Observations of wall conditioning by means of boron powder injection in DIII-D H-mode plasmas

Bortolon, A.; Maingi, R.; Nagy, A.; Ren, Jun; Duran, Jonah; Maan, A.; Donovan, David; Boedo, J.A.; Rudakov, D.L.; Hyatt, A.W.; Wilks, Teresa; Shafer, M.W.; Samuell, Cameron; Fenstermacher, M.E.; Gilson, Erik; Lunsford, R.; Mansfield, D. K.; Abrams, T.; Nazikian, R.

doi:10.1088/1741-4326/abaf31

Cited by 33 publications

(30 citation statements)

References 41 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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“…While IPDs have previously been installed and operated on other metal-walled tokamaks such as AUG [14,15] and EAST [16,17], the long pulse capabilities and full-W environment make WEST an excellent test bed to extend the evaluation of the IPD as a real-time wall conditioning technique. The present results can additionally be compared with powder injection experiments in carbon-walled machines, namely DIII-D [18], KSTAR [19], W7-X [20], and LHD [21,22].…”

Section: Introductionmentioning

confidence: 92%

Initial results from boron powder injection experiments in WEST lower single null L-mode plasmas

Bodner¹,

Gallo²,

Diallo³

et al. 2022

Nucl. Fusion

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Using a recently installed impurity powder dropper (IPD), boron powder (< 150 μm) was injected into lower single null (LSN) L-mode discharges in WEST. IPDs possibly enable real-time wall conditioning of the plasma-facing components and may help to facilitate H-mode access in the full-tungsten environment of WEST. The discharges in this experiment featured Ip = 0.5 MA, BT = 3.7 T, q95 = 4.3, tpulse = 12–30 s, ne,0 ~ 4×1019 m-2, and PLHCD ~ 4.5 MW. Estimates of the deuterium and impurity particle fluxes, derived from a combination of visible spectroscopy measurements and their corresponding S/XB coefficients, showed decreases of ~ 50% in O+, N+, and C+ populations during powder injection and a moderate reduction of these low-Z impurities (~ 50%) and W (~ 10%) in the discharges that followed powder injection. Along with the improved wall conditions, WEST discharges with B powder injection observed improved confinement, as the stored energy WMHD, neutron rate, and electron temperature Te increased significantly (10–25% for WMHD and 60–200% for the neutron rate) at constant input power. These increases in confinement scale up with the powder drop rate and are likely due to the suppression of ion temperature gradient (ITG) turbulence from changes in Zeff and/or modifications to the electron density profile.

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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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Observations of wall conditioning by means of boron powder injection in DIII-D H-mode plasmas

Cited by 33 publications

References 41 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

Initial results from boron powder injection experiments in WEST lower single null L-mode plasmas

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

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