QUASi-Axisymmetric Research (QUASAR) Experiment D. A. Gates1, A. Boozer2, T. E. Evans3, R. J. Goldston1, A. Hassam4, B. Lipschultz5, D. A. Maurer6, G.

H. Neilson1, R. Parker5, K. Tritz7, F. Volpe2, H. Weitzner8, G. A. Wurden9, M. C. Zarnstorff1 Princeton Plasma Physics Laboratory1 Auburn University6 Columbia University2 Johns Hopkins University7 General Atomics3 Courant Institute, New York University8 University of Maryland4 Los Alamos National Laboratory9 Plasma Science and Fusion Center, MIT5  

Research Description - Enabling world leading high temperature plasma science: Grade: (A) absolutely critical QUASAR is a new facility to solve two critical problems for fusion, disruptions and steady-state, and to provide new insights into the role of magnetic symmetry in plasma confinement. If constructed it will be the only quasi-axisymmetric (QA) stellarator in the world. QUASAR can be viewed as an advanced tokamak topologically modified using 3D shaping to improve stability and sustainment. The innovative principle of quasi-axisymmetry will be used in QUASAR to study how “tokamak-like” systems can be made:

1) Disruption-free, 2) Steady-state with low recirculating power,

while preserving or improving upon features of axisymmetric tokamaks, including

1) Stable at high pressure simultaneous with 2) High confinement (similar to tokamaks), and 3) Scalable to a low capital-cost reactor

Stellarator research is absolutely critical to the US fusion program because the physics basis of the tokamak to operate efficiently in steady-state, without disruptions at reactor-relevant parameters is not yet established. The large stellarator experiments with which the US is collaborating, - LHD in Japan and W7-X under construction in Germany - are facilities of enormous capabilities. However, LHD is not optimized for confinement and scales to a reactor of major radius R ~13m, and the optimized W7-X design extrapolates to a reactor with R ~ 20 m and aspect ratio ~ 11. The QUASAR design is unique in being optimized for confinement, stability, and moderate aspect ratio (4.5). It yields a reactor with a major radius of ~8m similar to advanced tokamak concepts. It is striking that (a) the EU DEMO is a pulsed (~2.5 hour) tokamak with major R ~ 9 m and (b) the ITER physics scenarios do not presume steady-state behavior. Accordingly, the stellarator is not merely a back-up, but a line of research equally important to tokamaks, and QUASAR is a mandatory component of the world stellarator program. Thus, QUASAR is “absolutely critical” for the development of fusion energy. With this experiment the US will have a facility clearly at the world forefront. Quasi-axisymmetry is the axial symmetry of the magnitude of the magnetic field, in magnetic coordinates [1, 2], and is a generalization of true axisymmetry of the vector magnetic field (such as in tokamaks). Quasi-symmetric stellarators, such as the quasi-helically-symmetric HSX stellarator in Wisconsin, are predicted and demonstrated to have good orbit and neoclassical confinement. The parameter that characterizes the neoclassical confinement in stellarators is called the effective helical ripple [3]. The helical ripple in QUASAR will be the lowest of any stellarator ever built, by making the magnitude of magnetic field be approximately constant in the toroidal direction. The QUASAR design uses this property of low helical ripple to capture the confinement properties of tokamaks while retaining the stability and steady-state properties of stellarators. One of the clear advantages of the stellarator concept is disruption immunity. A quasi-axisymmetric stellarator has a shape dominated by toroidicity, which is intrinsically

