Overview of the SPARC tokamak Creely, A. J.; Greenwald, M. J.; Ballinger, S. B. ...
Journal of plasma physics,
10/2020, Letnik:
86, Številka:
5
Journal Article
Recenzirano
Odprti dostop
The SPARC tokamak is a critical next step towards commercial fusion energy. SPARC is designed as a high-field ($B_0 = 12.2$ T), compact ($R_0 = 1.85$ m, $a = 0.57$ m), superconducting, D-T tokamak ...with the goal of producing fusion gain $Q>2$ from a magnetically confined fusion plasma for the first time. Currently under design, SPARC will continue the high-field path of the Alcator series of tokamaks, utilizing new magnets based on rare earth barium copper oxide high-temperature superconductors to achieve high performance in a compact device. The goal of $Q>2$ is achievable with conservative physics assumptions ($H_{98,y2} = 0.7$) and, with the nominal assumption of $H_{98,y2} = 1$, SPARC is projected to attain $Q \approx 11$ and $P_{\textrm {fusion}} \approx 140$ MW. SPARC will therefore constitute a unique platform for burning plasma physics research with high density ($\langle n_{e} \rangle \approx 3 \times 10^{20}\ \textrm {m}^{-3}$), high temperature ($\langle T_e \rangle \approx 7$ keV) and high power density ($P_{\textrm {fusion}}/V_{\textrm {plasma}} \approx 7\ \textrm {MW}\,\textrm {m}^{-3}$) relevant to fusion power plants. SPARC's place in the path to commercial fusion energy, its parameters and the current status of SPARC design work are presented. This work also describes the basis for global performance projections and summarizes some of the physics analysis that is presented in greater detail in the companion articles of this collection.
•The ARC conceptual design study has been extended to include a divertor.•Long legged X-point target divertors are implemented with no impact on core plasma.•All superconducting coils are shielded ...and the tritium breeding ratio is ≈1.08.•An ITER-like tungsten swirl-tube cooling channel with molten FLiBe coolant is used.•The ARC reactor divertor design simplifies detachment control and diagnostics.
The ARC pilot plant conceptual design study has been extended beyond its initial scope B. N. Sorbom et al., FED 100 (2015) 378 to explore options for managing ∼525 MW of fusion power generated in a compact, high field (B0 = 9.2 T) tokamak that is approximately the size of JET (R0 = 3.3 m). Taking advantage of ARC’s novel design – demountable high temperature superconductor toroidal field (TF) magnets, poloidal magnetic field coils located inside the TF, and vacuum vessel (VV) immersed in molten salt FLiBe blanket – this follow-on study has identified innovative and potentially robust power exhaust management solutions. The superconducting poloidal field coil set has been reconfigured to produce double-null plasma equilibria with a long-leg X-point target divertor geometry. This design choice is motivated by recent modeling which indicates that such configurations enhance power handling and may attain a passively-stable detachment front that stays in the divertor leg over a wide power exhaust window. A modified VV accommodates the divertor legs while retaining the original core plasma volume and TF magnet size. The molten salt FLiBe blanket adequately shields all superconductors, functions as an efficient tritium breeder, and, with augmented forced flow loops, serves as an effective single-phase, low-pressure coolant for the divertor, VV, and breeding blanket. Advanced neutron transport calculations (MCNP) indicate a tritium breeding ratio of ∼1.08. The neutron damage rate (DPA/year) of the remote divertor targets is ∼3–30 times lower than that of the first wall. The entire VV (including divertor and first wall) can tolerate high damage rates since the demountable TF magnets allow the VV to be replaced every 1–2 years as a single unit, employing a vertical maintenance scheme. A tungsten swirl tube FLiBe coolant channel design, similar in geometry to that used by ITER, is considered for the divertor heat removal and shown capable of exhausting divertor heat flux levels of up to 12 MW/m2. Several novel, neutron tolerant diagnostics are explored for sensing power exhaust and for providing feedback control of divertor conditions over long time scales. These include measurement of Cherenkov radiation emitted in FLiBe to infer DT fusion reaction rate, measurement of divertor detachment front locations in the divertor legs with microwave interferometry, and monitoring “hotspots” on the divertor chamber walls via IR imaging through the FLiBe blanket.
Owing to its high magnetic field, high power, and compact size, the SPARC experiment will operate with divertor conditions at or above those expected in reactor-class tokamaks. Power exhaust at this ...scale remains one of the key challenges for practical fusion energy. Based on empirical scalings, the peak unmitigated divertor parallel heat flux is projected to be greater than 10 GW m−2. This is nearly an order of magnitude higher than has been demonstrated to date. Furthermore, the divertor parallel Edge-Localized Mode (ELM) energy fluence projections (~11–34 MJ m−2) are comparable with those for ITER. However, the relatively short pulse length (~25 s pulse, with a ~10 s flat top) provides the opportunity to consider mitigation schemes unsuited to long-pulse devices including ITER and reactors. The baseline scenario for SPARC employs a ~1 Hz strike point sweep to spread the heat flux over a large divertor target surface area to keep tile surface temperatures within tolerable levels without the use of active divertor cooling systems. In addition, SPARC operation presents a unique opportunity to study divertor heat exhaust mitigation at reactor-level plasma densities and power fluxes. Not only will SPARC test the limits of current experimental scalings and serve for benchmarking theoretical models in reactor regimes, it is also being designed to enable the assessment of long-legged and X-point target advanced divertor magnetic configurations. Experimental results from SPARC will be crucial to reducing risk for a fusion pilot plant divertor design.
