Calibration of the high-frequency magnetic fluctuation diagnostic in plasma devices

The increasing reservoirs of energetic particles which drive high-frequency modes, together with advances in the understanding of magnetohydrodynamics, have led to a need for higher-frequency (50 kHz to >20MHz) measurements of magnetic field fluctuations in magnetic fusion devices such as tokamaks. This article uses transmission line equations to derive the voltage response of a Mirnov coil at the digitizer end of a transmission line of length ℓ. It is shown that, depending on the terminations of the line, resonances can occur even for ℓ/λ⪡1, with λ the wavelength of a fluctuation in the transmission line. A lumped-circuit model based on the approach of Heeter et al. [R. F. Heeter, A. F. Fasoli, S. Ali-Arshad, and J. M. Moret. Rev. Sci. Instrum.71, 4092 (2000)] is extended to enable the inclusion simultaneously of both serial resistance and parallel conductance elements. As originally proposed by Heeter et al. the lumped-circuit model offers the advantage of remote calibration; this may be of particular value when upgrading existing systems to operate at frequencies above the original design specification. It is formally shown that the transmission line equations for the transfer function and measured impedance reduce to those of the lumped circuit model of Heeter et al. under specific conditions. The result extends the use of the lumped-circuit model of Heeter et al., which can be used to extract the transfer function from measurement of the impedance, beyond the case of an open-circuit termination. Although the numerical procedure does exhibit some problems associated with non-uniqueness, it provides a simple calibration method for systems that are not well defined. Using typical parameters for a high-frequency Mirnov coil installed on the Joint European Torus (JET) tokamak, the lumped-circuit approximation agrees with the steady-state transmission line model to within 0.015° in phase and 22% in amplitude for frequencies up to 1 MHz. A matched termination, though eliminating line resonances and reducing the length of time for the system to reach steady state, is inappropriate for the JET-type coils which exhibit significant temperature-dependent resistance. Finally, for fluctuations of finite duration, a method of computing the discrepancy due to the simplifying assumption of Fourier-stationary conditions is described.This work was funded jointly by the United Kingdom Engineering and Physical Sciences Research Council and by EURATOM

Carboxyhaemoglobin concentration, smoking habit, and mortality in 25 years in the Renfrew/Paisley prospective cohort study

Objective: To investigate how carboxyhaemoglobin concentration is related to smoking habit and to assess whether carboxyhaemoglobin concentration is related to mortality. Design: Prospective cohort study. Setting: Residents of the towns of Renfrew and Paisley in Scotland. Participants: The whole Renfrew/Paisley study, conducted between 1972 and 1976, consisted of 7048 men and 8354 women aged 45–64 years. This study was based on 3372 men and 4192 women who were screened after the measurement of carboxyhaemoglobin concentration was introduced about halfway through the study. Main outcome measures: Deaths from coronary heart disease (CHD), stroke, chronic obstructive pulmonary disease (COPD), lung cancer, and all causes in 25 years after screening. Results: Carboxyhaemoglobin concentration was related to self reported smoking and for each smoking category was higher in participants who reported inhaling than in those who reported not inhaling. Carboxyhaemoglobin concentration was positively related to all causes of mortality analysed (relative rates associated with a 1 SD (2.93) increase in carboxyhaemoglobin for all causes, CHD, stroke, COPD, and lung cancer were 1.26 (95% confidence interval (CI) 1.19 to 1.34), 1.19 (95% CI 1.13 to 1.26), 1.19 (95% CI 1.13 to 1.26), 1.64 (95% CI 1.47 to 1.84), and 1.69 (95% CI 1.60 to 1.79), respectively). Adjustment for self reported cigarette smoking attenuated the associations but they remained relatively strong. Conclusions: Self reported smoking data were validated by the objective measure of carboxyhaemoglobin concentration. Since carboxyhaemoglobin concentration remained associated with mortality after adjustment for smoking, carboxyhaemoglobin seems to capture more of the risk associated with smoking tobacco than does self reported tobacco consumption alone. Analysing mortality by self reported cigarette smoking underestimates the strength of association between smoking and mortality

Cryptococcus neoformans chitin synthase 3 plays a critical role in dampening host inflammatory responses

