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Edge Ion Heating by Launched High Harmonic Fast Waves in NSTX

Description: A new spectroscopic diagnostic on the National Spherical Torus Experiment (NSTX) measures the velocity distribution of ions in the plasma edge simultaneously along both poloidal and toroidal views. An anisotropic ion temperature is measured during high-power high harmonic fast wave (HHFW) radio-frequency (rf) heating in helium plasmas, with the poloidal ion temperature roughly twice the toroidal ion temperature. Moreover, the measured spectral distribution suggests that two populations of ions are present and have temperatures of typically 500 eV and 50 eV with rotation velocities of -50 km/s and -10 km/s, respectively (predominantly perpendicular to the local magnetic field). This bi-modal distribution is observed in both the toroidal and poloidal views (for both He{sup +} and C{sup 2+} ions), and is well correlated with the period of rf power application to the plasma. The temperature of the hot component is observed to increase with the applied rf power, which was scanned between 0 and 4.3 MW . The 30 MHz HHFW launched by the NSTX antenna is expected and observed to heat core electrons, but plasma ions do not resonate with the launched wave, which is typically at >10th harmonic of the ion cyclotron frequency in the region of observation. A likely ion heating mechanism is parametric decay of the launched HHFW into an Ion Bernstein Wave (IBW). The presence of the IBW in NSTX plasmas during HHFW application has been directly confirmed with probe measurements. IBW heating occurs in the perpendicular ion distribution, consistent with the toroidal and poloidal observations. Calculations of IBW propagation indicate that multiple waves could be created in the parametric decay process, and that most of the IBW power would be absorbed in the outer 10 to 20 cm of the plasma, predominantly on fully stripped ions. These predictions are in qualitative agreement with the observations, ...
Date: December 1, 2004
Creator: Biewer, T.M.; Bell, R.E.; Diem, S.J.; Phillips, C.K.; Wilson, J.R. & Ryan, P.M.

Edge Localized Mode Control in DIII-D Using Magnetic Perturbation-Induced Pedestal Transport Changes

Description: Edge localized mode (ELM) control is a critical issue for ITER because the impulsive power loading from ELMs is predicted to limit the divertor lifetime to only a few hundred full-length pulses. Consequently, a technique that replaces the ELM-induced transport with more continuous transport while preserving the H-mode pedestal height and core performance would significantly improve the viability of ITER. One approach is to use edge resonant magnetic perturbations (RMPs) to enhance pedestal transport enough to reduce the pedestal pressure gradient {del}p{sub ped} below the stability limit for Type I ELMs. In DIII-D, n = 3 RMPs have been used to eliminate Type I ELMs when the edge safety factor is in the resonant window q95 {approx} 3.5 without degrading confinement in H-modes with ITER-relevant pedestal collisionalities v*{sub e} {approx} 0.2. The RMP reduces {del}p{sub ped} as expected, with {del}p{sub ped} controlled by the RMP amplitude. Linear peeling-ballooning (P-B) stability analysis indicates that the ELMs are suppressed by reducing {del}p{sub ped} below the P-B stability limit. The {del}p{sub ped} reduction results primarily from an increase in particle transport, not electron thermal transport. This result is inconsistent with estimates based on quasi-linear stochastic diffusion theory based on the vacuum field (no screening of the RMP). The particle transport increase is accompanied by changes in toroidal rotation, radial electric field, and density fluctuation level {tilde n} in the pedestal, suggesting increased fluctuation-driven particle transport.
Date: September 27, 2006
Creator: Moyer, R A; Burrell, K H; Evans, T E; Fenstermacher, M E; Joseph, I; Osborne, T H et al.

Edge Localized Mode Dynamics and Transport in the Scrape-Off Layer of the DIII-D Tokamak

