ARC: A compact, high-field, fusion nuclear science facility and demonstration power plant with demountable magnets
Graphical abstract
Introduction
Most fusion reactor designs, such as the ARIES studies [1], [2], [3], [4], assume a large, fixed 1000 MWe output for a power plant. However, large-scale designs make fusion engineering research and development difficult because of the high cost and long construction time of experiments. This paper presents a smaller, less costly, timelier, and lower risk alternative, the 200 MWe ARC reactor. ARC is a conceptual point design of a fusion nuclear science facility/Pilot power plant that demonstrates the advantages of a compact, high-field design utilizing REBCO superconducting magnets and inboard launched lower hybrid current drive (LHCD). The design was carried out as a follow-on to the Vulcan conceptual design; a tokamak for studying plasma–material interaction (PMI) physics that also utilized the demountable REBCO tape and high-field side LHCD [5]. A goal of the ARC design is to minimize the reactor size in order to reduce the plant capital cost. Like Vulcan and several other proposed tokamaks [2], [6], [7], [8], ARC makes use of high-temperature superconductors (HTS), which enables large on-axis magnetic fields and ultimately reduces the size of the reactor. It is important to emphasize that ARC represents one of many possible compact, high-field design configurations. As discussed later in this paper, the modular nature of ARC allows it to change experimental direction and pursue the nuclear materials and vacuum vessel configurations that are determined to be most promising. This enables more innovative and speculative designs because the cost and operational implications of failure are reduced. Indeed a starting design philosophy of ARC is that failure should and will occur as various fusion materials and power exhaust technologies are tried and tested. However, because they can be readily fixed, these failures should not compromise the overall capacity of the device to produce fusing plasmas.
This paper is organized in the following way. Section 2 presents an overview of the ARC design. Section 3 describes the plasma physics basis for the reactor and discusses the current drive system. Section 4 details the design of the magnet system. Section 5 presents the design of the fusion power core, consisting of the tritium breeding/heat exchange blanket and the neutron shield. Section 6 presents a simple costing estimate. Section 7 briefly lists the most vital research and development necessary to enable a design similar to ARC. Lastly, Section 8 provides some concluding remarks.
Section snippets
Design motivation and overview
The ARC reactor is a conceptual tokamak design that can function as both a demonstration fusion power plant for energy generation and a fusion nuclear science facility (FNSF) for integrated materials and component irradiation testing in a D-T neutron field. The starting objective of the ARC study was to determine if a reduced size D-T fusion device (fusion power ≤500 MW) could benefit from the high magnetic field technology offered by recently developed high temperature superconductors. The
0-D point design optimization
In order to determine a starting point for the ARC parameters, a 0-D design exercise was performed. After the initial parameters in this section were determined, the design was iterated several times using codes such as ACCOME, MCNP, and COMSOL. Note that in many cases the final design parameters (e.g. in Table 1 and in the sections following this one) differ from the initial parameters calculated in this section. A fundamental equation for any magnetic fusion reactor design is the scaling [22]
Magnet design
A central aspect of the ARC conceptual design is exploring possible fusion reactor/FNSF scenarios at the much higher field afforded by REBCO superconductors. It is imperative to explore these new magnet designs to understand the tradeoffs and limitations. The magnet system, shown in Fig. 17, is divided into four groups: toroidal field (TF) coils, poloidal field (PF) coils, the central solenoid (CS), and auxiliary (AUX) coils. The first two groups are steady state superconducting magnets that
Fusion power core
Traditional tritium breeding and neutron absorbing blankets for fusion reactor designs involve complex components, including significant solid, structural material. Since the blanket is generally contained within the TF coils, these structures must also be separable into toroidal sections so they can be installed through access ports between the TF coils. This results in challenging engineering constraints, difficult remote handling, and a low tritium breeding ratio (TBR) because the structural
Economics
The main driver for minimizing the size of ARC is to reduce the cost of building the reactor. While a full costing of the ARC reactor is beyond the scope of this paper, a rough costing based on volumes and materials prices has been performed. With a major radius of 3.3 m, ARC is similar in size to experiments that have already been built (JET and TFTR). The following analysis aims to justify that ARC is feasible from a materials cost standpoint.
In order to assess the bulk materials costs of the
Plasma physics and current drive
First, the I-mode regime must be further studied, characterized, and demonstrated with non-inductive profiles. As with all small reactor designs the core scenario exploits enhanced confinement from current profile and q control. Therefore, a fully developed and consistent non-inductive scenario with the required physics parameters should be explored more completely. Ideally, we would use a burning plasma experiment in order to also test the self-determining effect of alpha-dominated heating on
Conclusions
With a major radius of 3.3 m and minor radius of 1.1 m, ARC is significantly smaller in size and thermal output than most current reactor designs, which typically generate ∼1 GWe. ARC produces 525 MW of fusion power (∼ 200 MWe), operating in the promising I-mode regime. Steady state plasma current is driven by ICRF fast wave and lower hybrid waves, both launched from the high field side. The reactor has a bootstrap fraction of only 63%, which gives operators greater control of the current profile.
Acknowledgements
We thank Leslie Bromberg, Charles Forsberg, Martin Greenwald, Amanda Hubbard, Brian LaBombard, Bruce Lipschultz, Earl Marmar, Joseph Minervini, Geoff Olynyk, Michael Short, Pete Stahle, Makoto Takayasu, and Stephen Wolfe for conversations and comments that improved this paper. We also thank Zach Hartwig for allowing us to use his C++ wrapper for MCNP and for advice regarding neutronics. BNS was supported by U.S. DoE Grant No. DE-FG02-94ER54235. JB was supported by U.S. DoE Grant No. DE-SC008435
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