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Improved system for perpendicular electron-cyclotron emission measurements on TMX-Upgrade

Description: Perpendicular electron-cyclotron emission (PECE) is used on TMX-U to diagnose thermal-barrier hot electrons (T/sub H/ approx. 100 to 400 keV); yielding the time history of the temperature of these relativistic electrons. We describe an improved quasi-optical viewing system for these measurements that uses high sensitivity superheterodyne receivers at fixed frequencies of 60, 98, 130, and 196 GHz. The improved viewing and transport system consists of an off-axis ellipsoidal mirror that images the plasma onto a V-band conical collection horn, an overmoded circular waveguide (7/8'' diam) that transports the radiation outside the vacuum vessel where the polarization is selected, and a high absorptivity Macor beam dump to prevent internal wall reflections from entering the viewing system. A relativistic code is used to calculate optically thin PECE signals from relativistic electrons for various energy and pitch angle distributions. 4 refs., 4 figs.
Date: March 7, 1986
Creator: Lasnier, C.J.; Ellis, R.F. & James, R.A.
Partner: UNT Libraries Government Documents Department

Optically thin perpendicular electron-cyclotron emission from hot electrons in TMX-U

Description: Perpendicular electron-cyclotron emission (PECE) from relativistic (T/sub H/ approx. 100 to 400 keV) hot electrons within the thermal-barrier region of TMX-U is detected at 35, 60, 94 and 98 GHz. For the operating regime of TMX-U these signals are optically thin (tau<<1) and thus proportional to the radial hot electron line density. A relativistic code is used to calculate the theoretical temperature dependence of the perpendicular emission coefficient, j perpendicular(..omega..,T/sub H/), for each of the detected frequencies. This dependence has been verified experimentally by x-ray measurements of the hot electron temperature, T/sub H/. The observed qualitative agreement demonstrates that optically thin PECE signals can be used to determine the temporal evolution of T/sub H/. An inability to absolutely calibrate the present PECE waveguide system has prevented quantitative agreement.
Date: March 4, 1986
Creator: James, R.A.; Lasnier, C.J. & Ellis, R.F.
Partner: UNT Libraries Government Documents Department

Numerical Modelling of the Nonlinear ELM Cycle in Tokamaks

Description: A numerical model of the nonlinear evolution of edge localized modes (ELMs) in tokmaks is presented. In the model discussed here it is assumed that thermoelectric currents flow in short connection length flux tubes, initially established by error fields or other non-axisymmetric magnetic perturbations. Magnetic perturbations resulting from the currents are incorporated into the magnetic topology. The predictions are compared to measurements at the DIII-D tokamak. Excellent agreement between the calculated magnetic structures on the vessel wall and camera observations during an ELM cycle is shown. The ELM collapse process is discussed.
Date: June 2, 2009
Creator: Wingen, A; Evans, T E; Lasnier, C J & Spatschek, K H
Partner: UNT Libraries Government Documents Department

Characteristics of the scrape-off layer in DIII-D high-performance negative central magnetic shear discharges

Description: In this paper the authors present measurements of the global power and particle balance in the high-performance phase of negative central magnetic shear (NCS) discharges and compare with reference VH-mode discharges. The principal differences observed are that NCS has a much lower fraction of the total input power flowing into the boundary, less core radiation, and larger rate of stored energy increase as a fraction of total power. Scrape-off layer (SOL) temperature and divertor heat flux profiles, and radiation profiles at the midplane, are similar to VH-mode. Due to the good core particle confinement and efficient fueling by neutral beam injection (NBI), with little gas puffing, the gas load on the walls and the recycling are very low during the NCS discharges. This results in a rate of density rise relative to beam fueling at the L to H transition time which is 1/3 of the value for VH transitions, which is in turn 1/2 that for L-to-ELMing-H-mode transitions.
Date: October 1, 1996
Creator: Lasnier, C.J.; Maingi, R. & Leonard, A.W.
Partner: UNT Libraries Government Documents Department

Perpendicular electron cyclotron emission from hot electrons in TMX-U

Description: Perpendicular electron cyclotron emission (PECE) from the electron cyclotron resonant heating of hot electrons in TMX-U is measured at 30 to 40 and 50 to 75 GHz. This emission is optically thin and is measured at the midplane, f/sub ce/ approx. = 14 GHz, in either end cell. In the west end cell, the emission can be measured at different axial positions thus yielding the temporal history of the hot electron axial profile. These profiles are in excellent agreement with the axial diamagnetic signals. In addition, the PECE signal level correlates well with the diamagnetic signal over a wide range of hot electron densities. Preliminary results from theoretical modeling and comparisons with other diagnostics are also presented.
Date: September 14, 1984
Creator: James, R.A.; Ellis, R.F.; Lasnier, C.J.; Casper, T.A. & Celata, C.M.
Partner: UNT Libraries Government Documents Department


