will continue over a broader range of parameters and higher power levels.

TFTR experience with D-T operation

Temperatures, densities and confinement of deuterium plasmas confined in tokamaks have been achieved within the last decade that are approaching those required for a D-T reactor. As a result, the unique phenomena present in a D-T reactor plasma (D-T plasma confinement, alpha confinement, alpha heating and possible alpha-driven instabilities) can now be studied in the laboratory. Recent experiments on the Tokamak Fusion Test Reactor (TFTR) have been the first magnetic fusion experiments to study plasmas with reactor fuel concentrations of tritium. The injection of ≈20 MW of tritium and 14 MW of deuterium neutral beams into the TFTR produced a plasma with a T/D density ratio of ≈1 and yielded a maximum fusion power of ≈9.2 MW. The fusion power density in the core of the plasma was ≈1.8 MW m −3 , approximating that expected in a D-T fusion reactor. A TFTR plasma with a T/D density ratio of ≈1 was found to have ≈20% higher energy confinement time than a comparable D plasma, indicating a confinement scaling with average ion mass, A , of τ E ≈ A 0.6 . The core ion temperature increased from 30 keV to 37 keV due to a 35% improvement in ion thermal conductivity. Using the electron thermal conductivity from a comparable deuterium plasma, about 50% of the electron temperature increase from 9 keV to 10.6 keV can be attributed to electron heating by the alpha-particles. The ∼5% loss of alpha-particles, as observed on detectors near the bottom edge of the plasma, was consistent with classical first orbit loss without anomalous effects. Initial measurements have been made of the confined energetic alphas and the resultant alpha ash density. At fusion power levels of 7.5 MW, fluctuations at the toroidal Alfvén eigenmode frequency were observed by the fluctuation diagnostics. However, no additional alpha loss due to the fluctuations was observed. These D-T experiments will continue over a broader range of parameters and higher power levels.

Deuterium-Tritium Experiments on the Tokamak Fusion Test Reactor

The deuterium-tritium (D-T) experimental program on the Tokamak Fusion Test Reactor (TFTR) is underway and routine tritium operations have been established. The technology upgrades made to the TFTR facility have been demonstrated to be sufficient for supporting both operations and maintenance for an extended D-T campaign. To date fusion power has been increased to ∼9 MW and several physics results of importance to the D-T reactor regime have been obtained: electron temperature, ion temperature, and plasma stored energy all increase substantially in the D-T regime relative to the D-D regime at the same neutral beam power and comparable limiter conditioning; possible alpha electron heating is indicated and energy confinement improvement with average ion mass is observed; and alpha particle losses appear to be classical with no evidence of TAE mode activity up to the PFUS ∼ 6 MW level. Instability in the TAE mode frequency range has been observed at PFUS > 7 MW and its effect on performance is under investigation. Preparations are underway to enhance the alpha particle density further by increasing fusion power and by extending the neutral beam pulse length to permit alpha particle effects of relevance to the ITER regime to be more fully explored.

D-T experiments on TFTR

Temperatures, densities and confinement of deuterium plasmas confined in tokamaks have been achieved within the last decade that are approaching those required for a D-T reactor. As a result, the unique phenomena present in a D-T reactor plasma (D-T plasma confinement, alpha confinement, alpha heating and possible alpha driven instabilities) can now be studied in the laboratory. Recent experiments on the Tokamak Fusion Test Reactor (TFTR) have been the first magnetic fusion experiments to study plasmas with reactor fuel concentrations of tritium. The injection of ∼20 MW of tritium and 14 MW of deuterium neutral beams into the TFTR produced a plasma with a T/D density ratio of ∼1 and yielded a maximum fusion power of ∼9.2 MW. The fusion power density in the core of the plasma was ∼1.8 MW m−3 approximating that expected in a D-T fusion reactor. In other experiments TFTR has produced 6.4 MJ of fusion energy in one pulse satisfying the original 1976 goal of producing 1 to 10 MJ of fusion energy per pulse. A TFTR plasma with T/D density ratio of ∼1 was found to have ∼20% higher energy confinement time than a comparable D plasma, indicating a confinement scaling with average ion mass, A, of τE∼. The core ion temperature increased from 30 keV to 37 keV due to a 35% improvement of ion thermal conductivity. Using the electron thermal conductivity from a comparable deuterium plasma, about 50% of the electron temperature increase from 9 keV to 10.6 keV can be attributed to electron heating by the alpha particles. At fusion power levels of 7.5 MW, fluctuations at the Toroidal Alfven Eigenmode frequency were observed by the fluctuation diagnostics. However, no additional alpha loss due to the fluctuations was observed. These D-T experiments will continue over a broader range of parameters and higher power levels.

On the low-pressure mode transition in electron cyclotron heated plasmas

The properties of plasmas created and sustained by electron cyclotron heating (ECH) have often been found to undergo an abrupt change as the ambient gas pressure is reduced below a value that is typically around 10−5–10−4 Torr. A model is presented in which ambipolar transport of particles and energy are balanced by electron impact ionization and microwave power absorption, respectively. In the absence of magnetic-mirror confinement of high energy electrons, the equilibria predicted by the model exist only for gas pressures greater than a value determined by the ionization rate constant, the average ion mass, and the axial length (along the steady magnetic field) of the discharge. At the critical pressure, the equilibria bifurcate into high-temperature/low-density and low-temperature/high-density branches. Magnetic-mirror confinement of high-energy electrons can lower the critical pressure and modify the bifurcation somewhat. In all cases the equilibrium electron temperature is governed primarily by gas pressure while the plasma density is proportional to the microwave power density absorbed by the plasma.

Transmission Optical Properties of Polycrystalline Alumina with Submicron Grains

Translucent alumina ceramics with extremely high in-line optical transmittance to visible light and light mechanical strength were produced by applying HIP process to a sample which was densified at a relatively low temperature after injection molding. Measurements of bulk density and average grain size, X-ray diffraction (XRD) and secondary ion mass spectroscopy (SIMS) analysis, and SEM and TEM observations were conducted