compatible with lower aspect ratio, and produces bootstrap current that increases the rotational transform. In current carrying stellarators, studies of the transition between tokamak-like and stellarator-like disruption behavior found that as long as the external transform (i.e the part of the rotational transform that is due to vacuum fields) exceeds 0.14 [4] disruptions are eliminated. QUASAR is designed to have an external transform fraction that is well above this, such that 75% of the transform is generated by the coils and 25% is from the bootstrap current. As a result QUASAR is predicted to be resilient to disruptions, and this will be validated experimentally. Because a stellarator does not require plasma current to create its magnetic equilibrium, it is an inherently steady-state solution to magnetic fusion energy. Moreover, studies of quasi-axisymmetric stellarator reactor designs have indicated that it is substantially easier to achieve high fusion energy gain, with Qeng >>1 [5] (where Qeng is the ratio of electric power produced to that consumed) because of lower re-circulating power (no current drive required). While this feature of stellarators is inherent so does not require dedicated research, it is a strong primary motivation for stellarator research. QUASAR will study the role of magnetic symmetry in plasma confinement. An important property is plasma confinement at high plasma pressure as a result of a design optimization process that eliminated all known large-scale plasma instabilities [6]. Another important prediction of quasi-axisymmetry is the ability to support relatively large plasma flows, which have been shown in tokamaks to suppress the small-scale instabilities that lead to turbulent energy loss. The similarity between the QA stellarator and the axisymmetric tokamak has enabled the knowledge gained in tokamak research to be applied directly to the design of the QUASAR device. Further optimization studies indicate that it may be possible to minimize small-scale turbulence by exploiting plasma-shaping capabilities. Flexible shaping design allows for experiments that investigate equilibria that may substantially improve the plasma energy confinement, providing a powerful test of micro-turbulence theory [7]. QUASAR experiments will validate the extensive numerical models and optimization methods used in its design and the associated 3D science will inform tokamaks in areas such as Edge Localized Mode (ELM) control, divertor heat control, and error field penetration. Because of the above stated features, QA stellarators have been shown to scale to low capital cost reactors using conservative physics assumptions. In particular both the ARIES-CS and PPPL pilot plant studies showed that a QA based reactor had similar cost characteristics to advanced tokamak designs, but with a more plausible steady state scenario. Device description QUASAR is a Proof-of-Principle scale device designed [8] to demonstrate simultaneous good confinement and high β using the QA principle. The stellarator fields are provided by

modular coils with additional flexibility provided by toroidal and poloidal field coil set. In addition, a complete set of trim coils allows for error field correction, error field studies, and limited 3D shaping capability. The modular coils are liquid nitrogen cooled to provide extended pulse length. A table of machine parameters is given in Table 1. A photograph showing a partially assembled field period is given in Figure 1, along with a view of a 3-pack of modular field coils. The primary heating system will be neutral beams.

Parameter   Value  Major  Radius   1.4m  Maximum  axial  field   2.0Tesla  Pulse  length   0.5(max  field)-­‐2.0sec(@1.0Tesla)  External  iota   0.0-­‐0.9  Heating  power   6MW  NBI  (+6MW  RF  -­‐  upgrade)  

Table 1: QUASAR device parameters

QUASAR in the international context As the only quasi-axisymmetric stellarator in the world, QUASAR’s uniqueness in the international context is essentially guaranteed. Letters in support of the QUASAR facility from leaders of the Chinese, German, and Japanese fusion programs have been submitted along with this white paper. The Chinese have offered significant in kind contributions (see Estimated Cost section below)  because the contributions of QUASAR are so strongly needed. Such a material contribution is quite unusual, indicating that the international support is remarkably strong, typified by the comment in the letter from the full scientific directorate of the Max Planck Institute for Plasma Physics that QUASAR would “be the most innovative fusion experiment in the US since many years.” QUASAR will be operated as a collaborative National and International facility, similar to NSTX and DIII-D. Discussions have indicated interest in participation by several US institutions and from the EU, Japan, and China.

Estimated construction and operations costs QUASAR will be constructed from components already manufactured for NSCX. All costs are based on escalated NCSX closeout estimates – see closeout report [9].

Notional start year: 2014 Construction costs: $128M total ($86M device construction, $42M diagnostics, heating systems, and instrumentation), 2015-18 Operations costs: ~$25M/yr Operation + $25M/yr physics(+escalation), 2019-2029 Value at completion: ~$300M (Site credits+NCSX investment+QUASAR investments)

Cost-saving opportunity - Partnership with China: During a visit to PPPL on 7-8 January by Jiangang Li, Director of the Insitute of Plasma Physics of the Academy of Science and Jianuo Huo, President of the University of Science and Technology, the possibility of a U.S.-China partnership to develop advanced stellarators was discussed in specific terms. Given the new U.S. discussion of the possibility of constructing a U.S. stellarator facility, the visitors stated unequivocally that China would be willing to make substantial in-kind contributions to completing the construction of QUASAR. By completing many of the remaining engineering and large component

 Figure  1:  View  of  an  assembled  3-­‐pack  of  modular  coils  (left)  and  a  partially  assembled  field  period  including  a  3-­‐pack  of  modular  coils  and  a  vacuum  vessel  segment  (right).    

fabrication tasks, and providing a team to support assembly at PPPL, it was agreed that China could reduce U.S. costs to complete construction, possibly by as much as ~30%.