Description: The tangentially viewing visible and vertically viewing infrared cameras systems on DIII-D were upgraded to permit emission measurements during edge localized modes (ELMs) with integration times as short as 1 and 100 {micro}s respectively. The visible system was used to obtain 2-D poloidal profiles of CIII (465 nm) and D{sub {alpha}} (656.3 nm) emission with 20 {micro}s integration during various stages of ELM events in the lower DIII-D divertor. The infrared (IR) system was used to measure the heat flux to the divertor targets at 10 kHz with 100 {micro}s exposure. Upgrades to the data processing and storage systems permitted efficient comparison of the temporal evolution of these measurements.
Date: August 1, 2002
Partner: UNT Libraries Government Documents Department

Divertor E X B Plasma Convection in DIII-D

Description: Extensive two-dimensional measurements of plasma potential in the DIII-D tokamak divertor region are reported for standard (ion VB{sub T} drift toward divertor X-point) and reversed B{sub T} directions; for low (L) and high (H) confinement modes; and for partially detached divertor mode. The data are consistent with recent computational modeling identifying E x B{sub T} circulation, due to potentials sustained by plasma gradients, as the main cause of divertor plasma sensitivity to B{sub T} direction.
Date: July 1, 1999
Creator: Boedo, J.A.; Schaffer, M.J.; Maingi, M.; Lasnier, C.J. & Watkins, J.G.
Partner: UNT Libraries Government Documents Department

Toroidally Asymmetric Distributions of Hydrocarbon (CD) Emission and Chemical Sputtering Sources in DIII-D

Description: Measurements in DIII-D show that the carbon chemical sputtering sources along the inner divertor and center post are toroidally periodic and highest at the upstream tile edge. Imaging with a tangentially viewing camera and visible spectroscopy were used to monitor the emission from molecular hydrocarbons (CH/CD) at 430.8 nm and deuterium neutrals in attached and partially detached divertors of low-confinement mode plasmas. In contrast to the toroidally periodic CD distribution, emission from deuterium neutrals was observed to be toroidally symmetric along the inner strike zone. The toroidal distribution of the measured tile surface temperature in the inner divertor correlates with that of the CD emission, suggesting larger parallel particle and heat fluxes to the upstream tile edge, either due to toroidal tile gaps or height steps between adjacent tiles.
Date: May 16, 2006
Creator: Groth, M; Brooks, N H; Fenstermacher, M E; Lasnier, C J; McLean, A G & Watkins, J G
Partner: UNT Libraries Government Documents Department

Measurements of optically thin electron cyclotron emission from relativistic electrons

Description: Electron cyclotron emission (ECE) from hot, relativistic electrons has been measured simulataneously at several optically thin frequencies (f/f/sub ce/ = 4.6, 7.0, and 9.6) on the Tandem Mirror Experiment-Upgrade. A method to determine the temporal evolution of the hot electron density, n/sub h/, and temperature T/sub h/ is discussed. Calculations of T/sub h/ agree with the analysis of the high energy x-ray spectra. Heating rates vary between 3 keV/ms and 13 keV/ms and temperatures over 300 keV have been reached by the end of the 50 ms discharge. The ECE analysis provides an order of magnitude improvement in time resolution over the x-ray analysis and shows that fast reductions in the diamagnetic loop signals are predominantly a loss of perpendicular energy stored by the mirror trapped hot electrons. These techniques for determining n/sub h/(t) and T/sub t/(t) will be used on the DIII-D tokamak in order to parameterize the nonthermal electron tail produced during ECH current drive experiments. A vertical view will be utilized and a fast (70 Hz) scanning Michelson interferometer will be used to measure the ECE spectrum between the 2nd and the 15th harmonic. 11 refs., 7 figs.
Date: October 1, 1987
Creator: James, R.A.; Silver, E.; Boyd, D.; Ellis, R.F.; Jantz, S.; Lasnier, C.J. et al.
Partner: UNT Libraries Government Documents Department

