Nuclear Fusion最新文献

{"title":"Corrigendum: Tritium burn efficiency in deuterium–tritium magnetic fusion (2023 Nucl. Fusion 63 126019)","authors":"D.G. Whyte, R. Delaporte-Mathurin, S.E. Ferry and S. Meschini","doi":"10.1088/1741-4326/ad6337","DOIUrl":"https://doi.org/10.1088/1741-4326/ad6337","url":null,"abstract":"The controlling parameters regarding tritium burn efficiency (TBE) are derived from first principles and shown to depend fundamentally on the permitted He gas fraction in the divertor and effective pumping speeds of He ash and unburned hydrogenic fuel. The analysis is generic to any equilibrated magnet fusion plasma using a divertor for particle exhaust. The He gas fraction in the plasma limits the maximum TBE due to the link between ash dilution effects in the core plasma and fusion performance. High TBE in magnetic fusion devices is counter-correlated to achieving high gain and power density for commercial fusion. The impact of TBE on fusion performance for several figures of merit are derived, including power density, required product, and plasma energy gain . The TBE formulation presented here is applied to existing devices, based on published data of enrichment and from research tokamaks. This assessment strongly motivates exploration of technologies that would enhance the effective pumping speed of He to fuel out of the plasma.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"21 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-07-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141742517","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Isotope effects and Alfvén eigenmode stability in JET H, D, T, DT, and He plasmas","authors":"R.A. Tinguely, P.G. Puglia, S. Dowson, M. Porkolab, D. Douai, A. Fasoli, L. Frassinetti, D. King, P. Schneider and JET Contributors","doi":"10.1088/1741-4326/ad6013","DOIUrl":"https://doi.org/10.1088/1741-4326/ad6013","url":null,"abstract":"While much about Alfvén eigenmode (AE) stability has been explored in previous and current tokamaks, open questions remain for future burning plasma experiments, especially regarding exact stability threshold conditions and related isotope effects; the latter, of course, requiring good knowledge of the plasma ion composition. In the JET tokamak, eight in-vessel antennas actively excite stable AEs, from which their frequencies, toroidal mode numbers, and net damping rates are assessed. The effective ion mass can also be inferred using measurements of the plasma density and magnetic geometry. Thousands of AE stability measurements have been collected by the Alfvén Eigenmode Active Diagnostic in hundreds of JET plasmas during the recent Hydrogen, Deuterium, Tritium, DT, and Helium-4 campaigns. In this novel AE stability database, spanning all four main ion species, damping is observed to decrease with increasing Hydrogenic mass, but increase for Helium, a trend consistent with radiative damping as the dominant damping mechanism. These data are important for confident predictions of AE stability in both non-nuclear (H/He) and nuclear (D/T) operations in future devices. In particular, if radiative damping plays a significant role in overall stability, some AEs could be more easily destabilized in D/T plasmas than their H/He reference pulses, even before considering fast ion and alpha particle drive. Active MHD spectroscopy is also employed on select HD, HT, and DT plasmas to infer the effective ion mass, thereby closing the loop on isotope analysis and demonstrating a complementary method to typical diagnosis of the isotope ratio.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"60 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141742519","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"High performance power handling in the absence of an H-mode edge in negative triangularity DIII-D plasmas","authors":"F. Scotti, A. Marinoni, A.G. McLean, C. Paz-Soldan, K.E. Thome, M. Zhao, S. Allen, M. Austin, M.G. Burke, D. Eldon, M. Fenstermacher, A. Hyatt, C.J. Lasnier, A. Leonard, J. Lore, A.O. Nelson, T. Osborne, O. Sauter, D. Truong, M.A. Van Zeeland, H.Q. Wang and R. Wilcox","doi":"10.1088/1741-4326/ad5f41","DOIUrl":"https://doi.org/10.1088/1741-4326/ad5f41","url":null,"abstract":"Experiments performed during strongly-shaped high-power diverted negative triangularity (NT) experiments in DIII-D achieved detached divertor conditions and a transient-free edge, showcasing the potential for application of NT to a core-edge integrated reactor-like scenario and providing the first characterization of the parametric dependencies for detachment onset. Detached divertor conditions will be required in future devices to mitigate divertor heat fluxes. Access to dissipative divertor conditions was investigated via an increase in upstream density. Detachment onset at the outer strike point was achieved with H-mode level confinement and reactor-relevant normalized pressures . Confinement degradation was observed with deeper detachment, associated with the loss of an electron temperature pedestal. Differences in geometry, radial transport, impact of cross field drifts are discussed to explain differences in access to detachment in NT discharges. Higher normalized densities, with respect to equivalent discharges in positive triangularity, were necessary to achieve detachment, partially explained by the shorter parallel connection length to the targets. The effect of cross-field particle drifts (E×B, B B) on access to detachment was demonstrated by the lower upstream density needed to access detachment with ion B B drift directed outside of the active divertor (Greenwald fraction 0.9–1.0 vs 1.3). The upstream density at detachment onset was observed to increase linearly with plasma current with ion B B drift into the divertor, consistent with the observed narrowing of the scrape-off layer heat flux width λq. Edge fluid simulations capture separatrix densities needed to achieve detachment in NT plasma and their dependence on drift direction. The ability to reproduce detachment dynamics in NT plasma increases the confidence in future design studies for NT divertors.