Japan’s Efforts to Develop the Concept of JA DEMO During the Past Decade

Abstract

This paper summarizes the evolution of Japanese DEMO design studies in a retrospective manner by highlighting efforts to resolve critical design issues on DEMO. Japan is currently working on the conceptual study of a steady-state DEMO (JA DEMO) with a major radius Rp of 8.5 m and fusion power Pfus of 1.5 to 2 GW based on water-cooled solid breeding blanket with pressurized water reactor water condition (290ºC to 325ºC, 15.5 MPa). Such a lower Pfus allows to find realistic design solutions for divertor heat removal. Recognizing that divertor heat removal is one of the most challenging issues on DEMO, the divertor design has been carried out in different approaches, including numerical divertor plasma simulation, magnetic configurations, heat sink design, etc. It is noteworthy that the latest divertor simulation led to a design window allowing divertor heat removal of the peak heat flux of <10 MW/m 2 . The breeding blanket (BB) design has been concentrated on simplification of the internal structure and pressure tightness of the BB casing against the in-box loss-of-coolant accident. Due to a large amount of radioactive waste generated in periodic replacement of in-vessel components, downsizing of waste-related facilities has come to be regarded as a significant design issue. A possible waste management for reducing temporary waste storage was proposed, and its impact on the plant layout was assessed.

Empirical Formulas for Estimating Self and Mutual Inductances of Toroidal Field Coils and Structures

“…where the normalized valueM k was found by using the Neumann formula with the number of TF-coils N T FC = 16 selected for JA Demo design [4], i.e., i, j = 1 -16, 0 ≤ k = |i − j| ≤ 8, andM 16-k =M k for k > 8. Table 1 presents optimized coefficients for each k and calculated values ofM * k are compared toM k in Fig.…”

“…2.3), which gives the increment inM 0 of 1.4% as mentioned above with taking account the contribution of the self inductance L OM0 to L being ∼36%. Figure 5 shows an example of conceptual design drawing for JA Demo [4], which shows poloidal cross section of the TF coil and the vacuum vessel (VV). We consider poloidal eddy-current inductions in and their influences on reactor structures in the case of emergency fast discharge of the TF-coil current.…”

“…The self inductance of TF coil set becomes larger with increasing its size as in the case of fusion demo reactors [4] that have enormous magnetic stored energy to be thermally and safely dissipated during the fast discharge [2]. These inductances are accurately and numerically evaluated by the well-known Neumann formula [5].…”

“…In this paper, we will present empirical formulas for evaluating self and mutual inductances of TF coils and toroidal-shape structures with defining their crosssectional shape parameters such as elongation, aspect ratio, and triangularity. For showing an example of application of the simplified inductance calculation, we will also demonstrate an analysis of eddy currents induced in TFcoil structures and the vacuum vessel in the fast discharge of TF coils of a fusion demo reactor, JA DEMO [4], for rough estimations of their thermal and mechanical impacts.…”

Structure and dynamical steady state of the peeling mode in edge-localized mode-free, high-confinement tokamak plasmas

“…Studies of explosive dynamical events in controlled-nuclear-fusion devices (known as edge-localized modes (ELMs) [1][2][3] ) display many similarities to solar-flare events on the sun, revealing a new connection between laboratory plasma physics and astronomy [4][5] . Improved understanding of the common physics of ELMs and solar/stellar flares not only can contribute to our intellectual understanding of plasma physics, but also can improve the controllability of burning plasmas in selfregulating, combined/complex next-step devices such as ITER [6][7] and DEMO [8][9] . In particular, highconfinement-mode (H-mode) operation, which has a high pedestal pressure, may be impossible without a proper physics understanding of the "peeling" mode (and/or coupled peeling-ballooning modes).…”