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  • 1
    Electronic Resource
    Electronic Resource
    Identification of Alfvén mode location via multichannel interferometer measurements (abstract) : Proceedings of the eleventh topical conference on high temperature plasma diagnostics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 698-698 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Quasicoherent magnetohydrodynamics modes with an Alfvén frequency scaling are seen routinely in TFTR neutral beam heated plasmas as well as some Ohmic plasmas. So far, they are only observed in external magnetic fluctuation measurement (Mirnov coils). A close correlation is observed between the changes in the mode frequency and electron density measured by the multichannel infrared interferometer. This correlation allows us to determine the location of the Alfvén modes. The result shows that they are near the plasma edge, r/a〉0.85. This method is also used to identify the location of the toroidicity-induced Alfvén eigenmode driven by fast ions in a radiowave heating experiment. The result is consistent with the location determined by the reflectometer measurement.© 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147925
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  • 2
    Electronic Resource
    Electronic Resource
    Results from the TFTR high-frequency toroidal Mirnov array for detection of modes in the Alfvén range of frequencies : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 813-815 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Toroidal Alfvén eigenmodes and other Alfvénic modes have been predicted to be destabilized by the presence of a fusion α population in TFTR and future D-T machines, possibly resulting in significant loss of the fast α population. A new array of Mirnov coils has been added primarily for the measurement of moderate to high toroidal mode numbers. Initial measurements of the n number of ICRF generated toroidal Alfvén eigenmodes modes is presented. The array has also been used to measure the toroidal correlation length of the edge magnetic turbulence. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146529
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  • 3
    Electronic Resource
    Electronic Resource
    Transient nonthermal electron cyclotron emission phenomena in high β TFTR plasmas : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 830-832 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Intense bursts of nonthermal electron cyclotron emission (ECE), measured with a grating polychromator, have been observed to coincide with edge localized modes in TFTR H-mode plasmas. These bursts contain random 10–150 μs emission spikes. Similar nonthermal ECE bursts or spikes have been observed just before the thermal quench during major disruptions in high β TFTR plasmas. The recent installation of a second fast ECE grating polychromator system, at a different toroidal location, has provided additional data on this bursting phenomenon which suggests that the source of the nonthermal ECE may be highly anisotropic and/or poloidally localized on a helical flux surface. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146237
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  • 4
    Electronic Resource
    Electronic Resource
    Analysis of nuclear-radiation-induced noise in spectroscopic and x-ray diagnostics during high power deuterium–tritium experiments on the tokamak fusion test reactor : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 913-915 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Intense fluxes of 14-MeV neutrons from deuterium–tritium (DT) fusion reaction in TFTR resulted in significantly enhanced background noise levels and reduced quality of data from the shielded UV (SPRED) and visible (VIPS) grating spectrometers and the x-ray imaging system (XIS) camera. Both enhanced background levels, attributed to gamma rays and small angle neutron scattering, and large spikes, attributed to nuclear reactions in the silicon detectors, were observed. Both the enhanced background and the frequency of spikes were higher, on a per neutron basis, and the spike amplitudes were higher for DT than for DD operation. The VIPS shield reduced noise by 1/100 for DD radiation; the noise per DT neutron was 4 times higher than per DD neutron. The SPRED detector shield reduction factor was 1/12 in DD; extension of the shield around the vacuum chamber resulted in another factor of 1/5.5 reduction for DT plasmas. Spikes with amplitude up to 10 MeV were observed in the XIS detectors. The shielding effectiveness agrees with predictions. The spike heights are consistent with (n,p) and (n,α) reactions in the silicon detectors. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146203
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  • 5
    Electronic Resource
    Electronic Resource
    Operation of two grating polychromators on TFTR and new observations of magnetohydrodynamic phenomena : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 668-670 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A second grating polychromator instrument has been installed recently on the Tokamak Fusion Test Reactor device. Both this new instrument and the original one, at a different toroidal location, measure electron cyclotron emission from which electron temperature fluctuations and profiles can be obtained. This combination of instruments is designed to provide crucial information on both the poloidal and toroidal structure of magnetohydrodynamic phenomena internal to the TFTR plasma. These instruments are designed to operate within the high neutron flux environment of deuterium-tritium operation in TFTR. Already, this combination of instruments has proven extremely valuable in identifying toroidally nonaxisymmetric phenomena. In addition to toroidal mode numbers, these instruments have yielded valuable new information on the evolution of the structure of the temperature profile during both high-density and high-beta disruptions, and the precursors to these disruptions. In the high-density case, the fast growing (m,n)=(1,1) structure of a cold bubble is verified conclusively. In the high-beta case, a ballooning type of precursor, toroidally and poloidally localized, appears to play an important role in the disruption. Also, this combination of instruments has provided positive verification of the existence of locked and stationary modes, and the temporal evolution of these modes. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146255
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  • 6
    Electronic Resource
    Electronic Resource
    Phenomenology of intense electron cyclotron emission bursts during high power neutral beam heating on TFTR (abstract) : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 4622-4622 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A 20-channel grating polychromator has been used to study intense bursts of electron cyclotron emission (ECE) from TFTR deuterium plasmas predominantly heated by 90–110-keV neutral beams (Pinj/Poh(approximately-greater-than)30). The ECE bursts have a duration of 20–150 μs and are usually seen 300–500 ms after the start of neutral beam injection, when the stored energy and neutron production are collapsing or rolling over. In most cases the ECE bursts have Δf/f∼0.2–0.5, if this frequency spread is due entirely to relativistic broadening it implies an electron energy of 10–100 keV (Core electron temperatures in these plasmas are typically 7–12 keV). The ECE bursts are often correlated with ELM activity during limiter H modes and appear to occur at the beginning of the rise in the Dα signal. In some instances the spectral width of the ECE burst is narrow enough (Δf/f∼0.1) to allow identification of the origin of the emission, in these cases the source appears to be within 0.2 m of the plasma edge and the ECE burst exhibits a delay characteristic of an outwardly directed velocity of 2–3×103 m/s. This work is supported by U.S. Department of Energy Contract No. DE-AC02-76-CHO-3073.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143636
