Peter H. Titus

Overview of the ARIES-RS reversed-shear tokamak power plant study

The ARIES-RS tokamak is a conceptual, D‐T-burning 1000 MWe power plant. As with earlier ARIES design studies, the final design of ARIES-RS was obtained in a self-consistent manner using the best available physics and engineering models. Detailed analyses of individual systems together with system interfaces and interactions were incorporated into the ARIES systems code in order to assure self-consistency and to optimize towards the lowest cost system. The ARIES-RS design operates with a reversed-shear plasma and employs a moderate aspect ratio (A4.0). The plasma current is relatively low (Ip11.32 MA) and bootstrap current fraction is high ( fBC 0.88). Consequently, the auxiliary power required for RF current drive is relatively low ( 80 MW). At the same time, the average

ARIES-RS magnet systems

A conceptual design of toroidal and poloidal field systems for the ARIES-RS reactor study is presented in this paper. Means of designing the toroidal and poloidal field system for minimized size and cost, optimized structure and increased access for maintenance are presented in the paper. Supports of the out-of-plane TF loads that do not interfere with maintenance operation have been designed. Structural analyses of several cases that have the common feature of avoiding material in between the outer legs of the TF coil are presented in this paper. The implications on the structural amount of material required are investigated. Methods of handling failure conditions in the toroidal field coil due to unbalanced currents are studied. Optimization of the conductor in the poloidal and toroidal field systems is carried out. Implications of the use of very fine superconducting strands for conductor stability and minimization of co-wound normal-conducting material are evaluated. Implications of novel schemes for magnet protection such as internal dump, are described.

The ARIES-III D-3He tokamak-reactor study

A description of the ARIES-III research effort is presented, and the general features of the ARIES-III reactor are described. The plasma engineering and fusion-power-core design are summarized, including the major results, the key technical issues, and the central conclusions. Analyses have shown that the plasma power-balance window for D-/sup 3/He tokamak reactors is small and requires a first wall (or coating) that is highly reflective to synchrotron radiation and small values of tau /sub ash// epsilon /sub e/ (the ratio of ash-particle to energy confinement times in the core plasma). Both first and second stability regimes of operation have been considered. The second stability regime is chosen for the ARIES-III design point because the reactor can operate at a higher value of tau /sub ash// tau /sub E// tau /sub E/ approximately=2 (twice that of a first stability version), and because it has a reduced plasma current (30 MA), magnetic field at the coil (14 T), mass, and cost (also compared to a first-stability D-/sup 3/He reactor). The major and minor radii are, respectively 7.5 and 2.5 m.<<ETX>>

Design concept for the GEM detector magnet

The magnet has two symmetric and independent halves, each containing a cold mass assembly operating nominally at 4.5 K, a set of vapor cooled leads, a cold mass support system, a liquid nitrogen shield system, and a vacuum vessel. Also included in each half is a forward field shaper which provides a component of magnetic induction normal to the path of low angle muons in the forward region, thereby improving their resolution. The unique features of this magnet are the conductor design itself and the large coil diameter, which demands an on-site winding and assembly operation. The use of a natural convection thermosiphon loop for thermal radiation cooling eliminates plumbing complications. Locating the aluminium sheath outside the conduit for quench protection permits optimizing the copper-to-superconductor ratio inside the conduit for stability alone. The conceptual design for the magnet, including the design for the detector dependent magnetics, the superconducting coils and coil structure (cold mass), the coil winding process, the vacuum vessel and liquid nitrogen shields, the cold mass supports, and the magnet assembly procedure, are described.<<ETX>>

The ITER Central Solenoid

The central solenoid for the International Thermonuclear Experimental Reactor (ITER), a fusion tokamak experiment with the goal of generating 500 MW of fusion power with high gain (Q>10), must provide most of the volt-seconds needed to induce and sustain a 15 MA plasma for burn times of >400 s. The 6.4 GJ central solenoid design requires a 45 kA conductor and has a peak field of 13 T. The central solenoid consists of six pancake-wound modules, stacked vertically, and held in axial compression by an external structure. The five-stage cable has 1/3 copper and 2/3 advanced Nb3Sn strands in a thick superalloy conduit and is cooled by the forced-flow of supercritical helium through the cable space. Key design issues include the qualification of a conduit with adequate fatigue strength, avoiding filament damage from transverse Lorentz loads, eliminating axial tension in the winding insulation, and qualification of space-saving intramodule butt joints

Thermal Analysis to Calculate the Vessel Temperature and Stress in Alcator C-Mod due to the Divertor Upgrade

