Modelling of passive charge exchange emission and neutral background density deduction in JET

Tunklev, Magnus; Breger, P.; Günther, K.; Hellermann, M. von; König, R.; O’Mullane, M.; Zastrow, K.‐D.

doi:10.1088/0741-3335/41/8/305

Cited by 25 publications

(17 citation statements)

References 10 publications

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“…Then, if the background emission (i.e. from Bremsstrahlung, CX with naturally occurring neutrals, and electron excitation of the hydrogen-like impurity, A (Z−1)+ ) is known previously from measurement or modelling 32,33 , the amount of injected gas needed for a particular signal/background ratio can be calculated. The CXRS radiance is given by the usual equation: First, if the optics are properly aligned to be tangent to flux surfaces at the point of emission, q ef f,i and n A Z+ can assumed to be constant over the LOS integral.…”

Section: Estimates Of Expected Gp-cxrs Signalmentioning

confidence: 99%

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Development of the gas puff charge exchange recombination spectroscopy (GP-CXRS) technique for ion measurements in the plasma edge

Churchill

Theiler

Lipschultz

et al. 2013

Review of Scientific Instruments

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A novel charge-exchange recombination spectroscopy (CXRS) diagnostic method is presented, which uses a simple thermal gas puff for its donor neutral source, instead of the typical high-energy neutral beam. This diagnostic, named gas puff CXRS (GP-CXRS), is used to measure ion density, velocity, and temperature in the tokamak edge/pedestal region with excellent signal-background ratios, and has a number of advantages to conventional beam-based CXRS systems. Here we develop the physics basis for GP-CXRS, including the neutral transport, the charge-exchange process at low energies, and effects of energy-dependent rate coefficients on the measurements. The GP-CXRS hardware setup is described on two separate tokamaks, Alcator C-Mod and ASDEX Upgrade. Measured spectra and profiles are also presented. Profile comparisons of GP-CXRS and a beam based CXRS system show good agreement. Emphasis is given throughout to describing guiding principles for users interested in applying the GP-CXRS diagnostic technique.

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Section: Estimates Of Expected Gp-cxrs Signalmentioning

confidence: 99%

“…The neutral emission measurements are used in the calculation of impurity density, as will be shown in Section VII. Additionally, optical periscopes are installed that don't intersect the gas puff, for use as effective background views, to remove passive light contribution to the GP-CXRS signal 32 .…”

Section: Alcator C-mod Gp-cxrs Systemmentioning

confidence: 99%

Development of the gas puff charge exchange recombination spectroscopy (GP-CXRS) technique for ion measurements in the plasma edge

Churchill

Theiler

Lipschultz

et al. 2013

Review of Scientific Instruments

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“…A second class of non-Gaussian synthetic line shape arises in the case of passive CX line emission [17], which represent the non-local, line-of-sight integrated, measurement of spectra induced by the interaction of neutral hydrogen streaming from the wall into the plasma and fully stripped confined impurity ions:…”

Section: Introduction To the Sos Projectmentioning

confidence: 99%

Simulation of Spectra Code (SOS) for ITER Active Beam Spectroscopy

Hellermann

Bock

Marchuk

et al. 2019

Atoms

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The concept and structure of the Simulation of Spectra (SOS) code is described starting with an introduction to the physics background of the project and the development of a simulation tool enabling the modeling of charge-exchange recombination spectroscopy (CXRS) and associated passive background spectra observed in hot fusion plasmas. The generic structure of the code implies its general applicability to any fusion device, the development is indeed based on over two decades of spectroscopic observations and validation of derived plasma data. Four main types of active spectra are addressed in SOS. The first type represents thermal low-Z impurity ions and the associated spectral background. The second type of spectra represent slowing-down high energy ions created from either thermo-nuclear fusion reactions or ions from injected high energy neutral beams. Two other modules are dedicated to CXRS spectra representing bulk plasma ions (H+, D+, or T+) and beam emission spectroscopy (BES) or Motional Stark Effect (MSE) spectrum appearing in the same spectral range. The main part of the paper describes the physics background for the underlying emission processes: active and passive CXRS emission, continuum radiation, edge line emission, halo and plume effect, or finally the charge exchange (CX) cross-section effects on line shapes. The description is summarized by modeling the fast ions emissions, e.g., either of the α particles of the fusion reaction or of the beam ions itself.

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“…Along the NBI trajectory a local CX signal can be detected leading to a spatially localized measurement since the detected impurity ions radiate in the region where the chords of the CXRS diagnostic intersect the path of the neutral beam particles. CX processes occur also between fully ionized impurities and neutral background atoms, which enter the plasma from the walls and represent localized sources of neutrals, leading to a passive or thermal CX emission line [4,5]. Most of the background neutrals are ionized at the very edge of the plasma, however, a few transfer their charge after a CX reaction.…”

Section: Measurement Techniquementioning

confidence: 99%

Investigation of passive edge emission in charge exchange spectra at the ASDEX Upgrade tokamak

Viezzer

Pütterich

Dux

et al. 2011

Plasma Phys. Control. Fusion

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Abstract. The influence of passive edge emission on the charge exchange spectra of carbon (C 5+ , n=8→7 at 529 nm) measured in fusion plasmas at the ASDEX Upgrade tokamak is investigated. The spectra are obtained viewing the plasma edge tangentially with 8 lines of sight while the plasma is swept to enhance the spatial density of the measurements. A forward model to deconvolute the measured line-integrals is employed. The local emissions are then compared to the simulated radiation obtained with the 1-D impurity transport code STRAHL using transport coefficients which are determined independently. Depending on the background neutral deuterium densities the simulation predicts the absolute line intensities and the relative contributions of electron impact excitation and thermal charge exchange to the measured signals. Therefore, a background neutral deuterium density profile has been determined. For the passive emission line of C 5+ , the comparison between forward model and simulations yields that electron impact excitation and thermal charge exchange are both important for understanding the passive line. Indeed, thermal charge exchange proves to be affecting the passive emission line considerably via two mechanisms, i.e. change of ionization equilibrium through charge exchange recombination and radiation due to local charge exchange reactions.

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Modelling of passive charge exchange emission and neutral background density deduction in JET

Cited by 25 publications

References 10 publications

Development of the gas puff charge exchange recombination spectroscopy (GP-CXRS) technique for ion measurements in the plasma edge

Development of the gas puff charge exchange recombination spectroscopy (GP-CXRS) technique for ion measurements in the plasma edge

Simulation of Spectra Code (SOS) for ITER Active Beam Spectroscopy

Investigation of passive edge emission in charge exchange spectra at the ASDEX Upgrade tokamak

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