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"20 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-07-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141718884","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Impurity transport study based on measurement of visible wavelength high-n charge exchange transitions at W7-X","authors":"Colin Swee, Benedikt Geiger, Oliver Ford, Mark Nornberg, Martin O’Mullane, Peter Poloskei, Felix Reimold, Thilo Romba, Thomas Wegner and the W7-X Team","doi":"10.1088/1741-4326/ad5aad","DOIUrl":"https://doi.org/10.1088/1741-4326/ad5aad","url":null,"abstract":"A recently installed high-speed charge exchange diagnostic at the W7-X stellarator has been used to identify several high-n Rydberg emission lines near 500 nm following impurity injections. The wavelengths of observed high-n Rydberg transitions are independent of the impurity species and originate from ions with ionization states ranging from 14+ to 45+ suggesting that this approach can be applied to a variety of heavy impurities. Moreover, little to no passive signal is observed since the high-n energy levels are unlikely to be populated by electron impact excitation. The combination of the newly developed diagnostic and the observation of high-n Rydberg states provides spatially resolved, high-speed measurements of multiple charge states which are analyzed in a Bayesian inference framework to determine both impurity diffusion and convection profiles. Measurements from the 2023 experimental campaign conclusively show high diffusion and an inward pinch in the core, well above predictions by neoclassical theory.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"41 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141588520","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Observation of alpha-particles in recent D–T experiments on JET","authors":"V.G. Kiptily, C.D. Challis, R. Dumont, M. Fitzgerald, J. Garcia, L. Garzotti, Z. Ghani, J. Hobirk, P. Jacquet, A. Kappatou, D. Keeling, Ye. Kazakov, P. Mantica, M.J. Mantsinen, S.E. Sharapov, E.R. Solano, D. Van Eester, P.J. Bonofiglo, T. Craciunescu, A. Dal Molin, J. Eriksson, V. Goloborodko, M.V. Iliasova, E.M. Khilkevitch, D. King, I. Lengar, M. Nocente, S. Menmuir, M. Podestà, M. Poradzinski, D. Rigamonti, J. Rivero-Rodriguez, Z. Stancar, A.E. Shevelev, P. Siren, H. Sun, D.M. Taylor, M. Tardocchi, P. Beaumont, F. Belli, F.E. Cecil, R. Coelho, M. Curuia, M. Garcia-Munoz, E. Joffrin, C. Lowry, M. Lennholm, E. Lerche, C.F. Maggi, J. Mailloux, D. Marocco, M. Maslov, C. Perez Von Thun, F. Rimini, V. Zoita and JET Contributors","doi":"10.1088/1741-4326/ad5c81","DOIUrl":"https://doi.org/10.1088/1741-4326/ad5c81","url":null,"abstract":"The fusion reaction between deuterium and tritium, D(T,n)4He is the main source of energy in future thermonuclear reactors. Alpha-particles (4He-ions) born with an average energy of 3.5 MeV transferring energy to the thermal plasma during their slowing down, should provide the self-sustained D–T plasma burn. The adequate confinement of α-particles is essential to provide efficient heating of the bulk plasma and steady burning of a reactor plasma. That is why the fusion-born α-particle studies have been a priority task in the second D–T experiments (DTE2) on the Joint European Torus (JET) to understand the main mechanisms of their slowing down, redistribution and losses and to develop optimal plasma scenarios. JET with Be-wall and W-divertor, enhanced auxiliary heating systems and improved energetic-particle diagnostic capabilities, producing significant population of α-particles, provided the possibility for comprehensive studying of the α-particle behaviour. Selected results of the confined and lost α-particle measurements, evidence of α-particle self-heating and assessments of the fusion performance are presented in this paper giving an opportunity for further modelling and extrapolation to the International Thermonuclear Experimental Reactor and burning plasma reactors.