Nuclear Fusion最新文献

{"title":"Plasma performance enhancement and impurity control using a novel technique of argon–hydrogen mixture fueled glow discharge wall conditioning in the ADITYA-U tokamak","authors":"K.A. Jadeja, J. Ghosh, K.M. Patel, A.B. Patel, R.L. Tanna, Kiran Patel, B.G. Arambhadiya, K.D. Galodiya, Rohit Kumar, S. Aich, Harshita Raj, L. Pradhan, M.B. Chowdhuri, R. Manchanda, N. Ramaiya, Nandini Yadava, Sharvil Patel, Kajal Shah, Dipexa Modi, A. Gauttam, K. Singh, S. Dolui, Ankit Kumar, B. Hegde, A. Kumawat, Minsha Shah, R. Rajpal, U. Nagora, P.K. Atrey, S.K. Pathak, Shishir Purohit, A. Adhiya, Manoj Kumar, Kumudni Assudani, D. Kumavat, S.K. Jha, K.S. Shah, M.N. Makwana, Shivam Gupta, Supriya Nair, Kishore Mishra, D. Raju, P.K. Chattopadhyay, B.R. Kataria","doi":"10.1088/1741-4326/ad6a6e","DOIUrl":"https://doi.org/10.1088/1741-4326/ad6a6e","url":null,"abstract":"Effective control of impurities and precise regulation of the fueling gas are supreme prerequisites for optimal operation in any fusion device. Conventional wall-conditioning methods fall short of achieving optimal wall conditioning. Conventional wall-conditioning methods, such as vessel baking and H₂/(D₂)-fueled glow discharge cleaning (GDC), are generally required to remove wall-absorbed impurities in bulk after vessel venting. The excess amount of hydrogen, injected during H₂ GDC, can be reduced by helium (He)-fueled GDC. However, He removal from the vessel is more challenging due to its low molecular mass, very low condensation temperature, and inert characteristics. In ADITYA-U, optimal wall conditioning cannot be achieved using H₂ followed by He-fueled GDC when applied for extended periods spanning hours or days. A GDC with a mixture of argon and hydrogen (Ar–H₂) is introduced in the ADITYA-U tokamak to obtain better wall conditioning than H₂ followed by He GDC. In Ar–H₂ GDC, long-lived ArH⁺ ions are formed in sufficient numbers and accelerated toward the vessel wall with high momentum. This results in the breaking of high energy bonds of impurities with the wall/plasma facing components, which is not possible by H⁺, H₂^+, H₃⁺ ions in H₂ GDC due to their lower momentum. An optimal blend ratio of Ar to H₂ is established at 15%–20% for the mixture. This composition ensures that the introduction of high-<italic toggle=\"yes\">Z</italic> Ar does not adversely affect tokamak plasma operations. The C- and O-containing impurities are reduced beyond the limit of the prolonged operation of H₂ GDC. Relative low pressures of dominant impurities such as CO, CH₄, and H₂O are obtained due to the Ar–H₂ GDC compared to routinely operated H₂ GDC. A comparison study of H₂ GDC and the developed Ar–H₂ GDC is performed in terms of wall conditioning and tokamak plasma operation. The encouraging results of the Ar–H₂ GDC are obtained in both wall cleaning and tokamak operation scenarios in the midsize tokamak ADITYA-U. This development and application of Ar–H₂ GDC are beneficial for large-sized fusion devices, leading to improved impurity reduction, reduced operational fuel consumption (H₂/D₂/He), and enhanced control over fuel recycling/extraction.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"12 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211962","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":"Direct optimization of neoclassical ion transport in stellarator reactors","authors":"B.F. Lee, S.A. Lazerson, H.M. Smith, C.D. Beidler and N.A. Pablant","doi":"10.1088/1741-4326/ad75a6","DOIUrl":"https://doi.org/10.1088/1741-4326/ad75a6","url":null,"abstract":"We directly optimize stellarator neoclassical ion transport while holding neoclassical electron transport at a moderate level, creating a scenario favorable for impurity expulsion and retaining good ion confinement. Traditional neoclassical stellarator optimization has focused on minimizing , the geometric factor that characterizes the amount of radial transport due to particles in the regime. Under expected reactor-relevant conditions, core electrons will be in the regime and core fuel ions will be in the regime. Traditional optimizations thus minimize electron transport and rely on the radial electric field (Er) that develops to confine the ions. This often results in an inward-pointing Er that drives high-Z impurities into the core, which may be troublesome in future reactors. In this work, we increase the ratio of the thermal transport coefficients , which previous research has shown can create an outward-pointing Er. This effect is very beneficial for impurity expulsion. We obtain self-consistent density, temperature, and Er profiles at reactor-relevant conditions for an optimized equilibrium. This equilibrium is expected to enjoy significantly improved impurity transport properties.