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This paper describes a highly accurate dose control circuit (DCC) for the emission of a desired number of electrons from vertically aligned carbon nanofibers (VACNFs) in a massively parallel maskless e-beam lithography system. The parasitic components within the VACNF device cause a premature termination of the electron emission, resulting in underexposure of the photoresist. In this paper, we compensate for the effects of the parasitic components and noise while reducing the area of the chip and achieving a precise count of emitted electrons from the VACNFs to obtain the optimum dose for the e-beam lithography.

Cone-shaped nanostructures of mixed composition (nanocones) and largely graphitic nanofibers were synthesized on silicon substrates using iron/platinum alloy nanoparticles as the catalyst in a direct-current plasma enhanced chemical vapor deposition reactor. The catalyst nanoparticles were monodisperse in size with an average diameter of 3 (±1) nm. The nanocones were produced on laterally widely dispersed catalyst particles and were oriented perpendicular to the substrate surface with an amorphous internal structure. The nanocones were produced by gas phase mixing and deposition of plasma-sputtered silicon, nitrogen, carbon, and oxygen species on a central backbone nucleated by the Fe–Pt catalyst particle. Field emission measurements showed that a very high turn-on electric field was required for electron emission from the nanocones. In contrast, the graphitic nanofibers that were produced when silicon sputtering and redeposition were minimized had the “stacked-cup” structure, and well-defined voids could be observed within nanofibers nucleated from larger catalyst particles.

Previous in silico analysis of selenoprotein genes in Archaea revealed that the selenocysteine insertion (SECIS) motif necessary to recode UGA with selenocysteine was not adjacent to the UGA codon as is found in Bacteria. Rather, paralogous stem-loop structures are located in the 3' untranslated region (3' UTR), reminiscent of the situation in Eukarya. To assess the function of such putative SECIS elements, the Methanococcus jannaschii MJ0029 (fruA, which encodes the A subunit of the coenzyme F420-reducing hydrogenase) mRNA was mapped in vivo and probed enzymatically in vitro. It was shown that the SECIS element is indeed transcribed as part of the respective mRNA and that its secondary structure corresponds to that predicted by RNA folding programs. Its ability to direct selenocysteine insertion in vivo was demonstrated by the heterologous expression of MJ0029 in Methanococcus maripaludis, resulting in the synthesis of an additional selenoprotein, as analysed by 75Se labelling. The selective advantage of moving the SECIS element in the untranslated region may confer the ability to insert more than one selenocysteine into a single polypeptide. Evidence for this assumption was provided by the finding that the M. maripaludis genome contains an open reading frame with two in frame TGA codons, followed by a stem-loop structure in the 3' UTR of the mRNA that corresponds to the archaeal SECIS element.

Photoresist removal was studied using single-crystal silicon samples mounted on a ceramic heater in an UHV compatible chamber. The photoresist-coated sample was exposed to an ozone-oxygen mixture at atmospheric pressure and at a flow rate of 4 s l/min. Resist removal rate was measured using in situ laser interferometry. The removal rate was found to be a linear function of ozone concentration with a slope of 0.82 nm/s/unit mass fraction at a substrate temperature of 200 °C. The linearity is consistent with a simple chemical rate model. Typical photoresist removal rates at a mass density fraction ozone concentration of 0.09 ranged from 2.5 to 13 nm/s for substrate temperatures ranging from 150 to 300 °C, respectively. These rates are comparable with those observed by others. Over this temperature range, removal rates follow standard Arrhenius behavior from which an activation energy of 5.2 kcal/mol was determined. This value is similar to the known activation energy of 6.0 kcal/mol for the thermal dissociation of ozone leading us to conclude that thermal dissociation is the rate limiting step in the process. Our result is also significantly lower than reported previously and may be more accurate since the substantial shrinkage of photoresist with temperature was accounted for in these results. Additionally, the combination of concentration and temperature information is shown to lead to an effective chemical reaction rate constant for the removal of photoresist with ozone.

Present diamond deposition reactors have been very successful in furthering our understanding of how diamond grows at low pressures. However, their primary disadvantage is that changes in reactor conditions (e.g., filament temperature or microwave power, substrate temperature, and CH4:H2 concentration ratio in methane‐based reactors) change all chemical species and their relationships. Changes in diamond growth created by independent changes to a single species are not directly accessible. For example, it is known that making atomic hydrogen is required for the growth of diamond films. However, changes to film growth rate have not been tied quantitatively to changes in the amount of atomic hydrogen available. A high‐yield atomic hydrogen source was fabricated and pretested in a diamond growth setup. A previously developed atomic hydrogen sensor was used to measure atomic hydrogen density output as a function of both power and pressure. Diamond was then grown as a function of atomic hydrogen density, and g...