Description: High temporal and spatial resolution measurements in the boundary of the DIII-D tokamak show that edge localized modes (ELMs) are produced in the low field side, are poloidally localized and are composed of fast bursts ({approx}20 to 40 {micro}s long) of hot, dense plasma on a background of less dense, colder plasma ({approx}5 x 10{sup 18} m{sup {+-}3}, 50 eV) possibly created by the bursts themselves. The ELMs travel radially in the scrapeoff layer (SOL), starting at the separatrix at {approx}450 m/s, and slow down to {approx}150 m/s near the wall, convecting particles and energy to the SOL and walls. The temperature and density in the ELM plasma initially correspond to those at the top of the density pedestal but quickly decay with radius in the SOL. The temperature decay length ({approx}1.2 to 1.5 cm) is much shorter than the density decay length ({approx}3 to 8 cm), and the latter decreases with increasing pedestal (and SOL) density. The local particle and energy flux at the midplane wall during the bursts are 10% to 50% ({approx}1 to 2 x 10{sup 21} m{sup {+-}2} s{sup {+-}1}) and 1% to 2 % ({approx}20 to 30 kW/m{sup 2}) respectively of the LCFS average fluxes, indicating that particles are transported radially much more efficiently than heat. Evidence is presented suggesting toroidal rotation of the ELM plasma in the SOL. The ELM plasma density and temperature increase linearly with discharge/pedestal density up to a Greenwald fraction of {approx}0.6, and then decrease resulting in more benign (grassier) ELMs.
Date: December 3, 2004
Creator: Boedo, J A; Rudakov, D L; Hollmann, E; Gray, D S; Burrell, K H; Moyer, R A et al.

Edge Minority Heating Experiment in Alcator C-Mod

Description: An attempt was made to control global plasma confinement in the Alcator C-Mod tokamak by applying ion cyclotron resonance heating (ICRH) power to the plasma edge in order to deliberately create a minority ion tail loss. In theory, an edge fast ion loss could modify the edge electric field and so stabilize the edge turbulence, which might then reduce the H-mode power threshold or improve the H-mode barrier. However, the experimental result was that edge minority heating resulted in no improvement in the edge plasma parameters or global stored energy, at least at power levels of radio-frequency power is less than or equal to 5.5 MW. A preliminary analysis of these results is presented and some ideas for improvement are discussed.
Date: March 25, 2005
Creator: Zweben, S.J.; Terry, J.L.; Bonoli, P.; Budny, R.; Chang, C.S.; Fiore, C. et al.

Edge plasma and current profile diagnostic development. Final report

Description: This is the final report covering the research conducted under DOE Grant No. DE-FG03-92ER54150 entitled ``Edge Plasma and Current Profile Diagnostic Development.`` It is intended to summarize the investigation and will go into somewhat more detail regarding the aims, techniques, and results of the project research than the standard technical progress reports submitted previously. During the course of this work the authors developed and implemented an atomic beam-based diagnostic technique for investigating edge plasma density behavior on the TEXT Tokamak. The project required the modification of the existing 100 keV TEXT lithium beam to operate at 20--30 keV and the addition of a new 20 detector chain to collect the fluorescence emissions. The modifications were completed and experimental density profiles were unfolded using a new inversion technique.
Date: May 1, 1997
Creator: McChesney, J.M.

Edge Plasma Boundary Layer Generated By Kink Modes in Tokamaks

Description: This paper describes the structure of the electric current generated by external kink modes at the plasma edge using the ideally conducting plasma model. It is found that the edge current layer is created by both wall touching and free boundary kink modes. Near marginal stability, the total edge current has a universal expression as a result of partial compensation of the δ-functional surface current by the bulk current at the edge. The resolution of an apparent paradox with the pressure balance across the plasma boundary in the presence of the surface currents is provided.
Date: November 22, 2010
Creator: Zakharov, L.E.

Edge plasma control by a local island divertor in the Compact Helical System

Description: A local island divertor (LID) experiment was performed on the Compact Helical System (CHS) to demonstrate the principle of the LID. It was clearly demonstrated that the particle flow is controlled by adding a resonant perturbation field to the CHS magnetic configuration, and is guided to the back of an m/n = 1/1 island which is created by the perturbation field. The particles recycled there were pumped out with a pumping rate in the range from a few percent to about 10%. As a result, the line averaged core density was reduced by a factor of about 2 in comparison with non-LID discharges at the same gas puffing rate. In addition to the demonstration of these fundamental divertor functions, a modest improvement of energy confinement was observed, which could be attributed to the edge plasma control by the LID.
Date: December 31, 1997
Creator: Komori, A.; Ohyabu, N. & Masuzaki, S.

