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Journal articles on the topic 'Stellarator'

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Author: Grafiati

Published: 4 June 2021

Last updated: 6 September 2023

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1

Beidler, C. D., H. M. Smith, A. Alonso, T. Andreeva, J. Baldzuhn, M. N. A. Beurskens, M. Borchardt, et al. "Demonstration of reduced neoclassical energy transport in Wendelstein 7-X." Nature 596, no. 7871 (August 11, 2021): 221–26. http://dx.doi.org/10.1038/s41586-021-03687-w.

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AbstractResearch on magnetic confinement of high-temperature plasmas has the ultimate goal of harnessing nuclear fusion for the production of electricity. Although the tokamak1 is the leading toroidal magnetic-confinement concept, it is not without shortcomings and the fusion community has therefore also pursued alternative concepts such as the stellarator. Unlike axisymmetric tokamaks, stellarators possess a three-dimensional (3D) magnetic field geometry. The availability of this additional dimension opens up an extensive configuration space for computational optimization of both the field geometry itself and the current-carrying coils that produce it. Such an optimization was undertaken in designing Wendelstein 7-X (W7-X)2, a large helical-axis advanced stellarator (HELIAS), which began operation in 2015 at Greifswald, Germany. A major drawback of 3D magnetic field geometry, however, is that it introduces a strong temperature dependence into the stellarator’s non-turbulent ‘neoclassical’ energy transport. Indeed, such energy losses will become prohibitive in high-temperature reactor plasmas unless a strong reduction of the geometrical factor associated with this transport can be achieved; such a reduction was therefore a principal goal of the design of W7-X. In spite of the modest heating power currently available, W7-X has already been able to achieve high-temperature plasma conditions during its 2017 and 2018 experimental campaigns, producing record values of the fusion triple product for such stellarator plasmas3,4. The triple product of plasma density, ion temperature and energy confinement time is used in fusion research as a figure of merit, as it must attain a certain threshold value before net-energy-producing operation of a reactor becomes possible1,5. Here we demonstrate that such record values provide evidence for reduced neoclassical energy transport in W7-X, as the plasma profiles that produced these results could not have been obtained in stellarators lacking a comparably high level of neoclassical optimization.

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2

Landreman, M., S. Buller, and M. Drevlak. "Optimization of quasi-symmetric stellarators with self-consistent bootstrap current and energetic particle confinement." Physics of Plasmas 29, no. 8 (August 2022): 082501. http://dx.doi.org/10.1063/5.0098166.

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Quasi-symmetry can greatly improve the confinement of energetic particles and thermal plasma in a stellarator. The magnetic field of a quasi-symmetric stellarator at high plasma pressure is significantly affected by the bootstrap current, but the computational cost of accurate stellarator bootstrap calculations has precluded use inside optimization. Here, a new efficient method is demonstrated for optimization of quasi-symmetric stellarator configurations such that the bootstrap current profile is consistent with the geometry. The approach is based on the fact that all neoclassical phenomena in quasi-symmetry are isomorphic to those in axisymmetry. Therefore, accurate formulas for the bootstrap current in tokamaks, which can be evaluated rapidly, can be applied also in stellarators. The deviation between this predicted parallel current and the actual parallel current in the magnetohydrodynamic equilibrium is penalized in the objective function, and the current profile of the equilibrium is included in the parameter space. Quasi-symmetric configurations with significant pressure are thereby obtained with self-consistent bootstrap current and excellent confinement. In a comparison of fusion-produced alpha particle confinement across many stellarators, the new configurations have significantly lower alpha energy losses than many previous designs.

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3

Garrido, Izaskun, Javier Maseda, Itziar Martija, and Aitor J. Garrido. "Real-Time Control for the EHU Stellarator." Symmetry 12, no. 1 (December 19, 2019): 11. http://dx.doi.org/10.3390/sym12010011.

