Demountable Toroidal Field Magnets for Use in a Compact Modular Fusion Reactor

A concept of demountable toroidal field magnets for a compact fusion reactor is discussed. The magnets generate a magnetic field of 9.2 T on axis, in a 3.3 m major radius tokamak. Subcooled YBCO conductors have a critical current density adequate to provide this large magnetic field, while operating at 20 K reduces thermodynamic cooling cost of the resistive electrical joints. Demountable magnets allow for vertical replacement and maintenance of internal components, potentially reducing cost and time of maintenance when compared to traditional sector maintenance. Preliminary measurements of contact resistance of a demountable YBCO electrical joint between are presented

ARC: A compact, high-field, fusion nuclear science facility and demonstration power plant with demountable magnets

The affordable, robust, compact (ARC) reactor is the product of a conceptual design study aimed at reducing the size, cost, and complexity of a combined fusion nuclear science facility (FNSF) and demonstration fusion Pilot power plant. ARC is a ∼200–250 MWe tokamak reactor with a major radius of 3.3 m, a minor radius of 1.1 m, and an on-axis magnetic field of 9.2 T. ARC has rare earth barium copper oxide (REBCO) superconducting toroidal field coils, which have joints to enable disassembly. This allows the vacuum vessel to be replaced quickly, mitigating first wall survivability concerns, and permits a single device to test many vacuum vessel designs and divertor materials. The design point has a plasma fusion gain of Q[subscript p] ≈ 13.6, yet is fully non-inductive, with a modest bootstrap fraction of only ∼63%. Thus ARC offers a high power gain with relatively large external control of the current profile. This highly attractive combination is enabled by the ∼23 T peak field on coil achievable with newly available REBCO superconductor technology. External current drive is provided by two innovative inboard RF launchers using 25 MW of lower hybrid and 13.6 MW of ion cyclotron fast wave power. The resulting efficient current drive provides a robust, steady state core plasma far from disruptive limits. ARC uses an all-liquid blanket, consisting of low pressure, slowly flowing fluorine lithium beryllium (FLiBe) molten salt. The liquid blanket is low-risk technology and provides effective neutron moderation and shielding, excellent heat removal, and a tritium breeding ratio ≥ 1.1. The large temperature range over which FLiBe is liquid permits an output blanket temperature of 900 K, single phase fluid cooling, and a high efficiency helium Brayton cycle, which allows for net electricity generation when operating ARC as a Pilot power plant.United States. Department of Energy (Grant DE-FG02-94ER54235)United States. Department of Energy (Grant DE-SC008435)United States. Department of Energy. Office of Fusion Energy Sciences (Grant DE-FC02-93ER54186)National Science Foundation (U.S.) (Grant 1122374

Design of demountable toroidal field coils with REBCO superconductors for a fusion reactor

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2016.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 139-145).The recent development of REBCO superconducting tapes, cabling methods and joint concepts could be a revolutionary development for magnetic fusion. REBCO has significantly better performance at high magnetic fields than traditional low temperature superconductors (LTS), and can be operated at a higher temperature than LTS for reduced thermodynamic cost of cooling. Use of REBCO superconductors in the magnet systems of tokamaks allows building demountable toroidal field (TF) coils, greatly simplifying reactor construction and maintenance. A demountable TF coil system with REBCO superconductors for a fusion reactor has been conceptually designed. The coil system operates at 20 K, with a maximum magnetic field of 20 T. The magnets are divided into two coil segments and can be detached and remounted to allow the internal components of the reactor to be removed vertically as one piece. Operating at 20 T and 20 K, the stress in most of the coils is acceptable (less than 2/3 the yield strength and less than 1/2 the ultimate tensile strength of the structural materials). The strain in the superconductors is lower than the reversible degradation limit. The electrical resistance in each conductor joint is 10 n [Omega]. The total heat generation in the reactor superconducting TF magnets is approximately 1.9 MW, of which about 25 % is nuclear heating and 75 % joint heating. 71 MW of electricity are required for cooling the coils at 20 K, about 7 % of the electric energy the reactor generates. The expected time to warm-up the magnets from the operation temperature to room temperature is 7 days, and approximately the same for cool-down back to the operation temperature. The analysis of the conceptual magnet design is encouraging, as no insuperable problems have been identified. This conceptual design can be used as a starting point for a full engineering design of demountable fusion reactors magnets.by Franco Julio Mangiarotti.Ph. D

