Princeton Large Torus Research Articles

Charge exchange measurements of MHD activity during neutral beam injection in the Princeton Large Torus and the Poloidal Divertor Experiment

The horizontally scanning, multi-angle charge exchange analysers on the Princeton Large Torus (PLT) and the Poloidal Divertor Experiment (PDX) were used to study the effects of MHD activity on the background ion distribution function and on the beam ion slowing-down process during high power neutral injection. Sawtooth oscillations were observed in the fast ion flux on PLT and PDX, and measurements with neutral beams providing local neutral density enhancement indicated that the ions were transported radially when these events occurred. With nearperpendicular injection in PDX, at the lower toroidal fields necessary to maximize the plasma beta, repetitive bursts of greatly enhanced charge exchange flux were observed. These were associated with the ‘fishbone’ MHD instability, and a substantial depletion of the perpendicular slowing-down spectrum below the injection energy was seen. A simple phenomenological model for this loss mechanism was developed, and its use in simulation codes has been successful in providing good agreement with the experimental data. The behaviour and characteristics of this model are well matched by direct theoretical calculations.

Intercombination lines of the zinc isoelectronic sequence for Z = 50-70.

The intercombination lines of the zinc sequence corresponding to the transition 4s4p ${}^{3}$${P}_{1}$\ensuremath{\rightarrow}4${s}^{2}$ ${}^{1}$${S}_{0}$ have been observed for xenon, lanthanum, neodymium, europium, gadolinium, and ytterbium in the Princeton Large Torus tokamak discharges.

Time-resolved spectra in the 80–340-Å wavelength region from Princeton Large Torus tokamak plasmas

High-resolution spectra from the Princeton Large Torus plasma have been recorded by a 2-m Schwob–Fraenkel soft-x-ray multichannel spectrometer. Spectra covering a wavelength range of approximately 50 A were recorded every 50 msec, and the spectra were normalized and added together to produce composite spectra covering the region 80–340 A. Several well-known reference lines were used to establish an absolute wavelength scale, and transition wavelengths were measured to an accuracy of approximately 0.02 A. By subtracting spectra recorded at various times throughout the discharge, transitions from ions formed in the cooler and hotter plasmas were easily distinguished, and blends between hot and cold transitions were resolved. Wavelengths of transitions in C, O, Ti, Cr, Mn, Fe, and Ni have been measured.

Power deposition and thermal response of PLTs rotatable limiter

Two-dimensional temperature contours of the Princeton Large Torus (PLT) rotatable limiter have been measured using a calibrated infrared camera with ∼ 30 ms time resolution. These experiments were performed during intense ion cyclotron range of frequencies (ICRF) heating (1.0–5.0 MW) and lower hybrid current drive (LHCD) ( P > 500 kW at 800 MHz or 2.45 GHz). Different expressions of energy deposition from the scrape-off region ( λ = 0.05 cm to 2.00 cm) are used to compare to the thermal contours on the limiter's front surface. One model of the scrape-off region assumes a simple exponential decay of particles and is derived from the intersection of a toroid and an infinite plane. A second model, derived from the diffusive motion of individual particle trajectories, has a near gaussian particle flux profile. The effects of Debye length and gyromotion are also modeled. Temperature predictions generated by a three-dimensional finite difference thermal model of the limiter have the following inputs: a temporal and spatial variation of power on the limiter's surfaces, nonlinear temperature-dependent material properties, surface radiation to the vacuum vessel walls and surface sublimation effects. The contour maps of the limiter's front surface are generated from the thermal model's temperature predictions for cases with and without limiter rotation.

Spectrum lines of highly ionized zinc, germanium, selenium, zirconium, molybdenum, and silver injected into Princeton Large Torus and Tokamak Fusion Test Reactor tokamak discharges

Measured wavelengths of a number of highly ionized atoms are reported. These include the 3s23p–3s3p2 and 3s23p–3s23d transitions in the aluminum isoelectronic sequence of Zn xviii, Ge xx, Se xxii, Zr xxviii, Mo xxx, and Ag xxxv; several transitions in the n = 2 shell of Zn xxii, Zn xxiii, and Zn xxiv; and the resonance and intercombination lines of Ag xxxvi–Ag xxxvii and of Ge xxix–Ge xxx.

Dielectronic satellite spectra of hydrogenlike titanium.