Magnetic and thermal energy flow during disruptions in DIII-D

Description: The authors present results from disruption experiments where they measure magnetic energy flow across a closed surface surrounding the plasma using a Poynting flux analysis to measure the electromagnetic power, bolometers to measure radiation power and IR scanners to measure radiation and particle heat conduction to the divertor. The initial and final stored energies within the volume are found using the full equilibrium reconstruction code EFIT. From this analysis they calculate an energy balance and find that they can account for all energy deposited on the first wall and the divertor to within about 10%.
Date: July 1, 1996
Creator: Hyatt, A.W.; Lee, R.L.; Humphreys, D.A.; Kellman, A.G.; Taylor, P.L.; Cuthbertson, J.W. et al.
Partner: UNT Libraries Government Documents Department


Description: Carbon penetration into the core plasma during midplane and divertor methane puffing has been measured for DIII-D ELMing H-mode plasmas. The methane puffs are adjusted to a measurable signal, but global plasma parameters are only weakly affected (line average density, &lt;n{sub e}&gt; increases by &lt; 10%, energy confinement time, {tau}{sub E} drops by &lt; 10%). The total carbon content is derived from C{sup +6} density profiles in the core measured as a function of time using charge exchange recombination spectroscopy. The methane penetration factor is defined as the difference in the core content with the puff on and puff off, divided by the carbon confinement time and the methane puffing rate. In ELMing H-mode discharges with ion {del}B drift direction into the X-point, increasing the line averaged density from 5 to 8 x 10{sup 19} m{sup -3} dropped the penetration factor from 6.6% to 4.6% for main chamber puffing. The penetration factor for divertor puffing was below the detection limit (&lt;1%). Changing the ion {del}B drift direction to away from the X-point decreased the penetration factor by more than a factor of five for main chamber puffing.
Date: June 1, 2002
Creator: WEST, W.P.; LASNIER, C.J.; WHYTE, D.G.; ISLER, R.C.; EVANS, T.E.; JACKSON, G.L. et al.
Partner: UNT Libraries Government Documents Department

Effect of Magnetic Geometry on ELM Heat Flux Profiles

Description: In this paper we explore how precisely the magnetic up/down symmetry must be controlled to insure sharing of edge localized mode (ELM) heat flux between upper and lower diverters in a double-null tokamak. We show for DIII-D, using infrared thermography, that the spatial distribution of Type-I ELM energy is less strongly affected by variations in magnetic geometry than is the time-averaged peak heat flux in attached discharges. The degree of control necessary to share ELM heat flux deposition equally between diverters was less stringent than the control needed to balance the time averaged heat flux. ELM energy is transported more than four times further into the scrape-off layer than the time-averaged heat flux.
Date: May 15, 2000
Creator: Lasnier, C.J.; Leonard, A.W.; Petrie, T.W. & Watkins, J.G.
Partner: UNT Libraries Government Documents Department

Measurements of divertor impurity concentrations on DIII-D

Description: Carbon emissions in the DIII-D divertor during partial detachment have been measured, and the deduced radiated power and the temporal behavior of the impurity emissions from spectroscopy are in good agreement with bolometer measurements. Effective electron temperatures from line ratios for CIV (9-11 eV) and CIII (6-8 eV) are correlated with DTS measured electron temperatures to determine the spatial location of the carbon radiation zone. During PDD operation, the bulk of the divertor radiation is emitted from CIV near the X- point while deuterium radiation is strongest near the outer strikepoint. The carbon ion concentrations are in the range of 1% - 4% of the electron density.
Date: October 1, 1996
Creator: Wood, R.; Isler, R. C.; Allen, S. L.; Fenstermacher, M. E.; Lasnier, C. J.; Leonard, A. W. et al.
Partner: UNT Libraries Government Documents Department

Thermal deposition analysis during disruptions on DIII-D using infrared scanners

Description: The DIII-D tokamak generates plasma discharges with currents up to 3 MA and auxiliary input power up to 20 MW from neutral beams and 4 MW from radio frequency systems. In a disruption, a rapid loss of the plasma current and internal thermal energy occurs and the energy is deposited onto the torus graphite wall. Quantifying the spatial and temporal characteristics of the heat deposition is important for engineering and physics-related issues, particularly for designing future machines such as ITER. Using infrared scanners with a time resolution of 120 {micro}s, measurements of the heat deposition onto the all-graphite walls of DIII-D during two types of disruptions have been made. Each scanner contains a single point detector sensitive to 8--12 {micro}m radiation, allowing surface temperatures from 20 C to 2,000 C to be measured. A zinc selenide window that transmits in the infrared is used as the vacuum window. Views of the upper and lower divertor regions and the centerpost provide good coverage of the first wall for single and double null divertor discharges. During disruptions, the thermal energy is not deposited evenly onto the inner surface of the tokamak, but is deposited primarily in the divertor region when operating diverted discharges. Analysis of the heat deposition during a radiative collapse disruption of a 1.5 MA discharge revealed power densities of 300--350 MW/m{sup 2} in the divertor region. During the thermal quench of the disruption, the energy deposited onto the divertor region was more than 70% of the stored thermal energy in the discharge prior to the disruption. The spatial distribution and temporal behavior of power deposition during high {beta} disruptions will also be presented.
Date: December 1, 1995
Creator: Lee, R.L.; Hyatt, A.W.; Kellman, A.G.; Taylor, P.L. & Lasnier, C.J.
Partner: UNT Libraries Government Documents Department

