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USBPO Mission Statement: Advance the scientific understanding of burning plasmas and ensure the greatest benefit from a burning plasma experiment by coordinating relevant U.S. fusion research with broad community participation.

CONTENTS

Announcements
Director’s Corner	C.M. Greenfield
Research Highlight	Francesca M. Poli
Schedule of Burning Plasma Events
Contact and Contribution Information

 

ITER internships

An announcement for ITER internship opportunities for undergraduate and graduate students was recently posted. Please see the following link for a description: https://www.iter.org/jobs/internships

The proposed topics can be found here:

https://www.iter.org/doc/www/content/com/Lists/WebText_2014/Attachments/321/Call_for_topics-Internship_2018_V3.pdf

 

 

By C.M. Greenfield

This is our first issue of 2018 and I’d like to take the opportunity to wish all of our readers a Happy New Year.

ITER is moving ahead

Preparations continue to progress rapidly on the ITER site, with construction having recently passed the halfway-to-first-plasma point. Some of you have asked exactly what it means for ITER to be 50% complete, and the ITER Organization heard you (https://www.iter.org/newsline/-/2894). The short answer is that every task included in preparing the facility was assigned a value in “ITER Units of Account” (IUA). At the beginning of the project this was a tool that allowed dividing up the scope among the ITER parties on a level basis, but it can also be used as a scorecard as we move along. By this measure, when we reach 100% we’ll be ready for first plasma. If you want a more thorough explanation please click on the above link.

By this measure, ITER passed the 50% mark in November, and progress has continued, with the bioshield that will surround the tokamak being completed this month. ITER component building is in full swing in all seven domestic agencies.

Just to remind you, there is a lot of information about ITER available at http://iter.org, including the weekly ITER Newsline (you can subscribe to it and have it show up in your inbox every week). You can also find information about jobs at ITER there. Which leads me to…

Monaco/ITER Postdoctoral Fellowship program

The ITER Organization is recruiting now for the Monaco/ITER Postdoctoral Fellowship program. If you are a national of one of the ITER Members (China, the European Union plus Switzerland, India, Japan, Korea, Russia and the US) or of the Principality of Monaco—and your PhD was awarded after 1 January 2015 (or will be awarded soon)—you may be eligible for a two-year postdoctoral position in the ITER Organization.

More information about the program and all application information can be found at https://www.iter.org/monaco2018. Applications close 1 March 2018.

National Academies study

The National Academies study on A Strategic Plan for U.S. Burning Plasma Research recently published their interim report (https://www.nap.edu/catalog/24971/interim-report-of-the-committee-on-a-strategic-plan-for-us-burning-plasma-research). I strongly recommend having a look at the report yourself, but I would like to highlight two of the seven assessments given in the opening summary of the report:

Assessment 1: Burning plasma research is essential to the development of magnetic fusion energy and contributes to advancements in plasma science, materials science, and the nation’s industrial capacity to deliver high-technology components.

Assessment 6: Any strategy to develop magnetic fusion energy requires study of a burning plasma. The only existing project to create a burning plasma at the scale of a power plant is ITER, which is a major component of the U.S. fusion energy program. As an ITER partner, the United States benefits from the long-recognized value of international cooperation to combine the scientific and engineering expertise, industrial capacity, and financial resources necessary for such an inherently large project. A decision by the United States to withdraw from the ITER project as the primary experimental burning plasma component within a balanced long-term strategic plan for fusion energy could isolate U.S. fusion scientists from the international effort and would require the United States to develop a new approach to study a burning plasma.

The committee is still inviting the community to submit input by the end of March, 2018, using the Community Input Form at http://sites.nationalacademies.org/BPA/BPA_177107.

A second and final report will provide greater detail on the options for a long-term strategic plan for a national program of burning plasma science and technology research, including developing various supporting capabilities and participating in international activities. Strategic guidance for scenarios where the United States both is and is not a participant in ITER will be described. To the extent possible, the final report will include considerations of the health of fusion research sectors within the United States, the role of international collaboration in the pursuit of national fusion energy goals, the capability and prospects of private-sector ventures to advance fusion energy concepts and technologies, the impact of science and technology innovations, and the design of research strategies that may shorten the time and reduce the cost required to develop commercial fusion energy.

Break out the popcorn!