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"8 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141586723","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Interfaces enhanced plasma irradiation resistance in CrMoTaWV/W multilayer films through blocking He diffusion","authors":"Chenyi Qu, Mengqing Hong, Guo Wei, Wentao Ge, Enkai Guo, Fen Zhong, Guangxu Cai, Yongqiang Wang and Feng Ren","doi":"10.1088/1741-4326/ad5aaf","DOIUrl":"https://doi.org/10.1088/1741-4326/ad5aaf","url":null,"abstract":"The performance of plasma-facing materials (PFMs) is one of the key factors that significantly impact the stability of operation in fusion reactors. Herein, a new CrMoTaWV/W (high entropy alloy (HEA)/W) multilayer structure is designed as PFM to investigate its resistance to He plasma irradiation. It was observed that the introduction of the interfaces effectively absorbed plenty of He atoms, preventing them from diffusing into the material and delaying the formation of fuzz incubation zone, therefore, enhancing the resistance to plasma irradiation. The thickness transformed to fuzz in the HEA/W multilayer films was observed to be about two-thirds of those in the CrMoTaWV (HEA) film. Additionally, the fuzz growth rates in HEA/W multilayer films are lower than the average growth rate of bulk W and HEA films combined. These findings highlight a promising new avenue for the exploration of high-performance PFMs.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"47 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141569215","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Turbulence link to L-mode, I-mode, and H-mode confinement in the DIII-D tokamak","authors":"J. Chen, D.L. Brower, J. McClenaghan, Z. Yan, A.E. Hubbard, R. Groebner","doi":"10.1088/1741-4326/ad5aae","DOIUrl":"https://doi.org/10.1088/1741-4326/ad5aae","url":null,"abstract":"Understanding the physics of low-confinement (L-), improved-confinement (I-), and high-confinement (H-) modes is critical for fusion reactors. The finding herein reports observations of two types of turbulence coexisting near the L-mode edge, one magnetohydrodynamic (MHD)-like and another micro-tearing mode (MTM)-like, linked to the H-mode and I-mode confinement in the DIII-D tokamak. Ion-scale magnetic and density turbulence is measured using a Faraday-effect radial-interferometer-polarimeter and beam-emission-spectroscopy (BES). Broadband turbulence spectra of up to ∼600 kHz are observed in two discharges where transitions between L-mode, I-mode, and H-mode occurs. Turbulence is found to be inversely correlated with confinement, meaning lower turbulence power at higher confinement. Distinctively, the high-frequency (HF, >∼100 kHz) magnetic turbulence power changes by the most (55%) during transitions primarily involving energy confinement change, whereas the low-frequency (LF, <∼100 kHz) magnetic and density turbulence power changes by the most (80%) during transitions primarily involving particle confinement change. The LF turbulence amplitude oscillates with and leads to deuterium-alpha emission oscillations before an H-mode. These results imply that HF turbulence mainly affects energy confinement whereas LF turbulence can affect particle confinement. The magnetic and density turbulence exhibits coherence up to 0.6 and cross-phase magnitude close to <inline-formula>\u0000<tex-math><?CDATA $pi /2$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mi>π</mml:mi><mml:mrow><mml:mo>/</mml:mo></mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"nfad5aaeieqn1.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> in most cases, suggesting they have a common origin in both the LF and HF ranges. BES suggests that LF turbulence resides at the edge (<inline-formula>\u0000<tex-math><?CDATA $rho = 0.95$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mi>ρ</mml:mi><mml:mo>=</mml:mo><mml:mn>0.95</mml:mn></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"nfad5aaeieqn2.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula>) and HF turbulence can be at the outer core (<inline-formula>\u0000<tex-math><?CDATA $rho = 0.8$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mi>ρ</mml:mi><mml:mo>=</mml:mo><mml:mn>0.8</mml:mn></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"nfad5aaeieqn3.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula>) or edge (<inline-formula>\u0000<tex-math><?CDATA $rho = 0.95$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mi>ρ</mml:mi><mml:mo>=</mml:mo><mml:mn>0.95</mml:mn></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"nfad5aaeieqn4.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula>). Comparisons of measurements, theory, and gyrokinetic simulations suggest that HF turbulence is MTM-like in all cases, whereas LF turbulence is more consistent with MHD-like modes and th","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"61 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141577591","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Hybrid model predictive control techniques for safety factor profile and stored energy regulation while incorporating NBI constraints","authors":"Brian Leard, Zibo Wang, Sai Tej Paruchuri, Eugenio Schuster, Tariq Rafiq","doi":"10.1088/1741-4326/ad5c7f","DOIUrl":"https://doi.org/10.1088/1741-4326/ad5c7f","url":null,"abstract":"A novel hybrid Model Predictive Control (MPC) algorithm has been designed for simultaneous safety factor (<italic toggle=\"yes\">q</italic>) profile and stored energy (<italic toggle=\"yes\">w</italic>) control while incorporating the pulse-width-modulation constraints associated with the neutral beam injection (NBI) system. Regulation of the <italic toggle=\"yes\">q</italic>-profile has been extensively shown to be a key factor for improved confinement as well as non-inductive sustainment of the plasma current. Simultaneous control of <italic toggle=\"yes\">w</italic> is necessary to prevent the triggering of pressure-driven magnetohydrodynamic instabilities as the controller shapes the <italic toggle=\"yes\">q</italic> profile. Conventional MPC schemes proposed for <italic toggle=\"yes\">q</italic>-profile control have considered the NBI powers as continuous-time signals, ignoring the discrete-time nature of these actuators and leading in some cases to performance loss. The hybrid MPC scheme in this work has the capability of incorporating the discrete-time actuator dynamics as additional constraints. In nonlinear simulations, the proposed hybrid MPC scheme demonstrates improved <italic toggle=\"yes\">q</italic>-profile+<italic toggle=\"yes\">w</italic> control performance for NSTX-U operating scenarios.