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At present, two main magnetic confinement fusion devices exist: tokamaks and stellarators. Moreover, stellarators have been demonstrated to be a good alternative to tokamaks, due to their ability to operate in continuous mode, which eventually translates into a higher commercial profitability. In stellarators, the magnetic confinement of the plasma is achieved exclusively by the coils, thus no electric current through the plasma is needed. In particular, this article presents the Columbia Non-Neutral Torus stellarator that is located in the Automatic Control Group of Euskal Herriko Unibertsitatea (EHU). This EHU stellarator maintains symmetry in its structure due to the topology of the mesh that is formed by its coils. A cornerstone of future fusion reactors is to obtain real-time control that enables a sustained reaction. In this article, a control-oriented model for the installed magnetic confinement coils is presented. The model is based on matrices that preserve symmetry, which is defined from physical principles and then validated by different sets of experimental data. Then, based on this model, a novel predictive control suited to this particular model with symmetric objective function is implemented in the numerical simulations, and its response is compared to that of traditional controllers. Finally, this control is implemented in a real plant and the satisfactory experiment results provide validation of both the numerical model and proposed controller.

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4

Nikulsin, N., R. Ramasamy, M. Hoelzl, F. Hindenlang, E. Strumberger, K. Lackner, and S. Günter. "JOREK3D: An extension of the JOREK nonlinear MHD code to stellarators." Physics of Plasmas 29, no. 6 (June 2022): 063901. http://dx.doi.org/10.1063/5.0087104.

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Although the basic concept of a stellarator was known since the early days of fusion research, advances in computational technology have enabled the modeling of increasingly complicated devices, leading up to the construction of Wendelstein 7-X, which has recently shown promising results. This recent success has revived interest in the nonlinear 3D MHD modeling of stellarators in order to better understand their performance and operational limits. This study reports on the extension of the JOREK code to 3D geometries and on the first stellarator simulations carried out with it. The first simple simulations shown here address the classic Wendelstein 7-A stellarator using a reduced MHD model previously derived by us. The results demonstrate that stable full MHD equilibria are preserved in the reduced model: the flux surfaces do not move throughout the simulation and closely match the flux surfaces of the full MHD equilibrium. Furthermore, both tearing and ballooning modes were simulated, and the linear growth rates measured in JOREK are in reasonable agreement with the growth rates from the CASTOR3D linear MHD code.

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5

Lonigro, Nicola, and Caoxiang Zhu. "Stellarator coil design using cubic splines for improved access on the outboard side." Nuclear Fusion 62, no. 6 (April 6, 2022): 066009. http://dx.doi.org/10.1088/1741-4326/ac2ff3.

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Abstract In recent years many efforts have been undertaken to simplify coil designs for stellarators due to the difficulties in fabricating non-planar coils. The FOCUS code removes the need for a winding surface and represents the coils as arbitrary curves in 3D. In the following work, the implementation of a spline representation for the coils in FOCUS is described, along with the implementation of a new engineering constraint to design coils with a straighter outer section. The new capabilities of the code are shown as an example on HSX, NCSX, and a prototype quasi-axisymmetric reactor-sized stellarator. The flexibility granted by splines along with the new constraint will allow for stellarator coil designs with improved accessibility and simplified maintenance.

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6

Tykhyy, A. V. "Stochastic Diffusion of Energetic Ions in Wendelstein-Type Stellarators." Ukrainian Journal of Physics 63, no. 6 (July 12, 2018): 495. http://dx.doi.org/10.15407/ujpe63.6.495.

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The collisionless stochastic diffusion of energetic ions in optimized stellarators of the Wendelstein type has been considered. The phenomenon concerned was predicted earlier in the framework of a simplified theory describing the separatrix crossing by ions. The jumps of the adiabatic invariant in magnetic configurations of a stellarator are calculated. The analysis of the results obtained confirms the importance of the stochastic diffusion and demonstrates that the diffusion coefficient can considerably exceed the available result.

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7

Zhang, Yichao, Haifeng Liu, Jie Huang, Yuhong Xu, Jian Zhang, Akihiro Shimizu, Shinsuke Satake, et al. "Suppression of non-axisymmetric field-induced α-particle loss channels in a quasi-axisymmetric stellarator." AIP Advances 12, no. 5 (May 1, 2022): 055214. http://dx.doi.org/10.1063/5.0079827.

