ARC fusion reactor
The ARC fusion reactor (short for affordable, robust, compact) is a theoretical design for a compact fusion reactor developed by the Massachusetts Institute of Technology (MIT) Plasma Science and Fusion Center (PSFC). The ARC design aims to achieve an engineering breakeven of three (to produce three times the electricity required to operate the machine) while being about half the diameter of the ITER reactor and cheaper to build.
The ARC has a conventional advanced tokamak layout, as opposed to other small designs like the spherical tokamak. The ARC design improves on other tokamaks through the use of rare-earth barium copper oxide (REBCO) high-temperature superconductor magnets in place of copper wiring or conventional low-temperature superconductors. These magnets can be run at much higher field strengths, 23 T, roughly doubling the magnetic force on the fuel. The confinement time for a particle in plasma varies with the square of the size and the fourth power of the magnetic field, so doubling the field offers the performance of a machine 4 times larger. The smaller size reduces construction costs, although this is offset to some degree by the expense of the REBCO magnets.
The use of REBCO also raises the possibility of allowing the magnet windings to be flexible when the machine is not operational. This offers the significant advantage that they can be "folded open" to allow access to the interior of the machine. Accomplishing this would greatly lower the cost of maintenance, which with other designs generally requires the maintenance to be carried out through small access ports using remote manipulators. If realized, this could improve the reactor's capacity factor, an important metric in power generation costs.
The ARC design has several major departures from traditional tokamak-style reactors. The changes occur in the design of the reactor components, whilst making use of the same D–T (deuterium - tritium) fusion reaction as current-generation fusion devices.
To achieve a near tenfold increase in fusion power density, the design makes use of rare-earth barium-copper-oxide (REBCO) superconducting tape for its toroidal field coils. The intense magnetic field allows sufficient confinement of superhot plasma in such a small device. In theory, the achievable fusion power density of a reactor is proportional to the fourth power of the magnetic field intensity.
The design point has a fusion energy gain factor Qp ≈ 13.6 (the plasma produces 13 times more fusion energy than is required to heat it), yet is fully non-inductive, with a bootstrap fraction of ~63%.
The design is enabled by the ~23 T peak field on coil. External current drive is provided by two inboard RF launchers using 25 megawatts of lower hybrid and 13.6 MW of ion cyclotron fast wave power. The resulting current drive provides a steady-state core plasma far from disruptive limits.
Removable vacuum vessel
The design includes a removable vacuum vessel (the solid component that separates the plasma and the surrounding vacuum from the liquid blanket) that does not require dismantling the entire device. That makes it well-suited for research on other design changes.
Most of the solid blanket materials used to surround the fusion chamber in conventional designs are replaced by a fluorine lithium beryllium (FLiBe) molten salt that can easily be circulated/replaced, reducing maintenance costs.
The liquid blanket provides neutron moderation and shielding, heat removal, and a tritium breeding ratio ≥ 1.1. The large temperature range over which FLiBe is liquid permits blanket operation at 800 K with single-phase fluid cooling and a Brayton cycle.
- Commonwealth Fusion Systems, a company aiming to build the reactor
- Yttrium barium copper oxide, the most studied/useful rare-earth barium copper oxide
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