Edge plasma control using an LID configuration on CHS

Description: A Local Island Divertor (LID) has been proposed to enhance energy confinement through neutral particle control. For the case of the Large Helical Device (LHD), the separatrix of an m/n = 1/1 magnetic island, formed at the edge region, will be utilized as a divertor configuration. The divertor head is inserted in the island, and the island separatrix provides connection between the edge plasma region surrounding the core plasma and the back plate of the divertor head through the field lines. The particle flux and associated heat flux from the core plasma strike the back plate of the divertor head, and thus particle recycling is localized in this region. A pumping duct covers the divertor head to form a closed divertor system for efficient particle exhaust. The advantages of the LID are ease of hydrogen pumping because of the localized particle recycling and avoidance of the high heat load that would be localized on the leading edge of the divertor head. With efficient pumping, the neutral pressure in the edge plasma region will be reduced, and hence the edge plasma temperature will be higher, hopefully leading to a better core confinement region. A LID configuration experiment was done on the Compact Helical System (CHS) to confirm the effect of the LID. The typical effects of the LID configuration on the core plasma are reduction of the line averaged density to a half, and small or no reduction of the stored energy. In this contribution, the experimental results which were obtained in edge plasma control experiments with the LID configuration in the CHS are presented.
Date: July 1, 1997
Creator: Masuzaki, S.; Komori, A. & Morisaki, T.

Edge Plasma Effects in DIII-D Impurity Seeded Discharges

Description: DIII-D, ELMing H-mode radiating mantle discharges have been obtained with electron density near the Greenwald density limit and a large fraction of the input power radiated inside the last closed flux surface, significantly reducing peak divertor heat fluxes. In these ''puff and pump'' discharges, the introduction of argon reduces particle flux to divertor tiles by a factor of 4 while peak heat flux is half of the no impurity value, suggesting that impurity seeding may be a useful control tool to reduce wall heat and particle fluxes in fusion reactors. A robust H-mode transport barrier is maintained and there is little change in the ELM energy or in the ELM frequency.
Date: June 1, 2002
Creator: Jackson, G.L.; Boedo, J.A.; Lasnier, C. J.; Leonard, A.W.; McKee, G. R.; Murakami, M et al.

Edge plasma modeling of limiter surfaces in a Tokamak divertor configuration

Description: During the startup phase of a tokamak the plasma configuration may evolve from a limiter to a divertor configuration. Some of the particle and heat flux from the core will be deposited on material surfaces near the separatrix instead of the divertor plates. Examples of such surfaces include the center-post in most tokamaks, baffles near the x-point that create closed divertors, and outboard limiter surfaces. Two-dimensional edge plasma models for tokamak divertor configurations typically give detailed information about the particle and heat fluxes on the divertor plates, but yield little or no information about fluxes on these other localized surfaces near the core plasma. To realistically model the startup phase of a tokamak it is necessary to compute the plasma interaction with both limiter and divertor surfaces. The UEDGE code [l] has been modified to include these limiter surfaces. In this report we present simulation results for an idealized ITER [2] startup configuration with variations in the limiter penetration depth and surface shape.
Date: May 11, 1998
Creator: Rensink, M. E.

Edge Polynomial Fractal Compression Algorithm for High Quality Video Transmission. Final report

Description: In this final report, Physical Optics Corporation (POC) provides a review of its Edge Polynomial Autonomous Compression (EPAC) technology. This project was undertaken to meet the need for low bandwidth transmission of full-motion video images. In addition, this report offers a synopsis of the logical data representation study that was performed to compress still images and video. The mapping singularities and polynomial representation of 3-D surfaces were found to be ideal for very high image compression. Our efforts were then directed to extending the EPAC algorithm for the motion of singularities by tracking the 3-D coordinates of characteristic points and the development of system components. Finally, we describe the integration of the software with the hardware components. This process consists of acquiring and processing each separate camera view, combining the information from different cameras to calculate the location of an object in three dimensions, and tracking the information history and the behavior of the objects.
Date: June 1, 1999
Creator: Lin, Freddie

Edge preserving smoothing and segmentation of 4-D images via transversely isotropic scale-space processing and fingerprint analysis

Description: Enhancements are described for an approach that unifies edge preserving smoothing with segmentation of time sequences of volumetric images, based on differential edge detection at multiple spatial and temporal scales. Potential applications of these 4-D methods include segmentation of respiratory gated positron emission tomography (PET) transmission images to improve accuracy of attenuation correction for imaging heart and lung lesions, and segmentation of dynamic cardiac single photon emission computed tomography (SPECT) images to facilitate unbiased estimation of time-activity curves and kinetic parameters for left ventricular volumes of interest. Improved segmentation of lung surfaces in simulated respiratory gated cardiac PET transmission images is achieved with a 4-D edge detection operator composed of edge preserving 1-D operators applied in various spatial and temporal directions. Smoothing along the axis of a 1-D operator is driven by structure separation seen in the scale-space fingerprint, rather than by image contrast. Spurious noise structures are reduced with use of small-scale isotropic smoothing in directions transverse to the 1-D operator axis. Analytic expressions are obtained for directional derivatives of the smoothed, edge preserved image, and the expressions are used to compose a 4-D operator that detects edges as zero-crossings in the second derivative in the direction of the image intensity gradient. Additional improvement in segmentation is anticipated with use of multiscale transversely isotropic smoothing and a novel interpolation method that improves the behavior of the directional derivatives. The interpolation method is demonstrated on a simulated 1-D edge and incorporation of the method into the 4-D algorithm is described.
Date: January 19, 2004
Creator: Reutter, Bryan W.; Algazi, V. Ralph; Gullberg, Grant T & Huesman, Ronald H.