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In future fusion reactors, the confinement of α-particles is a crucial issue. The perfect omnigenity may be difficult to achieve in the quasi-isodynamic and quasi-symmetric stellarators when a multi-objective optimization is considered. Non-axisymmetric field can result in collisionless particles’ transport via localized trapping by ripples. Specific loss channels have been revealed to essentially exist in quasi-axisymmetric stellarators [Yang et al., Europhys. Lett. 129, 35001 (2020)] and W7-X [J. M. Faustin et al., Nucl. Fusion 56, 092006 (2016)]. It indicates a drastic loss of collisionless ions through these channels. This paper is devoted to investigate the effects of axisymmetry-breaking magnetic fields on collisionless α-particle transport in the CFQS (Chinese First Quasi-axisymmetric Stellarator) -like reactor configuration. A semi-analytic representation of radial and poloidal drifts in Boozer coordinates is given, by which we found an effective route to mitigate α-particle losses, i.e., adjusting the location of the quasi-axisymmetric radial position. Such a route enables the enhancement of the poloidal drift and decrease of radial drift in peripheral regions of the identified loss channels. The particles launched inside the quasi-axisymmetric radial surface can be well confined because localized particles that may fall in loss channels can transit into blocked particles near the quasi-axisymmetric surface, escaping from loss channels, which is beneficial for the improvement of the particle confinement. Moreover, this paper may provide a set of proxy functions for suppression of energetic particle losses to optimize stellarator configurations.

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8

Baillod, A., J. Loizu, J. P. Graves, and M. Landreman. "Stellarator optimization for nested magnetic surfaces at finite β and toroidal current." Physics of Plasmas 29, no. 4 (April 2022): 042505. http://dx.doi.org/10.1063/5.0080809.

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Good magnetic surfaces, as opposed to magnetic islands and chaotic field lines, are generally desirable for stellarators. In previous work, Landreman et al. [Phys. of Plasmas 28, 092505 (2021)] showed that equilibria computed by the Stepped-Pressure Equilibrium Code (SPEC) [Hudson et al., Phys. Plasmas 19, 112502 (2012)] could be optimized for good magnetic surfaces in vacuum. In this paper, we build upon their work to show the first finite- β, fixed-, and free-boundary optimization of SPEC equilibria for good magnetic surfaces. The objective function is constructed with the Greene's residue of selected rational surfaces, and the optimization is driven by the SIMSOPT framework [Landreman et al., J. Open Source Software 6, 3525 (2021)]. We show that the size of magnetic islands and the consequent regions occupied by chaotic field lines can be minimized in a classical stellarator geometry (rotating ellipse) by optimizing either the injected toroidal current profile, the shape of a perfectly conducting wall surrounding the plasma (fixed-boundary case), or the vacuum field produced by the coils (free-boundary case). This work shows that SPEC can be used as an equilibrium code both in a two-step or single-step stellarator optimization loop.

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9

Zhu, Caoxiang, Kenneth Hammond, Adam Rutkowski, Keith Corrigan, Douglas Bishop, Arthur Brooks, Peter Dugan, et al. "PM4Stell: A prototype permanent magnet stellarator structure." Physics of Plasmas 29, no. 11 (November 2022): 112501. http://dx.doi.org/10.1063/5.0102754.

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Permanent magnets provide a possible solution to simplify complicated stellarator coils. A prototype permanent magnet stellarator structure, PM4Stell, has been funded to demonstrate the technical feasibility of using permanent magnets to create the shaping field of a stellarator. Permanent magnets in uniform cubes with three polarization directions will be carefully placed to generate the required magnetic field for a National Compact Stellarator eXperiment-like equilibrium together with planar toroidal field coils. Discrete magnets will be glued together and inserted into a “post-office-box-like” supporting structure. Electromagnetic and structural analyses have been done to validate the design. Error field correction magnets will be used to shim possible error fields. The design efforts of the prototype permanent magnet stellarator structure are discussed.

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10

Zanca, P., F. Sattin, D. F. Escande, and F. Auriemma. "A power-balance model for the L-mode radiative density limit in fusion plasmas." Plasma Physics and Controlled Fusion 64, no. 5 (March 30, 2022): 054006. http://dx.doi.org/10.1088/1361-6587/ac57cc.

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Abstract A 1D cylindrical power-balance model of the radiation density limit (DL) gives a unified description of this phenomenon for stellarators, reversed field pinches and L-mode tokamaks (Zanca et al 2019 Nucl. Fusion 59 126011). The DL scaling laws for the three different configurations are all derived from a combination of just two equations: (a) a single-fluid heat-transport equation; (b) on-axis Ohm’s law with Spitzer resistivity, taken in a suitable limit for the stellarator. Here, we present a refined version of the model, alongside further experimental evidence supporting its successful application.

