The plasma in a tokamak fusion reactor would have a major diameter in the range of 10 metres (33 feet) and a minor diameter of roughly 2 to 3 metres. The transport of radial pressure and current density caused by heat and current drive sources is not modelled. 12, 424434 (2016). the spheromak and the Field-Reversed Configuration, attempt to combine the good confinement of closed magnetic surfaces configurations with the simplicity of machines without a central core. Fusion Eng. This demonstrates accurate control of a complex time-varying target with several coupled objectives. Cassirer, A. et al. 4a), without being explicitly told to do so. Overview of the ITER TBM Program. We successfully produce and control a diverse set of plasma configurations on the Tokamak Configuration Variable1,2, including elongated, conventional shapes, as well as advanced configurations, such as negative triangularity and snowflake configurations. Open Access J. Nucl. All tasks are performed successfully, with a tracking accuracy below the desired thresholds. Additionally, the network needs to perform this inference to sufficient numerical accuracy on the control system, which uses a different processor architecture from the hardware used for training. a,bPhotographs showing the part of the TCV inside the bioshield. This current is called the bootstrap current. We also controlled shape and plasma current to their target values, with an Ip RMSE of 1.2kA and shape RMSE of 1.6cm. The control policies are learned through interaction with a tokamak simulator and are shown to be directly capable of tokamak magnetic control on hardware, successfully bridging the sim-to-real gap. and JavaScript. When the tokamak was introduced in 1968, interest in the stellarator vanished, and the latest design at Princeton University, the Model C, was eventually converted to the Symmetrical Tokamak. This architecture meets control objectives specified at a high level, at the same time satisfying physical and operational constraints. An unavoidable diffusion of energy across the magnetic field lines will occur from the collisions between the particles. A Conceptual Study of Commercial Fusion Power Plants; (European Fusion Development Agreement, 2005); https://www.euro-fusion.org/wpcms/wp-content/uploads/2012/01/PPCS_overall_report_final-with_annexes.pdf, Safety and Environmental Impact of Fusion (European Fusion Development Agreement, 2001); https://www.euro-fusion.org/wpcms/wp-content/uploads/2012/01/SEIF_report_25Apr01.pdf. Lett. Hoffman, M. et al. This has the effect of propagating the nuclei from the inside to outside as it orbits the device, thereby cancelling out the drift across the axis, at least if the nuclei orbit fast enough. The aforementioned characteristics should be readily available, as these are typically part of the design process for a given tokamak. In Proc. The program is installing additional tools to optimize tokamak operation and exploring edge plasma and materials interactions. Mazon, D., Fenzi, C. & Sabot, R. As hot as it gets. Angioni, C. et al. Plasmas 20, 092509 (2013). B. et al. First, a designer specifies objectives for the experiment, potentially accompanied by time-varying control targets. The evolution of total plasma current Ip is modelled using a lumped-circuit equation. Nucl. Provided by the Springer Nature SharedIt content-sharing initiative, Science China Physics, Mechanics & Astronomy (2023). Fusion 47, 315 (2005). 12, 384386 (2016). In contrast, an unstable plasma would likely depart from its equilibrium state and rapidly (perhaps in less than one-thousandth of a second) escape the confining magnetic field following any small perturbation. Chapter 3: MHD stability, operational limits and disruptions. Magnetic confinement fusion: a brief review Chuanjun Huang & Laifeng Li Frontiers in Energy 12 , 305-313 ( 2018) Cite this article 824 Accesses 4 Citations Metrics Abstract Fusion energy is considered to be the ultimate energy source, which does not contribute to climate change compared with conventional fossil fuel. Magnetized liner inertial fusion (MagLIF) is an emerging method of producing controlled nuclear fusion. We applied targeted parameter variation during training across an appropriate range for the plasma pressure, current density profile and plasma resistivity through analysis of experiment data, to account for varying, uncontrolled experimental conditions. Mele, A. et al. Fusion 54, 125001 (2014). Google Scholar. Plasma wall interaction in long-pulse helium discharge in LHD Microscopic modification of the wall surface and its impact on particle balance and impurity generation. We obtained a good match between the targeted and the desired elongation, with an RMSE of 0.018. Open Access articles citing this article. Kaye, S. M. & Goldston, R. J. The architecture was able to successfully stabilize droplets over the entire 200ms control window and ramp the current within each domain, as shown in Fig. 99, 035002 (2007). These may be grouped into two classes: closed, toroidal configurations and open, linear configurations. D.P., F.F., J.B., J.D., M.R. In the standard setup, the critic network is much larger than the policy network (718,337 parameters compared with 266,280 parameters) and also uses a recurrent LSTM. 7, 206217 (1995). Wolf et al 2017 Nucl. Simulations of tokamak plasmas for magnetic fusion using a finite On multi-objective policy optimization as a tool for reinforcement learning. 