PurposeThe main parties in construction projects are the engineers, clients, architects, contractors, material suppliers, and consultants such as the project managers. They play the most important ...roles in implementing construction projects, and their activities have a significant impact on their risk attitudes during the execution of projects. Because each participant has their particular interests, by proprietary information, each participant is driven to achieve maximum benefit, which can result in improper behaviour concerning each other. The risk in this situation is that there would be a moral hazard and adverse selection based on information asymmetry among principal construction participants especially contractors; this outcome is called risk attitudes. Behaviour is affected by various risk factors and the successful implementation of construction projects depends on effective management of the key risk factors part of which is a personal factor. The purpose of this paper is to identify the critical factors affecting contractors’ risk attitudes among Malaysian construction companies with the moderating role of government policy. Organizational control theory and expected utility theory were used to develop the theoretical framework. The study investigated G7 contractors in the Malaysian construction industry. Data were collected through the use of a questionnaire.Design/methodology/approachThe research analysis was based on structural equation modelling (SEM), and the research model was ascertained through the Smart PLS 3.0 software (Ringle et al., 2012). Partial least square-SEM is an appropriate analysis that was used to assess the results in the current research because its algorithm permits the unrestricted computation of cause-effect relationship models that use both reflective and formative measurement models. This study uses the quantitative method to identify the individual factors influencing contractors’ risk attitude and the moderating role of government policy among construction companies in Malaysia. This study also focussed on the G7 contractors operating in the Malaysia construction industry that specializes in building, bridge and road construction projects. The duration of the data collection was between two and three weeks. The questionnaire was prepared both in Malay and English languages to allow the respondents to respond most conveniently. Before the copies of the questionnaire were distributed, the selected contractors’ committees were duly informed about the details of the survey procedures. The adopted Likert scale was originally a five-point scale that ranges from “very low” to “very high” with “low or high” in between.FindingsThe result of this study moderately supports the hypothesized relationships proposed in the theoretical model. In particular, the results recommended that personal factors that affect risk attitudes (working experience, emotional intelligence, professional competence and physical health) have a significant relation with contractors’ risk attitudes in the construction companies in Malaysia. Also, it has been found that government policy (rules and regulations) are important determinants of risk attitudes.Research limitations/implicationsThe study focussed on individual factors affecting contractors’ risk attitudes in the construction company’s in Malaysia. Therefore, the dimensions of factors affecting risk attitudes can be used in another aspect of construction projects such as management factors, economic factors and technical factors. Therefore, further research might investigate other grades of Malaysian construction companies apart from Grade 7 contractors to know if there is a similarity in the results; other grades of the contractors might have potential positive contributions to the construction industry as well.Practical implicationsWith consider to the practical, the current research findings have several contributions for the contractors and project managers. The research results demonstrate that government policy plays an important role in the construction industry and organizational support will also help contractors to control their attitudes in working place. Individual factor has a direct relationship with contractor risk attitudes (CRA), project managers must ensure that the government policy has an impact in all their workers and offered is competitive, fair and by their employees’ contribution. Apart from that managers should also focus on organizational goals especially in managing professional and skilled contractors in the companies. Employees who perceived their employers as uncaring or not supporting their needs and well-being may not be happy working with the organization and the tendency for them to change their attitudes towards risk will be high.Social implicationsThis study also contributes knowledge by lending empirical support to the organizational control theory and expected utility theory system’s effect on CRA and confirming that changing one individual attitude will change the whole equilibrium. This is useful to aid in further synthesis of organizational control theory and expected utility theory in construction companies.Originality/valueThis study is the first attempt at evaluating the direct and moderating effect relationships among individual factor affecting risk attitudes, government policy and CRA in Malaysian construction companies. These findings also prop up the applicability of the organizational control theory and expected utility theory within the context of construction companies in Malaysia. Also, this study contributed to the literature on psychology by subjective (psychological) measures of individuals’ behaviour and decisions. In the CRA literature, there has been much discussion on personal characteristics to understand behaviours such as attitudes of a contractor towards risk and morals.
The Alcator C-Mod mirror Langmuir probe system has been used to sample data time series of fluctuating plasma parameters in the outboard mid-plane far scrape-off layer. We present a statistical ...analysis of one second long time series of electron density, temperature, radial electric drift velocity and the corresponding particle and electron heat fluxes. These are sampled during stationary plasma conditions in an ohmically heated, lower single null diverted discharge. The electron density and temperature are strongly correlated and feature fluctuation statistics similar to the ion saturation current. Both electron density and temperature time series are dominated by intermittent, large-amplitude burst with an exponential distribution of both burst amplitudes and waiting times between them. The characteristic time scale of the large-amplitude bursts is approximately 15 s . Large-amplitude velocity fluctuations feature a slightly faster characteristic time scale and appear at a faster rate than electron density and temperature fluctuations. Describing these time series as a superposition of uncorrelated exponential pulses, we find that probability distribution functions, power spectral densities as well as auto-correlation functions of the data time series agree well with predictions from the stochastic model. The electron particle and heat fluxes present large-amplitude fluctuations. For this low-density plasma, the radial electron heat flux is dominated by convection, that is, correlations of fluctuations in the electron density and radial velocity. Hot and dense blobs contribute only a minute fraction of the total fluctuation driven heat flux.
Abstract
The design and understanding of alternative divertor configurations may be crucial for achieving acceptable steady-state heat and particle material loads for magnetic confinement fusion ...reactors. Multiple X-point alternative divertor geometries such as snowflakes and X-point targets have great potential in reducing power loads, but have not yet been simulated widely in codes with kinetic neutrals. This paper discusses recent changes made to the SOLPS-ITER code to allow for the simulation of X-point target and low-field side snowflake divertor geometries. Snowflake simulations using this method are presented, in addition to the first SOLPS-ITER simulation of the X-point target. Analysis of these results show reasonable consistency with the simple modelling and theoretical predictions, supporting the validity of the methodology implemented.
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