Key results from the first plasma operation phase and outlook for future performance in Wendelstein 7-X

Pedersen, T. S.; Dinklage, A.; Turkin, Y.; Wolf, R. C.; Bozhenkov, S.; Geiger, J.; Fuchert, G.; Bosch, H.‐S.; Rahbarnia, K.; Thomsen, H.; Neuner, U.; Klinger, T.; Langenberg, A.; Mora, H. Trimiño; Kornejew, P.; Knauer, J.; Hirsch, M.; Pablant, N.

doi:10.1063/1.4983629

Cited by 71 publications

(82 citation statements)

References 43 publications

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“…The solver is based on a Fourier pseudo-spectral discretization of the surface. Figure 8: Reference solutions on the W7X geometry [4,48] for the convergence results in Table 7. The fields correspond to λ = 0 and λ = 1 respectively.…”

Section: Discussionmentioning

confidence: 99%

“…This is an advantage of our integral formulation, which leads to linear systems which are as well-conditioned as the underlying physical problem. Table 7: Convergence results for our BIE code and the SPEC code on the W7-X geometry [4,48]. We show convergence in the relative L ∞ -norm of the error by comparing the solutions with a reference solution.…”

Section: Toroidal-shell Domainmentioning

confidence: 99%

“…In Table 7, we compare our solver with the SPEC code of [40]. We present results for the geometry corresponding to the plasma boundary in the Wendelstein 7-X (W7-X) stellarator [4,48]. We constructed reference solutions for λ = 0 and λ = 1 with our BIE code using very fine discretization (N = 8.2E+5, ǫ GMRES = 1E-12).…”

Section: Comparison With Specmentioning

confidence: 99%

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Taylor states in stellarators: A fast high-order boundary integral solver

Malhotra

Cerfon

Imbert-Gérard

et al. 2019

Journal of Computational Physics

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We present a boundary integral equation solver for computing Taylor relaxed states in non-axisymmetric solid and shell-like toroidal geometries. The computation of Taylor states in these geometries is a key element for the calculation of stepped pressure stellarator equilibria. The integral representation of the magnetic field in this work is based on the generalized Debye source formulation, and results in a well-conditioned secondkind boundary integral equation. The integral equation solver is based on a spectral discretization of the geometry and unknowns, and the computation of the associated weakly-singular integrals is performed with high-order quadrature based on a partition of unity. The resulting scheme for applying the integral operator is then coupled with an iterative solver and suitable preconditioners. Several numerical examples are provided to demonstrate the accuracy and efficiency of our method, and a direct comparison with the leading code in the field is reported.

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Section: Discussionmentioning

confidence: 99%

Section: Toroidal-shell Domainmentioning

confidence: 99%

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Taylor states in stellarators: A fast high-order boundary integral solver

Malhotra

Cerfon

Imbert-Gérard

et al. 2019

Journal of Computational Physics

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“…In December 2015 W7-X started its first operation phase (OP1.1) in limiter configuration. The main purpose of OP1.1 was the commissioning of the machine [5], but a successful physics program could already be conducted in parallel [6][7][8]. The final goal is a high-density high-power steady state operation with 30-minutes plasma pulses at an ECRH power of about 10 MW while using an actively cooled divertor (OP2).…”

Section: Introductionmentioning

confidence: 99%

Upgrades of edge, divertor and scrape-off layer diagnostics of W7‐X for OP1.2

Hathiramani

Ali

Anda

et al. 2018

Fusion Engineering and Design

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Wendelstein 7-X (W7-X) is the world's largest superconducting nuclear fusion experiment of the optimized stellarator type. In the first Operation Phase (OP1.1) helium and hydrogen plasmas were studied in limiter configuration. The heating energy was limited to 4 MJ and the main purpose of that campaign was the integral commissioning of the machine and diagnostics, which was achieved very successfully. Already from the beginning a comprehensive set of diagnostics was available to study the plasma. On the path towards high-power, high-performance plasmas, W7-X will be stepwise upgraded from an inertially cooled (OP1.2, limited to 80 MJ) to an actively cooled island divertor (OP2, 10 MW steady-state plasma operation). The machine is prepared for OP1.2 with 10 inertially cooled divertor units, and the experimental campaign has started recently.The paper describes a subset of diagnostics which will be available for OP1.2 to study the plasma edge, divertor and scrape-off layer physics including those already available for OP1.1, plus modifications, upgrades and new systems. The focus of this summary will be on technical and engineering aspects, like feasibility and assembly but also on reliability, thermal loads and shielding against magnetic fields.

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confidence: 99%

Approaches for quantitative study of divertor heat loads on W7-X

Gao¹,

Jakubowski

Drewelow

et al. 2018

Proceedings of the 2018 International Conference on Quantitative InfraRed Thermography

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Aimed to show the fusion-reactor relevance of optimized stellarators, Wendelstein 7-X (W7-X) [1], as the world's largest stellarator (plasma volume 30 m 3 , major radius 5.5 m, minor radius 0.5 m), completed successfully its first experimental campaign with island divertor in December 2017. To demonstrate the capabilities of steady-state operation with reactor-relevant plasma parameters, island divertor concept is commissioned for a tolerable plasma power and particle exhaust. Pre-defined magnetic islands at the plasma boundary are cut open by the divertor plates, so that these open field lines will lead the unconfined plasmas to the graphite tiles, which are designed to allow a high power load of up to 10 MW/m 2 .Infrared thermography system has been developed in many fusion devices as a key diagnostic to monitor the temperature and to study the heat loads on the plasma facing components, thus to prevent them from excessive damage. W7-X are designed with superconducting coils for plasma pulses with 30 mins duration at a heating power of 10 MW. For the safety of the experimental exploration aimed at high performance long discharges, a full coverage of the field of view by infrared diagnostics for the first wall and divertor plates is essential. In this campaign, ten thermography systems were installed for the first time, with each infrared camera monitoring one half module of the machine, realized by the welldesigned wide-angle optics [2]. Figure 1 shows the field of view of the nine infrared cameras behind the immersion tubes, the temperature distributions indicate a rather symmetry target heat loads. The systems have been operated through the whole campaign with great liability, producing temperature evolution on the plasma facing components during pulses.The infrared cameras were controlled to record the thermal emissions with a frame rate of 100 Hz in a wavelength range of 8 -10 μm. The sensor array contains 768 x 1024 pixels, with a varied spatial resolution at different parts of the divertor surface from ~ 3 mm (low iota part) to ~ 10 mm (high iota tail). The exposure time has been set manually (1 to 10 μs) for each discharge, depending on the heating power, to generate accurate digital levels. The Planck's law calibration under the designed optical routes, against a cavity radiator with known emissivity and temperature, has been carried out in the laboratory before the campaign. The relation between the received digital levels and the temperature has been compiled into look-up tables. The camera control and temperature conversion have been incorporated into a software platform for a real time observation of surface temperature during the experiments [3].Except for being one of the key diagnostics for the safety of the machine [4], the divertor thermal footprints provide important inputs for the study of the intrinsic three dimensional magnetic topology and the heat transport inside the boundary islands. A quantitative analysis and comparison of the divertor temperature in different machine modules are requ...

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Key results from the first plasma operation phase and outlook for future performance in Wendelstein 7-X

Cited by 71 publications

References 43 publications

Taylor states in stellarators: A fast high-order boundary integral solver

Taylor states in stellarators: A fast high-order boundary integral solver

Upgrades of edge, divertor and scrape-off layer diagnostics of W7‐X for OP1.2

Approaches for quantitative study of divertor heat loads on W7-X

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