1b. Des. Austin, M. E. et al. 394, 594614 (2019). The high-speed ions travel toroidally along the magnetic field and collide with the electrons, pushing them in one direction and thereby producing a current. The magnetic pressure offsets the plasma pressure. We also plot the growth rate, , and the plasma current, Ip, along with the associated target value. By submitting a comment you agree to abide by our Terms and Community Guidelines. Internet Explorer). Nature Phys 12, 398410 (2016). Phys. Only a few months after its public announcement in January 1958, these claims had to be retracted when it was discovered the neutrons being seen were created by new instabilities in the plasma mass. Lister, J. This loose specification gives the architecture the freedom to choose how to best adapt the droplet shapes as Ip increases to maintain stability. This approach could be applied to larger fusion devices like ITER and contribute to core-edge integration in future fusion power plants. Porkolab, M. RF heating and current drive in magnetically confined plasma: ahistorical perspective. Inertial confinement uses laser beams or ion beams to squeeze and heat the hydrogen plasma. Correspondence to In magnetic confinement the particles and energy of a hot plasma are held in place using magnetic fields. Lett. The first successful human-made fusion device was the boosted fission weapon tested in 1951 in the Greenhouse Item test. Preprint at https://arxiv.org/abs/2106.08199 (2021). C.G., D.C., F.F., J.B., J.D., M.N., S.N. This time-varying trace of targets is defined by a sequence of values at points in time, which are linearly interpolated for all time steps in between. Overview of JET results. Fusion 38, 1055 (1998). Activation analyses updating the ITER radioactive waste assessment. Furthermore, RL greatly simplifies the control system. Turbulence in the plasma has proven to be a major problem, causing the plasma to escape the confinement area, and potentially touch the walls of the container. Nucl. Fusion 47, S1S414 (2007); corrigendum 48, 099801 (2008). Additionally, the set of control targets can be expanded, for example, to reduce target heat loads through flux expansion5, aided by the use ofprivileged information in the critic to avoid requiring real-time observers. The precise reward definitions used in each of our experiments are listed in Extended Data Table 3 and the implementations are available in the supplementary material. & Tang, W. Predicting disruptive instabilities in controlled fusion plasmas through deep learning. Magnetic control of tokamak plasmas through deep reinforcement learning Confinement and heating of a deuteriumtritium plasma. Confinement alternatives Magnetic. Helander, P. Theory of plasma confinement in non-axisymmetric magnetic fields. These are all independently sampled from a parameter-specific log-uniform distribution. In the stellarator the magnetic field is produced by external coils only. Abadi, M. et al. Dumont, R. J. et al. 53, 943952 (2008). Nucl. In the case of a vector-valued objective (for example, distance to each target-shape point), the individual differences are first merged into a single scalar through a combiner, a weighted non-linear function. To obtain The toroidal field is produced by coils that surround the toroidal vacuum chamber containing the plasma. This technique efficiently drives a pulsed plasma current. Pace, D. C. et al. Software available from https://www.tensorflow.org/ 2015. What Does Magnetic Confinement Mean? Early use of neural networks in a control loop for plasma control is presented by Bishopetal.15, who used a small-scale neural network to estimate the plasma position and low-dimensional shape parameters, which were subsequently used as error signals for feedback control. Fusion 55, 124041 (2013). Both RF and neutral-beam current-drive techniques have a low efficiency (i.e., they require a large amount of power to drive the plasma current). We therefore use a fast, four-layer feedforward neural network in the actor (Fig. Seo, J. et al. Fusion Reactors: Magnetic Confinement - How Nuclear Fusion Reactors Finally, we use a last linear layer to output the Q-value. Rev. These bent the plasma into a new shape that was concave at all points, avoiding the problem Teller had pointed out. Source data are provided with this paper. The interaction trajectories are sampled at random from the buffer by a learner, which executes the MPO algorithm to update the control-policy parameters. The green line shows the RMSE distance between the LCFS in the two experiments, providing a direct measure of the shape similarity between the two shots. Resilience of