EyeSteelFilm has produced a 90 minute documentary on fusion and ITER, entitled “Let There Be Light.” Some of you have had a chance to see it recently, but now it is available for free viewing by Amazon Prime members. It is also available for rent or purchase on the Vimeo platform. Subtitled ''The 100 Year Journey to Fusion,'' the documentary shows work underway around the world at both ends of the fusion spectrum—from the giant ITER Project to the warehouse-based startup. It has had success at film festivals in North America and Europe since its launch in early 2017.

 

Modeling and Simulation Topical Group (Leaders: Lang Lao & Xueqiao Xu)

This month’s research highlight by Dr. Francesca Poli of PPPL provides a comprehensive overview of integrated tokamak modeling activities. It includes a review of various approaches and components, updated international and national research status and challenges. Dr. Poli presented a tutorial talk on this subject at the recent APS-DPP 2017 meeting in Milwaukee.

Integrated tokamak modeling: present status and needs

Francesca M. Poli

Princeton Plasma Physics Laboratory, Princeton NJ 08543

Email: fpoli@pppl.gov

As of today, the tokamak represents the most promising concept towards a nuclear fusion reactor. Modeling tokamaks enables a deeper understanding of how to run and control experiments and how to design stable and reliable reactors. To this purpose, a tokamak simulator needs to provide the right balance between physics fidelity and computation turnaround to model the plasma dynamics during an entire discharge, from startup to termination [1].

The basic components of a tokamak simulator are the macroscopic plasma equilibrium, which evolves over the slower current diffusion time scales, and the profiles of density, temperature, momentum and current, which evolve over the faster transport time scales. Figure 1 depicts the main physics components that need to be modeled in a tokamak. Magnetic equilibrium and profiles evolve under the effect of external actuators, like sources of heating, current and momentum and injection of gas and solid pellets. Moving from the center to the wall, plasmas are colder, processes of ionization and recombination dominate and atomic physics becomes a critical contribution to the modeling of the plasma dynamics. In the absence of turbulence the transport would be described by collisional transport (neoclassical transport). Instead, it is observed that heat transport exceeds neoclassical levels by at least an order of magnitude, because of turbulence driven by low frequency, small-scales fluctuations that are excited by gradients in the density and temperature profiles. Understanding and modeling tokamak turbulent transport requires theory-based prediction of flux-gradient relationships and of the onset threshold for micro-turbulence instabilities. Reduced models for turbulent transport have been derived both from analytical models of electrostatic and electromagnetic gradient-driven instabilities, as well as from gyrokinetic equations. The quest for fast, reduced models for real-time control applications has further driven the development of neural networks for transport solvers [2,3].

Most time-dependent transport solvers used nowadays for scenario modeling include a range of physics-based models for core transport predictions and heating and current drive sources, with different levels of fidelity. Examples of time-dependent solvers include CORSICA, TRANSP and TSC in the United States, ASTRA, CRONOS and JINTRAC in Europe and TOPICS in Japan. Over the past ten years, tokamak simulators have undergone significant improvement in their predictive capabilities to include reduced full wave solvers and ray-tracing calculations coupled to Fokker-Planck solvers to model the propagation of electromagnetic waves, and high fidelity orbit following Monte Carlo codes for Neutral Beam injection. The most advanced solvers include self-consistent calculations of core and edge transport, with transport prescription to account for the regulating effect of Edge Localized Modes in the pedestal region. While increasing the number of modules in a tokamak simulator is required to enhance its inclusiveness, it is imperative to maintain a good computation turnaround time. An example is the extension of integrated modeling to self-consistent simulations that include both the core and the edge of the plasma, which is a big challenge, because of the multi-scale and multi-physics characteristics of the plasma boundary.

The plasma boundary consists of three distinct regions across the plasma separatrix (Fig.2): the pedestal (shaded red region), the Scrape-Off-Layer (SOL, blue shaded region) and the wall and divertor plates (right margin of the plot). Moving from the pedestal to the wall the plasma temperature decreases by about four orders of magnitude and the plasma becomes highly collisional. Because of the large gradients in the density, temperature and current profile, spatial scale separation is no longer valid in the plasma boundary. Here the typical scale lengths of macroscopic profiles overlap with turbulence scales and particle drift orbits and time scales can span six orders of magnitude. Detailed simulations of these processes present computational challenges that make the modeling of the plasma boundary possible only on exascale computers. Workflows have been extremely valuable to demonstrate converged solutions of core transport and pedestal stability [4] and then extend these solutions to the coupling with a two-dimensional model for the Scrape-Off-Layer and a MonteCarlo model for the neutrals transport [5].

