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Two similar experimental set-ups were used to measure axial and radial distribution of discharge plasma parameters at different magnetic fields. Both systems were cylindrical magnetrons with outer cylindrically-shaped anode and coaxially placed cathode -both the discharge vessels had diameters approximately 6 cm and they were 30 cm and 11 cm long respectively. In the longer magnetron the measurements were made using three radially movable cylindrical Langmuir probes placed at three different axial positions and in the shorter magnetron the axially movable probe was used. From the measurements there were evaluated electron density, electron mean energy, plasma potential and floating potential.

A cylindrical magnetron discharge (CMD) with two coaxial electrodes, a uniform axially directed magnetic field, and discharge ends closed by the shields biased at the cathode potential is considered. The presence of the shields creates axial inhomogeneity of plasma, which is taken into account in this study. At low pressures and small magnetic fields the pronounced nonlocal regime of the electron distribution function (EDF) formation is realized. The electron component is analyzed on the basis of radially and axially inhomogeneous Boltzmann kinetic equation. Unmagnetized electrons that move in axial direction are trapped in the axial potential well, their energy relaxation length exceeds the discharge vessel length, and the kinetic equation can be averaged over axial flights of electrons. Using a model two-dimensional potential profile, the EDFs at the different axial positions are obtained and two-dimensional distributions of the electron density, ionization rate, and current on cathode are calculated. The results of the modeling and experiments are compared for the dc CMD in Ar at a pressure of 3 Pa, magnetic field strength of 10 mT, and current of 150 mA.

SwYnmaryThe structure of 6-hydroxy-khydroxymethyltropolone-5-carboxylic acid y-lactone was established for a new tropolone metabolite.SEVERAL years ago three fungal tropolones of Penicillium stipitatuwz Thom were discovered : stipitatic acid (I) ,1 stipitatonic acid (11),2 and ethyl tipi it ate.^ Now, a new tropolone derivative, stipitalide (111), has been isolated.* Similar y-lactone-ring compounds were found in some fungal and lichen metabolites5 * I. Kuhr and J. Fuska, A @ Microbiol., in the press.