Real-time wall conditioning by controlled injection of boron and boron nitride powder in full tungsten wall ASDEX Upgrade

Bortolon, A.; Rohde, V.; Maingi, R.; Wolfrum, E.; Dux, R.; Herrmann, A.; Lunsford, R.; McDermott, R. M.; Nagy, A.; Kallenbach, A.; Mansfield, D. K.; Nazikian, R.; Neu, R.

doi:10.1016/j.nme.2019.03.022

Cited by 40 publications

(47 citation statements)

References 8 publications

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“…Wall conditions improved significantly after injecting powders into the closed divertor. The substantial reduction in recycling, carbon, and oxygen levels is consistent with results reported earlier for dedicated realtime wall conditioning experiments in lower single null configurations [25,26]. An important difference in the present work is that wall conditions also improve by injecting boron powder into the divertor (compared to an upstream injection location in the plasma crown).…”

Section: Discussionsupporting

confidence: 89%

“…More recently, the injection of low-Z solid materials in powder, dust or small granule form was introduced as a novel technique for various real-time applications. First applications focused on disruption mitigation, real-time wall conditioning, mitigation of edge localized modes (ELMs), and confinement improvement with boron, boron nitride (BN), and lithium powders at T-10, DIII-D, EAST, ASDEX Upgrade, KSTAR, LHD, and W7-X [24,25,26,27,28,29,30,31,32].…”

Section: Introductionmentioning

confidence: 99%

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Mitigation of plasma-wall interactions with low-Z powders in DIII-D high confinement plasmas

Effenberg,

Bortolon,

Casali

et al. 2022

Preprint

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Experiments with low-Z powder injection in DIII-D high confinement discharges demonstrated increased divertor dissipation and detachment while maintaining good core energy confinement. Lithium (Li), boron (B), and boron nitride (BN) powders were injected in H-mode plasmas (Ip =1 MA, Bt =2 T, P NB =6 MW, ne = 3.6 − 5.0 • 10 19 m −3 ) into the upper small-angle slot (SAS) divertor for 2-s intervals at constant rates of 3-204 mg/s.The multi-species BN powders at a rate of 54 mg/s showed the most substantial increase in divertor neutral compression by more than an order of magnitude and lasting detachment with minor degradation of the stored magnetic energy W mhd by 5%. Rates of 204 mg/s of boron nitride powder further reduce ELM-fluxes on the divertor but also cause a drop in confinement performance by 24% due to the onset of an n = 2 tearing mode.The application of powders also showed a substantial improvement of wall conditions manifesting in reduced wall fueling source and intrinsic carbon and oxygen content in response to the cumulative injection of non-recycling materials.The results suggest that low-Z powder injection, including mixed element compounds, is a promising new core-edge compatible technique that simultaneously enables divertor detachment and improves wall conditions during high confinement operation.

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Section: Discussionsupporting

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Mitigation of plasma-wall interactions with low-Z powders in DIII-D high confinement plasmas

Effenberg,

Bortolon,

Casali

et al. 2022

Preprint

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“…Advantages over the standard glow discharge boronization include no need for the toxic diborane gas B 2 H 6 or to interrupt the plasma operation. This technique has already been shown to improve wall conditioning in tokamaks [7][8][9][10] . It reduces wall recycling and impurity content, which allows the plasma performances to be improved by accessing lower plasma collisionalities, similarly to the case of glow discharge boronization.…”

Section: Impurity Powder Injection Experimentsmentioning

confidence: 99%

Observation of a reduced-turbulence regime with boron powder injection in a stellarator

et al. 2022

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In state-of-the-art stellarators, turbulence is a major cause of the degradation of plasma confinement. To maximize confinement, which eventually determines the amount of nuclear fusion reactions, turbulent transport needs to be reduced. Here we report the observation of a confinement regime in a stellarator plasma that is characterized by increased confinement and reduced turbulent fluctuations. The transition to this regime is driven by the injection of submillimetric boron powder grains into the plasma. With the line-averaged electron density being kept constant, we observe a substantial increase of stored energy and electron and ion temperatures. At the same time, the amplitude of the plasma turbulent fluctuations is halved. While lower frequency fluctuations are damped, higher frequency modes in the range between 100 and 200 kHz are excited. We have observed this regime for different heating schemes, namely with both electron and ion cyclotron resonant radio frequencies and neutral beams, for both directions of the magnetic field and both hydrogen and deuterium plasmas.

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“…Advantages over the standard glow discharge boronization include no need for the toxic diborane gas B 2 H 6 , and to interrupt the plasma operation. This technique has been shown to improve wall conditioning already in tokamaks [4,5,6,7], reducing wall recycling and impurity content, and in general increasing the plasma performances by accessing lower plasma collisionalities. Furthermore, the IPD has revealed itself an effective tool for ELMs suppression, allowing the access ELM-free H-mode [8].…”

Section: Motivationmentioning

confidence: 99%

Observation of a novel reduced-turbulence regime with boron powder injection in a stellarator

Nespoli¹,

Masuzaki²,

Tanaka³

et al. 2021

Preprint

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We report the first observation of a novel confinement regime in a stellarator plasma, characterized by increased confinement and reduced turbulent fluctuations. The transition to this new regime is driven by the injection of sub-millimetric boron powder grains into the plasma. With the line averaged electron density being kept constant, substantial increase of stored energy, electron and ion temperature have been observed. At the same time, the amplitude of the plasma turbulent fluctuations is halved. While lower frequency fluctuations are damped, higher frequency modes in the range 100 ≤ f [kHz] ≤ 200 are excited. The access to this regime has been observed for different heating schemes, namely with both electron and ion cyclotron resonant radio frequency, and neutral beams, for both directions of the magnetic field, and for both hydrogen and deuterium plasmas.

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Real-time wall conditioning by controlled injection of boron and boron nitride powder in full tungsten wall ASDEX Upgrade

Cited by 40 publications

References 8 publications

Mitigation of plasma-wall interactions with low-Z powders in DIII-D high confinement plasmas

Mitigation of plasma-wall interactions with low-Z powders in DIII-D high confinement plasmas

Observation of a reduced-turbulence regime with boron powder injection in a stellarator

Observation of a novel reduced-turbulence regime with boron powder injection in a stellarator

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