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11

Moroz, Paul E. "Stellarator-spheromak." Physics Letters A 236, no. 1-2 (December 1997): 79–83. http://dx.doi.org/10.1016/s0375-9601(97)00668-3.

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12

Dewar, R. L., and S. R. Hudson. "Stellarator symmetry." Physica D: Nonlinear Phenomena 112, no. 1-2 (January 1998): 275–80. http://dx.doi.org/10.1016/s0167-2789(97)00216-9.

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13

Hitchon, W. N. G., and H. E. Mynick. "Ripple transport in ‘transport-optimized’ stellarators." Journal of Plasma Physics 37, no. 3 (June 1987): 383–404. http://dx.doi.org/10.1017/s0022377800012265.

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Transport in ‘transport-optimized’ stellarators at low collision frequencies has been studied using a numerical method of solution of the bounce-averaged Fokker–Planck equation which describes both ripple-trapped and non-ripple-trapped particles in a stellarator. Diffusion rates in ‘transport-optimized’ stellarators had not previously been calculated at collision frequencies which are low enough for the effects of a radial electric field to be important. It was found that the configurations which were optimized for transport at the highest collision frequencies at which ripple-trapped particles exist give improved transport at all lower collision frequencies of interest, and also at higher collision frequencies. Standard stellarators have also been studied since in these cases the results can be compared with existing analytic theories and the transport mechanisms have been clarified as a result. Comparisons with Monte Carlo calculations show excellent agreement, and, although existing analytic methods of solution can strictly only be applied in rather few cases, some extensions of analytic results are discussed which enable us to explain quantitatively the behaviour observed.

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14

Sosa, David, and Iole Palermo. "Neutronic Assessments towards a Novel First Wall Design for a Stellarator Fusion Reactor with Dual Coolant Lithium Lead Breeding Blanket." Energies 16, no. 11 (May 30, 2023): 4430. http://dx.doi.org/10.3390/en16114430.

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The Stellarator Power Plant Studies Prospective R&D Work Package in the Eurofusion Programme was settled to bring the stellarator engineering to maturity, so that stellarators and particularly the HELIAS (HELical-axis Advanced Stellarator) configuration could be a possible alternative to tokamaks. However, its complex geometry makes designing a Breeding Blanket (BB) that fully satisfies the requirements for such a HELIAS configuration, which is a difficult task. Taking advantage of the acquired experience in BB design for DEMO tokamak, CIEMAT is leading the development of a Dual Coolant Lithium Lead (DCLL) BB for a HELIAS configuration. To answer the specific HELIAS challenges, new and advanced solutions have been proposed, such as the use of fully detached First Wall (FW) based on liquid metal Capillary Porous Systems (CPS). The proposed solutions have been studied in a simplified 1D model that can help to estimate the relative variations in Tritium Breeding Ratio (TBR) and displacement per atom (dpa) to verify their effectiveness in simplifying the BB integration and improving the machine availability while keeping the main BB nuclear functions (i.e., tritium breeding, heat extraction and shielding). This preliminary study demonstrates that the use of FW CPS would drastically reduce the radiation damage received by the blanket by 29% in some of the selected configurations along with a small decrease of 4.9% in TBR. This could even be improved to just a 3.8% TBR reduction by using a graphite reflector. Such an impact on the TBR is considered affordable, and the results presented, although preliminary in essence, have shown the existence of margins for further development of the FW CPS concept for HELIAS, as they have been not found, at least to date, to be significant showstoppers for the use of this technological solution.

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15

D'Haeseleer, W. D., W. N. G. Hitchon, and J. L. Shohet. "Numerical determination of the ambipolar electric field in a stellarator-reactor plasma." Journal of Plasma Physics 42, no. 1 (August 1989): 133–51. http://dx.doi.org/10.1017/s0022377800014227.

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A numerical parametric study of the radial ambipolar electric field in a stellarator reactor has been undertaken. With the numerical neoclassical code FLOCS (Flow Code for Stellarators), which is capable of handling both ions and electrons of all relevant kinetic energies, the radial ambipolar field (Er)AMB is determined from the algebraic condition that ion and electron fluxes are equal. As expected, the potential is of the same order of magnitude as the temperature. Somewhat surprisingly at first sight, however, the potential does not change much with the temperature (in the parameter range under consideration), being somewhat insensitive to moderate variations of T. An explanation for this behaviour is presented. Finally, the radial particle fluxes, consistent with the obtained (Er)AMB, and the particle confinement time are computed.

