MHD-Induced Alpha Particle Loss in TFTR

MHD-induced increases in alpha particle loss to the wall were observed for both coherent modes and transient reconnection events using an array of scintillator detectors near the wall of Tokamak Fusion Test Reactor (TFTR). The magnitude of the coherent MHD-induced alpha loss as seen by these detectors was normally comparable to the MHD-quiescent first-orbit or toroidal-field ripple loss, but the magnitude of the alpha loss during reconnection events was up to 1000 times higher than this for a short time. Modeling suggest that the coherent MHD loss mechanism will be even less significant for future reactor-scale deuterium-tritium tokamaks due to the smaller ratio of the alpha gyroradius to minor radius

Measurements of the intercombination and forbidden lines from helium-like ions in Tokamaks and Electron Beam Ion Traps

The paper reviews the results from tokamak experiments for the line ratios x/w, y/w, and z/w from helium-like ions with Z in the range from 14 to 28. With exception of the DITE experiments, where these line ratios were found to be in agreement with theoretical predictions, all other tokamak experiments yielded values that were significantly larger than predicted. The reasons for these discrepancies are not yet understood. It is possible that radial profile effects were not properly taken into account in the majority of the tokamak experiments. The paper also gives a short historical review of the X-ray diagnostic developments and also presents very recent data from a new type of X-ray imaging crystal spectrometer, which records spatially resolved spectra with a spatial resolution of about 1 cm in the plasma. These new data can be Abel inverted, so that it will be possible to determine line ratios at each radial position in the plasma. Effects of radial profiles, which may have affected the chord-integrated measurements of the past, will thus be eliminated in the future

Conformation of a Polyelectrolyte Complexed to a Like-Charged Colloid

We report results from a molecular dynamics (MD) simulation on the conformations of a long flexible polyelectrolyte complexed to a charged sphere, \textit{both negatively charged}, in the presence of neutralizing counterions in the strong Coulomb coupling regime. The structure of this complex is very sensitive to the charge density of the polyelectrolyte. For a fully charged polyelectrolyte the polymer forms a dense two-dimensional "disk", whereas for a partially charged polyelectrolyte the monomers are spread over the colloidal surface. A mechanism involving the \textit{overcharging} of the polyelectrolyte by counterions is proposed to explain the observed conformations.Comment: 4 pages, 4 figures (6 EPS files

Tokamak x ray diagnostic instrumentation

Three classes of x-ray diagnostic instruments enable measurement of a variety of tokamak physics parameters from different features of the x-ray emission spectrum. (1) The soft x-ray (1 to 50 keV) pulse-height-analysis (PHA) diagnostic measures impurity concentrations from characteristic line intensities and the continuum enhancement, and measures the electron temperature from the continuum slope. (2) The Bragg x-ray crystal spectrometer (XCS) measures the ion temperature and neutral-beam-induced toroidal rotation velocity from the Doppler broadening and wavelength shift, respectively, of spectral lines of medium-Z impurity ions. Impurity charge state distributions, precise wavelengths, and inner-shell excitation and recombination rates can also be studied. X rays are diffracted and focused by a bent crystal onto a position-sensitive detector. The spectral resolving power E/..delta..E is greater than 10/sup 4/ and time resolution is 10 ms. (3) The x-ray imaging system (XIS) measures the spatial structure of rapid fluctuations (0.1 to 100 kHZ) providing information on MHD phenomena, impurity transport rates, toroidal rotation velocity, plasma position, and the electron temperature profile. It uses an array of silicon surface-barrier diodes which view different chords of the plasma through a common slot aperture and operate in current (as opposed to counting) mode. The effectiveness of shields to protect detectors from fusion-neutron radiation effects has been studied both theoretically and experimentally

Dielectronic satellite spectrum of helium-like iron (Fe XXV)

Dielectronic satellite spectra of Fe XXV near 1.8500 A have been observed from PLT (Princeton Large Torus) tokamak plasma discharges for electron temperatures in the range from 1.5 to 3 keV and an electron density of 2 x 10/sup 13/ cm/sup -3/. The electron temperature was independently determined from the electron cyclotron radiation emitted by the plasma. The quality of the spectra allows a detailed comparison with theoretical prediction, which is of importance in view of diagnostic applications

Dimuon production by protons in Tungsten

The mass spectrum of dimuons produced by 400 GeV/c protons in Tungsten has been measured for masses greater than 7 GeV. A clear resonant signal of 2700 upsilons has been seen. The dependence of dimuon production on xF and pT has been determined for dimuon masses in the range 7.0 to 8.25 GeV as well as for masses in the upsilon region 8.25 to 9.75 GeV.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87470/2/93_1.pd

Spatial Resolution Attainable with Cathode Strip Chambers at the Trigger Level

A simple network of comparators applied to the strip signals of a cathode strip chamber allows quick hit localization to within a halfstrip width, or +/- a quarter-strip. A six-plane chamber with 6.4 mm wide strips was tested in a high-energy muon beam. The chamber was placed behind a 30 cm thick iron block. We show that patterns of hits localized to within a halfstrip allowed us to identify 300 GeV/c muon tracks with 99% probability and 0.7 mm spatial resolution in the presence of muon bremsstrahlung radiation. This technique of finding muon tracks will be used in the cathode strip chambers of the CMS Endcap Muon System