The envisioned U.S.-China partnership would include collaboration in the QUASAR research program, and in stellarator optimization and simulation. China would benefit by gaining knowledge and experience in stellarators, which they believe are critical for contributing to DEMO solutions, and U.S. design and physics support for a possible experiment at USTC.

The readiness of the facility for construction Grade: Ready to construct

The QUASAR facility will employ the device components that were developed as part of the NCSX project, which was terminated in 2008 [9]. QUASAR will benefit from lessons learned during the closeout phase of the NCSX project. Potential modifications to the NCSX design would be limited to minor changes to the shaping capability (the trim coils) required to achieve targeted nearby equilibria that are predicted to have reduced turbulent losses. An extensive body of documentation has been developed that addresses the remaining construction activities including a detailed assembly plan and risk assessment. An international engineering review in 2007 [10] confirmed the feasibility of construction, based on the completion of critical assembly operations. The most challenging components have already been fabricated (Modular coils, vacuum vessel sectors, TF coils – see figure). Some large components are still to be fabricated and the bulk of the assembly task remains. As a result of having assembled the first 3-coil module, ideas for saving time in the assembly process have been identified and these ideas will be implemented where feasible.

Scientific community considerations and assessments The need for a quasi-axisymmetric research facility has long been recognized by the US and international fusion communities. In March 2001, there was a positive physics validation review of the NCSX project that affirmed the design principles of the compact QA design of NCSX. The NCSX project was positively reviewed by FESAC sub-committees; first in March 2001 [11] and again in October 2007. In the 2007 FESAC report the committee noted: “NCSX will be unique in the world stellarator research program, because of both its quasi-axisymmetry and its compactness” and “…resemblance to the tokamak should allow NCSX to illuminate a number of issues concerning symmetry”. The Greenwald Priorities Panel identified QA stellarators as an important element in the US fusion program in October, 2007. The need for optimized stellarators was emphasized in Thrust 17 of the Research Needs Workshop (ReNeW, Bethesda MD, June 2009). This Thrust was chosen to be in the top 5 thrusts in a recent preliminary report delivered to the FESAC committee (the Rosner panel). QUASAR also provide an alternative solution to ReNeW Thrusts 1, 2, 5, and 8. The theoretical pioneers of the quasi-symmetry principle were awarded the prestigious Hannes Alfvén Prize by the European Physical Society (Dublin Ireland, June 2010). The experimental investigation of the quasi-axisymmetry principle awaits QUASAR.                                                                                                                [1] A. H. Boozer, Phys. Fluids 26 496 (1984) [2] L. P. Ku and A. H. Boozer, Phys. Plasmas 16, 082506 (2009) [3] W. Dommaschk, W. Lotz, J. Nürhenberg, Nucl. Fusion 24 794 (1984) [4] J.D. Hanson, S. F. Knowlton, B. A. Stevenson, and G. J. Hartwell, Contrib. Plasma Phys. 50, 724 (2010) [5] J. E. Menard, et al., Nucl. Fusion 51 103014 (2011) [6] M. Zarnstorff, et al., Plasma Phys. Control. Fusion, 43 A237 (2001) [7] H. Mynick, N. Pomphrey, P. Xanthopoulos, Phys. Rev. Letters 105 095004 (2010) [8] G. H. Neilson, Proc. 21st IEEE/NPS Symposium on Fusion Engineering (2005) [9] NCSX Closeout report (2008) [10] NCSX Contructibility Review (2007) [11] NCSX Physics Validation Review (2001)

To: Prof. Stewart Prager, Director, PPPL Date: 2013-01-29 Dear Prof. Prager: I am glad to know that FESAC was charged to construct a list of attractive fusion

facilities for consideration by the DOE Office of Science. We believe it is a time for

proposal NCSX again. As you know, both Prof. Yuanxi Wan and I think that advanced

3D Stellarator is unique for its disruption free and steady-state capabilities and could be

one of future DEMO option.

For this reason, USTC and ASIPP have serious interest in a partnership to construct and

perform research on NCSX. If it would be granted by DOE, we would contribute

components and staff for helping to reduce the U.S. costs for NCSX. Staff can include

researchers, engineers, on-site assembly labor, etc. I certainly will support this proposal

and encourage your colleagues to work closely with colleagues from ASIPP and USTC if

further joint works are needed.