Abstract Alcator C-Mod is planning an upgrade to its outer divertor. The upgrade is intended to correct the existing outer divertor alignment with the plasma, and to operate at elevated temperatures. Higher temperature operation will allow study of edge physics behavior at reactor relevant temperatures. The outer divertor and tiles will be capable of operating at 600 °C. Longer pulse length, together with the plasma and RF heat of 9 MW, and the inclusion of heater elements within the outer divertor produces radiative energy which makes the sustained operation much more difficult than before. An ANSYS model was built for the global thermal analysis of C-Mod. It models the radiative surfaces inside the vessel and between the components, and also includes plasma energy deposition. Different geometries have been simulated and compared. Results show that steady state operation with the divertor at 600 °C is possible with no damage to major vessel internal components. The differential temperature between inner divertor structure, or “girdle” and inner vessel wall is ~70 °C. This differential temperature is limited by the capacity of the studs that hold the inner divertor backing plates to the vessel wall. At a 70 °C temperature differential the stress on the studs is within allowable limits. The thermal model was then used for a stress pass to quantify vessel shell stresses where thermal gradients are significant.

Optical diagnostics of mercury jet for an intense proton target

An optical diagnostic system is designed and constructed for imaging a free mercury jet interacting with a high intensity proton beam in a pulsed high-field solenoid magnet. The optical imaging system employs a backilluminated, laser shadow photography technique. Object illumination and image capture are transmitted through radiation-hard multimode optical fibers and flexible coherent imaging fibers. A retroreflected illumination design allows the entire passive imaging system to fit inside the bore of the solenoid magnet. A sequence of synchronized short laser light pulses are used to freeze the transient events, and the images are recorded by several high speed charge coupled devices. Quantitative and qualitative data analysis using image processing based on probability approach is described. The characteristics of free mercury jet as a high power target for beam-jet interaction at various levels of the magnetic induction field is reported in this paper.

Real-time simultaneous temperature and strain measurements at cryogenic temperatures in an optical fiber

A novel fiber optic sensor has been developed to be used in superconducting magnets for fusion reactors and other large cable-in-conduit superconductor (CICC) magnet applications. These large superconducting magnets need a diagnostic that can measure the temperature and strain throughout the magnet in real-time, which was not possible until now. Simultaneous temperature and strain measurements at cryogenic temperatures have been demonstrated, using spontaneous Brillouin scattering in an optical fiber. Using an extremely narrow (100 Hz) linewidth Brillouin laser with very low noise as a frequency shifted local oscillator, the frequency shift of spontaneous Brillouin scattered light was measured using heterodyne detection. A pulsed laser was used to probe the fiber using Optical Time Domain Reflectometry (OTDR) to determine spatial resolution. The spontaneous Brillouin frequency shift and linewidth as a function of temperature agree with previous literature on stimulated Brillouin scattering data from room temperature down to 4 K. For the first time, the spontaneous Brillouin frequency shift, linewidth, and intensity as a function of strain have been measured down to 4 K. Analyzing the frequency spectrum of the scattered light after an FFT gives the Brillouin frequency shift, linewidth, and intensity of the scattered light. 65,000 pulses, with 53 ns pulse widths, were averaged in under one second, providing a 5 meter spatial resolution along a fiber that was about 100 m long. Measuring these three parameters allow the simultaneous determination of temperature and strain in real-time throughout a fiber with a spatial resolution on the order of several meters.

Systems testing of a free hg jet system for use in a high-power target experiment

The design and operational testing of a mercury jet delivery system is presented. The equipment is part of the Mercury Intense Target (MERIT) Experiment, which is a proof-of-principle experiment to be conducted at CERN in the summer of 2007 to determine the feasibility of using an unconstrained jet of mercury as a target in a Neutrino Factory or Muon Collider. The Hg system is capable of producing a 1 cm diameter, 20 m/s jet of Hg inside a high-field solenoid magnet. A high-speed optical diagnostic system allows observation of the interaction of the jet with a 24 GeV proton beam. Performance of the Hg system will be presented, along with results of integrated systems testing without a beam.

Performance of the Conduction‐Cooled LDX Levitation Coil

The Levitated Dipole Experiment (LDX) was developed to study plasma confinement in a dipole magnetic field. Plasma is confined in the magnetic field of a 680‐kg Nb3Sn Floating Coil (F‐coil) that is electromagnetically supported at the center of a 5‐m diameter by 3‐m tall vacuum chamber. The Levitation Coil (L‐coil) is a 2800‐turn, double pancake winding that supports the weight of the F‐coil and controls its vertical position within the vacuum chamber. The use of high‐temperature superconductor (HTS) Bi‐2223 for the L‐coil minimizes the electrical and cooling power needed for levitation. The L‐coil winding pack and support plate are suspended within the L‐coil cryostat and cooled by conduction to a single‐stage cryocooler rated for 25‐W heat load at approximately 20 K. The coil current leads consist of conduction‐cooled copper running from room temperature to 80 K and a pair of commercially‐available, 150‐A HTS leads. An automatically filled liquid‐nitrogen reservoir provides cooling for the coil’s radiat...