A Robust Design Window for the Heliotron DEMO Reactors

Abstract

According to the achievements in the Large Helical Device (LHD) experiments, a design of a DEMO reactor with a LHD-type heliotron system is foreseeable. On the other hand, a DEMO is the next step reactor and high reliability and feasibility are demanded in its design. In this study, a robust design window, i.e., the design window that is not sensitive to a change in uncertain physics parameters, was surveyed through parametric scans using a system design code. It was found that a difference in main design parameters (major radius, magnetic field strength, fusion output) gives only a small change in a dependence of physics requirements on the physics conditions. Therefore, it is important to find the design window with a lower requirement on the confinement improvement to assure the design robustness. In this respect, a reduction in the minimum inboard blanket space, one of the key parameters in a LHD-type heliotron reactor design, can effectively expand the design window and contributes to the design robustness. An acceptance of higher neutron wall load and an achievement of further high confinement improvement are also expected to make both a DEMO and a commercial reactor to be more feasible and economically attractive.

Physics design point of high-field stellarator reactors

“…However, in doing so, one would require the reactor to operate at larger ratios of density over the critical density n e /n ec , since n ec ∼ P 0.57 h B 0.34 R −1. 25 . In consequence, if n e /n ec is to be kept constant while reducing the fusion power at fixed device size, the magnetic field needs to be increased.…”

“…In the scientific literature, there exist stellarator reactor studies based on several magnetic configurations, including compact quasi-symmetric [24], force-free heliotron [25,26] and HELIAS [27][28][29]. An early comparison of them was published in [30].…”

Visualization of the Plasma Shape in a Force Free Helical Reactor, FFHR

“…The profiles of this device and the magnetic field lines can be seen in Fig. 1 [5]. In the limited space between the coil and the plasma, blankets modules will be installed in the immediate vicinity of the plasma in order to achieve the most effective utilization of the neutron energy generated by the fusion reaction.…”

Design studies on three-dimensional issues for liquid blanket systems in helical reactor FFHR

“…At the start of the activity, design window analyses have been performed [8,9] mainly from the view points of (1) plasma confinement parameters extrapolated from experimental results of the Large Helical Device (LHD) at NIFS [10], (2) stored magnetic energy in a helical coil system and (3) the minimum blanket space required for installation of a tritium breeding blanket and radiation shield.…”