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"25 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141569220","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Real-time plasma equilibrium reconstruction and shape control for the MAST Upgrade tokamak","authors":"H. Anand, W. Wehner, D. Eldon, A. Welander, Z. Xing, A. Lvovskiy, J. Barr, E. Cho, B. Sammuli, D. Humphreys, N. Eidietis, A. Leonard, M. Kochan, C. Vincent, G. McArdle, G. Cunningham, A. Thornton, J. Harrison, V. Soukhanovskii, J. Lovell","doi":"10.1088/1741-4326/ad5c80","DOIUrl":"https://doi.org/10.1088/1741-4326/ad5c80","url":null,"abstract":"Real-time magnetic control has been developed to deliver precise control of multiple plasma shape parameters for advanced divertor configurations, including double-null, Super-X, X-point target and X-divertor for the first time on the MAST Upgrade (MAST-U) spherical tokamak. Successful real-time magnetic equilibrium control of different plasma shape variables has been accomplished in the 2022–2023 MAST-U experimental campaign for the advanced MAST-U divertor configurations. Application of the MAST-U boundary reconstruction algorithm, LEMUR, is described and compared with off-line equilibrium reconstruction and diagnostic measurements. The process of design and verification of the axisymmetric magnetic control schemes using a suite of control analysis tools (known collectively as TokSys) is also described.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"15 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141569217","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Numerical modelling of sawteeth and sawtooth-free regime","authors":"Q. Yu, S. Günter, K. Lackner","doi":"10.1088/1741-4326/ad5c7e","DOIUrl":"https://doi.org/10.1088/1741-4326/ad5c7e","url":null,"abstract":"To better understand the sawteeth physics and the sawtooth-free regime associated with the hybrid scenario in tokamak experiments, numerical calculations up to quasi-steady state have been carried out for realistic middle-size tokamak plasma parameters, including the bootstrap current perturbation and basing on both the single- and two-fluid equations with the large aspect ratio approximation. Two types of the sawtooth crash are found in multiple sawteeth simulations: (1) For a low equilibrium bootstrap current fraction, the crash is caused by the internal kink mode, as expected; (2) When the bootstrap current density fraction is larger than 10% in the core region, however, the crash is caused by the non-ideal double kink mode, in contrary to the conventional understanding. In this case, a non-monotonic radial profile of the safety factor <inline-formula>\u0000<tex-math><?CDATA $q$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mi>q</mml:mi></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"nfad5c7eieqn1.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> with two <inline-formula>\u0000<tex-math><?CDATA $q = 1$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mi>q</mml:mi><mml:mo>=</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"nfad5c7eieqn2.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> surfaces emerges before the crash, caused by the bootstrap current density and plasma resistivity perturbations, although the original equilibrium has only single <italic toggle=\"yes\">q</italic> = 1 surface. In both types of sawtooth crashes, the crash time in two-fluid simulations is tens of microseconds, as observed in experiments. Furthermore, for a relatively low ion density and finite bootstrap current density fraction, a transition from the sawtooth to the sawtooth-free regime is found, in which flat <inline-formula>\u0000<tex-math><?CDATA $q$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mi>q</mml:mi></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"nfad5c7eieqn3.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> profiles with the <inline-formula>\u0000<tex-math><?CDATA $q$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mi>q</mml:mi></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"nfad5c7eieqn4.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> value being about unity in the central region, similar to that observed in hybrid scenario experiments, are maintained by the dynamo effect. To enter into the sawtooth-free regime in two-fluid simulations, a much larger Alfvén velocity than that in single-fluid simulations is required due to the diamagnetic drift.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"19 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141569219","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}