Reactor similarity for plasma–material interactions in scaled-down tokamaks as the basis for the Vulcan conceptual design

• Published in: Fusion engineering and design Vol. 87; no. 3; pp. 234 - 247
• Main Authors: Whyte, D.G., Olynyk, G.M., Barnard, H.S., Bonoli, P.T., Bromberg, L., Garrett, M.L., Haakonsen, C.B., Hartwig, Z.S., Mumgaard, R.T., Podpaly, Y.A.
• Format: Journal Article
• Language: English
• Published: United States Elsevier B.V 01-03-2012
• Subjects: Atomic processes in plasmas; Design engineering; Devices; Dimensional analysis; Dimensionless parameters; Low cycle fatigue; Magnetic fields; Mathematical models; Plasma-facing materials; Plasma–material interactions; Reactors; Scaling; Similarity; Tokamaks; 52.55.Fa; Plasma–material interactions; Plasma-facing materials; Dimensional analysis; 28.52.−s; 52.40.Hf; Atomic processes in plasmas; Dimensionless parameters; Scaling; 28.52.Fa; 52.55.Rk
• ISSN: 0920-3796; 1873-7196
• DOI: 10.1016/j.fusengdes.2011.12.011

► Discussion of similarity scalings for reduced-size tokamaks. ► Proposal of a new set of scaling laws for divertor similarity. ► Discussion of how the new scaling provides fidelity to a reactor. ► The new scaling is used as the basis for the Vulcan conceptual design.
Dimensionless parameter scaling techniques are a powerful tool in the study of complex physical systems, especially in tokamak fusion experiments where the cost of full-size devices is high. It is proposed that dimensionless similarity be used to study in a small-scale device the coupled issues of the scrape-off layer (SOL) plasma, plasma–material interactions (PMI), and the plasma-facing material (PFM) response expected in a tokamak fusion reactor. Complete similarity is not possible in a reduced-size device. In addition, “hard” technological limits on the achievable magnetic field and peak heat flux, as well as the necessity to produce non-inductive scenarios, must be taken into account. A practical approach is advocated, in which the most important dimensionless parameters are matched to a reactor in the reduced-size device, while relaxing those parameters which are far from a threshold in behavior. “Hard” technological limits are avoided, so that the reduced-size device is technologically feasible. A criticism on these grounds is offered of the “P/R” model, in which the ratio of power crossing the last closed flux surface (LCFS), P, to the device major radius, R, is held constant. A new set of scaling rules, referred to as the “P/S” scaling (where S is the LCFS area) or the “PMI” scaling, is proposed: (i) non-inductive, steady-state operation; (ii) P is scaled with R2 so that LCFS areal power flux P/S is constant; (iii) magnetic field B constant; (iv) geometry (elongation, safety factor q*, etc.) constant; (v) volume-averaged core density scaled as n≈n¯e∼R−2/7; and (vi) ambient wall material temperature TW,0 constant. It is shown that these scaling rules provide fidelity to reactor conditions in the divertor of the reduced-size device, allowing for reliable extrapolation of the behavior of the coupled SOL/PMI/PFM system from the reduced-size device to a reactor. The P/S scaling is used as the basis for the Vulcan tokamak conceptual design.