Experimental device for critical surface characterization of yttrium barium copper oxide tape superconductors

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (p. 81-83).The twisting stacked tape cabling (TSTC) method for YBCO superconductors is very attractive for high current density, high magnetic field applications, such as nuclear fusion reactors and high energy physics experiments. Industrial scale assembling methods have been proposed, and cable samples have been tested at 77 K and 4.2 K. A new experimental device has been designed and built to measure critical current of YBCO tapes and TSTC as a function of magnetic field and temperature. The probe allows controlling the temperature between 4.2 K and 80 K within +/-1 K in liquid and gaseous helium ambient, and can be used in a 2 T magnet facility at MIT-PSFC and a 14 T magnet facility at NHMFL-FSU. Its current leads are designed to carry up to 5 kA. The device consists in a 0.9 m long, 25 x 38 mm rectangular vacuum-insulated canister. The superconducting sample and a superconducting current return lead fit inside the canister, in such a way that the Lorentz force and torque produced by the external magnetic field is cancelled. The sample temperature is controlled in a 200 mm long area inside the canister where critical current measurements are performed. Critical current measurements were performed on a single YBCO tape at self-field at temperatures between 20 K and 70 K. The results are similar to data provided by the superconductor's manufacturer. The temperature reached the set point in approximately 10 minutes, and was controlled within +/-1 K. Results of heating power required and difference between set point temperature and measured temperature as functions of set point temperature are presented for two temperature control methods.by Franco Julio Mangiarotti.S.M

Designing a tokamak fusion reactor—How does plasma physics fit in?

This paper attempts to bridge the gap between tokamak reactor design and plasma physics. The analysis demonstrates that the overall design of a tokamak fusion reactor is determined almost entirely by the constraints imposed by nuclear physics and fusion engineering. Virtually, no plasma physics is required to determine the main design parameters of a reactor: a, R[subscript 0], B[subscript 0], T[subscript i], T[subscript e], p, n, τ[subscript E], I. The one exception is the value of the toroidal current I, which depends upon a combination of engineering and plasma physics. This exception, however, ultimately has a major impact on the feasibility of an attractive tokamak reactor. The analysis shows that the engineering/nuclear physics design makes demands on the plasma physics that must be satisfied in order to generate power. These demands are substituted into the well-known operational constraints arising in tokamak physics: the Troyon limit, Greenwald limit, kink stability limit, and bootstrap fraction limit. Unfortunately, a tokamak reactor designed on the basis of standard engineering and nuclear physics constraints does not scale to a reactor. Too much current is required to achieve the necessary confinement time for ignition. The combination of achievable bootstrap current plus current drive is not sufficient to generate the current demanded by the engineering design. Several possible solutions are discussed in detail involving advances in plasma physics or engineering. The main contribution of the present work is to demonstrate that the basic reactor design and its plasma physics consequences can be determined simply and analytically. The analysis thus provides a crisp, compact, logical framework that will hopefully lead to improved physical intuition for connecting plasma physic to tokamak reactor design.United States. Department of Energy (Grant DE-FG02-91ER54109)United States. Department of Energy (Grant DE-FC02-93ER54186

Superconductors for fusion: A roadmap

With the first tokamak designed for full nuclear operation now well into final assembly (ITER), and a major new research tokamak starting commissioning (JT60SA), nuclear fusion is becoming a mainstream potential energy source for the future. A critical part of the viability of magnetic confinement for fusion is superconductor technology. The experience gained and lessons learned in the application of this technology to ITER and JT60SA, together with new and improved superconducting materials, is opening multiple routes to commercial fusion reactors. The objective of this roadmap is, through a series of short articles, to outline some of these routes and the materials/technologies that go with them