The present work has been characterized by higher order modes in the cavities of the Gyrotron; they are capable of producing RF plasma by developments of it. It uses for fusion systems. We choose the TE31,8 mode in our study. The main problem of gyrotron is the device of the thermal cavity loading. The problem of the thermal loading is solved when any parasitic modes suppress, absence of desired modes; the thermal loading is increased when the high power tube of gyrotron operation is unstable. The mathematical interaction model contains equations that describe the electron motion and the field profiles of the transferred electric modes of the resonator, these are interacting with electrons based on the finite difference method that has been designed to study the starting current, the frequency, quality factor and calculates the roots of the Bessel function by the program we designed in Fortran language. They are used to calculate the operation frequency. Good agreement is between our results and the previous published results both confirm the accuracy of the performance of the designed program.

Nickel oxide (NiO) microparticles were synthesized by pulsed laser ablation in double deionized water and intensively studied using Nd:YAG laser. The obtained sample was examined by X-ray diffraction, XRD measurement which tests the existence of polycrystalline. The structural parameters introduced and surface morphology was studied using field emission scanning electron microscopy devices. The optical properties of microparticles in a liquid were investigated through UV-VIS spectroscopy. The CO/CO2 sensing properties of the NiO microstructure sensors were systematically investigated, and the effects of different laser fluencies on the CO/CO2 sensing characteristics were analyzed. XRD measurements reflected the existence of polycrystalline, the optical result shows that The absorption spectra peak centered around 360 nm and a tail extending to the red region (600 nm), the scanning electron microscopy images showed that the morphologies of NiO thin films have microspheres in various. The sample affected by laser fluence 1.9 J/cm2 which exhibits the best sensitivity for CO2 gas.

This paper is concerned with the analysis and design of a gyrotron oscillator with 460 GHz that can excite both modes (TE231) the fundamental (230GHz) and (TE061, TE261) second harmonic (near 460GHz). The oscillator is operated with 12KV beam voltage and 100mA beam current, and a computer program was developed to study the cavity in this oscillator and the wave-particle interaction inside it using the forward finite difference technique as a numerical method. The input data of the program are electron energy, velocity ratio, normalized cavity length, the normalized value of the external magnetic field, the mode number (m,n,l), and nth-non van shining root of J_m^' (x)=0 to calculate the beam and starting currents, frequency and quality factor of the cavity. The results show good agreement with other reported works [10]- [12]- [13]- [14], [15] .This oscillator can serve as a millimeter-wave source at the magnetic field of (16.4T) for enhanced nuclear magnetic resonance and can be used to perform the biological experiment.