Sincerely yours,

Jiangang Li

Director of ASIPP, Professor

Tel: +86-551-5591371

Fax: +86-551-5591310

Email: j_li@ipp.ac.cn

PO Box 1126, Hefei, Anhui, 230031, P. R. China

 

National Institute for Fusion Science 322-6 Oroshi-cho, Toki, Gifu 509-5292, Japan

Feb.9th, 2013

Dear Sir/Madam,

With regard to the Department of Energy’s future facilities, here I would like to strongly support the QUASAR (QUASi-Axisymmetric Research) Experiment as an absolutely central facility.

Energy crisis is the most critical issue for mankind, which is global and long lasting. Resolution of this issue in conjunction of preservation of the environment is directly linked with the world-wide security. Therefore, the leadership of the US is the most critical in cooperation with developed countries.

Fusion energy has abundant potential attractiveness. I believe fusion energy is promising and at the same time I would like to point out that the fusion power development needs further steps to convince society its reality. The most essential demonstration to show feasibility of fusion energy is to control the burning plasmas through fusion reaction and to keep them efficiently in safe and steady-state.

The control of burning plasmas is the mission of ITER (used to be an abbreviation of International Thermonuclear Experimental Reactor), which is under construction by world-wide efforts in France. The central concept of ITER lies in the tokamak. Indeed, tokamaks have been explored in many developed countries for 50 years and have shown very good performance to lead us to the ITER project. But, tokamaks need a lot of complicated feedback control to sustain plasmas in them. Major reason is attributed to huge currents of more than 10 million amperes in plasmas. It can be compared to the control of thunderbolt in a device. Therefore, continuous operation of tokamaks is an unresolved issue which could be fatal for an energy production system.

Stellarator, which was invented by an American physicist, Prof.Lyman Spitzer, Jr., is an alternative and complementary concept to tokamaks. Since stellarators do not need currents in plasmas, they have intrinsic feature for continuous steady-state operation. But, stellartors have not reached the tokamak performance yet and are still not matured to convince us to ignite fusion reaction in them. In Japan, the first large scale device of this kind; our Large Helical Device (LHD) has been operated for 15 years. LHD employs superconducting coil systems and has already achieved to sustain the plasma with more than 20 million degrees in Celsius for 1 hour. While these steady-state plasmas have never been explored by tokamaks, the envelope of obtained plasmas has suggested further need of optimization to be a fusion reactor.

Optimization of a concept and cutting edge technology needs a certain diversity of approaches. Japan will be optimizing the operational scenario by using the existing device LHD in the next decade and planning the next step after the LHD in parallel. Germany is constructing the second but advanced large scale device; Wendelstein 7-X, which will be available in 2015. LHD as well as Wendelstein 7-X do not rely on currents in the plasma at all,

 

National Institute for Fusion Science 322-6 Oroshi-cho, Toki, Gifu 509-5292, Japan

which means that they are contrasting concepts to tokamaks and at the same time means that there is no hybrid approach of tokamaks and stellarators. Although to seek the advantage of a certain single concept is one of approaches of optimization, to integrate advantages of plural concepts is also optimization. QUASAR is the world first challenge in the latter approach. QUASAR will provide the epoch-making knowledge to resolve or at least mitigate burden due to a demand of huge currents in the plasmas.

While fusion power development has been advanced to have burning plasmas in 15 years, there is a gap between a feasible fusion reactor and how an ideal fusion reactor should be. The concept of QUASAR is quite unique and the QUASAR can definitely explore unexplored horizon of fusion plasmas. In parallel with its own development of this novel concept, it is confidently expected that QUASAR promotes discovery science which will have large innovative impact on ITER and beyond, and enable acceleration of fusion power development.

Last not least, the hosting laboratory of QUASAR; Princeton Plasma Physics Laboratory (PPPL) has enormous international competitiveness as well as capability of education to nurture next generation.

I am sure that PPPL and collaborating teams have sufficient potential to conduct this challenging project and lead it to success. Again, I strongly recommend the proposal of QUASAR as an absolutely central facility among the Department of Energy’s future facilities. I hope the QUASAR will play a critical role in tri-lateral international network with our LHD and Wendelstein 7-X, and bridge the missing link between tokamaks and stellarators.

Best regards,

Prof.Dr. Hiroshi Yamada Executive Scientific Director Large Helical Device Project

National Institute for Fusion Science 322-6 Oroshi-cho, Toki, Gifu 509-5292, Japan

hyamada@lhd.nifs.ac.jp