Theoretical atomic parameters calculated with the q$Z$-expansion method and with the multicon-figuration Thomas-Fermi model set were recently reported and used in the analyses of dielectronic satellite spectra of hydrogenlike titanium observed from the Princeton Large Torus tokamak discharges. A comparison of our calculations, based on the Hartree-Fock-Slater atomic model, with the other two theoretical results show reasonable agreement with $n=2$ satellites but systematic and sometimes significant differences are found for $n=3 \mathrm{and} 4$ satellites.

Use of graphite in Langmuir-calorimeter probe heads

Graphite has become an important material in magnetically confined fusion devices, being used for components such as limiter blades, divertor plates, and Faraday shields. Langmuir-calorimeter probes on the tokamak fusion test reactor (TFTR) and the Princeton large torus (PLT) have utilized graphite in probe heads, active elements, protective shields, and in an epoxy compound for various applications. Most recently, all-graphite edge probes have been used successfully on these machines. The advantages and disadvantages of using this material as a collecting element and a heat resistant support are discussed, with reference to its survivability and usefulness in the TFTR environment. A three-dimensional finite difference thermal analysis of a TFTR graphite calorimeter is presented which calculates its temperature response to selected power inputs. This was used to estimate power densities at the edge of TFTR plasmas.

PLT and PDX perpendicular charge exchange analyzers

The perpendicular charge-exchange systems used on the poloidal divertor experiment and the Princeton large torus are comprised of ten-channel, mass-resolved, charge-exchange analyzers. Results from these systems indicate that instrumental effects can lead to erroneous temperature measurements during deuterium neutral beam injection or at low hydrogen concentrations.

High-resolution n=3 to n=2 spectra of neonlike silver.

Spectra of the n=3 to n=2 transitions in neonlike silver emitted from the Princeton Large Torus have been recorded with a high-resolution Bragg-crystal spectrometer. The measurements cover the wavelength region 3.3--4.1 A\r{} and include the forbidden 3p\ensuremath{\rightarrow}2p electric quadrupole lines. Transitions in the adjacent sodiumlike, magnesiumlike, and aluminumlike charge states of silver have also been observed and identified. The Ly-\ensuremath{\alpha} spectra of hydrogenlike argon and iron, the K\ensuremath{\alpha} spectra of heliumlike argon, potassium, manganese, and iron, and the K\ensuremath{\beta} spectrum of heliumlike argon fall in the same wavelength region in first or second order and have been measured concurrently. These spectra provide a coherent set of wavelength reference data obtained with the same spectrometer and from the same tokamak. This set is used as a basis to compare wavelength predictions for one- and two-electron systems to each other and to determine the transition energies of the silver lines with great accuracy.

PLT data acquisition and analysis system

The data acquisition and analysis system for PLT (Princeton Large Torus) is being moved from a DEC-10 to a VAX 11/785. Most of the major diagnostics are currently running on the VAX, with approximately 1 Mbyte of data being taken each shot. The system uses the MIT model data system (MDS) for acquisition and archival of data and the PPPL event-controlled scheduler (ECS) for scheduling. The analysis programs use the MDS data retrieval subroutines which deliver correctly calibrated results to the user program.

Multichannel Thomson scattering systems with high spatial resolution (invited)

Thomson scattering systems capable of providing snapshot profiles of electron temperature and density with high spatial resolution (>50 points) have become routine diagnostics on the Princeton large torus (PLT), Princeton divertor experiment (PDX), and tokamak fusion test reactor (TFTR) tokamaks. The design parameters of these systems are compared. Particular attention is given to describing those new components and techniques which have contributed most to improved data quality and reliability in the ten-year evolution of these systems. Examples of recent TFTR Te(R) and ne(R) profiles are presented.

Probes for edge plasma studies of TFTR (invited)

Tokamak fusion test reactor (TFTR) probes are designed to study the interaction of the plasma with material surfaces such as the wall and limiters, and to study the transport of particles and energy between the core and edge. Present probe heads have evolved from prototypes in Princeton large torus (PLT), poloidal divertor experiment (PDX) [Princeton BETA experiment (PBX)], and the initial phase of TFTR operation. The newest heads are capable of making several simultaneous measurements and include Langmuir probes, heat flux probes, magnetic coils, rotating calorimeter fast ion probes, and sample exposure specimens. This paper describes these probe heads and presents some of the data they and their prototypes have acquired. The paper emphasizes measurement of transient plasma effects such as fast ion loss during auxiliary heating, the evolution of the edge plasma during heating, compression, and free expansion, and fluctuations in the edge plasma.