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"61 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211952","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":"Kinetic profile inference with outlier detection using support vector machine regression and Gaussian process regression","authors":"Minseok Kim, W.H. Ko, Sehyun Kwak, Semin Joung, Wonjun Lee, B. Kim, D. Kim, J.H. Lee, Choongki Sung, Yong-Su Na and Y.-C. Ghim","doi":"10.1088/1741-4326/ad7304","DOIUrl":"https://doi.org/10.1088/1741-4326/ad7304","url":null,"abstract":"We propose an outlier-resilient Gaussian process regression (GPR) model supported by support vector machine regression (SVMR) for kinetic profile inference. GPR, being a non-parametric regression using Bayesian statistics, has advantages in that it imposes no constraints on profile shapes and can be readily used to integrate different kinds of diagnostics, while it is vulnerable to the presence of even a single outlier among a measured dataset. As an outlier classifier, an optimized SVMR is developed based only on the measurements. Hyper-parameters of the developed GPR model with informative prior distributions are treated in two different ways, i.e. maximum a posteriori (MAP) estimator and marginalization using a Markov Chain Monte Carlo sampler. Our SVMR-supported GPR model is applied to infer ion temperature Ti profiles using measured data from the KSTAR charge exchange spectroscopy system. The GPR-inferred Ti profiles with and without an outlier are compared and show prominent improvement when the outlier is removed by the SVMR. Ti profiles inferred with the MAP estimator and the marginalization scheme are compared. They are noticeably different when observation uncertainties are not small enough, and the marginalization scheme generally provides a smoother profile.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"9 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211950","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":"First experiments on RF plasma production at relatively low magnetic fields in the LHD","authors":"Yu.V. Kovtun, S. Kamio, V.E. Moiseenko, H. Kasahara, T. Seki, K. Saito, R. Seki, S. Masuzaki, S. Brezinsek, A. Dinklage","doi":"10.1088/1741-4326/ad70cc","DOIUrl":"https://doi.org/10.1088/1741-4326/ad70cc","url":null,"abstract":"The results of the first experimental series to produce a plasma using the radio frequency discharge (RF) above the ion cyclotron frequency at relatively low magnetic fields (0.5–0.6 T) in the Large Helical Device (LHD) are presented 1.43 MW of RF power produced target plasma with density up to 6 × 10¹⁸ m⁻³ to deuterium. Tangential NBI application into such a plasma increases plasma parameters. Electron temperatures up to ≈0.9 keV and densities up to ≈2.4 × 10¹⁹ m⁻³ had been achieved, and the maximum value of &lt;<italic toggle=\"yes\">β</italic>_dia&gt; was 2.6%. These experiments open possibilities for new regimes of LHD operation which are also interested to W7-X.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"18 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211969","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":"The multi-faced nature of the quasicoherent mode in EDA H-mode","authors":"G. Grenfell, L. Gil, P. Manz, C. Silva, J. Adamek, D. Brida, G.D. Conway, T. Eich, M. Faitsch, T. Happel, M. Spolaore, U. Stroth, B. Tal, B. Vanovac, E. Wolfrum, the ASDEX Upgrade Teama, the EUROfusion Tokamak Exploitation Teamb","doi":"10.1088/1741-4326/ad751b","DOIUrl":"https://doi.org/10.1088/1741-4326/ad751b","url":null,"abstract":"In order to extend the enhanced D-Alpha H-mode to future devices, it is crucial to understand the properties of the main signature of this regime, the quasicoherent mode (QCM), that likely clamps the pressure gradient below the ideal magnetohydrodynamic limit. The turbulent character of the QCM is investigated with scanning probes in ASDEX Upgrade. Analysis reveals the multi-faced character of the mode that spans both the confined region (where the radial electric field is negative) and the near scrape-off layer (SOL) (where it is positive). Fluctuations of density and potential at the QCM frequency are more anti-correlated towards the confined region, which is a fingerprint of electromagnetic instabilities, while they become more correlated in the SOL, as expected for a drift-wave, inducing cross-field transport across the separatrix.