Multichannel light detector system for visible continuum measurements on Alcator C

Foord, M. E.; Marmar, E.S.; Terry, J. L.

doi:10.1063/1.1137176

Cited by 58 publications

(34 citation statements)

References 4 publications

(3 reference statements)

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“…Thorough investigations of the plasma radiation spectra and of the atomic processes in the plasma in the vicinity of the density pedestal show that the measured visible continuum 6 emissivity is the free-free bremsstrahlung emissivity of the plasma [9]. Therefore, the only assumption not supported directly by experimental evidence, which is used when deriving the density profile, is the assumption of constant Z eff across the pedestal region.…”

Section: Pedestal Measurementsmentioning

confidence: 99%

“…Visible continuum profiles are measured with a 2048 element 1-D CCD array, which images emission from the plasma in a passband at 536±3 nm. The emission is dominated by free-free bremsstrahlung for T e > 20 eV [9] and therefore the electron density profile can be obtained from the emissivity measurements. The toroidal midplane views are abel-inverted to yield local emissivity profiles, with chordal resolution near the pedestal region of 2 mm, and time resolution of 4 ms. Soft x-ray emissivity is measured simultaneously at the top of the plasma and the outer midplane by photodiode arrays viewing the plasma edge region through 10 µm beryllium filters.…”

Section: Pedestal Measurementsmentioning

confidence: 99%

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Measurements and scalings of the H-mode pedestal on Alcator C-Mod

Mossessian

Hubbard²,

Marmar³

et al. 2000

Plasma Phys. Control. Fusion

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In this paper we summarize the results of recent measurements of the high confinement mode (H-mode) edge transport barrier in Alcator C-Mod. A number of new, high resolution edge diagnostics provide measurements of plasma parameters (electron density and temperature, and impurities density) in the pedestal region. Pedestal parameters are measured both at the top edge of the plasma and at the midplane. Very narrow (2 -5 mm) electron density and temperature and impurity density pedestals are observed. The impurity pedestal is located inside the density and temperature pedestals in the midplane measurements, but coincides with n e pedestal at the top edge. Correlation of both width and height of the pedestals at the midplane is observed with global plasma parameters and core confinement characteristics.At the same time there are no clear indications of scaling for the electron density and impurity pedestal widths measured at the top of the plasma.2

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Section: Pedestal Measurementsmentioning

confidence: 99%

Section: Pedestal Measurementsmentioning

confidence: 99%

Measurements and scalings of the H-mode pedestal on Alcator C-Mod

Mossessian

Hubbard²,

Marmar³

et al. 2000

Plasma Phys. Control. Fusion

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“…DOI: 10.21517/0202-3822-2017-40-3-14-22 ВВЕДЕНИЕ В составе оптических диагностик плазмы в современных термоядерных установках широко ис-пользуются кварцевые оптоволоконные коллекторы. Кварцевое оптоволокно имеет высокое свето-пропускание в видимом диапазоне спектра и позволяет передать свет из плазмы на детекторы в ди-агностической пультовой с хорошим пространственным разрешением и малыми потерями [1,2] . В большинстве случаев применяется оптоволокно типа кварц-кварц-полимер с сердцевиной из чис-того кварца и фторсодержащей наплавкой диаметром от 0,1 до 0,6 мм и с численной апертурой 0,22.…”

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Features of the Fiber Optics Application in Iter

