[en] Magnetic fusion devices require fast-responding, versatile, and accurate gas injection systems in order to initiate and modulate the plasma density. We describe the gas injection control system (GICS), which regulates the gas injected into the torus of Princeton's Tokamak Fusion Test Reactor (TFTR). Synchronized with each TFTR discharge, a PDP 11/23 microcomputer provides real-time control for one to six fast injection valves, each allocated to feedback or open loop operation. Up to four feedback sources, including torus pressure gauges and plasma density measurements, are checked once each cycle for 1000 cycles; the cycle duration can be set to any multiple of 2 ms up to 16 ms. Detection of various fault conditions can cause automatic shutdown or modification of GICS operation. Data is archived after each TFTR discharge, and subsequently used for particle fueling studies and analysis of system drifts. A steady state mode of operation is used for vacuum vessel discharge cleaning. The system also provides for valve calibration and torus pumping speed measurements

[en] The design and operation of instrumentation included in the gas injection system of the Tokamak Fusion Test Reactor (TFTR) for torus pressure and gas flow measurements are described. Magnetically shielded ion gauges, located on the torus boundary, are used for fast (1 kHz) torus pressure measurements over the range 10^-7--10^-3 Torr. Gas injection assemblies comprising an array of piezoelectric gas injection valves are situated at three toroidal locations. The gas injection valves are programmed for various discharge conditions including feedback control from the torus pressure gauges and plasma density measurement. Gas flow through the injection valves is monitored by strain-gauge-type pressure transducers on each injection valve. The resulting gas flow measurements are used for gas fueling, particle balance, and recycling studies

[en] High-level nuclear waste produced from fuel reprocessing operations at the Savannah River Site (SRS) requires pretreatment to remove Cs-137, Sr-90 and alpha-emitting radionuclides (i.e., actinides) prior to disposal onsite as low level waste. Separation processes planned at SRS include sorption of Sr-90 and alpha-emitting radionuclides onto monosodium titanate (MST) and caustic side solvent extraction, for Cs-137 removal. The MST and separated Cs-137 will be encapsulated into a borosilicate glass wasteform for eventual entombment at the federal repository. The predominant alpha-emitting radionuclides in the highly alkaline waste solutions include plutonium isotopes Pu-238, Pu-239 and Pu-240. This paper describes recent results to produce an improved sodium titanate material that exhibits increased removal kinetics and capacity for Sr-90 and alpha-emitting radionuclides compared to the baseline MST material. (authors)

[en] A new vanadium(III) phosphate, Ba[V^III₂(HPO₄)₄](H₂O), has been synthesized by hydrothermal methods, and its structure solved by single-crystal X-ray diffraction. This vanadium phosphate crystallizes in the monoclinic system, space group P2₁. The cell parameters are a=9.441(2), b=7.913(2), c=9.521(2) A; β=117.91(2) ; V=628.5(3) A³; Z=2; D_calc=3.387 mg mm^-3; R=0.055 and R_w=0.065 for 1885 reflections with F>6.0σ(F). The three-dimensional [V₂(HPO₄)₄(H₂O)]^2- lattice can be described as being built up of chains of eight-membered rings along the c axis, formed by corner-shared VO₆ octahedra and HPO₄ tetrahedra (-V-O-P-O-), which are crosslinked via interchain V-O-P bonding to produce a three-dimensional lattice. The crosslinking interaction produces 16-membered rings. Contrary to other low-valent vanadium phosphates, cavities are found in the solid, rather than tunnels. The Ba²⁺ and H₂O are located in these cavities. (orig.)