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16

Lewandowski, J. LV, and M. Persson. "Effect of magnetic field structure on collisional drift waves." Canadian Journal of Physics 77, no. 6 (October 1, 1999): 447–61. http://dx.doi.org/10.1139/p99-044.

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A 3-field model for collisional drift waves, in the ballooning representation, for a low-pressure stellarator plasma is presented. The 3-field model, which includes the effects of a finite radial mode number (θk) , is solved as an initial-value problem along the magnetic field line. It is shown that for a stellarator with low global magnetic shear, θk= 0 corresponds to the fastest linear growth rate. The effects of the magnetic field structure for the tokamak and stellarator configurations are discussed in a comparative way. PACS Nos.: 52.35Kt, 52.30Jb, 52.35Ra

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17

Maaßberg, H. "Stellarator Kinetic Theory." Fusion Technology 37, no. 2T (March 2000): 63–70. http://dx.doi.org/10.13182/fst00-a11963200.

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18

Moroz, Paul E. "Spherical Stellarator Configuration." Physical Review Letters 77, no. 4 (July 22, 1996): 651–54. http://dx.doi.org/10.1103/physrevlett.77.651.

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19

Feder, Toni. "US stellarator aborted." Physics Today 61, no. 7 (July 2008): 25–26. http://dx.doi.org/10.1063/1.2963004.

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20

Fujita, J., and K. Matsuoka. "JIPP stellarator/tokamak." Nuclear Fusion 25, no. 9 (September 1, 1985): 1253–57. http://dx.doi.org/10.1088/0029-5515/25/9/043.

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21

Moroz, Paul E. "Helical post stellarator." Plasma Physics and Controlled Fusion 40, no. 6 (June 1, 1998): 1127–47. http://dx.doi.org/10.1088/0741-3335/40/6/018.

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22

Grebenshchikov, Stanislav, Dmitriy Vasilkov, Vyacheslav Ivanov, Karen Sarksyan, Maksim Tereshchenko, and Nikolay Kharchev. "Study of electric currents excitation in the plasma of the L-2M stellarator with its electronic cyclotronic creation and heating." ADVANCES IN APPLIED PHYSICS 9, no. 4 (September 22, 2021): 310–24. http://dx.doi.org/10.51368/2307-4469-2021-9-4-310-324.

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The results of measuring the longitudinal electric current excited in the toroidal plasma of the L-2M stellarator as a result of powerful pulsed microwave heating (power up to 600 kW, pulse duration up to 20 ms) are presented. In the experi-ments, to create and heat plasma in the stellarator, microwave radiation of gyro-trons with a frequency of 75 GHz, equal to the frequency of the 2nd harmonic of electron cyclotron resonance for a magnetic field with induction B = 1.34 T at the center of the plasma column, was used. To measure the currents in the plasma, di-agnostic systems of the stellarator were used, designed to record changes in time of the transverse and poloidal magnetic fields. It is shown that the presence of an ohmic heating iron transformer in the stellarator design significantly affects the temporal development of equilibrium currents due to the significant inductance of the toroidal plasma. When compensating the inductance of these devices, the ex-pected value of the current excited in the plasma can reach a value of about 7 kA.

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23

NEILSON, George H., Michael C. ZARNSTORFF, and James F. LYON. "Quasi-Symmetry in Stellarator Research. 5. Status of Physics Design of Quasi-Axisymmetric Stellarators. 5.1. Physics Design of the National Compact Stellarator Experiment." Journal of Plasma and Fusion Research 78, no. 3 (2002): 214–19. http://dx.doi.org/10.1585/jspf.78.214.

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24

Swee, C., B. Geiger, R. Dux, S. T. A. Kumar, J. F. Castillo, A. Bader, and M. Gerard. "Impurity transport studies at the HSX stellarator using active and passive CVI spectroscopy." Plasma Physics and Controlled Fusion 64, no. 1 (November 29, 2021): 015008. http://dx.doi.org/10.1088/1361-6587/ac3965.