A new type of antenna for launching waves in the ion cyclotron frequency range in toroidal plasma devices has been developed and tested in the Phaedrus-T tokamak. This antenna, a stacked stripline (SSL), generates a radiofrequency (RF) magnetic field similar to that of a conventional strap antenna but develops voltages 2 orders of magnitude less, and can operate without a Faraday shield. In comparison tests with a conventional strap antenna at a power level of 69 kW, the RF induced density rise and the impurity production (as indicated by soft X ray and loop voltage increases) were reduced by a factor of 3. In addition, it was demonstrated that capacitive loading effects were reduced or eliminated in comparison with those observed on a conventional strap antenna operated without a Faraday shield, and in the operation of a pair of SSL antennas at 90 degrees phase, small current drive effects were observed

Atomic hydrogen is a very important constituent for a number of important processes. These include the removal of oxides from GaAs, the effective cleaning of oxides and hydrocarbons from Ge and Si surfaces, the chemical passivation and surface reconstruction of cleaned Si surfaces, the annealing of amorphous silicon, and the deposition of diamond films. Because the usual techniques for measuring the atomic fraction are either expensive and cumbersome to use or unsuitable for application to highly dissociated hydrogen, a specially designed sensor was developed. Sensor design is based on a diffusion tube with noncatalytic walls, having one end open to the atom source and a catalytic closure at the other end. The sensor is simple and inexpensive to fabricate, and determining atom density is straightforward. Sensor design also inhibits thermal runaway, which occurs when the atom density is high enough to impart enough recombination energy to the noncatalytic surface to substantially raise its temperature. While recombination coefficients for such surfaces are very low near room temperature, they increase nearly exponentially with temperature unless actively cooled. With the use of a straightforward calibration scheme to determine the variation in species fraction along the diffusion tube, the atomic fraction at the tube opening is determined. Design strategy, implementation considerations, and calibration method are presented. In addition, data obtained from an atomic hydrogen source are compared to relevant published data.

This paper presents dose control electronics and a digital addressing method for the vertically aligned carbon nanofiber (VACNF) based massively parallel maskless e-beam lithography system. The Digital Electrostatically focused e-beam Array direct-write Lithography (DEAL) developed by our research group in Oak Ridge National Laboratory [1] incorporates digitally addressable field emission arrays (DAFEAs) of the VACNFs which function as the lithography heads during the exposure of the resist. A logic and memory control circuit (LMC) and a dose control circuit (DCC) have been designed to write a desired pattern and control the dose of electrons, respectively. This paper summarizes our previous works on different versions of the DCCs [2–4] designed and optimized in the effort of obtaining a fixed and optimum dosage with the smaller circuit area.

ICRF power levels of up to 2.8 MW were achieved during the 1988 experimental run on TFTR. Metal impurity concentrations (Ti/el, Cr, Fe, Ni) and Zeff were monitored during ICRF heating by X-ray pulse height analysis and UV spectroscopy. Antenna phasing was the key variable affecting ICRF performance. No increase in metallic impurities was observed for Pr.f. or approximately=1.0 MW with 0-0 phasing.

Field emission (FE) of electrons from nanostructured graphitic carbon-based materials has been an area of intense investigation in recent years. Each field emitting device has control gates and an electron emitting cathode, which emits electron when a sufficient voltage is applied at the gate electrode. Recently, a technique for fabricating gated cathode structures that uses a single in situ grown vertically aligned carbon nanofiber (VACNF) as a FE element has been reported. This paper presents digitally addressable VACNFs for implementation of massively parallel maskless lithography.

The digital electrostatically focused e-beam array direct-write lithography (DEAL) concept is currently under development at Oak Ridge National Laboratory (ORNL) . This concept incorporates a digitally addressable field-emission array (DAFEA) employing electrostatic focusing with an integrated dose control circuit to function as the write head for an e-beam lithography tool. Electron beams from each emitter cathode are individually addressable, thus enabling parallel patterning of a target substrate by multiple electron sources.