Workflows have an important role: explore efficient ways to integrate and couple multiple physics models, support models with varying levels of physics hierarchy for given physics phenomena, support a flexible approach to tokamak plasma simulations. They provide an interface with experimental data, with data processing tools and with a number of physics models for transport, heating and current drive, MHD stability and edge transport. Based on open collaboration, workflows have great potential for rapid expansion towards the development of a Whole Device Model, because they provide an ideal framework for code benchmarking, for verification of reduced models against first principle calculations, for validation of simulations against experiments and for uncertainty quantification [6,7].

Because the pedestal structure is a critical boundary condition for the core transport, developing better models for the transition to H-mode, for the particle and heat fluxes across the separatrix that include the contribution of micro-turbulence, MHD instabilities, coherent structures in the SOL and kinetic effects that differentiate between the ion and electron transport in the pedestal region is highest priority. This is an area where gyrokinetic simulations and Vlasov approaches that include the core and edge plasma can help developing better models for the formation of the edge transport barrier.

A reduced model of the plasma boundary would improve the calculation of propagation and losses of Ion Cyclotron and Lower Hybrid waves in the Scrape-Off-Layer and of the atomic processes undergone by neutral beam fast ions. Hybrid approaches to the modeling of RF wave propagation have recently been proposed [8] and are a promising avenue towards implementation in a tokamak simulator. They use the standard Fourier approach on an axisymmetric flux surface grid in the confined plasma to represent the hot plasma conductivity, an unstructured mesh in the edge to accommodate arbitrary antenna geometry for the representation of the collisional plasma and a matching technique at the boundary between core and edge.

The performance of plasmas is limited by MHD instabilities, whose effect on the transport and on the self-regulating activity of the plasma needs to be taken into account. The presence of magnetic islands induced by tearing modes can not only reduce the confinement, but is detrimental for the stability of the plasma and can even lead to disruptions. Although a self-consistent approach in the modeling of the suppression of tearing modes would be possible only with 3D nonlinear MHD simulations, approaches based on a Modified Rutherford Equation (MRE) are possible in time-dependent simulations with limited computational efforts [9]. The main limitation of these reduced models based on a MRE is that they use a quasi-cylindrical approximation and do not include nonlinear interactions between tearing modes or with the internal kink. Reduced models for neoclassical tearing modes would benefit from a better estimate of the onset of instabilities, both from nonlinear MHD simulations and from analytic theory.

Significant improvement in the fidelity of the models used to simulate tokamak discharges has occurred over the past decade and the most advanced frameworks include today self-consistent solution of the core and edge plasma transport, as well as non-axisymmetric effects on the toroidal plasma rotation. Still, important opportunities exist to take greater advantage of physics understanding obtained from high-fidelity simulations. One of the great long-term challenges in integrated tokamak modeling is to address multiscale and multiphysics phenomena, such as the interaction between low toroidal number MHD instabilities (sawteeth and tearing modes) and short wavelength drift-like fluctuations. While high-fidelity MHD codes are not suitable for a direct coupling in a tokamak simulator because of their computational burden, they are critical for helping developing reduced models that can be used in time-dependent simulations to predict the onset of instabilities. Analytical theory should continue to be an important part towards the improvement of our models, since in some cases - like for Neoclassical Tearing Modes - an exhaustive theory for the onset is not available yet. Longer term challenges thus include derivation and numerical solution of unified extended-MHD/drift-wave equations that describe island formation currents, and drift-wave cross-field transport, with the ultimate capability of self-consistently simulating island evolution, saturation and stabilization via feedback.

The modeling of plasma rotation, either spontaneous or induced by external coils, is another field of research where more integrated solutions are needed. Reduced models for NTV would improve modeling and predicting capabilities of the plasma response under the effect of resonant magnetic perturbations, for ELM control and for plasma rotation control.

Alpha particles and fast ions, either from NBI or from IC, can excite weakly damped Alfven modes. The subsequent redistribution of fast particles might cause a reduction in the heating efficiency and in the performance, cause localized losses and damages to first-wall components when fast ions are expelled from the plasma. The effect of enhanced fast ion transport by instabilities should be included in time-dependent simulations for a correct accounting of the heating sources of thermal plasma (through slowing down), of the neutron rate and of transport induced by tearing modes. A fully self-consistent treatment of the fast ion interaction with instabilities is challenging, especially for time-dependent scenarios with varying parameters. As an alternative, several reduced fast ion transport models are being developed to account for enhanced energetic particle transport by instabilities in integrated tokamak simulations. Their inclusion in time-dependent simulations is an active line of research in fast ion physics. Most models target transport by Alfvenic instabilities, assuming that the saturation amplitude of the modes can be inferred from the existence of a critical gradient in either configuration space (i.e., flattening of the fast ion pressure vs radius) or in phase space (i.e., flattening of gradients in the constants of motion). At present, the latter approach is being pursued in the NUBEAM module of TRANSP by the inclusion of the so-called kick model [10], which provides a platform to include fast ion transport in phase space by prescribing transport probability matrices derived from either theory or other (first-principle) numerical codes.