Cryptococcus neoformans is the most common disseminated fungal pathogen in AIDS patients, resulting in ∼200,000 deaths each year. There is a pressing need for new treatments for this infection, as current antifungal therapy is hampered by toxicity and/or the inability of the host’s immune system to aid in resolution of the disease. An ideal target for new therapies is the fungal cell wall. The cryptococcal cell wall is different from the cell walls of many other pathogenic fungi in that it contains chitosan. Strains that have decreased chitosan are less pathogenic and strains that are deficient in chitosan are avirulent and can induce protective responses. In this study, we investigated the host responses to a chs3Δ strain, a chitosan-deficient strain, and found that mice inoculated with the chs3Δ strain all died within 36 h and that death was associated with an aberrant hyperinflammatory immune response driven by neutrophils, indicating that chitosan is critical in modulating the immune response to Cryptococcus.Cryptococcus neoformans infections are significant causes of morbidity and mortality among AIDS patients and the third most common invasive fungal infection in organ transplant recipients. One of the main interfaces between the fungus and the host is the fungal cell wall. The cryptococcal cell wall is unusual among human-pathogenic fungi in that the chitin is predominantly deacetylated to chitosan. Chitosan-deficient strains of C. neoformans were found to be avirulent and rapidly cleared from the murine lung. Moreover, infection with a chitosan-deficient C. neoformans strain lacking three chitin deacetylases (cda1Δcda2Δcda3Δ) was found to confer protective immunity to a subsequent challenge with a virulent wild-type counterpart. In addition to the chitin deacetylases, it was previously shown that chitin synthase 3 (Chs3) is also essential for chitin deacetylase-mediated formation of chitosan. Mice inoculated with the chs3Δ strain at a dose previously shown to induce protection with the cda1Δcda2Δcda3Δ strain die within 36 h after installation of the organism. Mortality was not dependent on viable fungi, as mice inoculated with a heat-killed preparation of the chs3Δ strain died at the same rate as mice inoculated with a live chs3Δ strain, suggesting that the rapid onset of death was host mediated, likely caused by an overexuberant immune response. Histology, cytokine profiling, and flow cytometry indicate a massive neutrophil influx in the mice inoculated with the chs3Δ strain. Mice depleted of neutrophils survived chs3Δ inoculation, indicating that death was neutrophil mediated. Altogether, these studies lead us to conclude that Chs3, along with chitosan, plays critical roles in dampening cryptococcus-induced host inflammatory responses

A flowing plasma model to describe drift waves in a cylindrical helicon discharge

A two-fluid model developed originally to describe wave oscillations in the vacuum arc centrifuge, a cylindrical, rapidly rotating, low temperature and confined plasma column, is applied to interpret plasma oscillations in a RF generated linear magnetised plasma (WOMBAT), with similar density and field strength. Compared to typical centrifuge plasmas, WOMBAT plasmas have slower normalised rotation frequency, lower temperature and lower axial velocity. Despite these differences, the two-fluid model provides a consistent description of the WOMBAT plasma configuration and yields qualitative agreement between measured and predicted wave oscillation frequencies with axial field strength. In addition, the radial profile of the density perturbation predicted by this model is consistent with the data. Parameter scans show that the dispersion curve is sensitive to the axial field strength and the electron temperature, and the dependence of oscillation frequency with electron temperature matches the experiment. These results consolidate earlier claims that the density and floating potential oscillations are a resistive drift mode, driven by the density gradient. To our knowledge, this is the first detailed physics model of flowing plasmas in the diffusion region away from the RF source. Possible extensions to the model, including temperature non-uniformity and magnetic field oscillations, are also discussed

Report to the Towns of Brookhaven and Islip, N.Y. on the hydrography of Great South Bay and Moriches Bay