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Abstract The transport of carbon impurities has been studied in the helically symmetric stellarator experiment (HSX) using active and passive charge exchange recombination spectroscopy (CHERS). For the analysis of the CHERS signals, the STRAHL impurity transport code has been re-written in the python programming language and optimized for the application in stellarators. In addition, neutral hydrogen densities both along the NBI line of sight as well as for the background plasma have been calculated using the FIDASIM code. By using the basinhopping algorithm to minimize the difference between experimental and predicted active and passive signals, significant levels of impurity diffusion are observed. Comparisons with neoclassical calculations from DKES/PENTA show that the inferred levels exceed the neoclassical transport by about a factor of four in the core and more than 100 times towards the plasma edge, thus indicating a high level of anomalous transport. This observation is in agreement with experimental heat diffusivites determined from a power balance analysis which exhibits strong anomalous transport as well.

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25

Nespoli, F., S. Masuzaki, K. Tanaka, N. Ashikawa, M. Shoji, E. P. Gilson, R. Lunsford, et al. "Observation of a reduced-turbulence regime with boron powder injection in a stellarator." Nature Physics 18, no. 3 (January 10, 2022): 350–56. http://dx.doi.org/10.1038/s41567-021-01460-4.

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AbstractIn state-of-the-art stellarators, turbulence is a major cause of the degradation of plasma confinement. To maximize confinement, which eventually determines the amount of nuclear fusion reactions, turbulent transport needs to be reduced. Here we report the observation of a confinement regime in a stellarator plasma that is characterized by increased confinement and reduced turbulent fluctuations. The transition to this regime is driven by the injection of submillimetric boron powder grains into the plasma. With the line-averaged electron density being kept constant, we observe a substantial increase of stored energy and electron and ion temperatures. At the same time, the amplitude of the plasma turbulent fluctuations is halved. While lower frequency fluctuations are damped, higher frequency modes in the range between 100 and 200 kHz are excited. We have observed this regime for different heating schemes, namely with both electron and ion cyclotron resonant radio frequencies and neutral beams, for both directions of the magnetic field and both hydrogen and deuterium plasmas.

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26

Gates, David A., David Anderson, S. Anderson, M. Zarnstorff, Donald A. Spong, Harold Weitzner, G. H. Neilson, et al. "Stellarator Research Opportunities: A Report of the National Stellarator Coordinating Committee." Journal of Fusion Energy 37, no. 1 (February 2018): 51–94. http://dx.doi.org/10.1007/s10894-018-0152-7.

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27

Beidler, C. D., and W. N. G. Hitchon. "Ripple transport in helical-axis advanced stellarators: a comparison with classical stellarator/torsatrons." Plasma Physics and Controlled Fusion 36, no. 2 (February 1, 1994): 317–53. http://dx.doi.org/10.1088/0741-3335/36/2/007.

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28

Nemov, V. V., S. V. Kasilov, W. Kernbichler, and B. Seiwald. "Calculation of the magnetic surface function gradient in stellarators with broken stellarator symmetry." Physics of Plasmas 17, no. 5 (May 2010): 052512. http://dx.doi.org/10.1063/1.3396366.

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29

Nührenberg, C. "Ideal magnetohydrodynamic stability in stellarators with subsonic equilibrium flow." Plasma Physics and Controlled Fusion 63, no. 12 (November 17, 2021): 125035. http://dx.doi.org/10.1088/1361-6587/ac35ef.

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Abstract The effect of a subsonic flow, inherent to most stellarators because of a radial electric field, on their ideal magnetohydrodynamic (MHD) stability properties is studied employing the quasi-Lagrangian picture developed by Frieman and Rotenberg (1960 Rev. Mod. Phys. 32 898). The Mach number of the perpendicular E × B flow in stellarators is of order 0.01 and, therefore, admits the usage of a subsonic approximation in form of a static equilibrium. A mathematical formulation of the weak form of the stability equation with flow has been implemented in the ideal-MHD stability code CAS3D. This formulation uses magnetic coordinates and does not involve any derivatives across magnetic surfaces. In addition to the expected Doppler shift of frequencies, properties of the spectrum of the ideal MHD force operator, which are already known for tokamaks, but now also shown in the stellarator case, are: firstly, the appearance of unstable flow-induced continua stemming from the coupling of sound and Alfvén continuum branches with equal mode numbers; and, secondly, the existence of flow-induced, global, stable modes near extrema of sound continuum branches, the extrema, in turn, being generated by the influence of a sheared flow on the static sound continua.

