Spectroscopy of highly charged tungsten ions relevant to fusion plasmas

Biedermann, C.; Radtke, R.; Seidel, Robert; Pütterich, T.

doi:10.1088/0031-8949/2009/t134/014026

Cited by 87 publications

(76 citation statements)

References 14 publications

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“…Measurements performed at EBITs in the EUV range [31,32] are consistent with the calculations in terms of dominant spectral lines and detailed benchmarks with the data from the Berlin EBIT in the soft X-ray range yield good agreement [33,34]. It has been found in [33,34], that the important spectral features are reproduced by the LR calculations predicting most of the spectral lines within an accuracy of factor of 2, while only a few special spectral lines exhibited larger discrepancies. This yields the same accuracy as found for the tokamak spectra in the range of 0.4-0.8 nm.…”

Section: Observation Of Spectral Featuressupporting

confidence: 66%

Calculation and experimental test of the cooling factor of tungsten

Pütterich¹,

Neu²,

Dux³

et al. 2010

Nucl. Fusion

217

196

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Abstract. The cooling factor of W is evaluated using state of the art data for line radiation and an ionization balance which has been benchmarked with experiment. For the calculation of line radiation, level-resolved calculations were performed with the Cowan code to obtain the electronic structure and excitation cross sections (plane-wave Born approximation). The data were processed by a collisional radiative model to obtain electron density dependent emissions. These data were then combined with the radiative power derived from recombination rates and Bremsstrahlung to obtain the total cooling factor. The effect of uncertainties in the recombination rates on the cooling factor were studied and were identified to be of secondary importance. The new cooling factor is benchmarked, by comparisons of the line radiation to spectral measurements as well as to a direct measurement of the cooling factor. Additionally, a less detailed calculation using a configuration averaged model was performed. It was used to benchmark the level-resolved calculations and to improve the prediction on radiation power from line radiation for ionization stages which are computationally challenging. The obtained values for the cooling factor validate older predictions from literature. Its ingredients and the absolute value are consistent with the existing experimental results regarding the value itself, the spectral distibution of emissions and the ionization equilibrium. A table of the cooling factor versus electron temperature is provided. Finally, the cooling factor is used to investigate the operational window of a fusion reactor with W as intrinsic impurity. The minimum value of ¤ ¦ ¥ § © , for which a thermonuclear burn is possible, is increased by 20% for a W concentration of " !

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Section: Observation Of Spectral Featuressupporting

confidence: 66%

Calculation and experimental test of the cooling factor of tungsten

Pütterich¹,

Neu²,

Dux³

et al. 2010

Nucl. Fusion

217

196

View full text Add to dashboard Cite

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“…Detailed laboratory measurements on tungsten ions are well suited for electron beam ion traps (EBITs), where charge-state selection is good and the ion temperature and electron density low. Several studies of tungsten in various ionization stages and spectral ranges have been conducted using EBITs; see, e.g., [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. Although designed to have a very wide electron-beam energy range, EBITs have mostly been used at energies above several hundred electron volts, leading to a focus on highly or moderately charged ions with little attention on the first few charge states.…”

Section: Introductionmentioning

confidence: 99%

Extreme Ultraviolet Spectra of Few-Times Ionized Tungsten for Divertor Plasma Diagnostics

Clementson

Lennartsson

Beiersdörfer

2015

Atoms

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The extreme ultraviolet (EUV) emission from few-times ionized tungsten atoms has been experimentally studied at the Livermore electron beam ion trap facility. The ions were produced and confined during low-energy operations of the EBIT-I electron beam ion trap. By varying the electron-beam energy from around 30-300 eV, tungsten ions in charge states expected to be abundant in tokamak divertor plasmas were excited, and the resulting EUV emission was studied using a survey spectrometer covering 120-320 Å. It is found that the emission strongly depends on the excitation energy; below 150 eV, it is relatively simple, consisting of strong isolated lines from a few charge states, whereas at higher energies, it becomes very complex. For divertor plasmas with tungsten impurity ions, this emission should prove useful for diagnostics of tungsten flux rates and charge balance, as well as for radiative cooling of the divertor volume. Several lines in the 194-223 Å interval belonging to the spectra of five-and seven-times ionized tungsten (Tm-like W VI and Ho-like W VIII) were also measured using a high-resolution spectrometer.

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“…Figure 1 shows simulated spectra for typical plasma parameters measured in ASDEX Upgrade and predicted for ITER. In very recent EBIT investigations [23,24,25] most of the predicted lines could be identified. However, due to the different electron densities in the EBIT (n e ≤ 10 19 m −3 ) and in the centre of fusion plasmas (n e ≥ 10 20 m −3 ) and the mono-energetic electron beam (EBIT) instead of a Maxwellian distribution, investigations in fusion devices are still indispensable, to explore the composition of the spectra emitted from fusion plasmas.…”

Section: Diagnostic Of W In Fusion Devicesmentioning

confidence: 98%

Benefits and Challenges of the Use of High-Z Plasma Facing Materials in Fusion Devices

Neu

2010

AIP Conference Proceedings

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Abstract.The use of high-Z plasma facing components requires intensive research in all areas, i.e. in plasma wall-interaction, in the physics of the confined plasma, diagnostic, and in material development. Only a few present day divertor tokamaks -mainly Alcator C-Mod and ASDEX Upgrade -gained experience with the refractory metals molybdenum and tungsten, respectively. ASDEX Upgrade was stepwise converted from graphite to tungsten PFCs and in parallel a reduction of the deuterium retention by almost a factor of ten has been observed due to the strong suppression of D co-deposition with carbon. The deuterium retained in W is in line with laboratory results. In order to diagnose W sources and the W content in the main plasma adequate spectroscopic methods had to be developed. As expected from the sputtering threshold of Mo and W, negligible erosion by the thermal divertor background plasma is found in ASDEX Upgrade and Alcator C-Mod under low temperature divertor conditions. However, erosion by fast particles and intrinsic impurities, which additionally might be accelerated in rectified electrical fields observed during ion cyclotron frequency heating, plays an important role. The Mo and W concentrations in the plasma centre are strongly affected by plasma transport and variations up to a factor of 50 are observed for similar influxes. However, it could be demonstrated that sawteeth and turbulent transport driven by central heating can suppress central accumulation. The inward transport of high-Z ions at the edge can be efficiently reduced by 'flushing' the pedestal region caused by frequent edge instabilities. Since with metal walls the edge radiation by low-Z impurities is reduced, it has to be substituted in a pure high-Z device by artificially injected low-Z impurities in order to keep the power load at an acceptable level. Experiments at ASDEX Upgrade suggest that a regime with benign erosion and favourable confinement can be achieved. Extrapolations to ITER and DEMO are difficult since the physics of plasma transport is not yet completely understood, the particle and energy fluxes are orders of magnitude higher and the technical boundary conditions in DEMO strongly differ from those of present day devices.

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Spectroscopy of highly charged tungsten ions relevant to fusion plasmas

Cited by 87 publications

References 14 publications

Calculation and experimental test of the cooling factor of tungsten

Calculation and experimental test of the cooling factor of tungsten

Extreme Ultraviolet Spectra of Few-Times Ionized Tungsten for Divertor Plasma Diagnostics

Benefits and Challenges of the Use of High-Z Plasma Facing Materials in Fusion Devices

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