First measurements of error fields on W7-X using flux surface mapping<sup>a</sup>

Lazerson, S.; Otte, M.; Bozhenkov, S.; Biedermann, C.; Pedersen, T. S.

doi:10.1088/0029-5515/56/10/106005

Cited by 29 publications

(33 citation statements)

References 18 publications

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“…For the first measurements of the n =1 error field, a special magnetic surface configuration was used31, where ɩ varies slowly and passes through the resonance ɩ =1/2, see Fig. 6.…”

Section: Resultsmentioning

confidence: 99%

Confirmation of the topology of the Wendelstein 7-X magnetic field to better than 1:100,000

et al. 2016

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Fusion energy research has in the past 40 years focused primarily on the tokamak concept, but recent advances in plasma theory and computational power have led to renewed interest in stellarators. The largest and most sophisticated stellarator in the world, Wendelstein 7-X (W7-X), has just started operation, with the aim to show that the earlier weaknesses of this concept have been addressed successfully, and that the intrinsic advantages of the concept persist, also at plasma parameters approaching those of a future fusion power plant. Here we show the first physics results, obtained before plasma operation: that the carefully tailored topology of nested magnetic surfaces needed for good confinement is realized, and that the measured deviations are smaller than one part in 100,000. This is a significant step forward in stellarator research, since it shows that the complicated and delicate magnetic topology can be created and verified with the required accuracy.

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“…For the first measurements of the n =1 error field, a special magnetic surface configuration was used31, where ɩ varies slowly and passes through the resonance ɩ =1/2, see Fig. 6.…”

Section: Resultsmentioning

confidence: 99%

Confirmation of the topology of the Wendelstein 7-X magnetic field to better than 1:100,000

et al. 2016

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“…In these mapping measurements, the overall required precision of the W7-X construction was successfully confirmed [21] and an about 2% reduction in the rotational transform caused by coil deformations was found at the field of 2.5 T [22]. From the error field spectrum only the m/n = 2/1 component was assessed, and its amplitude was found to be below 0.1 • 10 −4 [23]. Error field components relevant for the divertor operation were not addressed, because of a minor effect on the limiter operation and due to restrictions for the operation of the magnet system at that time.…”

Section: Introductionmentioning

confidence: 89%

Measurements and correction of the 1/1 error field in Wendelstein 7-X

et al. 2018

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In this paper, vacuum flux surface mapping is used to measure the 1/1 error field in Wendelstein 7-X. Two methods for discriminating the 1/1 perturbation from other co-resonant modes are applied: measurements of the helical axis shift in a magnetic configuration with the rotational transform barely above one on the axis; and measurements of the edge island structure with cancellation of intrinsic 5/5 islands by divertor control coils. The normalized radial 1/1 amplitude in Boozer coordinates is found to be about 0.8 • 10 −4 in the first case and about 0.5 • 10 −4 in the second one, with the discrepancy being attributable to different currents in the planar coils. The 1/1 error field can be reliably compensated by using error field trim coils with currents about 100 A. This compensation also helps to identify the 2/2 error field of about 0.6 • 10 −4. During plasma operation in divertor configurations, it is confirmed that the present 1/1 field leads to asymmetries in the power distribution and that the 1/1 compensation improves this symmetry.

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“…Figure 1 depicts the first wall and divertor structures of W7-X. Superimposed on this image are strike lines and a Poincaré plot of the standard magnetic configuration in vacuum (as calculated using the FIELDLINES code [6]). Here the five lobes of the divertor are clearly visible, forming five independent flux bundles.…”

Section: Introductionmentioning

confidence: 99%

Tuning of the rotational transform in Wendelstein 7-X

et al. 2019

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The control of rotational transform in Wendelstein 7-X (W7-X) is key to both the island divertor operation and safety of plasma facing components. The island divertor concept in W7-X relies on an edge flux surface with rotational transform of ι -= 1 resonating with an intrinsic n/m = 5/5 resonance to form a five lobed island chain. This island chain intersects with divertor plates to give rise to the island divertor. Changes in the relative position of the rational surface and the divertor plates can result in changes in divertor performance, thus the control of the rotational transform is essential to operation of the W7-X device. During the first divertor campaign electromagnetic loads resulted in elastic deformations of the shaped modular stellarator coils. Such deformations made these coils more planar, reducing the vacuum rotational transform, subsequently shifting the ι -= 1 resonance outward.

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First measurements of error fields on W7-X using flux surface mapping^a

Cited by 29 publications

References 18 publications

Confirmation of the topology of the Wendelstein 7-X magnetic field to better than 1:100,000

Confirmation of the topology of the Wendelstein 7-X magnetic field to better than 1:100,000

Measurements and correction of the 1/1 error field in Wendelstein 7-X

Tuning of the rotational transform in Wendelstein 7-X

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First measurements of error fields on W7-X using flux surface mappinga

Cited by 29 publications

References 18 publications

Confirmation of the topology of the Wendelstein 7-X magnetic field to better than 1:100,000

Confirmation of the topology of the Wendelstein 7-X magnetic field to better than 1:100,000

Measurements and correction of the 1/1 error field in Wendelstein 7-X

Tuning of the rotational transform in Wendelstein 7-X

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Resources

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First measurements of error fields on W7-X using flux surface mapping^a