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30

Bañón Navarro, A., A. Di Siena, J. L. Velasco, F. Wilms, G. Merlo, T. Windisch, L. L. LoDestro, J. B. Parker, and F. Jenko. "First-principles based plasma profile predictions for optimized stellarators." Nuclear Fusion 63, no. 5 (March 22, 2023): 054003. http://dx.doi.org/10.1088/1741-4326/acc3af.

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Abstract In the present Letter, first-of-its-kind computer simulations predicting plasma profiles for modern optimized stellarators—while self-consistently retaining neoclassical transport, turbulent transport with 3D effects, and external physical sources—are presented. These simulations exploit a newly developed coupling framework involving the global gyrokinetic turbulence code GENE-3D, the neoclassical transport code KNOSOS, and the 1D transport solver TANGO. This framework is used to analyze the recently observed degradation of energy confinement in electron-heated plasmas in the Wendelstein 7-X stellarator, where the central ion temperature was ‘clamped’ to T i ≈ 1.5 keV regardless of the external heating power. By performing first-principles based simulations, we provide key evidence to understand this effect, namely the inefficient thermal coupling between electrons and ions in a turbulence-dominated regime, which is exacerbated by the large T e / T i ratios, and show that a more efficient ion heat source, such as direct ion heating, will increase the on-axis ion temperature. This work paves the way towards the use of high-fidelity models for the development of the next generation of stellarators, in which neoclassical and turbulent transport are optimized simultaneously.

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31

White, Roscoe. "Resonant alpha particle loss in stellarators." Physics of Plasmas 29, no. 9 (September 2022): 092504. http://dx.doi.org/10.1063/5.0104923.

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Particle resonances in stellarators can produce islands in the space of passing particle orbits without the presence of an unstable Alfvén mode, provided the period of the resonance matches the period of the equilibrium magnetic field. In this case, the equilibrium itself plays the role of a mode amplitude, and the islands appear on surfaces where the orbital helicity matches the field period. At low energy, these surfaces are given by the field line helicity, but at higher energy, cross field drift causes them to move. The resonances are also felt by trapped particles bouncing back and forth on surfaces with matching helicity. The periodic variation of B along these orbits produces local wells, giving loss due to drift while trapped in a well. Stellarator designs that have equilibrium-induced resonance islands exhibit anomalous alpha particle loss and are unsuitable for reactors.

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32

Boozer, Allen H., and Alkesh Punjabi. "Simulation of stellarator divertors." Physics of Plasmas 25, no. 9 (September 2018): 092505. http://dx.doi.org/10.1063/1.5042666.

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33

Johnson, John L. "Stellarator and Heliotron Devices." Nuclear Fusion 39, no. 2 (February 1999): 293–94. http://dx.doi.org/10.1088/0029-5515/39/2/701.

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34

Helander, P., T. Bird, F. Jenko, R. Kleiber, G. G. Plunk, J. H. E. Proll, J. Riemann, and P. Xanthopoulos. "Advances in stellarator gyrokinetics." Nuclear Fusion 55, no. 5 (April 22, 2015): 053030. http://dx.doi.org/10.1088/0029-5515/55/5/053030.

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35

Garabedian, P. R. "Three-dimensional stellarator codes." Proceedings of the National Academy of Sciences 99, no. 16 (July 24, 2002): 10257–59. http://dx.doi.org/10.1073/pnas.162330399.

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36

Cartlidge, Edwin. "Rebirth of the stellarator." Physics World 27, no. 05 (May 2014): 12–13. http://dx.doi.org/10.1088/2058-7058/27/05/21.

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37

Clery, Daniel. "Novel stellarator begins operation." Physics World 28, no. 11 (November 2015): 10. http://dx.doi.org/10.1088/2058-7058/28/11/16.

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38

Jassby, Daniel. "Stellarator pro and con." Physics Today 61, no. 12 (December 2008): 14. http://dx.doi.org/10.1063/1.4796730.

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39

Miller, Ronald L. "Advanced Stellarator Power Plants." Fusion Technology 26, no. 3P2 (November 1994): 1127–32. http://dx.doi.org/10.13182/fst94-a40305.

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40

Boozer, Allen H. "Stellarator pro and con." Physics Today 61, no. 12 (December 2008): 12–14. http://dx.doi.org/10.1063/1.3047645.