This paper presents a prototype implementation of a circuit that can control charge emission from the vertically aligned carbon nanofibers (VACNF), for use in the implementation of digital electrostatic e-beam array lithography (DEAL). This lithography technique can be used to fabricate ultra-small feature size devices, while cutting down the manufacturing costs of photomasks. These VACNF's are found to be quite robust for use as micro-fabricated field emission devices. The all inverter based dose control circuit (DCC) presented in this paper was fabricated using a standard 0.5 /spl mu/m CMOS process to improve the dose-rate accuracy, when using these VACNF's for etching in maskless lithography. Simulation and measurement results are compared and analyzed, and future work for improving the design is discussed.

Prototype field emission devices have been fabricated in the 300-1000 eV range using vertically aligned carbon nanofibers as the field emitter. The devices are fabricated using a self-aligned process for the extraction gate opening and the focus grid opening is defined lithographically. Field emission tests of the completed devices are carried out in a vacuum chamber with a phosphor anode and show that the emission follows Fowler-Nordheim characteristics. A technique to selectively grow fibers with W in digitally addressable field-emission array (DAFEA) prototype devices is demonstrated by nanoscale electron beam induced deposition (EBID). A non-organometallic precursor, WF/sub 6/, is used to deposited metallic W fibers. Vacuum electrical testing revels that electrons are successfully extracted from the W nanofiber tip and have been used to draw lines in PMMA coated glass substrates in the DEAL lithography testbed. This growth technique can be used to repair DAFEA emitters thus providing a means to produce a reliable massive parallel e-beam write head.

The digital electrostatically focused e-beam array direct-write lithography (DEAL) concept incorporates a digitally addressable field-emission array (DAFEA) and an integrated dose control circuit to function as the write head for an e-beam lithography tool. Typically, DEAL devices have been fabricated using vertically aligned carbon nanofibers as the field emitter. To further improve device performance and patterning resolution, tungsten nanofibers formed by electron-beam-induced deposition (EBID) were used. Auger electron spectroscopy (AES) and transmission electron microscopy (TEM) characterization results have shown that high purity, single crystal beta-W nanofibers with sharp tips can be deterministically grown and used for field emission. Additional design modifications have been implemented in an attempt to further improve lithography results. These include the introduction of an integrated, 500-nm diameter, beam-forming aperture in an effort to increase the depth of focus and minimize beam divergence as well as to function as a focusing electrode. Fabrication and operation details will be discussed, as well as modeling results which predict the anticipated performance improvements

This article presents the integration of a dose control circuit (DCC) with vertically aligned carbon nanofiber (VACNF) field emission devices through a voltage boost up interface circuit for the implementation of the digital electrostatically focused e-beam array direct-write lithography concept. The VACNFs act as diodes with high turn on voltage (∼70V). Commercially available complementary metal-oxide-semiconductor technology is not capable of handling such magnitude of voltages. The voltage boost up interface circuit described in this article offers an efficient technique to shift the voltage level to a level adequate to start the emission of electron from the tips of the VACNFs. The integration of the DCC with the VACNF emitters via a voltage boost up interface circuit presented in this article facilitates the operation of the VACNFs for etching in maskless lithography while providing precise control of emission.

Regulatory focus theory distinguishes between self-regulatory processes that focus on promotion and prevention strategies for goal pursuit. Five studies provide support for the hypothesis that these strategies differ for individuals with distinct self-construals. Specifically, individuals with a dominant independent self-construal were predicted to place more emphasis on promotion-focused information, and those with a dominant interdependent self-construal on prevention-focused information. Support for this hypothesis was obtained for participants who scored high versus low on the Self-Construal Scale, participants who were presented with an independent versus interdependent situation, and participants from a Western versus Eastern culture. The influence of interdependence on regulatory focus was observed in both importance ratings of information and affective responses consistent with promotion or prevention focus.

In a recent review, S. E. Cross and L. Madson (1997) forwarded that many gender differences in social experience and behavior may be better understood through consideration of gender differences in independence and interdependence. In the current studies an expansion of the model to include both relational and collective aspects of interdependence was investigated (see R. F. BaumeisterK. L. Sommer, 1997). On the basis of the literature regarding gender differences in affect, behavior, and cognition, it was hypothesized that women would focus more on the relational aspects of interdependence, whereas men would focus more on the collective aspects of interdependence. Five studies in which gender differences in self-construals, emotional experience, selective memory, and behavioral intentions were examined supported the expansion of the model to include both relational and collective aspects of interdependence.