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Authors

Fusion product diagnostics on the princeton large torus

Abstract With recent increases in bulk and tail ion temperatures on tokamaks such as the Princeton Large Torus, fusion product measurements have become a popular passive diagnostic for fusion physics [1]. Solid-state charged-particle detectors which utilize 3.02 MeV proton emission from d(d,p)t thermonuclear reactions to determine local ion temperature gradients have been fabricated for use on PLT. Estimation of the radial ion thermal conduction during ohmic and RF wave-heated discharges should be possible using these data. Other applications of fusion product measurements from d(d,p)t [2], d(d,n)3He, d(t,n)α, and d(3He,p)α reactions are discussed.

Emission in the 50–80-Å region from highly ionized silver in Princeton Large Torus tokamak plasmas

The spectrum of silver emitted by Princeton Large Torus tokamak plasmas has been recorded in the 25–150-A region by a multichannel time-resolving grazing-incidence spectrometer. Silver atoms have been introduced in the tokamak plasma by using the laser blowoff technique. For the first time to our knowledge, lines emitted within the 3p–3d transitions of Ag xxix, Ag xxx, and Ag xxxi ions, between 50 and 80 A, have been identified.

Total scattering cross sections and interatomic potentials for neutral hydrogen and helium on some noble gases

Measurements of energy-dependent scattering cross sections for 30 to 1800 eV D incident on He, Ne, Ar, and Kr, and for 40 to 850 eV He incident on He, Ar, and Kr are presented. They are determined by using the charge-exchange efflux from the Princeton large torus tokamak as a source of D or He. These neutrals are passed through a gas-filled scattering cell and detected by a time-of-flight spectrometer. The cross section for scattering greater than the effective angle of the apparatus (≈20 mrad) is found by measuring the energy-dependent attenuation of D or He as a function of pressure in the scattering cell. The interatomic potential is extracted from the data.

Spectra of highly ionised zirconium and molybdenum in the 60-150 AA range from PLT tokamak plasmas

Transitions of the types 3s23pk-3s3pk+1 and 3pk-3pk-13d are identified in spectra of zirconium and molybdenum ions isoelectronic with K I to Mg I. These elements were introduced into the Princeton large torus (PLT) tokamak by the laser blow-off technique and their spectra were recorded in the 60-150 AA range using a time-resolving grazing incidence spectrography. Brightnesses of the observed lines are given. These lines should be useful for spectroscopic diagnostics of tokamak and other high-temperature fusion research plasmas. Difficulties related to the study of complex Delta n=0 spectra in the XUV region are discussed.

Comparison of the theory and the practice of lower-hybrid current drive.

The theory of rf-driven plasma currents is applied to the lower-hybrid experiments on the Princeton Large Torus, Princeton University, tokamak. Particular emphasis is placed on those experiments in which the plasma current was varying. The comparison between theory and experiment is made with respect to the efficiency with which rf energy was converted to poloidal magnetic field energy. Good agreement is found irrespective of whether the current was increasing, constant, or decreasing.

Ground configurations of highly ionized silver

A number of lines mostly corresponding to magnetic-dipole transitions in the n = 3 and n = 4 shells of silver have been identified. The lines were observed in the Princeton Large Torus tokamak discharges, into which silver was injected by means of the laser-ablation method.

Status of the Tokamak Fusion Test Reactor (TFTR)

The Tokamak Fusion Test Reactor (TFTR). the key toroidal confinement device of the US fusion energy research program, is directed toward the goal of demonstrating energy break-even under DT conditions by 1988. TFTR now is completing its second year of research operation. In this period it has extended the study of scaling in ohmic heated plasmas and found scaling to vary with the cube of length including observations relative to that of the Princeton Large Torus (PLT) tokamak; it has explored impurity effects and the influence of neutral beam heating on confinement. The ongoing experimental campaign is being conducted with plasma/machine parameters up to B T ~ 40 kG , I p ~ 1.5 MA , P NB ~ 2 MW(H) and τ NB ~ 0.3 s with τ c up to 0.3 s. With completion of this two year start-up phase the TFTR will be operated for a two-year period of machine optimization concluding with Q ~ 1 for DD operation, followed by a two year phase of plasma optimization culminating with DT operation at Q ~ 1 in 1988. A subsequent phase of D-T research is under consideration.