Landau damping is one of the most important mechanisms for the description of wave dissipation and efficient power absorption in helicon plasma sources. Numerical analysis using the MATLAB code is carried out to deter...
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Landau damping is one of the most important mechanisms for the description of wave dissipation and efficient power absorption in helicon plasma sources. Numerical analysis using the MATLAB code is carried out to determine the dispersion relation of the helicon plasma and calculate the axial wavenumber for m=0 mode in both Trivelpiece-Gould (TG) and helicon plasma density regimes. In addition, the MATLAB code is coupled to the cst Microwave Studio (Ms) code to examine the collisionless power absorption due to Landau damping in a helicon source driven by a single-loop antenna. The effects of some parameters, such as the electron temperature (T-e), the external magnetic field strength (B-0), and the antenna excitation frequency (f), on the Landau damping are investigated for electron density ranging from 1x10(16) to 1x10(20)m(-3). Our findings indicate that, for a given set of plasma parameters, Landau damping shows different behaviors on the power deposition. For instance, increasing the excitation frequency has considerable effect on the collisionless absorbed power in the range of values from 3x10(17) to 3x10(19)m(-3) of the electron density. Also, for f =13.56MHz, T-e=3eV, and B-0=100G, there is a specific electron density (i.e., n(e)=2x10(18)m(-3)) beyond which increasing the electron temperature causes a decrease in the collisionless power absorption;the opposite is true for lower plasma density (i.e., n(e)<2x10(18)m(-3)). Furthermore, the obtained results show that Landau damping has considerable effect on the power absorption in the helicon source at low pressure regime (e.g., P=1mTorr) with low external magnetic field strength (e.g., B-0<200G).
When the thermionic electron gun of the klystron operates, the structure around the cathode is subjected to thermal deformation due to the high operating temperature of the cathode. A thermal deformation analysis of t...
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When the thermionic electron gun of the klystron operates, the structure around the cathode is subjected to thermal deformation due to the high operating temperature of the cathode. A thermal deformation analysis of the existing electron gun with cold' dimensions (dimension on fabrication) was done using the ANSYS code to get the hot' dimensions of the electron gun on operation. After that, the optics of the emitted electron beam were simulated using two codes (EGUN and cst-PS) for the two cases of the cold' dimension and the hot' dimension. We compared the beam trajectories of the above two cases to investigate the change in the physical quantities, which would have a strong effect on the klystron performance due to the thermal deformation. The thermal deformation was found to cause a perveance change as large as 15%. The scalloping behavior was also investigated with an applied magnetic field for the two cases of cold and hot dimensions.
An 20 kV, 210 mA electron gun for a sheet beam traveling wave tube have been designed. BFE and anode dimensions are optimized using cst code to converge the beam coming from planar cathode of rectangular size 1.2 mm&#...
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ISBN:
(纸本)9781479927111
An 20 kV, 210 mA electron gun for a sheet beam traveling wave tube have been designed. BFE and anode dimensions are optimized using cst code to converge the beam coming from planar cathode of rectangular size 1.2 mm¡Á1 mm. The beam waist is formed at 11.2 mm from the cathode with the beam size of 1.1 mm¡Á 0.22 mm. Novel PPM focusing system is designed for stable transport of the beam. In this case no side magnets are used and pole-pieces are extended after beam edge. Absence of side magnets will reduce the cost of magnetic material, weight of the tube and make easier to insert couplers. The horizontal position of extended pole-piece is after 5 mm from the side wall of the drift tube tunnel in order to make mechanically possible to extend the pole-pieces. NdFeB magnates with Br value 1.4 T are considered. The shielding pole piece is extended towards cathode region to get Brillouin flow. Beam transmission is achieved more than 95 % up to 40 mm and 90 % up to 70 mm in a tunnel suitable for W-band sheet beam TWT.
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