| 1. |
- Sunn Pedersen, Thomas, et al.
(författare)
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Experimental confirmation of efficient island divertor operation and successful neoclassical transport optimization in Wendelstein 7-X
- 2022
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 62:4, s. 042022-042022
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Tidskriftsartikel (refereegranskat)abstract
- 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 ion-temperature-gradient 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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| 2. |
- Schmidt, B. S., et al.
(författare)
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4D and 5D phase-space tomography using slowing-down physics regularization
- 2023
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Ingår i: Nuclear Fusion. - : Institute of Physics (IOP). - 0029-5515 .- 1741-4326. ; 63:7
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Tidskriftsartikel (refereegranskat)abstract
- We compute reconstructions of 4D and 5D fast-ion phase-space distribution functions in fusion plasmas from synthetic projections of these functions. The fast-ion phase-space distribution functions originating from neutral beam injection (NBI) at TCV and Wendelstein 7-X (W7-X) at full, half, and one-third injection energies can be distinguished and particle densities of each component inferred based on 20 synthetic spectra of projected velocities at TCV and 680 at W7-X. Further, we demonstrate that an expansion into a basis of slowing-down distribution functions is equivalent to regularization using slowing-down physics as prior information. Using this technique in a Tikhonov formulation, we infer the particle density fractions for each NBI energy for each NBI beam from synthetic measurements, resulting in six unknowns at TCV and 24 unknowns at W7-X. Additionally, we show that installing 40 LOS in each of 17 ports at W7-X, providing full beam coverage and almost full angle coverage, produces the highest quality reconstructions.
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| 3. |
- Miettunen, J., et al.
(författare)
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Predictive ASCOT modelling of 10Be transport in JET with the ITER-like wall
- 2013
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 438:Suppl., s. S612-S615
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Tidskriftsartikel (refereegranskat)abstract
- We model the transport of a beryllium (10Be) marker during a sequence of an inner-wall limited and a diverted Ohmic plasma phase in JET with the objective of identifying principal migration pathways. The 3D orbit-following code ASCOT is used for predictive analysis of an experiment during the 2011-2012 campaign on JET where three central pieces of a wall tile enriched with 10Be were installed to an inner wall guard limiter (IWGL) of the tokamak. Assuming erosion during the inner-wall limited plasma, the simulations indicate that 10Be is deposited along the IWGLs during the limiter phase which, when assuming further erosion, can lead to high deposition on the inner (high-field side) divertor during the diverted phase. In contrast, beryllium confined in the core plasma during the limiter phase is seen to be predominantly uniformly deposited during the diverted phase on the outer (low-field side) wall limiters and divertor tiles.
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| 4. |
- Äkäslompolo, S, et al.
(författare)
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Calculating the 3D magnetic field of ITER for European TBM studies
- 2015
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Ingår i: Fusion Engineering and Design. - 0920-3796.
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic perturbation due to the ferromagnetic test blanket modules (TBMs) may deteriorate fast ion confinement in ITER. This effect must be quantified by numerical studies in 3D. We have implemented a combined finite element method (FEM) – Biot-Savart law integrator method (BSLIM) to calculate the ITER 3D magnetic field and vector potential in detail. Unavoidable geometry simplifications changed the mass of the TBMs and ferritic inserts (FIs) up to 26%. This has been compensated for by modifying the nonlinear ferromagnetic material properties accordingly. Despite the simplifications, the computation geometry and the calculated fields are highly detailed. The combination of careful FEM mesh design and using BSLIM enables the use of the fields unsmoothed for particle orbit-following simulations. The magnetic field was found to agree with earlier calculations and revealed finer details. The vector potential is intended to serve as input for plasma shielding calculations.
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| 5. |
- Äkäslompolo, S, et al.
(författare)
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ITER fast ion confinement in the presence of the European test blanket module
- 2015
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Ingår i: Nuclear Fusion. - 1741-4326 .- 0029-5515. ; 55:9, s. 093010-
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Tidskriftsartikel (refereegranskat)abstract
- This paper addresses the confinement of thermonuclear alpha particles and neutral beam injected deuterons in the 15 MA Q = 10 inductive scenario in the presence of the magnetic perturbation caused by the helium cooled pebble bed test blanket module using the vacuum approximation. Both the flat top phase and plasma ramp-up are studied. The transport of fast ions is calculated using the Monte Carlo guiding center orbit-following code ASCOT. A detailed three-dimensional wall, derived from the ITER blanket module CAD data, is used for evaluating the fast ion wall loads. The effect of the test blanket module is studied for both overall confinement and possible hot spots. The study indicates that the test blanket modules do not significantly deteriorate the fast ion confinement.
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| 6. |
- Hirvijoki, Eero, 1985, et al.
(författare)
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Monte Carlo method and High Performance Computing for solving Fokker–Planck equation of minority plasma particles
- 2015
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Ingår i: Journal of Plasma Physics. - 0022-3778 .- 1469-7807. ; 81:3, s. Art. no. 435810301 -
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Tidskriftsartikel (refereegranskat)abstract
- This paper explains how to obtain the distribution function of minority ions in tokamak plasmas using the Monte Carlo method. Since the emphasis is on energetic ions, the guiding-center transformation is outlined, including also the transformation of the collision operator. Even within the guiding-center formalism, the fast particle simulations can still be very CPU intensive and, therefore, we introduce the reader also to the world of high-performance computing. The paper is concluded with a few examples where the presented method has been applied.
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| 7. |
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