The folded waveguide (FWG) antenna is an advanced ICRF launcher under development at ORNL that offers many significant advantages over current‐strap type antennas. These features are particularly beneficial for reactor‐relevant applications such as ITER and TPX. Previous tests of a development folded waveguide with a low density plasma load have shown a factor of 5 increase in power capability over loop antennas into similar plasma conditions. The performance and reliability of a FWG with an actual tokamak plasma load must now be verified for further acceptance of this concept. A 58 MHz, 4 MW folded waveguide is being designed and built for the PBX‐M and TFTR tokamaks at Princeton Plasma Physics Laboratory. This design has a square cross‐section that can be installed as either a fast wave (FW) or ion‐Bernstein wave (IBW) launcher by 90° rotation. Two new features of the design are: a shorter quarter‐wavelength resonator configuration and a rear‐feed input power coupling loop. Loading calculations with a standard shorting plate indicate that a launched power level of 4 MW is possible on either machine. Mechanical and disruption force analysis indicates that bolted construction will withstand the disruption loads. An experimental program is planned to characterize the plasma loading, heating effectiveness, power capability, impurity generation and other factors for both FW and IBW cases. High power tests of the new configuration are being performed with a development FWG unit on RFTF at ORNL.

The processing of materials using rf and/or microwave power is a broad area that has grown significantly in the past few years. We have applied rf and microwave technology in the areas of ceramic sintering, plasma processing, and waste processing. The sintering of ceramics in the frequency range of 50 MHz‐28 GHz has lead to unique material characteristics compared to materials that have been sintered conventionally. It has been demonstrated that sintering can be achieved in a variety of materials, including alumina, zirconia, silicon carbide, and boron carbide. In the area of plasma processing, progress has been made in the development and understanding of high density plasma sources, including inductively coupled plasma (ICP) sources. The effects of processing conditions on the ion energy distribution at the substrate surface (a critical processing issue) have been determined for a variety of process gases. The relationship between modeling and experiment is being established. Microwave technology has also been applied to the treatment of radioactive and chemical waste. The application of microwaves to the removal of contaminated concrete has been demonstrated. Details of these programs and other potential application areas are discussed.

We report evidence of both correspondence and independence between participants' attitude report and a late positive potential (LPP) of the event-related potential. Attitude reports and LPPs to positive, neutral, and negative stimuli that were preceded by positive stimuli were recorded while participants either reported accurately their attitudes or misreported neutral or negative attitudes. Evaluatively inconsistent, in contrast to consistent, stimuli evoked a larger LPP regardless of whether participants reported accurately or misreported their attitudes. These results were replicated in a second study in which attitude reports and LPPs to negative, neutral, and positive stimuli that were preceded by negative stimuli were recorded. Findings suggest that the LPP evoked during evaluative judgments reflects attitude categorization rather than attitude report processes and can potentially assess attitudes that people are unwilling to report.

Atomic hydrogen is a very important constituent for processes ranging from cleaning oxide from GaAs and annealing amorphous silicon to the deposition of diamond. Because the usual techniques for measuring atomic fraction are either expensive and cumbersome to use, or unsuitable for application to highly dissociated hydrogen, a specially designed sensor was developed. Sensor design is based on a diffusion tube with noncatalytic walls, having one end open to the atom source and a catalytic closure at the other end. The sensor is simple and inexpensive to fabricate, and determining atom density is straightforward. Sensor design also inhibits thermal runaway, which occurs when atom density is high enough to impart enough recombination energy to the non-catalytic surface to substantially raise its temperature. While recombination coefficients for such surfaces are very low near room temperature, they increase nearly exponentially with temperature unless actively cooled. With the use of a straightforward calibration scheme to determine the variation in species fraction along the diffusion tube, the atomic fraction at the tube opening is determined. Design strategy, implementation considerations, and calibration method are presented. In addition, data obtained from an atomic hydrogen source are compared to relevant published data.

Attitudes can be conceptualized in terms of the elementary operations of evaluative categorization and response selection-execution. This article describes a component of the event-related potential that is associated with the first of these operations. Ss were exposed to sequences of 6 traits and performed a dichotomous evaluative categorization task. Evaluative inconsistency was varied by embedding very positive, moderately positive, moderately negative, and very negative traits in sequences containing predominantly very positive traits. Highly and moderately evaluatively inconsistent traits, compared with mildly inconsistent or consistent traits, evoked a larger amplitude late positive potential (LPP) that was maximal over centroparietal regions. Furthermore, extremely evaluatively inconsistent traits evoked a larger amplitude LPP than moderately evaluatively inconsistent traits even though both sets of traits were judged to be negative.