The path forward to an efficient and all-inclusive tokamak simulator should look into advancing the theoretical and analytical understanding of the physics processes, while at the same time exploiting first principle numerical models to the understanding of multiscale and multi-physics interactions with the aim of developing validated, reduced models that can be used in time-dependent simulations for high-fidelity calculations and fast turnaround time.

Acknowledgements

This work is supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences under contract numbers DE-AC02-09CH11466.

References

[1] P. Bonoli and L. McInnes, “Workshop on integrated simulations for magnetic fusion technical report, united states department of energy,” (2015).

[2] O. Meneghini et al, Nucl. Fusion 57, 086034 (2017).

[3] J. Citrin et al, Nucl. Fusion 55, 092001 (2015).

[4] O. Meneghini et al, Phys. Plasmas 23, 042507 (2016).

[5] D. Green et al, “Integrated core, edge pedestal, and scrape-of-layer modeling,” US-TTF, 2017

[6] O. Meneghini et al, Nuclear Fusion 55, 083008 (2015).

[7] W. Elwasif et al, 18th Int. Conf. on Parallel, Distributed and Network-Based Processing (IEEE) (2010).

[8] J. C. Wright and S. Shiraiwa, AIP Conference Proceedings 1689, 050007 (2015).

[9] F. Poli et al, Nucl. Fusion 58, 016007 (2018).

[10] M. Podesta et al, Plasma Phys. Control. Fusion 59, 095008 (2017).

USBPO Public Calendar:

2018                                               

January 30-February 2	ITPA Scrape-off Layer & Divertor Topical Group meeting	Chengdu, China
March 5-9	ITPA MHD, Disruptions & Control Topical Group meeting	Naka, Japan
April 4-6	ITPA Pedestal & Edge Physics Topical Group meeting	Stockholm, Sweden
April 9-11	ITPA Transport & Confinement Topical Group meeting	Daejeon, South Korea
April 16-19	High Temperature Plasma Diagnostics (HTPD) conference	San Diego, CA
April 23-25	Sherwood Theory Conference	Auburn, AL
April 23-26	ITPA Diagnostics Topical Group meeting	San Diego, CA
April 23-26	ITPA Integrated Operating Scenarios Topical Group meeting	Daejeon, South Korea
May 8-11	US Transport Task Force (US-TTF) meeting	San Diego, CA
May 23-25	ITPA Energetic Particles Topical Group meeting	ITER HQ, France
June 17-22	International Conference on Plasma Surface Interactions (PSI)	Princeton, NJ
June 24-28	2018 IEEE International Conference on Plasma Science (ICOPS)	Denver, CO
July 2-6	EPS Conference on Plasma Physics	Prague, Czech Rep.
Sept 11-14	EU Transport Task Force (EU-TTF) meeting	Seville, Spain
October 22-27	IAEA Fusion Energy Conference	Gandhinagar, Gujarat, India
November 5-9	60th Annual Meeting of the APS Division of Plasma Physics	Portland, OR
November 11-15	ANS 23rd Topical Meeting on the Technology of Fusion Energy (TOFE)	Orlando, FL
November 12-18	2nd Asia-Pacific Conference on Plasma Physics	Kanazawa, Japan
December 4-6	ITPA Coordinating Committee & CTP ExComm	ITER HQ, France

2019

JET DT-campaign (https://www.euro-fusion.org/newsletter/jet-full-throttle/)
October 21-25	61st Annual Meeting of the APS Division of Plasma Physics	Fort Lauderdale, Florida, USA

2020

JT60-SA First Plasma (http://jt60sa.org/)

 

This newsletter provides a monthly update on U.S. Burning Plasma Organization activities. The USBPO operates under the auspices of the U.S. Department of Energy, Fusion Energy Sciences (FES) division. All comments, including suggestions for content, may be sent to the Editor. Correspondence may also be submitted through the USBPO Website Feedback Form.

Become a member of the U.S. Burning Plasma Organization by signing up for a topical group.

Editor: Walter Guttenfelder (wgutten@pppl.gov)

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