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  • 7
    Electronic Resource
    Electronic Resource
    Diagnostics for investigation of magnetic reconnection in sawtooth crash on TFTR : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 4623-4626 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Magnetic reconnection phenomena are documented by a set of noninvasive fast diagnostics during the crash phase of sawtooth oscillations. The electron cyclotron emission diagnostic system provides the highest resolution for measuring time evolution of electron temperature profile during a typical Tokamak Fusion Test Reactor fast sawtooth crash. The x-ray tomography also contains fast time scale information of the electron temperature profile and additionally the impurity concentration. Just before the crash, a shrinking circular hot peak and growing crescent-shaped flat island appear in the inside of the inversion radius on a bird's-eye view of the electron temperature profile. The electron temperature gradient inside the inversion radius diminishes to nearly zero after the crash. Concomitantly, q(r) profile [q(r)=local safety factor] is measured by the motional stark effect (MSE) diagnostics to verify a magnetic field line reconnection during the sawtooth oscillation. Initial MSE data indicate that central q values increases by 5%–10% during the sawtooth crash phase even when the pressure gradient diminishes inside the q=1 region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143637
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  • 8
    Electronic Resource
    Electronic Resource
    Measurement of the nonaxisymmetric heat load distribution on the first wall of TFTR due to locked modes : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 4720-4723 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The first wall of TFTR is covered in large part (23%) by an inner-wall bumper limiter which is the primary power handling structure in TFTR. The limiter is comprised of more than 2000 tiles, and is instrumented with a large number ((approximately-greater-than)100) of thermocouples in a two-dimensional (2D) array, primarily for protection of the wall. While only about 5% of the tiles are monitored, this thermocouple system is nevertheless capable of mapping details in the nonaxisymmetric, as well as symmetric, heat load patterns encountered under different conditions. In particular, helical heating patterns are observed in discharges which have locked modes. The helical patterns clearly match the expected trajectories based on the m/n mode numbers obtained from Mirnov coils (m/n=2/1 and 4/1), so that the thermocouple system can and was used to identify the existence and mode number of a locked mode. While TFTR discharges rarely suffer from locked modes, locked modes always alter the heating pattern. The locked modes are found to very significantly redistribute the heat load for both ohmic and NBI heated discharges. Locked modes can make what were the coldest areas into the hottest areas, and vice versa. Locked modes also can alter the heat pattern resulting from the frequent disruptions which occur as a result of a locked mode.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143618
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  • 9
    Electronic Resource
    Electronic Resource
    Bursts of electron cyclotron emission during disruptions of high beta discharges in the Tokamak Fusion Test Reactor tokamak : Proceedings of the eleventh topical conference on high temperature plasma diagnostics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 505-508 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Disruptions are sudden terminations of tokamak plasma discharges. During disruptions at high beta β where β (Triple Bond) plasma pressure/magnetic pressure, short (order of μs) and intense bursts of electron cyclotron emission (ECE), an order magnitude above thermal levels, are observed in the second harmonic electron cyclotron frequency range, which corresponds to 100s of GHz in the Tokamak Fusion Test Reactor tokamak. A unique combination of two, fast, 500 kHz, 20-channel grating polychromator instruments, located at different toroidal positions, is used to measure the emission and characterize these bursts. New insights into the three-dimensional dynamics of these disruptions and the accompanying bursts of ECE have been obtained. Bursts of ECE occur at the beginning of the thermal quenches and exhibit strong toroidal asymmetries. Bursts are localized to the vicinity of the ballooning mode, a fast growing (few ms) medium toroidal mode number (n=10–20) precursor, localized toroidally, poloidally, and radially, which triggers the disruptions. Fast-particle losses occur with the explosive growth of the ballooning mode, followed by plasma/wall interaction. Bursts of ECE occur shortly afterwards, within 10s of μs of the fast particle losses. An explanation of the bursting is presented which is consistent both qualitatively and quantitatively, with observations predicting, for example, radiation enhancement factors of (approximate)10. Bursting can be explained not in terms of enhanced excitation of emission but rather in the reduction of absorption of thermal emission. Bursting is consistent with a modification to the electron distribution function fe due to a rapid energy or particle exchange between hot electrons and cold electrons from the edge, momentarily reducing the velocity gradient of fc in the thermal region. Large edge localized mode events also exhibit bursts of ECE due to a similar sequence of events. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147617
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  • 10
    Electronic Resource
    Electronic Resource
    Fast detection of 14 MeV neutrons on the TFTR neutron collimator (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 473-484 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Current mode operation of the NE451 ZnS scintillation detectors of the TFTR neutron collimator has enabled us to record the development of radial neutron emission profiles with much faster speed and higher accuracy than in the pulse counting mode. During high power deuterium–tritium (DT) operation, the intrinsic shot noise on the detector traces was so low that we could observe sawtooth instabilities and disruptions with good precision and, in addition, were able to identify precursor magnetohydrodynamic (MHD) activity and fishbone instabilities. These results demonstrate that in future tritium burning machines like ITER or TPX, the neutron collimator should be designed not only as a monitor of radial fusion power profiles but also as a wave detector for MHD activity. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146615
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