Published by Oak Ridge National Laboratory Building CR 5600 P.O. Box 2008 Oak Ridge, TN 37831-6169, USA Editor: James A. Rome Issue 143 April 2014 E-Mail: [email protected] Phone (865) 482-5643 On the Web at http://www.ornl.gov/sci/fed/stelnews Fusion Energy (CCFE), which is used in the EU to study Systems code approach for and optimize tokamak-based DEMO design concepts. For the heliotron line, the well-developed systems code burning plasma stellarator HELIOSCOPE [3] maintained by the National Institute for devices Fusion Science (NIFS), is used for purposes such as design window analysis of the force-free helical reactor With ITER now under construction as the first fusion [4]. Up to now, no such tool was available for the helical device to study the physics of a burning plasma in detail, advanced stellarator (HELIAS) line. Therefore a HELIAS an increased focus is being placed on a demonstration module has been developed by the Max Planck Institute power plant (DEMO). for Plasma Physics (IPP) and implemented into the frame- work of PROCESS by CCFE. This has been emphasized by the IAEA, which organized the “Second IAEA DEMO Programme Workshop” [1] in The advantage of developing a stellarator module for Vienna last December. This workshop was organized to PROCESS is that common routines for non-device-spe- facilitate the discussion of current physics and engineering cific systems such as plant power balance or routines for status and issues for a DEMO fusion device. One of the optimization are already available and have gained matu- main topics discussed was the fusion systems code rity through many applications. Moreover, this common approach illustrated in Fig. 1. framework allows direct comparative studies of tokamak and stellarator design concepts. Systems codes, also known as design codes, are compre- hensive yet simplified models of a complete fusion facil- In order to incorporate a stellarator module into PRO- ity. Since they combine physics, engineering, and CESS, stellarator-specific models are required that reflect economic aspects, they are used to develop conceptual the specific properties of the stellarator. These models design points and to conduct sensitivity studies. include Ö a geometry model based on Fourier coefficients that In this issue . Systems code approach for burning plasma stellarator devices A stellarator-specific (HELIAS) module has been developed and implemented in the systems code PROCESS. This approach is investigated to allow for detailed design studies of burning plasma HELIAS devices, and to facilitate a direct comparison of toka- mak and stellarator power plant concepts. ............. 1 Coordinated Working Group Meeting (CWGM13) for Stellarator-Heliotron Research Fig. 1. Concept of systems codes and their interaction with Minutes of the 13th Coordinated Working Group Meet- detailed simulations and experiments. ing (CWGM13) held 26–28 February 2014 at the Uji Campus of Kyoto University. .................................. 3 One commonly employed instrument is the systems code PROCESS [2] maintained by the Culham Centre for All opinions expressed herein are those of the authors and should not be reproduced, quoted in publications, or used as a reference without the author’s consent. Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for the U.S. Department of Energy. can represent the complex three-dimensional (3D) systems studies of HELIAS burning plasma devices can be plasma shape, carried out to find consistent design points. Ö a basic island divertor model that assumes diffusive This tool can be used not only for reactor-sized facilities cross-field transport and high radiation at the X-point but also for an intermediate-step stellarator. A direct step [5], from W7-X to a HELIAS reactor would be substantial and Ö a coil model which combines scaling aspects based on therefore poses certain risks. An intermediate step, an the Helias 5-B design [6] in combination with analytic ITER-like stellarator, may thus be desirable to study col- inductance and field calculations, and lective particle behavior in a burning plasma in 3D geome- Ö a transport model that employs a predictive confine- try. The systems code approach will be a valuable tool in ment time scaling derived from 1D neoclassical [7] designing and optimizing such a device. and 3D turbulence [8] simulations. One requirement of this development is to retain low cal- References culation times without compromising the necessary accu- [1] http://www-naweb.iaea.org/napc/physics/meetings/ racy and complexity of the 3D stellarator-specific TM45256.html properties. [2] D. Ward, Fusion Sci. Technol. 