The folded waveguide (FWG) has been tested to the megawatt level in RFTF and shows great promise for tokamak use. It has three primary advantages: low electric field (anywhere) per unit power coupled to the plasma, strong structural capabilities, and better spectral content than loops. A tokamak test is now needed. Potential candidates include C‐Mod at 80 MHz and FTU at 433 MHz. The waveguide test on the first machine will be directed at conventional ion cyclotron heating, while the test on the latter will be directed at direct electron heating. In addition, a variation of the folded waveguide is proposed to be tested on Phaedrus‐T. In this paper, we discuss the advantages of the waveguide, the design layout, some of the potential physics programs, and how these programs may have an impact on its potential use in ITER.

Two new concepts are being developed as possible upgrades to the folded waveguide launcher. The folded stripline is a folded waveguide with an additional conductor positioned inside. The term stripline refers to the resemblance of the design to microwave microstrip line. The conductor provides support for TEM mode propagation, which eliminates cutoff and the nonlinear frequency dependence of the waveguide impedance and phase velocity. A natural extension to the folded stripline is the stacked stripline, which comprises several stacked, independent TEM waveguides. Initial measurements indicate that both concepts have better magnetic flux coupling than the folded waveguide.

Donor attitudes, intentions, and behaviors have typically been conceptualized as organized along a bipolar continuum. This conceptualization is evident in I. G. Sarason et al.'s study of increasing participation in a bone-marrow registry in this issue. When the cumulative research on blood, bone-marrow, and organ donor behavior is considered, however, evidence suggests that a single, bipolar continuum may be insufficient and that a 2-dimensional (Positivity x Negativity) evaluative space may be minimally required to effectively represent and target the underlying substrates of donor behaviors. Negative beliefs and fears may constitute a particularly difficult obstacle to inducing donor behaviors and, thus, to promoting self-perceptions by people as donors. Understanding and changing these negative substrates, therefore, may be important if public health campaigns to increase donor behavior are to be cost-effective.

Experiments with the 80‐MHz prototype folded waveguide on the Radio‐Frequency Test Facility (RFTF) at Oak Ridge National Laboratory have achieved substantially higher power levels than any previous tests on comparably sized loop antennas. This result, combined with a superior wave spectrum, suggests that the folded waveguide should be capable of coupling several times the power flux of a loop antenna into a tokamak plasma.

Recently, vertically aligned carbon nanofiber based dual-gate field emission structures have been fabricated for use in parallel electron-beam lithography, and their electron-beam focus adjustment capability has been demonstrated. This article summarizes the results of a numerical investigation of device behavior due to geometry variation in an effort to better understand device characteristics and performance. The effect of electrode thickness on minimum beam diameter and depth of field (DOF) were investigated for axially symmetric structures using a two-dimensional simulation package. The results indicate both a decrease in minimum spot size from ∼30to∼20nm, and an increase in DOF from ∼1to∼6μm when the focus electrode thickness is increased from 100to500nm. The impact of misalignments of the focus electrode and the carbon nanofiber on the beam behavior was investigated with a three-dimensional simulation package. Results show that reasonably well-converged beams can be achieved even with considerable o...

This article presents a prototype implementation of a circuit that can control charge emission from the vertically aligned carbon nanofibers (VACNFs), for use in the implementation of digital electrostatically focused e-beam array direct-write lithography. This lithography technique can be used to fabricate ultra-small feature size devices, while cutting down the manufacturing costs of photomasks [Baylor et al., J. Vac. Sci. Technol. B 20, 2646 (2002)]. These VACNFs are found to be quite robust for use as microfabricated field-emission devices [Bolton et al., Sens. Actuators B 85, 179 (2002)]. The all-inverter based dose control circuit presented in this article was fabricated using a standard 0.5μm complementary metal oxide semiconductor process to improve the dose-rate accuracy, when using these VACNFs for etching in maskless lithography. Simulation and measurement results are compared and analyzed, and future work for improving the design is discussed.