[en] The Tokamak Fusion Test Reactor (TFTR) (R. J. Hawryluk, to be published in Rev. Mod. Phys.) experiments on high-temperature plasmas, that culminated in the study of deuterium endash tritium D endash T plasmas containing significant populations of energetic alpha particles, spanned over two decades from conception to completion. During the design of TFTR, the key physics issues were magnetohydrodynamic (MHD) equilibrium and stability, plasma energy transport, impurity effects, and plasma reactivity. Energetic particle physics was given less attention during this phase because, in part, of the necessity to address the issues that would create the conditions for the study of energetic particles and also the lack of diagnostics to study the energetic particles in detail. The worldwide tokamak program including the contributions from TFTR made substantial progress during the past two decades in addressing the fundamental issues affecting the performance of high-temperature plasmas and the behavior of energetic particles. The progress has been the result of the construction of new facilities, which enabled the production of high-temperature well-confined plasmas, development of sophisticated diagnostic techniques to study both the background plasma and the resulting energetic fusion products, and computational techniques to both interpret the experimental results and to predict the outcome of experiments. copyright 1998 American Institute of Physics

[en] Experiments in the Tokamak Fusion Test Reactor (TFTR) [Phys. Plasmas 2, 2176 (1995)] have explored several novel regimes of improved tokamak confinement in deuterium - tritium (D--T) plasmas, including plasmas with reduced or reversed magnetic shear in the core and high-current plasmas with increased shear in the outer region (high l_i). New techniques have also been developed to enhance the confinement in these regimes by modifying the plasma-limiter interaction through in situ deposition of lithium. In reversed-shear plasmas, transitions to enhanced confinement have been observed at plasma currents up to 2.2 MA (q_a∼4.3), accompanied by the formation of internal transport barriers, where large radial gradients develop in the temperature and density profiles. Experiments have been performed to elucidate the mechanism of the barrier formation and its relationship with the magnetic configuration and with the heating characteristics. The increased stability of high-current, high-l_i plasmas produced by rapid expansion of the minor cross section, coupled with improvement in the confinement by lithium deposition has enabled the achievement of high fusion power, up to 8.7 MW, with D--T neutral beam heating. The physics of fusion alpha-particle confinement has been investigated in these regimes, including the interactions of the alphas with endogenous plasma instabilities and externally applied waves in the ion cyclotron range of frequencies. In D--T plasmas with q₀>1 and weak magnetic shear in the central region, a toroidal Alfvn eigenmode instability driven purely by the alpha particles has been observed for the first time. The interactions of energetic ions with ion Bernstein waves produced by mode conversion from fast waves in mixed-species plasmas have been studied as a possible mechanism for transferring the energy of the alphas to fuel ions. copyright 1997 American Institute of Physics

[en] The Tomamak Fusion Test reactor has performed initial high-power experiments with the plasma fueled with nominally equal densities of deuterium and tritium. Compared to pure deuterium plasmas, the energy stored in the electron and ions increased by ∼20%. These increases indicate improvements in confinement associated with the use of tritium and possibly heating of electrons by α particles created by the D-T fusion reactions

[en] Peak fusion power production of 6.2±0.4 MW has been achieved in TFTR plasmas heated by deuterium and tritium neutral beams at a total power of 29.5 MW. These plasmas have an inferred central fusion alpha particle density of 1.2x10¹⁷ m^-3 without the appearance of either disruptive magnetohydrodynamics events or detectable changes in Alfven wave activity. The measured loss rate of energetic alpha particles agreed with the approximately 5% losses expected from alpha particles which are born on unconfined orbits

[en] Both global and thermal energy confinement improve in high-temperature supershot plasmas in the Tokamak Fusion Test Reactor (TFTR) when deuterium beam heating is partially or wholly replaced by tritium beam heating. For the same heating power, the tritium-rich plasmas obtain up to 22% higher total energy, 30% higher thermal ion energy, and 20-25% higher central ion temperature. Kinetic analysis of the temperature and density profiles indicates a favorable isotopic scaling of ion heat transport and electron particle transport, with τ_Ei(a/2) ∝ left angle A right angle ^0.7-0.8 and τ_pe(a) ∝ left angle A right angle ^0.8. (orig.)