Setup and initial results from the magnetic flux surface diagnostics at Wendelstein 7-X

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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“…5 as a clearly visible radial shift of the island chain. A more detailed analysis of these data can be found elsewhere30.…”

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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“…On each pass, the beam causes the rod or screen to fluoresce. In W7-X a hybrid rodemitter system is used [10]. In this system, two fluorescent rods (a third is prepared for installation after the initial operation phase) with electron emitters are installed on the machine, allowing one rod to serve as the emitter while the other sweeps across the electron beam while being imaged by a camera.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2016

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Abstract. Error fields have been detected and measured using the flux surface mapping diagnostic system on Wendelstein 7-X (W7-X). A low-field ' ι -= 1/2' magnetic configuration ( ι -= ι/2π), sensitive to error fields, was developed in order to detect their presence using the flux surface mapping diagnostic. In this configuration, a vacuum flux surface with rotational transform of n/m = 1/2 is created at the mid-radius of the configuration. If no error fields are present a small n/m = 5/10 island chain should be present. Modeling indicates that if an n = 1 perturbing field is applied by the trim coils, a large n/m = 1/2 island chain will be opened. This island chain is used to create a perturbation large enough to be imaged by the diagnostic. Phase and amplitude scans of the applied field allow the measurement of a small ∼ 0.04 m intrinsic island chain with a 140 o phase relative to the first module of the W7-X experiment. These error fields are determined to be small and easily correctable by the trim coil system.

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“…During the imaging of the n/m = 5/6 island chain in the OP1.1 limiter configuration, a dependence of the position with respect to field strength was detected [11]. Specifically a radial motion of the island island chain as the field strength was increased.…”

Section: Measurementsmentioning

confidence: 99%

Error field measurement, correction and heat flux balancing on Wendelstein 7-X ^a

et al. 2017

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Abstract:The measurement and correction of error fields in Wendelstein 7-X (W7-X) is critical to long pulse high beta operation, as small error fields may cause overloading of divertor plates. Accordingly, as part of a broad collaborative effort, the detection and correction of error fields on the W7-X experiment has been performed using the trim coil system in conjunction with the flux surface mapping diagnostic and high resolution infrared camera. In the early commissioning phase of the experiment, the trim coils were used to open an n/m=1/2 island chain in a specially designed magnetic configuration. The flux surfacing mapping diagnostic was then able to directly image the magnetic topology of the experiment, allowing the inference of a small ∼ 4 cm intrinsic island chain. The suspected main source of the error field, slight misalignment of the superconducting coils, is then confirmed through experimental modeling using the detailed measurements of the coil positions. Observations of the limiters temperatures in module 5 shows a clear dependence of the limiter heat flux pattern as the perturbing fields are rotated. Plasma experiments without applied correcting fields show a significant asymmetry in neutral pressure (centered in module 4) and light emission (visible, H-alpha, CII, and CIII). Such pressure asymmetry is associated with plasma-wall (limiter) interaction asymmetries between the modules. Application of trim coil fields with n=1 waveform correct the imbalance. Confirmation of the error fields allows the assessment of magnetic fields which resonate with the n/m=5/5 island chain.

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Setup and initial results from the magnetic flux surface diagnostics at Wendelstein 7-X

Cited by 33 publications

References 29 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

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

Error field measurement, correction and heat flux balancing on Wendelstein 7-X ^a

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Setup and initial results from the magnetic flux surface diagnostics at Wendelstein 7-X

Cited by 33 publications

References 29 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

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

Error field measurement, correction and heat flux balancing on Wendelstein 7-X a

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Product

Resources

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

Error field measurement, correction and heat flux balancing on Wendelstein 7-X ^a