We report on the fabrication and operation of integrated field emission cathodes containing single tungsten (W) nanofibers selectively grown by nanoscale electron beam induced deposition (EBID). A nonorganometallic precursor, WF6, was used to deposit metallic W fibers. Vacuum electrical testing reveals electrons were successfully extracted from the W nanofiber tip and were collected by a phosphor anode. Direct current versus voltage (I–V) curves exhibited Fowler–Nordheim behavior, indicating the occurrence of cold field emission. Electrical testing of these devices indicated that EBID direct-write is a promising technique for direct production or repair of field emission cathodes.

We report on the design, fabrication, and initial characterization of vertically aligned carbon nanofiber-based microfabricated field emission devices with an integrated out-of-plane electrostatic focusing electrode. The potential placed on this electrode was found to have a profound impact on the diameter of the beam emitted from the device as observed on a phosphor screen. Aspects of the device fabrication process and device operation are discussed. The experimental results obtained are compared to a numerical simulation of device performance and found to be within good agreement.

The Digital Electrostatically focused e-beam Array direct-write Lithography (DEAL) concept is currently under development at Oak Ridge National Laboratory (ORNL). This concept incorporates a digitally addressable field-emission array (DAFEA) built into a logic and control integrated circuit to function as the write head for an e-beam lithography tool. The electrostatic focusing is integrated on the DAFEA and consists of additional grids lithographically aligned above the emitters and extraction grid, each separated by a dielectric (nominally low-temperature SiO2) layer. Prototypes of the DAFEA have been fabricated and used to test the focusing of the electron beams and to pattern lines in PMMA resist. First lithography tests have used electron energies of 500 eV to pattern lines less than 1 μm wide at a working distance of 500 μm which extrapolates to

Ion beam technology has advanced immensely during the past 15 years in connection with the application of neutral beam injection heating for fusion research. Ion sources have been scaled up along with necessary modifications, yielding currently a few megawatts of extraction power (e. g., 40 keV-60 A, 0.3-sec pulse). The entire neutral beam injection system has become a multidisciplinary technology including plasma physics, accelerator and beam physics, pumping technology, heat transfer, electrical engineering, and so on. Since the neutral beam injection heating of fusion plasmas has been proved the most viable means of increasing the plasma temperature to ignition, the future demand and requirements are rising with the size of fusion plasma devices. A brief review of the state of the art of neutral beam technology is presented and the direction of the future neutral beam field is discussed.

Experimental comparison is made of four plasma grids, each with a specific aperture geometry, in an attempt to improve the ion optics of a multiple aperture ion source. It is clearly shown that a simple notch geometry outperforms the other candidates with a high transmission efficiency (∼68%) to a 2° target at high perveance (∼9.6 μperv).

The first pump limiter experiments were performed on ISX-B. Two pump limiter modules were installed in the top and bottom of one toroidal sector of the tokamak. The modules consist of inertia cooled, TiC-coated graphite heads and ZrAl getter pumps each with a pumping speed of 1000–2000 l/s. The objective of the initial experiments was the demonstration of plasma particle control with pump limiters. The first set of experiments were performed in ohmic discharges (OH) in which the effect of the pump limiters on the plasma density was clearly demonstrated. In discharges characterized by Ip = 110 kA, B T = 15 kG , n e = 1−5 × 10 13 cm −3 and t = 0.3 s, the pressure rise in the pump limiters was typically 2 mTorr with the pumps off and 0.7 mTorr after activating the pumps. When the pumps were activated, the line-average plasma density decreased by up to a factor 2 at identical gas flow rates. The second set of measurements were performed in neutral beam heated discharges (NBI) with injected powers between 0.6 MW and 1.0 MW. Due to a cooling problem on one of the ZrAl pumps, the NBI experiments were carried out with one limiter only. The maximum pressure observed in NBI-discharges was 5 mTorr without activating the pumps, i.e., approximately twice as high as in OH-discharges. The exhaust efficiency, which is defined as the removed particle flux divided by the total particle flux in the scrape-off layer, is estimated to be 5%.

Results are reported on improved confinement in the Impurity Study Experiment (ISX-B) neutral beam heated plasmas when a small amount of neon is injected shortly after the start of beam heating. The scaling of energy confinement is modified by the introduction of a dependence on line-averaged density. Calculations show the improvement is primarily caused by a reduction in electron heat conduction.