quasi-isodynamic stellarators against trapped-particle instabilities. The plasma is, in turn, modelled by the GradShafranov equation21, which results from the balance between the Lorentz force and the pressure gradient inside the plasma on the timescales of interest. MathSciNet 3, with further detail in Extended Data Fig. 48, 207221 (1988). and T.E. Lawson criterion - Wikipedia Injecting impurities heavier than the plasma particles into the plasma and power exhaust region (the Divertor) is crucial for cooling the plasma boundary without affecting the fusion performance. The net effect is to transport energy from the hot core to the wall. Toroidal devices are the most highly developed. Recently, Seoetal.49 have developed feedforward signals for beta control using RL, which have then been verified on the KSTAR tokamak. Plasma Phys. In the meantime, to ensure continued support, we are displaying the site without styles 2. Vlad, G. et al. and P.K. (The plasma must be situated within an evacuated chamber to prevent it from being cooled by interactions with air molecules.) Therefore we created a deployment system that compiles our neural network into real-time-capable code that is guaranteed to run within this time window. Magnetic control of tokamak plasmas through deep reinforcement learning, https://doi.org/10.1038/s41586-021-04301-9. 49, 14081412 (1982). Each experiment begins with standard plasma-formation procedures, in which a traditional controller maintains the location of the plasma and total current. This arrangement generated a field that extended only part way into the plasma, which proved to have the significant advantage of adding "shear", which suppressed turbulence in the plasma. Hilbert expansion based fluid models for kinetic equations describing Degrave, J., Felici, F., Buchli, J. et al. Energy confinement scaling in Tokamaks: some implications of recent experiments with Ohmic and strong auxiliary heating. Our control architecture can naturally choose to use a varying combination of poloidal field and ohmic coils to drive the inductive voltage required for sustaining the plasma current (Extended Data Fig. Nucl. A large part of the problem of fusion has been the attainment of magnetic field configurations that effectively confine the plasma. Joung, S. et al. Phys. Keilhacker, M. et al. The authors declare no competing financial interests. It makes use of the conductivity of plasma in order to confine it within magnetic fields. 1, 315330 (IAEA, 1997). Compact toroids, e.g. Control. consulted for the project. RL has not, however, been used for magnetic controller design, which is challenging due to high-dimensional measurements and actuation, long time horizons, rapid instability growth rates and the need to infer the plasma shape through indirect measurements. The ITER magnet systems: progress on construction. FIP/1-1. Google Scholar. Density peaking, anomalous pinch, and collisionality in tokamak plasmas. Bosch, H.-S. et al. This equilibrium must be stable, which is to say that the plasma will return to its original state following any small perturbation, such as continual random thermal noise fluctuations. Each demonstration has its own time-varying targets but, otherwise, uses the same architectural setup to generate a control policy, including the training and environment configuration, with only minor adjustments to the reward function (shown in Extended Data Table 3). MagLIF has characteristics of both inertial confinement fusion (due to the usage of a laser and pulsed compression) and magnetic confinement . It can be considered a type of thermoelectric effect, but its origin is in the complex particle dynamics that arise in a toroidal plasma. Next, ramp the plasma current to 150kA and then elongate the plasma from 1.24 to 1.44, thereby increasing the vertical instability growth rate to 150Hz. It then manipulated the far X-point to approach the limiting X-point, ending with a separation of 6.6cm. In the experiment with droplets, we vary the initial ohmic coil current values according to a uniform distribution. In the tokamak a current is periodically driven through the plasma itself, creating a field "around" the torus that combines with the toroidal field to produce a winding field in some ways similar to that in a modern stellarator, at least in that nuclei move from the inside to the outside of the device as they flow around it. 1h). https://doi.org/10.1038/nphys3745. Rev. Ishida, S. et al. Each of the MLP layers uses an exponential linear unit non-linearity. A solenoid located in the hole of the torus can be used to generate magnetic flux that increases over time. Fusion 26, 87103 (1984). How does magnetic confinement fusion work? | Eni Magnetic confinement is a mechanism used in the generation of fusion power. d, An illustration of the difference in cross sections between two different shots, in which the only difference is that the policy on the right was trained with a further reward for avoiding X-points in vacuum.
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