Edge reclamation in position-sensitive photomultiplier tubes

Description: We have investigated the performance of a position-sensitive, gamma-ray detector based on a CsI(Na) scintillator coupled to a Hamamatsu R3292 Position-Sensitive Photomultiplier Tube (PSPMT). The R3292 has an active area 10.0 cm in diameter (quoted). Utilization of the full active area of the photocathode is a goal that has been previously unrealized due to edge effects. Initial measurements with a 0.75 cm thick CsI(Na) crystal indicate that the performance (position resolution linearity) starts to degrade as one reaches a radius of only 3.5 cm, reducing the active area by 60%. Measuring the anode wires we have found that this fall off is not solely due to crystal edge effects, but rather is inherent to the tube crystal system. In this paper we describe the results of our measurements and how good performance can be maintained across a full 10cm of the tube face through the use of a few additional electronics channels.
Date: June 16, 1999
Creator: Nakae, L & Ziock, K

Edge Recycling and Heat Fluxes in L- and H-mode NSTX Plasmas

Description: Introduction Edge characterization experiments have been conducted in NSTX to provide an initial survey of the edge particle and heat fluxes and their scaling with input power and electron density. The experiments also provided a database of conditions for the analyses of the NSTX global particle sources, core fueling, and divertor operating regimes.
Date: August 5, 2003
Creator: Soukhanovskii, V.A.; Maingi, R.; Raman, R.; Kugel, H.; LeBlanc, B.; Roquemore, A.L. et al.

An Edge Rotation and Temperature Diagnostic on NSTX

Description: A new diagnostic for the National Spherical Torus Experiment (NSTX) is described whose function is to measure ion rotation and temperature at the plasma edge. The diagnostic is sensitive to C III, C IV, and He II intrinsic emission, covering a radial region of 15 cm at the extreme edge of the outboard midplane. Thirteen chords are distributed between toroidal and poloidal views, allowing the toroidal and poloidal rotation and temperature of the plasma edge to be simultaneously measured with 10 ms resolution. Combined with the local pressure gradient and the EFIT code reconstructed magnetic field profile, the edge flow gives a measure of the local radial electric field.
Date: August 29, 2003
Creator: Biewer, T.M.; Bell, R.E.; Feder, R.; Johnson, D.W. & Palladino, R.W.

Edge Simulation Laboratory Progress and Plans

Description: The Edge Simulation Laboratory (ESL) is a project to develop a gyrokinetic code for MFE edge plasmas based on continuum (Eulerian) techniques. ESL is a base-program activity of OFES, with an allied algorithm research activity funded by the OASCR base math program. ESL OFES funds directly support about 0.8 FTE of career staff at LLNL, a postdoc and a small fraction of an FTE at GA, and a graduate student at UCSD. In addition the allied OASCR program funds about 1/2 FTE each in the computations directorates at LBNL and LLNL. OFES ESL funding for LLNL and UCSD began in fall 2005, while funding for GA and the math team began about a year ago. ESL's continuum approach is a complement to the PIC-based methods of the CPES Project, and was selected (1) because of concerns about noise issues associated with PIC in the high-density-contrast environment of the edge pedestal, (2) to be able to exploit advanced numerical methods developed for fluid codes, and (3) to build upon the successes of core continuum gyrokinetic codes such as GYRO, GS2 and GENE. The ESL project presently has three components: TEMPEST, a full-f, full-geometry (single-null divertor, or arbitrary-shape closed flux surfaces) code in E, {mu} (energy, magnetic-moment) coordinates; EGK, a simple-geometry rapid-prototype code, presently of; and the math component, which is developing and implementing algorithms for a next-generation code. Progress would be accelerated if we could find funding for a fourth, computer science, component, which would develop software infrastructure, provide user support, and address needs for data handing and analysis. We summarize the status and plans for the three funded activities.
Date: June 5, 2007
Creator: Cohen, R