The results of a systematic investigation of the power flow along the Oak Ridge National Laboratory/Princeton Large Torus (ORNL/PLT) neutral beam line, using an intense modified duoPIGatron source with a 22‐cm active grid diameter and 1799 circular apertures that provide 53% transparency, are reported. The variation of power deposited on the different components of the beam line is measured over a wide range of perveance values. The maximum efficiency for beam power transmitted through a 20×25‐cm aperture located 4.1 m downstream was found to be 41%. This efficiency was raised to 53% when a voltage of about 175 V was applied to preaccelerate the ions entering the extraction apertures. Transmission efficiencies approaching 60% were obtained using shaped apertures on the plasma grid. Higher efficiencies should be attainable when used for PLT injection since the acceptance angle for the Princeton tokamak is 11% higher than that of the test facility. Detailed analysis of the results using straight circular ap...

Beam power transmission and grid loading characteristics of a two‐stage neutral beam source are presented. The dependence of power deposition on the target, the grids, and the gas cell was studied over a wide range of extraction perveance values with the accel‐to‐extraction gap field ratio as the other parameter. The results show that the power transmission improves remarkably with increasing field ratio. For sufficiently large field ratios (≈2.5), more than 80% of the input IV power was collected on a target located 4 m downstream and subtending 2 ° half angle to the source. The sum of the grid loading is approximately double that of single‐stage accelerators; the plasma grid loading is the highest, followed by ground grid, accel grid, and extraction grid in that order.

The injection of neutral hydrogen or deuterium particles continues to be the most promising means of heating magnetically confined fusion plasmas to ignition temperatures. Neutral beam injection systems that employ positive ion sources presently operate at energies of about 40-50 keV/nucleon at 60 A [Princeton Large Torus (PLT)] or 100 A [Princeton Divertor Experiment (PDX) or the Oak Ridge National Laboratory (ORNL) Impurities Study Experiment (ISX)] with about 60% conversion efficiency. However, the desire for multisecond beams in the 80-keV/nucleon energy range at ~ 10 MW/module has emphasized the need for technological advances in several areas. At such beam energies, as much as 75% of the initial beam energy is retained in the unneutralized ion components. As a result, two questions immediately come to mind: (1) how can one dispose of this energy; or better still, (2) how can one efficiently recover this energy? The conventional way of treating such a problem is to deflect the ions out of the neutral beam and onto water-cooled plates or beam dumps. This method has worked satisfactorily for 40-keV/nucleon beams in excess of 1.5 MW and ~0.5 s. However, the power per unit area to be disposed of in the high power, multisecond beams mentioned above is beyond present-day technology.

Experimental results from high-power neutral-beam--injection experiments on the Princeton Large Torus tokamak are reported. At the highest beam powers (2.4 MW) and lowest plasma densities (n/sub e/(0) = 5 x 10/sup 13/cm/sup -3/), ion temperatures of 6.5 keV are achieved. The ion collisionality v/sub i/* drops below 0.1 over much of the radial profile. Electron heating of ..delta..T/sub e//T/sub e/ approx. = 50% has also been observed, consistent with the gross energy-confinement time of the Ohmically heated plasma, but indicative of enhanced electron-energy confinement in the core of the plasma.

The properties of an intense 50‐kV neutral‐beam system are discussed. The salient features of this system are a transmission efficiency of 76% of the extracted ion beam through a 30×34 cm aperture that is 4.5 m from the ion source, a transmitted neutral power of 1.8 MW H0 (2.0 MW D0) at extraction parameters of 50 kV/100 A/0.1 s (53 kV/85 A/0.1 s), a proton fraction of ∼80%, an ion‐source arc efficiency of ∼1.3 A/kW, an ion‐source gas efficiency of ∼35%, and a reliability of ≳90%.

Conceptual and preliminary engineering design for the National RF Test Facility at Oak Ridge National Laboratory (ORNL) has been completed. The facility will comprise a single mirror configuration embodying two superconducting development coils from the ELMO Bumpy Torus Proof-of-Principle (EBT-P) program on either side of a cavity designed for full-scale antenna testing. The coils are capable of generating a 1.2-T field at the axial midpoint between the coils separated by 1.0 m. The vacuum vessel will be a stainless steel, water-cooled structure having an 85-cm-radius central cavity. The facility will have the use of a number of continuous wave (cw), radio-frequency (rf) sources at levels including 600 kW at 80 MHz and 100 kW at 28 GHz. Several plasma sources will provide a wide range of plasma environments, including densities as high as approx. 5 x 10/sup 13/ cm/sup -3/ and temperatures on the order of approx. 10 eV. Furthermore, a wide range of diagnostics will be available to the experimenter for accurate appraisal of rf testing.