Vukolov¹,

Andreenko²,

Afanasenko³

et al. 2017

PAST-TF

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Кварцевое оптоволокно имеет высокое светопропускание в видимом диапазоне спектра и широко используется в современных термоядерных установках для передачи света из плазмы к детекторам. Как правило, для этой цели применяют волокно типа кварц-кварц-полимер с сердцевиной из чистого кварца и фторсодержащей наплавкой. В статье рассматриваются проблемы, которые могут возникать при эксплуатации волоконной оптики в составе диагностики плазмы в ИТЭР. Приведены результаты расчётов нейтронных потоков и их спектров в месте возможного размещения оптоволоконных коллекторов в ИТЭР. Сделаны оценки нейтронных флюенсов, которые будут набраны коллекторами за время их работы в ИТЭР. Для анализа проблем радиа-ционной стойкости оптоволокна привлечены результаты радиационных испытаний оптических волокон в ядерном реакторе и на 14 МэВ генераторе нейтронов. На основе анализа результатов радиационных испытаний и нейтронных расчётов сделан вы-вод о необходимости использования в ИТЭР кварцевого волокна с высокой радиационной стойкостью. Оптоволоконные кол-лекторы рекомендовано размещать за первой биозащитой в «ячейке порта» ИТЭР, где поток нейтронов из плазмы ослаблен до величины порядка 10 7 н/(с•см 2 ). Сделано заключение о возможности применения современного оптоволокна в составе оптиче-ских диагностик плазмы (в спектральном диапазоне 450-700 нм), при этом оптоволокно способно выдержать радиационные нагрузки, возникающие в процессе всего периода работы ИТЭР.Ключевые слова: диагностика плазмы, оптоволокно, радиационная стойкость, ИТЭР. The silica-based optical fibers have high transmission in the visible range and they are widely used for transmitting light from plasma to detectors in the modern fusion devices. The pure silica-core/F-doped silica-clad fibers are the most used for plasma diagnostics. The possible problems of the fiber optics in ITER application are discussed in the paper. The estimates of the neutron spectra, fluxes and fluences throughout the ITER lifetime at the presumed fiber bundle location are given. A brief review is presented for the irradiation tests of the optical fibers in the fission reactors and at the 14 MeV neutron generator. The analysis of the irradiation tests and the neutron calculations shows necessity to use the modern silica fibers with high radiation resistance in ITER. The fiber bundles are recommended to be placed in the Port Cell behind the bioshield where the neutron flux from the plasma is attenuated to a value of ~10 7 n/(s•cm 2 ). It is concluded that radiation resistance of the modern optical fibers provides the opportunity for their application (in the spectral range of 450-700 nm) during the whole ITER lifetime. FEATURES OF THE FIBER OPTICS APPLICATION IN ITER

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“…A central line-averaged Z eff is routinely computed and is available online. The average Z eff is defined as (see [3])…”

Section: A Diagnostic For the Determination Of Z Eff On Textormentioning

confidence: 99%

Reconstruction of Zeff Profiles at the TEXTOR Tokamak Through Bayesian Source Separation

Verdoolaege¹

2004

AIP Conference Proceedings

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Abstract. We describe a work in progress on the reconstruction of radial profiles for the ion effective charge Z eff on the TEXTOR tokamak, using statistical data analysis techniques. We introduce our diagnostic for the measurement of bremsstrahlung emissivity signals. Z eff profiles can be determined by Abelinversion of line-integrated measurements of the bremsstrahlung emissivity (ǫ ff ) from the plasma and the plasma electron density (ne) and temperature (Te). However, at the plasma edge only estimated values are routinely used for ne and Te, which are moreover determined at different toroidal locations. These various uncertainties hinder the interpretation of a Z eff profile outside the central plasma. In order to circumvent this problem, we propose several scenarios meant to allow the extraction by (Bayesian) Blind Source Separation techniques of either (lineintegrated) Z eff waveshapes or absolutely calibrated signals from (line-integrated) emissivity signals, using also density and temperature signals, as required. The role of impurities and Z eff in a tokamak plasmaThe behavior of plasma impurities in a tokamak plasma is a critical issue [1]. On the one hand, these impurities increase the fuel dilution and, at reactor parameters, they can be responsible for a considerable power loss from the plasma core by bremsstrahlung. On the other hand, line radiation by low-Z impurities at the plasma edge can be advantageous for the reduction of the plasma-wall interaction. To study the behavior of impurities in the plasma, one needs a local measure for impurity concentration. A parameter of great interest is the so-called ion effective charge of the plasma, Z eff , which is averaged over all species. Once the plasma electron density (n e ) and temperature (T e ) are known, it is proportional to the bremsstrahlung emissivity (ǫ ff ) from the plasma [2], which originates mainly from the acceleration of electrons in the field of ions:and where n i and Z i are the density and charge of ion species i. A diagnostic for the determination of Z eff on TEXTORAt the tokamak TEXTOR (FZJ Jülich, Germany), we run a diagnostic for the determination of Z eff from measurements of bremsstrahlung emissivity in the visible (see also [2]). 21 fiber optic cables are directed along different lines of sight in a

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Multichannel light detector system for visible continuum measurements on Alcator C

Cited by 58 publications

References 4 publications

Measurements and scalings of the H-mode pedestal on Alcator C-Mod

Measurements and scalings of the H-mode pedestal on Alcator C-Mod

Features of the Fiber Optics Application in Iter

Reconstruction of Zeff Profiles at the TEXTOR Tokamak Through Bayesian Source Separation

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