Originally issued as Reference No. 52-26, series later renamed WHOI-.During the summer of 1950, The Woods Hole Oceanographic Institution conducted a study of the waters of Great South Bay for the Town of Islip, New York, with a view to seeking the cause of the decline of the oyster industry, which has deteriorated steadily during the past twenty years. The report of these studies was submitted in January 1951. The survey revealed two conditions which in combination appeared to be unfavorable to the oyster industry. One unfavorable condition was the local change in circulation occasioned by the opening of Moriches Inlet in 1931, which had increased the salinity of Bellport Bay, creating a condition which might well be detrimental to the production of seed oysters. Aside from this, it was concluded that little change had taken place in the salinity and tidal exchange of the central and western part of the bay during the past twenty years. The second unfavorable condition was the pollution of Great South Bay by wastes from the duck farms located along the Carmans River and the tributaries of Moriches Bay. Chemical studies indicated that the bay water is unusually rich in the products of decomposing organic matter. These materials appeared to arise from the mouth of the Carmans River and the tributaries of Moriches Bay, from which they are carried westward across Great South Bay. They provide nutriment for the growth of an unusually dense population of microscopic plants. Evidence existed that oysters do not feed properly on water containing such large concentrations of plant cells, and available statistics showed a clear correlation over a period of years between the condition of bay oysters and the numbers of plant cells in the water. Finally, the decline in oyster production has been closely paralleled by the growth of the duck industry, which increased fourfold during the period. In the report on the survey of 1950, it was pointed out that a number of questions had been revealed which were not anticipated when the field work was in progress and that these questions merited additional study. One of these related to the behavior of uric acid, the peculiar form in which birds secrete nitrogenous wastes, which promised to provide unambiguous evidence on whether the duck farms are the source of pollution. Another was the more detailed study of the circulation of Moriches Bay and its connection with Great South Bay through Narrow Bay, since this appeared to be the principal avenue of the pollution of Great South Bay. Finally, more detailed information was desired concerning the actual quantities of pollutants arising from the duck farms and of the alterations of its components by biological and other action upon introduction into the bay water. Before these additional studies could be undertaken, the problem acquired a new aspect be cause of the spontaneous closure of Moriches Inlet which occurred on May 15, 1951. While this terminated any possibility of increasing knowledge of the circulation between the bays as it previously existed, it afforded an opportunity to observe the effect of the opening on the condition of the bay waters. This information was of prime importance in view of the proposal to reopen and stabilize Moriches Inlet. Field parties visited the region on three occasions during the sumer. On July 12-14, 1951, a survey was made of the entire system of bays lying between the western extremity of Great South Bay and the Shintecock Canal. Between July 27 and August 5, studies were made of the chemical conditions in Moriches Bay and its approaches, and a detailed examination was carried out on the immediate conditions associated with the duck farms along the Terrell River. On September 24-29, an attempt was made to measure the exchange of water and associated pollutants between Moriches Bay and Great South Bay, and through the Quantuck Canal. On this occasion continuous observations were made at Smith Point and Beach Lane Bridge for a period of fifty hours, including four complete tidal cycles.The work conducted in 1951 was supported jointly by the appropriations made by the Towns of Brookhaven and Islip at the initiative of the Long Island Fishermen's Association

A high resolution Mirnov array for the Mega Ampere Spherical Tokamak

Over the past two decades, the increase in neutral-beam heating and alpha particle production in magnetically confined fusion plasmas has led to an increase in energetic particle driven mode activity, much of which has an electromagnetic signature which can be detected by the use of external Mirnov coils. Typically, the frequency and spatial wave number band of such oscillations increase with increasing injection energy, offering new challenges for diagnostic design. In particular, as the frequency approaches the megahertz range, care must be taken to model the stray capacitance of the coil, which limits the resonant frequency of the probe; model transmission line effects in the system, which if unchecked can produce system resonances; and minimize coil conductive shielding, so as to minimize skin currents which limit the frequency response of the coil. As well as optimizing the frequency response, the coils should also be positioned to confidently identify oscillations over a wide wave number band. This work, which draws on new techniques in stray capacitance modeling and coil positioning, is a case study of the outboard Mirnov array for high-frequency acquisition in the Mega Ampere Spherical Tokamak, and is intended as a roadmap for the design of high frequency, weak field strength magnetic diagnostics.This work was partly funded by the Australian National University, the United Kingdom Engineering and Physical Sciences Research Council, and by the European Communities under the contract of Association between EURATOM and CCFE