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41

Garabedian, Paul R., and Geoffrey B. McFadden. "The DEMO Quasisymmetric Stellarator." Energies 3, no. 3 (February 26, 2010): 277–84. http://dx.doi.org/10.3390/en3030277.

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42

Boozer, Allen H. "What is a stellarator?" Physics of Plasmas 5, no. 5 (May 1998): 1647–55. http://dx.doi.org/10.1063/1.872833.

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43

Moiseenko, V. E., A. V. Lozin, M. M. Kozulia, Yu K. Mironov, V. S. Romanov, V. G. Konovalov, and A. N. Shapoval. "Alfvén Plasma Heating in Stellarator Uragan-2M." Ukrainian Journal of Physics 62, no. 4 (May 2017): 311–17. http://dx.doi.org/10.15407/ujpe62.04.0311.

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44

Dinklage, A., E. Ascasíbar, C. D. Beidler, R. Brakel, J. Geiger, J. H. Harris, A. Kus, et al. "Assessment of Global Stellarator Confinement: Status of the International Stellarator Confinement Database." Fusion Science and Technology 51, no. 1 (January 2007): 1–7. http://dx.doi.org/10.13182/fst07-a1281.

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45

Buller, S., H. M. Smith, and A. Mollén. "Recent progress on neoclassical impurity transport in stellarators with implications for a stellarator reactor." Plasma Physics and Controlled Fusion 63, no. 5 (April 14, 2021): 054003. http://dx.doi.org/10.1088/1361-6587/abf313.

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46

Davidson, MG, RL Dewar, HJ Gardner, and J. Howard. "Hamiltonian Maps for Heliac Magnetic Islands." Australian Journal of Physics 48, no. 5 (1995): 871. http://dx.doi.org/10.1071/ph950871.

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Magnetic islands in toroidal heliac stellarator vacuum fields are explored with Hamiltonian chaos theory and the associated area-preserving maps. Magnetic field line island chains are examined first analytically, with perturbation theory, and then numerically to produce Poincaré sections, which are compared with H−1 Heliac stellarator puncture plot diagrams. Rotational transform profiles are chosen to permit the comparison of twist map and nontwist map predictions with field line behaviour computed by a field line tracing computer program and observed experimentally.

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47

Lazerson, Samuel A., Alexandra LeViness, and Jorrit Lion. "Simulating fusion alpha heating in a stellarator reactor." Plasma Physics and Controlled Fusion 63, no. 12 (November 16, 2021): 125033. http://dx.doi.org/10.1088/1361-6587/ac35ee.

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Abstract Gyrocenter following simulations of fusion born alpha particles in a stellarator reactor are preformed using the BEAMS3D code. The Wendelstein 7-X high mirror configuration is scaled in geometry and magnetic field to reactor relevant parameters. A 2 × 10 20 m−3 density plasma with 20 keV core temperatures is assumed and fusion birth rates calculated for various fusion products assuming a 50/50 deuterium-tritium mixture. It is found that energetic He4 ions comprise the vast majority of the energetic particle inventory. Slowing down simulations of the He4 population suggest plasma heating consistent with scaled energy confinement times for a stellarator reactor. Losses for this configuration appear large suggesting optimization beyond the scope of the W7-X device is key to a future fusion reactor. These first simulations are designed to demonstrate the capability of the BEAMS3D code to provide fusion alpha birth and heating profiles for stellarator reactor designs.

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48

Clery, Daniel. "Twisty device explores alternative path to fusion." Science 377, no. 6611 (September 9, 2022): 1132–33. http://dx.doi.org/10.1126/science.ade7660.

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49

Moiseenko, V. E., S. V. Chernitskiy, O. Ågren, N. B. Dreval, A. S. Slavnyj, Yu V. Kovtun, A. V. Lozin, et al. "DEVELOPMENTS FOR STELLARATOR-MIRROR FUSION-FISSION HYBRID CONCEPT." Problems of Atomic Science and Technology, Ser. Thermonuclear Fusion 44, no. 2 (2021): 111–17. http://dx.doi.org/10.21517/0202-3822-2021-44-2-111-117.

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50

Almagri, A. F., D. T. Anderson, F. S. B. Anderson, P. H. Probert, J. L. Shohet, and J. N. Talmadge. "A helically symmetric stellarator (HSX)." IEEE Transactions on Plasma Science 27, no. 1 (1999): 114–15. http://dx.doi.org/10.1109/27.763074.

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