Confinement studies on the Impurity Study Experiment (ISX-B) in beam-heated plasmas contaminated with small quantities of low-Z impurities are reported. Experimental results on the correlation of particle and energy confinement are presented. A linear relationship of energy confinement and plasma density is observed. As density is increased further, this effect saturates and energy confinement becomes independent of electron density. The experiments have been extended to higher beam power, resulting in an expansion of the ISX-B operating space. Impurities other than neon (carbon and silicon) have been tried and do not produce an enhancement in confinement. Edge cooling by the introduction of impurities has been demonstrated. The change in confinement has been shown to be correlated with changes in the normalized poloidal field fluctuation level (θ/Bθ) but not with the density fluctuation level (ne/ne). The experimental results are compared with models of drift-wave and resistive ballooning turbulence and an explanation is offered for the difference between the results with recycling and non-recycling impurities.

A quasi‐steady‐state (pulse duration of 30 s) ion source of the duoPIGatron type has been developed for fusion applications. It was designed to deliver an 80‐keV hydrogen ion beam of low beamlet divergence (Θrms= 0.26°) at a current density of 0.19 A cm−2. Hydrogen ion beams of 40 to 48 A were extracted at beam energies of 77 to 80 keV for 30‐s‐long pulses. The reliability and stability of the ion source operation were demonstrated by extracting about 600 beam pulses at full power and full pulse length. The ion source was also operated with deuterium as the working gas, and the optimum current at 80 keV was found to be about 33 A, in agreement with the expected inverse square‐root scaling of current density with atomic mass.

Scaling studies for a SITEX negative ion source to produce 200-keV, 10-A, long pulse D/sup -/ beams are under way at Oak Ridge National Laboratory (ORNL). Designs have been restricted to the use of established techniques and reasonably welldemonstrated scaling. The results show that the 1-A SITEX source can be directly scaled to produce 200-keV, 10-A long pulse ion beams with a source power efficiency of less than or equal to5 kW of total plasma generator power per ampere of D/sup -/ beam generated. Extracted electron-to-D/sup -/ ratios should be less than or equal to0.06, with all extracted electrons recovered at less than or equal to10% of the first gap potential energy difference. The close-coupled accelerating structure will be 5 cm long and have five electrodes with 21 slits each, with a 50-kV/cm field in each gap. No decel electrode was included because of the transverse magnetic field. Electrons formed in each gap by the about16% charge-exchange loss of D/sup -/ in the total accelerator column will be collected by electron recovery structures associated with the gaps at an average energy of 50% of a gap's potential energy difference. Atomic gas efficiency will be greater than or equal to67%. Beammore » divergence calculations using the ORNL optics code give theta /SUB rms/ = + or -0.4/sup 0/. The ion source magnetic field provides momentum dispersion of the extracted beam, separating out both the electrons and all heavy ion impurities and low energy D/sup 0/ particles formed by charge exchange in the accelerating column. A D/sub 2/ gas neutralization cell and a charge separation magnet provide 1 MW of D/sup 0/ beam at 200 keV for injection. The overall beam line dimensions are 2.2 X 1.0 X 5.0 m (H X W X L).« less

The effect of periodic toroidal field (TF) ripple on ion confinement has been studied in the ISX-B tokamak by comparing neutral-beam-heated plasma performance with 9 and 18 TF coils. Three ripple physics issues were treated by these experiments: (1) enhanced ion thermal conductivity, (2) enhanced loss of energetic ions, and (3) ripple damping of beam-induced toroidal plasma rotation, which may affect the plasma losses. Under a wide variety of plasma conditions, ripple reduced the central-ion temperature by a factor of approximately two (600 eV → 300 eV). Ion temperature was found to be nearly independent of applied neutral-beam power in the large ripple configuration (9 TF coils). These results are shown to be in reasonable agreement with theoretical models of ripple transport. Charge-exchange measurements of the fast-neutral flux indicated no loss of fast passing ions due to ripple, but a large depletion of the fast ions trapped in local ripple wells, as expected theoretically. The central toroidal rotation velocity was reduced by a factor of six by ripple, yielding a momentum confinement time substantially less (factor of about seven) than that expected from standard theoretical expressions for ripple-enhanced ion viscosity.