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"13 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211971","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":"Disappearance of dimits shift in realistic fusion reactor plasmas with negative magnetic shear","authors":"Dingkun Yang, Shengming Li, Yong Xiao, Zhihong Lin","doi":"10.1088/1741-4326/ad703d","DOIUrl":"https://doi.org/10.1088/1741-4326/ad703d","url":null,"abstract":"This study employs gyrokinetic simulations to investigate ion temperature gradient (ITG) turbulence in realistic fusion reactor plasmas featuring reversed magnetic shear. The weakly negative magnetic shear is observed to be more stable for the ITG instability than strongly positive shear in this equilibrium configuration, primarily stemming from the scarcity of mode rational surfaces induced by the weak negative shear. This superiority in suppression for the negative shear persists in nonlinear turbulence with zonal flow artificially eliminated, where the emergence of turbulence solitons is observed and found associated with locally dense mode rational surfaces. However, the difference in transport levels among different magnetic shears diminishes in the presence of self-consistently generated zonal flow, accompanied by the disappearance of turbulence solitons. The nonlinear generation of zonal flow is found to be significantly affected by the magnetic shear. The study reveals a remarkable phenomenon that the Dimits shift no longer exists for negative magnetic shear, which is attributed to the weakness of the zonal flow generation near the ITG marginal stability.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"5 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211968","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":"An integral approach to plasma-wall interaction modelling for EU-DEMO","authors":"D. Matveev, C. Baumann, J. Romazanov, S. Brezinsek, S. Ratynskaia, L. Vignitchouk, P. Tolias, K. Paschalidis, D. Tskhakaya, M. Komm, A. Podolník, J. Mougenot, Y. Charles, R. Delaporte-Mathurin, E. Hodille, C. Grisolia, F. Montupet-Leblond, K. Schmid, U. Von Toussaint, F. Granberg, F. Kporha, J. Kovačič, S. Costea","doi":"10.1088/1741-4326/ad73e7","DOIUrl":"https://doi.org/10.1088/1741-4326/ad73e7","url":null,"abstract":"An integral approach to plasma-wall interaction (PWI) modelling for DEMO is presented, which is part of the EUROfusion Theory and Advanced Simulation Coordination activities that were established to advance the understanding and predictive capabilities for the modelling of existing and future fusion devices using a modern advanced computing approach. In view of the DEMO design, the aim of PWI modelling activities is to assess safety-relevant information regarding the erosion of plasma-facing components (PFCs), including its impact on plasma contamination, dust production, fuel inventory, and material response to transient events. This is achieved using a set of powerful and validated computer codes that deal with particular PWI aspects and interact with each other by means of relevant data exchange. Steady state erosion of tungsten PFC and subsequent transport and re-deposition of eroded material are simulated with the ERO2.0 code using a DEMO plasma background produced by dedicated SOLPS-ITER simulations. Dust transport simulations in steady state plasma also rely on the respective SOLPS-ITER solutions and are performed with the MIGRAINe code. In order to improve simulations of tungsten erosion in the divertor of DEMO, relevant high density sheath models are being developed based on particle-in-cell (PIC) simulations with the state-of-the-art BIT code family. PIC codes of the SPICE code family, in turn, provide relevant information on multi-emissive sheath physics, such as semi-empirical scaling laws for field-assisted thermionic emission. These scaling laws are essential for simulations of material melting under transient heat loads that are performed with the recently developed MEMENTO code, the successor of MEMOS-U. Fuel retention simulations assess tritium retention in tungsten and structural materials, as well as fuel permeation to the coolant, accounting for neutron damage. Simulations for divertor monoblocks of different sizes are performed using the FESTIM code, while for the first wall the TESSIM code is applied. Respective code-code dependencies and interactions, as well as modelling results achieved to date are discussed in this contribution.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"71 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211970","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":"Achievement of the first tokamak plasma with low inductive electric field in JT-60SA","authors":"T. Wakatsuki, H. Urano, M. Yoshida, N. Tsujii, S. Inoue, S. Kojima, T. Nakano, M. Fukumoto, Y. Ohtani, R. Sano, S. Ide","doi":"10.1088/1741-4326/ad75a7","DOIUrl":"https://doi.org/10.1088/1741-4326/ad75a7","url":null,"abstract":"The world’s largest superconducting tokamak, JT-60SA, has successfully achieved its first plasma operation under the constraint of a low toroidal inductive electric field of 0.15 V m⁻¹. A plasma start-up scenario, leveraging the effective confinement of electrons accelerated by the electron cyclotron wave, proved to be instrumental in reaching this milestone under the challenging conditions. The demonstration of plasma start-up using second harmonic electron cyclotron heating, with an applied toroidal electric field of 0.15 V m⁻¹, strongly validates the feasibility of achieving first plasma operation in ITER.