http://nopr.niscair.res.in/handle/123456789/12933 Search the Channel search http://nopr.niscair.res.in/simple-search http://nopr.niscair.res.in/handle/123456789/12956 Title: Accurate estimation of start oscillation current for maximum output power in 42 GHz, 200 kW gyrotron <br/> <br/>Authors: Khatun, Hasina; Rao, Reddy R; Sinha, A K; Joshi, Sri Niwas <br/> <br/>Abstract: Design of a 42 GHz, 200 kW gyrotron operating at TE₀₃ involves optimization of a guiding magnetic field across the tapered cavity. The start oscillation current (SOC) or starting current is one of the most important parameter to estimate the guiding magnetic field to excite the desired operating mode irrespective of large numbers of competitive modes. This paper presents an accurate method to estimate SOC, based on the linear theory, yielding the guiding magnetic field at which the maximum desired power level is also achieved through the beam-wave interaction simulation using 3D MAGIC-PIC code. The method involves interpretation of the beam wave interaction length as e^-1 times of the normalized axial Gaussian electric field profile. This method is successfully applied to low order symmetric operating mode gyrotron. The minimum SOC from the linear theory for the operating mode TE₀₃and the maximum power from the non-linear theory/code are obtained at the same guiding magnetic field 1.607 T with an error of 0.12% only. The paper also reports the effect of noise on SOC and output power, simultaneously. <br/> <br/>Page(s): 776-781 http://nopr.niscair.res.in/handle/123456789/12955 Title: Effect of lead content on structural and <i>dc </i>electrical conductivity of perovskite Ca_XPb₍₁_-X)TiO₃ (CPT) ceramic <br/> <br/>Authors: El-Mallah, H M <br/> <br/>Abstract: Ceramic compositions of complex perovskite Ca_XPb₍₁_-_X)TiO₃ (CPT) systems with (x =1, 0.8, 0.7, 0.6, 0.4, 0.2 and 0) were prepared by mechanical mixing of their oxides (CaTiO₃ and PbTiO₃). The structure of the (CPT) ceramics was characterized by X-ray diffraction (XRD) not only to show the quality of the composition, but also to determine structure of the system and the lattice parameters. The effect of Pb on the local structure of the seven ceramic samples (CPT) has been studied. The ceramics transform gradually from orthorhombic phase (pseudo cubic phase) to cubic phase and to tetragonal phase by increasing Pb content per cent. Tetragonality of PbTiO₃ decreases with increasing Ca content and disappears at the composition Ca_0.6Pb_0.4TiO₃. The density, molar volume, atomic concentration and the atomic intermediate distance have been determined. The <i>dc. </i>conductivity of the compositions measured in the temperature range 303-770 K obeys Arrhenius law. Temperature dependence of conductivity revealed that the conductivity is thermally activated. The critical (phase transition) temperature <i>T</i>_C was deduced by differential thermal analysis (DTA) and <i>dc</i> conductivity data. Semiconductor-semiconductor-metal type for the compositions of <i>x</i> = 1.0, 0.8, 0.7, 0.4 and 0.2 have been observed. While semiconductor-metal behaviour was observed for the compositions Ca_0.6Pb_0.4TiO₃ and PbTiO₃ in the temperature range <i>T</i>_SM = 260-370°C and 230-480°C, respectively. <br/> <br/>Page(s): 769-775 http://nopr.niscair.res.in/handle/123456789/12954 Title: Studies on nanocrystalline ZnS thin films prepared by modified chemical bath deposition method <br/> <br/>Authors: Shinde, M S; Ahirrao, P B; Patil, I J; Patil, R S <br/> <br/>Abstract: Nanocrystalline zinc sulphide (ZnS) thin films have been grown on glass surface by modified chemical bath deposition method (M-CBD). The optimized preparative parameters including temperature, <i>p</i>H of solution, immersion time, immersion cycles, have been optimized for fine nanocrystalline film growth. As deposited nanocrystalline zinc sulphide (ZnS) thin films have been characterized for the structural, optical and electrical properties using X-ray diffraction (XRD), UV-Vis spectra and <i>dc</i> electrical conductivity by two point probe method. <br/> <br/>Page(s): 765-768 http://nopr.niscair.res.in/handle/123456789/12953 Title: High density plasma beam source for nitriding <br/> <br/>Authors: Ganguli, B <br/> <br/>Abstract: A high density plasma beam source has been developed for the purpose of surface treatment and study of low energy ions and neutrals with surfaces. The plasma is generated by pulse microwave power at 2.45 GHz. A pair of Helmholtz coils is used for generating axial magnetic field of 436 G which is also responsible for the production of plasma inside a stainless steel tube of 26 mm internal diameter. The plasma particles follow the axial magnetic field lines and hence, form a beam of same diameter as the internal diameter of the SS tube. The current measured by an interceptor plate (negatively biased) is about 60 mA while the plasma density is determined to be approximately 1.1X10¹² cm^-3 at the center and falling off to about 1X10¹¹ cm^-3 at 1 cm away from the center. The plasma source using a mixture of nitrogen and hydrogen (1:2) was used successfully to nitride a sample (diameter 16 mm) of SS201 at a low temperature of 400°C. The surface hardness achieved is rather high (1990 HV) which is more than five-fold increase compared to untreated surface (358 HV). The depth of the nitriding layer was found to be 26 microns. XRD results indicate efficient conversion of chromium to chromium nitride by the high plasma density of the present source accounting for the very efficient nitriding process. <br/> <br/>Page(s): 759-764