Transport studies using laser blow-off injection of low-Z trace impurities injected into the TJ-II stellarator

Zurro, B.; Hollmann, E. M.; Baciero, A.; Ochando, M. A.; Medina, F.; McCarthy, K. J.; Blanco, E.; Cal, E. de la; Carralero, D.; Pedrosa, M. A.; Team, Tj‐Ii

doi:10.1088/0029-5515/51/6/063015

Cited by 14 publications

(19 citation statements)

References 31 publications

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“…If the Signal-to-Noise ratio (SNR), dened here as M/σ F , is large enough it can be shown that the PDFs of the phase and amplitude can be well approximated by a Gaussian distribution function. The PDF of the amplitude can be found by integrating (12) over all the phases on a circle. The PDF of the phase can be found by integrating over all amplitudes on a line starting at the origin.…”

Section: Amplitude and Phase Distributions And Their Condence Boundsmentioning

confidence: 99%

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Estimation of the thermal diffusion coefficient in fusion plasmas taking frequency measurement uncertainties into account

Berkel

Zwart

Hogeweij

et al. 2014

Plasma Phys. Control. Fusion

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In this paper, the estimation of the thermal diusivity from perturbative experiments in fusion plasmas is discussed. The measurements used to estimate the thermal diusivity suer from stochastic noise. Accurate estimation of the thermal diusivity should take this into account. It will be shown that formulas found in the literature often result in a thermal diusivity that has a bias (a dierence between the estimated value and the actual value that remains even if more measurements are added) or have an unnecessarily large uncertainty. This will be shown by modeling a plasma using only diusion as heat transport mechanism and measurement noise based on ASDEX Upgrade measurements. The Fourier coecients of a temperature perturbation will exhibit noise from the Circular Complex Normal Distribution (CCND). Based on Fourier coecients with a CCND, it is shown that the resulting Probability Density Function (PDF) of the thermal diusivity is an inverse non-central chi-squared distribution. The thermal diusivity that is found by sampling this distribution will always be biased and averaging of multiple estimated diusivities will not necessarily improve the estimation. Condence bounds are constructed to illustrate the uncertainty in diusivity using several formulas that are equivalent in the noiseless case. Finally, a dierent method of averaging, that reduces the uncertainty signicantly, is suggested. The methodology is also extended to the case where damping is included and it is explained how to include the cylindrical geometry.

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Section: Amplitude and Phase Distributions And Their Condence Boundsmentioning

confidence: 99%

“…The PDF of the amplitude can be found by integrating (12) over the phase The resulting amplitude distribution is given by…”

Section: Appendix a Distributions Of Amplitude And Phasementioning

confidence: 99%

Estimation of the thermal diffusion coefficient in fusion plasmas taking frequency measurement uncertainties into account

Berkel

Zwart

Hogeweij

et al. 2014

Plasma Phys. Control. Fusion

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“…The laser blow-off (LBO) technique is a wide-spread method. It is not only used for impurity studies in fusion experiments [6][7][8][9][10][11][12][13][14] , but has also been applied for studying electron heat transport [15][16][17] , for measuring plasma temperatures and densities at the plasma edge [18][19][20][21][22][23] , investigating atomic processes [24][25][26][27][28][29][30][31] as well as laser induced metal deposition 32 and patterning of thin film solar cells 33 In Wendelstein 7-X stellarator (W7-X) a new LBO system has been installed in 2017 for the OP1.2a experimental campaign to inject non-intrinsic and non-recycling impurity ions with different nuclear charge Z for transport and confinement studies. The method is based on a high energy laser beam that passes through a transparent glass plate which is coated on the plasma facing side with the elements to be injected into the plasma.…”

Section: Introductionmentioning

confidence: 99%

Design, capabilities, and first results of the new laser blow-off system on Wendelstein 7-X

Wegner

Geiger

Kunkel

et al. 2018

Review of Scientific Instruments

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We present a detailed overview and first results of the new laser blow-off system on the stellarator Wendelstein 7-X. The system allows impurity transport studies by the repetitive and controlled injection of different tracer ions into the plasma edge. A Nd:YAG laser is used to ablate a thin metal film, coated on a glass plate, with a repetition rate of up to 20 Hz. A remote-controlled adjustable optical system allows the variation of the laser spot diameter and enables the spot positioning to non-ablated areas on the target between laser pulses. During first experiments, clear spectral lines from higher ionization stages of the tracer ions have been observed in the X-ray to the extreme ultraviolet spectral range. The temporal behavior of the measured emission allows the estimate of transport properties, e.g., impurity transport times in the order of 100 ms. Although the strong injection of impurities is well detectable, the global plasma parameters are barely changed.

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“…These different ablation processes enable a wide-spread field of applications. In particular, the laser blow-off technique has been applied in fusion experiments for impurity transport studies [2][3][4][5][6][7] , for electron heat transport investigation 8,9 and for plasma temperature and density measurement at the plasma edge [10][11][12][13] . It has also been used for studying atomic processes [14][15][16][17][18] , patterning of thin film solar cells 19,20 as well as laser induced metal deposition 21 .…”

Section: Introductionmentioning

confidence: 99%

Preparation, analysis, and application of coated glass targets for the Wendelstein 7-X laser blow-off system

Wegner

Geiger

Foest

et al. 2020

Review of Scientific Instruments

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Coated glass targets are a key component for the Wendelstein 7-X laser blow-off system that is used for impurity transport studies. The preparation and analysis of those glass targets as well as their performance is examined in this paper. The glass targets have a high laser damage threshold and are coated via physical vapor deposition with µm thick films. In addition, nm-thin layers of Ti are used as interface layer for improved ablation efficiency and reduced coating stress. Hence, the metallic or ceramic coating has a lateral homogeneity within 2% and contaminants less than 5% being optimal for laser ablation processing. With that method a short (few ms) and well defined pulse of impurities with about 10 17 particles can be injected close to the last closed flux surface of Wendelstein 7-X. In particular, a significant amount of atoms with an velocity of about 1 km/s enters the plasma within 1 ms. The atoms are followed by a negligible concentration of slower clusters and macro-particles. This qualifies the use of the targets and applied laser settings for impurity transport studies with the laser blow-off system in Wendelstein 7-X.

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Transport studies using laser blow-off injection of low-Z trace impurities injected into the TJ-II stellarator

Cited by 14 publications

References 31 publications

Estimation of the thermal diffusion coefficient in fusion plasmas taking frequency measurement uncertainties into account

Estimation of the thermal diffusion coefficient in fusion plasmas taking frequency measurement uncertainties into account

Design, capabilities, and first results of the new laser blow-off system on Wendelstein 7-X

Preparation, analysis, and application of coated glass targets for the Wendelstein 7-X laser blow-off system

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