56 (2009) 581. As an example, in Table 1 results for the coil module are [3] T. Goto et al., Nucl. Fusion 51 (2011) 083045. compared to actual values for Wendelstein 7-X (W7-X). [4] T. Goto et al., Plasma Fusion Res. 7 (2012) 2405084. Only the mass of the support structure and the mass of the [5] Y. Feng et al., Nucl. Fusion 45 (2005) 1684. winding pack (WP) differ by a small degree. Since the mass of support structure was not a costing factor for [6] F. Schauer et al., Fusion Eng. Des. 88 (2013) 1619. W7-X, it was not optimized in this regard. Also, the wind- [7] Y. Turkin et al., Phys. Plasmas 18 (2011) 022505. ing pack (WP) of W7-X includes additional materials, [8] P. Xanthopoulos et al., Phys. Rev. Lett. 99 (2007) explaining the higher mass compared to the calculation. If, 035002. in contrast, HELIAS burning plasma devices are consid- ered, the structure certainly needs to be optimized, which 1 1 1 1 1 means that the calculations will be more valid for larger F. Warmer , C.D. Beidler , A. Dinklage , Y. Feng , J. Geiger , R. 2 2 1 1 2 1 devices. Kemp , P. Knight , F. Schauer , Y. Turkin , D. Ward , R. Wolf , and P. Xanthopoulos1 1Max Planck Institute for Plasma Physics, Wendelsteinstr. 1, 17491 Greifswald, Germany 2Culham Centre for Fusion Energy, Abingdon, OX143 DB, Oxfordshire, United Kingdom Table 1. Comparison of the PROCESS stellarator coil model with the actual values from W7-X. Conclusions A stellarator module has been developed and implemented in the systems code PROCESS and benchmarked against W7-X, showing good agreement. With such a tool available, direct comparative studies of tokamak and stellarator reactors can be prepared. Also Stellarator News -2- April 2014 (FORTEC-3D, EUTERPE, fluid codes, ...) to assess the Coordinated Working Group existence of in-surface potential variation and its contribu- tion to radial impurity flux. R. Burhenn et al. published a Meeting (CWGM13) for joint paper on impurity issues in 2009 [“On impurity han- Stellarator-Heliotron Research dling in high performance stellarator/heliotron plasmas,” Nucl. Fusion 49 (2009) 065005]. Follow-up joint papers The 13th Coordinated Working Group Meeting (documenting subsequent developments) can be formu- (CWGM13) was held 26–28 February 2014 at the Uji lated by reactivating joint activities in CWGM. Campus of Kyoto University. The materials presented at this meeting are available at http://ishcdb.nifs.ac.jp/ and Highlights in experiments and invitation to joint experiment http://fusionwiki.ciemat.es/wiki/ Coordinated_Working_Group (Æ CWGM13). A brief Recent experiments in the Heliotron J device were summary of the meeting is provided here. reviewed. Plasma startup; the plasma parallel flow mea- surement and its comparison with neoclassical prediction; Three-dimensional (3D) transport in divertors fast-ion driven MHD and related particle flux studies by In response to a proposal made at the last CWGM using several probe systems; the external control of ener- (CWGM12 in Padova), recent progress on the experimen- getic-ion-driven MHD instabilities by ECCD; the fast ion tal identification and physics interpretation of the 3D distributions in ICRF experiments; high density operation effects of magnetic field geometry/topology on divertor through high intensity gas puff (HIGP) fueling and super- transport was reviewed. This information has passed the sonic molecular beam injection (SMBI); transition to domestic (Japan) selection process for presentation at the improved confinement in such a high-density regime; etc. 25th IAEA Fusion Energy Conference. Identification of were emphasized to trigger proposal and discussions for key parameters for 3D effects should open new perspec- joint experiments. From LHD, steady progress in plasma tives on divertor optimization for future reactors. Interac- parameters (ion temperature, simultaneous high tempera- tions between the 3D structure of the magnetic field, tures, and steady-state operation) was reported. New diag- current in the scrape-off layer (SOL)/stochastic layer, and nostics enabling high dynamic-range spectroscopic parallel and perpendicular electric fields should be system- measurement of the Balmer- lines, have facilitated quan- atically clarified through diagnostics and modeling for a titative understandings of the impacts of discharge clean- range of magnetic field configurations. Issues in formulat- ing on producing high ion temperature plasmas. RMP ing joint experiments, potential and current measurements, experiments have fertilized 3D physics, such as magnetic and 2D temperature and density measurements were dis- island dynamics (growth/healing), and observation of cussed among the HSX, LHD and TJ-II teams. Compari- peaked pressure profiles inside the magnetic island after son with linear devices “without 3D effects” is also pellet deposition. A tentative schedule of deuterium exper- recommended