Fueling efficiency of pellet injection on DIII-D

Description: Pellet injection has been used on the DIII-D tokamak to study density limits and particle transport in H-mode and inner wall limited L-mode plasmas. These experiments have provided a variety of conditions in which to examine the fueling efficiency of pellets injected into DIII-D plasmas. The fueling efficiency defined as the total increase in number of plasma electrons divided by the number of pellet fuel atoms, is determined by measurements of density profiles before and just after pellet injection. The authors have found that there is a decrease in the pellet fueling efficiency with increased neutral beam injection power. The pellet penetration depth also decreases with increased neutral beam injection power so that, in general, fueling efficiency increases with penetration depth. The fueling efficiency is generally 25% lower in ELMing H-mode discharges than in L-mode due to an expulsion of particles with a pellet triggered ELM. A comparison with fueling efficiency data from other tokamaks shows similar behavior.
Date: May 1998
Creator: Baylor, L. R.; Jernigan, T. C.; Maingi, R.; Lasnier, C. J. & Ali Mahdavi, M.
Partner: UNT Libraries Government Documents Department

High Density H-Mode Discharges with Gas Fueling and Good Confinement on DIII-D

Description: H-mode operation at high density is an attractive regime for future reactor-grade tokamaks [1]. High density maximizes fusion power output while the high confinement of H-mode keeps the plasma energy loss below the alpha heating power. One concern though is the energy released due to individual ELMs must be kept small to protect the diverter target from excess ablation. We report on discharges in DIII-D with electron densities as high as 1.45 times the Greenwald density, n{sub GW}(10{sup 20}m{sup -3})=I{sub p}(MA)/[{pi}{sup 2}(m)], with good confinement, H{sub ITER89P}=1.9, and ELMs with energy amplitude small enough to protect the divertor. These results were achieved at low triangularity single-null divertor, {delta}{approx}0.0 with a plasma current of 1.2 MA, q{sub 95} {approx} 3-4, and moderate neutral beam heating power of 2-4 MW. The density was controlled by moderate gas puffing and private flux pumping. A typical discharge is shown in Fig. 1 where upon gas puffing the pedestal density, n{sub e,epd}, quickly rises to {approx}0.8 x n{sub GW}. The confinement initially drops with the gas puff, on a longer timescale the central density rises, peaking the profile and increasing the confinement until an MHD instability terminates the high density and high confinement phase of the discharge. In this report we describe in detail edge pedestal changes and its effect on confinement as the density is increased. We then describe peaking of the density profile that offsets degradation of the pedestal at high density and restores good confinement. Finally we describe the small benign ELMs that result at these high densities.
Date: August 1, 2000
Creator: Leonard, A.W.; Osborne, T.H.; Mahdavi, M.A.; Fenstermacher, M.E.; Lasnier, C.J.; Petrie, T.W. et al.
Partner: UNT Libraries Government Documents Department

UEDGE simulation of detached divertor operation in DIII-D with a chemically sputtered carbon source

Description: We describe the response of the scrape-off layer (SOL) plasma to variations in the intensity, and geometry of an intrinsic carbon source in DIII-D. Using the multi species 2-D fluid plasma code UEDGE we find plasma modes which are similar to those seen experimentally. At high sputtering coefficient the plasma discontinuously transitions to a state in which the radiation power exceeds the input power and no steady state solution is obtained. We believe this corresponds to the MARFE (Multifaceted Asymmetric Radiation from Edge) state seen experimentally, in which the core confinement is reduced.
Date: May 21, 1997
Creator: Porter, G.D.; Rognlien, T.D.; Fenstermacher, M.E.; Hill, D.N.; Lasnier, C.J.; Isler, R.C. et al.
Partner: UNT Libraries Government Documents Department

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.
Partner: UNT Libraries Government Documents Department