ARC Fusion Reactor

[Montluc Advanced Engineering]

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MAE ARC FUSION REACTOR

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TECHNICAL TASK: The objective of this project is to find an optimal solution of power supply of MAE's experimental "Frederic Bartholdi" and other MAE's large vessels that is not relying on Promethene fuel.

The restoration of power supply on “Frederic Bartholdi” was a particular challenge for MAE engineers. It would be rather simple to put a standard Promethene-fuelled Gallic conventional reactor, yet with the scarce supply of Promethene and the needs of the Enclave’s fleet deemed this path a burden in the long run. Recent baron’s obsession with finding new systems to claim and the possibility of deploying “Frederic Bartholdi” as an exploration-colonization ship to systems where re-supply of Promethene would be limited if not impossible prompted the engineering team, even more, to look for alternative power supply.

The choice fell on an old rather simple in nature fusion reactor design, the ARC reactor. Known from the early days of Gallic colonization, this reactor was the main power supply of many early Gallic colonies due to its compact size. The refinement of the technology in the early 3rd century A.G.S. allowed them to be installed in mobile conditions such as large spaceships. The nascent of Promethene-fuelled reactors later on rendered ARC reactors atavism of old in light of the high energy output of the new counterparts. MAE undertook the task to update the ARC reactor to particular needs of “Frederic Bartholdi” and possibly other large MAE-produced ships in the future.

Unlike Promethene reactors, the ARC reactor (Advanced, robust, and compact) deals with more readily available materials. ARC-reactor is a tokamak-based fusion power generation plant for integrated materials and component irradiation in a D-T neutron field. Compared to many other fusion reactors, ARC is very stable against the disruption. This stability is enabled by a high magnitude magnetic field in a compact superconductive fusion chamber, additionally stabilized by a large in proportion to the fusion chamber heat exhaust pipe with additional heat dissipation plates. The design of the reactor can be seen on a schematic below:

This design allows both high energy gain Qe > 1, and simultaneous high plasma output Qp. An additional advantage of the design is its safety: extremely high margin to disruptive operational limits is enforced at all times of the operation with an edge safety factor, density limit and normalized below the nowall limit beta (pressure limit) are imposed at all times.
The ARC reactor design utilizes a combination of RF power in the “fast-wave” ion cyclotron range of frequencies (ICRF) and the lower hybrid range of frequencies (LHRF) to heat the plasma and shape the q profile. ICRF is required to drive current efficiently in the core while lower hybrid current drive (LHCD) provides increased efficiency for driving current near mid-radius and beyond. The goal of this combination of current drive methods is to create an “advanced tokamak” (AT) q-profile, characterized by weak reversed magnetic shear. This provides self-consistency to higher confinement and also avoids dangerous instabilities.

The principle of plasma utilization is also different from conventional fusion chambers. Lower hybrid waves, launched from the high field side (HFS) of the tokamak, are used to non inductively drive plasma current. The high field-side launch is shown in modelling to increase the current drive efficiency, which is crucial to maximizing the power plant gain and providing better external control of the radial current profile. Also, launching from the more quiescent HFS of the plasma is expected to reduce damage to the launcher from plasma–material interactions.

The use of YBCO (Yttrium barium copper oxide) superconducting technology in the toroidal field coils permits significantly higher on-axis magnetic fields than standard Nb3Sn superconductors. High magnetic field strength is essential in small reactor designs in order to achieve the necessary poloidal field/plasma current needed for sufficient confinement and stability against beta (pressure) limits. Since YBCO tapes allow the use of resistive joints in the superconducting coils, the toroidal field coils can be made demountable, meaning the coils can be split into two pieces (see below). MAE pursued this feasible demonstrability which provides a dramatically different and more attractive, modular maintenance scheme for magnetic fusion devices that is especially crucial in long exploration voyages to be undertaken by “Frederic Bartholdi”. Thus, MAE’s primary contribution to the ARC design is enabling its modular maintenance system making the reactor much easier to use with long periods of lack of supplies and reliance on space modular parts brought to the expedition with the ship.

The upper half of ARC’s superconducting coils can be removed, allowing the MAE © vacuum vessel to be removed from the blanket tank as a single piece.

The MAE-patented replaceable vacuum vessel is made of corrosion-resistant Inconel 718. The vessel is approximately shaped like an elliptical torus. It is double-walled and contains a channel through which FLiBe flows for cooling and tritium breeding. The vacuum vessel is attached to the blanket tank from above by 18 support columns, which are evenly spaced between the 18 toroidal field coils. All connections needed for in-vessel components (such as waveguides, vacuum ports, etc.) run though these columns, which are also curved to reduce the flux of neutrons streaming through. Thus, the vessel is isolated from the permanent tokamak components, so it can be designed to fail without damaging lifetime reactor components in the worst case of a full, unmitigated plasma disruption. In order to permit modular maintenance, the blanket is composed entirely of liquid FLiBe that acts as a neutron moderator, shield, and breeder. The FLiBe is contained in a large low-pressure tank, referred to as the blanket tank, and flows slowly past the vacuum vessel. The blanket tank is a robust lifetime component and serves as the primary nuclear containment boundary, as opposed to the vacuum vessel. Neutrons created by the deuterium-tritium fusion reaction are captured in the FLiBe, transferring their energy and breeding tritium to fuel the reactor. Tritium can then be extracted from the liquid FLiBe after it flows out of the blanket tank.

A neutron shield made of titanium dihydride (TiH2) surrounds the blanket tank. This is to protect the inboard leg of the superconducting toroidal field coil, which is particularly space-constrained and susceptible to neutron radiation damage. Such a design is what allows the relatively compact size of the reactor.

The MAE ARC modular reactor is a relatively simple, reliable, and easy to maintain solution to energy supply for bigger ships as compared to more energy-output and yet more complicated and difficult to maintain Promethene and other fusion reactors. Our team believes that the novelty introduced by MAE to ARC-reactor will allow giving second life to this unjustly forgotten Gallic technology.