Tuning of the rotational transform in Wendelstein 7-X

Lazerson, S.; Gao, Yu; Hammond, K. C.; Killer, C.; Schlisio, G.; Otte, M.; Biedermann, C.; Spolaore, M.; Bozhenkov, S.; Geiger, J.; Grulke, O.; Nicolai, D.; Satheeswaran, G.; Niemann, H.; Jakubowski, M.; Drewelow, P.; Sitjes, A. Puig; Ali, Adnan; Cannas, B.; Pisano, F.; König, R.; Wurden, G. A.; Kocsis, G.; Szepesi, T.; Wenzel, U.; Mulsow, Matthias; Schilling, J.; Neuner, U.; Andreeva, T.; Thomsen, H.; Knauer, J.; Brunner, K. J.; Blackwell, B. D.; Endler, M.; Klose, S.; Rudischhauser, L.

doi:10.1088/1741-4326/ab3df0

Cited by 18 publications

(22 citation statements)

References 29 publications

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“…This appears to be possible also for discharges exceeding the 10 MW plasma heating originally specified as the power level for quasi-steadystate operation). As reported earlier [14], the heat load patterns generally agree very well with numerical predictions, but there were some surprises which have largely been understood at this point [15,16,17]. The wetted area in a divertor can be thought of as a result of the balance in the scrape-off layer (SOL) between parallel transport (free-streaming towards the targets) and perpendicular transport.…”

Section: Divertor Operationsupporting

confidence: 77%

Experimental confirmation of efficient island divertor operation and successful neoclassical transport optimization in Wendelstein 7-X

Pedersen

2022

Nucl. Fusion

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We present recent highlights from the most recent operation phases of Wendelstein 7-X, the most advanced stellarator in the world. Stable detachment with good particle exhaust, low impurity content, and energy confinement times exceeding 100 ms, have been maintained for tens of seconds. Pellet fueling allows for plasma phases with reduced ITG turbulence, and during such phases, the overall confinement is so good (energy confinement times often exceeding 200 ms) that the attained density and temperature profiles would not have been possible in less optimized devices, since they would have had neoclassical transport losses exceeding the heating applied in W7-X. This provides proof that the reduction of neoclassical transport through magnetic field optimization is successful. W7-X plasmas generally show good impurity screening and high plasma purity, but there is evidence of longer impurity confinement times during turbulence-suppressed phases.

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Section: Divertor Operationsupporting

confidence: 77%

Experimental confirmation of efficient island divertor operation and successful neoclassical transport optimization in Wendelstein 7-X

Pedersen

2022

Nucl. Fusion

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“…Two types of error fields have been identified in W7-X, those which change the rotational transform and those which break the five fold symmetry of the edge island chain. Changes in ι have been measured using flux surface measurements [23] and the effect on the divertor strike lines measured [24]. Early estimates of the error fields using flux surface measurement were performed before divertor operation [25].…”

Section: Error Fields Correctionmentioning

confidence: 99%

Overview of the results from divertor experiments with attached and detached plasmas at Wendelstein 7-X and their implications for steady-state operation

et al. 2021

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Wendelstein 7-X (W7-X), the largest advanced stellarator, is built to demonstrate high power, high performance quasi-continuous operation. Therefore, in the recent campaign, experiments were performed to prepare for long pulse operation, addressing three critical issues: the development of stable detachment, control of the heat and particle exhaust, and the impact of leading edges on plasma performance. The heat and particle exhaust in W7-X is realized with the help of an island divertor, which utilizes large magnetic islands at the plasma boundary. This concept shows very efficient heat flux spreading and favourable scaling with input power. Experiments performed to overload leading edges showed that the island divertor yields good impurity screening. A highlight of the recent campaign was a robust detachment scenario, which allowed reducing power loads even by a factor of ten. At the same time, neutral pressures at the pumping gap entrance yielded the particle removal rate close to the values required for stable density control in steady-state operation.

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“…In cases with uncorrected ιa , intolerable baffle loads exceeding even the level of the main strike line on the vertical targets have been observed. For the discharge analyzed here, not only the ιa been adjusted correctly [17], but also the best target heat load symmetrization was achieved, using the additional coil system, i.e. the trim coils for compensating the n = 1 component of the error field and the control coils to additionally compensate also the n = 2 component [15,16].…”

Section: Observation Of the Overloaded Baffle Tilesmentioning

confidence: 99%

Understanding baffle overloads observed in high-mirror configuration on Wendelstein 7-X

et al. 2020

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The operational regimes in the first divertor campaign of W7-X were limited by unexpectedly high heat loads on certain baffle tiles. In the high-mirror configuration, a permanent hotspot on the baffle plate was detected by the thermographic system, which was further confirmed during the post-campaign inspections of the plasmafacing components. The maximum heat load on three baffle tiles reached about 4.5 MW m −2 , which was almost an order of magnitude above its designed value of 0.5 MW m −2 . The paper presents a detailed analysis to understand how the baffle plate, which is originally designed to screen the recycling neutrals and is therefore hidden from the hot plasma, can receive such a high heat load -a level that is expected for target plates. Three main causes have been identified: 1) the three baffle tiles are radially only about 5 mm away from a main heat channel towards a target, which is much shorter than the radial power decay length of several centimeters derived from the thermographic measurements in this region; 2) the three baffle tiles are intersected with field-lines of about 30 m length, which are long enough to collect considerable amount of heat via cross-field transport; 3) the baffle tiles have locally large grazing angles. In addition, the analysis method shown in this paper is of general use to estimate the heat flows in shadow areas of targets and thus to evaluate heat loads on the potentially critical components occurring in these areas, especially required for the design of complex 3D divertors like the one in W7-X.

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Tuning of the rotational transform in Wendelstein 7-X

Cited by 18 publications

References 29 publications

Experimental confirmation of efficient island divertor operation and successful neoclassical transport optimization in Wendelstein 7-X

Experimental confirmation of efficient island divertor operation and successful neoclassical transport optimization in Wendelstein 7-X

Overview of the results from divertor experiments with attached and detached plasmas at Wendelstein 7-X and their implications for steady-state operation

Understanding baffle overloads observed in high-mirror configuration on Wendelstein 7-X

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