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"12 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211972","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":"A long-pulse small edge-localized-mode high-confinement plasma with detachment feedback control by floating potential in an experimental advanced superconducting tokamak in a metal wall environment","authors":"G.F. Ding, G.S. Xu, Y.Q. Tao, K. Wu, L. Yu, X. Lin, L.Y. Meng, L. Wang, Q.Q Yang, R. Chen, R.R. Liang, K.D. Li, Q. Zang, Z.Q. Zhou, Q.P. Yuan, J.C. Xu","doi":"10.1088/1741-4326/ad6f28","DOIUrl":"https://doi.org/10.1088/1741-4326/ad6f28","url":null,"abstract":"One of the key challenges facing magnetic fusion research is to demonstrate the compatibility between high confinement and radiative divertors in long-pulse discharges with a metal wall environment. A small edge-localized-mode (ELM) high-confinement plasma with an energy confinement factor <italic toggle=\"yes\">H</italic>₉₈ ∼ 1.1 and Greenwald density fraction <italic toggle=\"yes\">f</italic>_GW ∼ 0.65 maintained for 26 s is obtained in the upgraded lower divertor of the Experimental Advanced Superconducting Tokamak (EAST), and periodical detachment is achieved through active control of neon impurity seeding in this long-pulse discharge. For the divertor region, partial detachment is achieved periodically on the outer divertor target plates with the plasma temperature near the outer strike point decreasing to below 5 eV and the peak surface temperature on the outer divertor target plates maintained below 350 °C. The peak heat flux of the lower outer divertor decreases significantly and its profile along the target becomes very flat in the detached state. Two low-frequency (&lt;10 kHz) fluctuations that are related to the rippling mode caused by a resistive instability appear in the detached state. For the pedestal region, the electron pressure profile is flatter and the ELM amplitude is smaller in the detached state than that in the attached state. Edge-coherent mode appears in the attached state and disappears in the detached state. To achieve this experimentally, a new impurity seeding feedback control scheme is applied, where the floating potential measured by divertor Langmuir probes is used as a feedback sensor, which is more reliable in long-pulse discharges with high heat fluxes and thus more suitable for application in future devices. This study provides a new approach for the actively controlled radiative divertor as a solution to the divertor heat loads of future fusion reactors.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"46 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211967","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":"Nonlinear MHD modeling of neon doped shattered pellet injection with JOREK and its comparison to experiments in KSTAR","authors":"S.-J. Lee, D. Hu, M. Lehnen, E. Nardon, Jayhyun Kim, D. Bonfiglio, F.J. Artola, M. Hoelzl, Yong-Su Na, JOREK teama","doi":"10.1088/1741-4326/ad6ea1","DOIUrl":"https://doi.org/10.1088/1741-4326/ad6ea1","url":null,"abstract":"3D nonlinear MHD simulations of neon-doped single shattered pellet injection (SPI) conducted with the JOREK code reveal rich physics during SPI-induced disruptions in KSTAR. In the early phase, pressure-driven modes dominate, and the perturbation of the plasma current is largely consistent with the perturbation of the Pfirsch–Schlüter current. As shards reach the <italic toggle=\"yes\">q</italic> = 1 surface, resistive current perturbations by helical electron cooling start to dominate, and the electron temperature in the core begins to collapse with convective mixing of the density driven by the internal <inline-formula>\u0000<tex-math><?CDATA $1/1$?></tex-math><mml:math overflow=\"scroll\"><mml:mrow><mml:mn>1</mml:mn><mml:mrow><mml:mo>/</mml:mo></mml:mrow><mml:mn>1</mml:mn></mml:mrow></mml:math><inline-graphic xlink:href=\"nfad6ea1ieqn1.gif\"></inline-graphic></inline-formula> kink mode. The confinement of the plasma is later completely destroyed as a cold bubble convects into the core via quasi-interchange mode. Comparisons with available experimental data demonstrate qualitative agreements between JOREK results and experiments, and possible reasons for deviations are discussed.","PeriodicalId":19379,"journal":{"name":"Nuclear Fusion","volume":"28 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2024-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211973","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}