Edge, Sol, and Diverter Plasma Turbulence and Macroscopic Transport

Description: In the last few years, it was clearly shown that cross-field transport in the far SOL could be significantly faster than previously thought and that this transport exhibited convective rather then diffusive features. As a result, in high density cases the plasma coming into the SOL from the core recycled at the wall of the tokamak main chamber, rather than flowing into the divertor and recycling there, as the conventional picture of edge plasma flows would suggest. It was also shown that coherent structures, often called ''blobs'', played very important roles in the particle and energy transport inside the SOL region for both L and H confinement modes. The blobs seen in the SOL are extended along the magnetic field lines and have a plasma density two to three times higher than the ambient SOL plasma density and poloidal and radial scales of about 1 cm. In experimental measurements, the blobs propagated in radial direction towards the chamber wall with a velocity {approx} 10{sup 5} cm/s, and the contribution of non-diffusive flux associated with transport of blobs to the total particle flux in the far SOL attained 70-90%. In addition, recent assessment of experimental data and theoretical models shows that plasma propagation into the SOL during ELM is somewhat similar to that of blobs.
Date: April 25, 2005
Creator: Krasheninnikov, Prof. Sergi

Edge State Propagation Direction in the Fractional Quantum Hall Regime: Multi-Terminal Magnetocapacitance Experiment

Description: The propagation direction of fractional quantum Hall effect (FQHE) edge states has been investigated experimentally via the symmetry properties of the multi-terminal capacitances of a two dimensional electron gas. Although strong asymmetries with respect to zero magnetic field appear, no asymmetries with respect to even denominator Landau level filling factor {nu} are seen. This indicates that current-carrying FQHE edge states propagate in the same direction as integer QHE edge states. In addition, anomalous capacitance features, indicative of enhanced bulk conduction, are observed at {nu} = 1/2 and 3/2.
Date: September 20, 1999

Edge states in a honeycomb lattice: effects of anisotropic hopping and mixed edges

Description: We study the edge states in graphene in the presence of a magnetic field perpendicular to the plane of the lattice. Most of the work done so far discusses the edge states in either zigzag or armchair edge graphene considering an isotropic electron hopping. In practice, graphene can have a mixture of armchair and zigzag edges and the electron hopping can be anisotropic, which is the subject of this article. We predict that the mixed edges smear the enhanced local density of states (LDOS) at E=0 of the zigzag edge and, on the other hand, the anisotropic hopping gives rise to the enhanced LDOS at E=0 in the armchair edge. The behavior of the LDOS can be studied using scanning tunneling microscopy (STM) experiments. We suggest that care must be taken while interpreting the STM data, because the clear distinction between the zigzag edge (enhanced LDOS at E=0) and armchair edge (suppressed LDOS at E=0) can be lost if the hopping is not isotropic and if the edges are mixed.
Date: January 1, 2008
Creator: Dahal, Hari P; Balatsky, Alexander V; Sinistsyn, N A; Hu, Zi - Xiang & Yang, Kun

Edge Turbulence Imaging in the Alcator C-Mod Tokamak

Description: The 2-D radial vs. poloidal structure of edge turbulence in the Alcator C-Mod tokamak [I.H. Hutchinson, R. Boivin, P.T. Bonoli et al., Nuclear Fusion 41(2001) 1391] was measured using fast cameras and compared with 3-D numerical simulations of edge plasma turbulence. The main diagnostic is Gas Puff Imaging (GPI), in which the visible D(subscript alpha) emission from a localized D(subscript 2) gas puff is viewed along a local magnetic field line. The observed D(subscript alpha) fluctuations have a typical radial and poloidal scale of approximately 1 cm, and often have strong local maxima (''blobs'') in the scrape-off layer. The motion of this 2-D structure motion has also been measured using an ultra-fast framing camera with 12 frames taken at 250,000 frames/sec. Numerical simulations produce turbulent structures with roughly similar spatial and temporal scales and transport levels as that observed in the experiment; however, some differences are also noted, perhaps requiring diagnostic improvement and/or additional physics in the numerical model.
Date: November 26, 2001
Creator: Zweben, S.J.; Stotler, D.P.; Terry, J.L.; LaBombard, B.; Greenwald, M.; Muterspaugh, M. et al.