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A sheet plasma is generated by a mesh anode and a single hot-filament cathode with a DC power supply, and its characteristics are experimentally investigated. The sheet plasma is observed to locate around the anode. Both electron density and electron temperature derived from the average energy of the energetic electrons in nitrogen are estimated to be 10 cm−3 and 20~ 40 eV, respectively, using the optical emission spectroscopy (OES) method based on a kinetic model of low-pressure nitrogen discharge. The electron density, electron temperature and their spatial distributions are found to be affected by the supplying voltage on the anode (70 V to 300 V), filament temperature (600°C to 780°C) and gas pressure (2 Pa to 20 Pa). By adjusting these parameters the discharge status can be easily controlled.

The pulse deformation and time delay, which appear when the laser propagates in a thick atom vapor, influence the ionization yield and selectivity of atomic multi-step photoionization process directly. In this paper, we study the propagation of laser pulse and atomic photoionization in a thick atom vapor medium according to the atom vapor laser isotope separation. The process of atomic multi-step photoionization and the propagation of laser in a thick medium are described by density matrix equation and Maxwell equations, respectively. The medium consists of target isotope and non-target isotope, which is non-resonantly excited. Through numerical solution of the coupled equations we illustrate the propagation characteristics of laser and the influences of atom vapor parameters and laser parameters on average ionization yield and average selectivity in a thick medium. The important results of calculation are as follows:when the atom vapor medium is rather thick, the average ionization yield increases while average selectivity decreases with the increase of laser power. When the atom vapor is relatively thin, the average ionization yield and average selectivity increase with the decrease of laser power simultaneously. Besides, there is a positive time delay between two laser pulses in which case the average ionization yield of target isotope reaches its maximum value. Moreover, when the parameters of atom vapor are constant, extending the width of laser pulses as great as possible can not only increase average ionization yield and average selectivity simultaneously, but also loosen the control accuracy of time delay between laser pulses.

The spatial distributions of macroscopic parameters such as density, bulk velocity and temperature of the metal vapor have influences on the photo ionization yield of target isotope and the utilization ratio of material, which is related to the separation efficiency and the cost of atomic vapor laser isotope separation. To study this problem more practically, a system of binary gas Bhatnagar-Gross-Krook (BGK) model equations, which describe both the metal vapor and the background gas, is established. The physical characteristics are dealt with by dimensionless method for simplifying the calculations. The model equations are discretized by one-order upwind difference and then are solved by iteration method for obtaining stable results. The computational grids are adjusted to the flow field in order to acquire modest computational cost and accurate result simultaneously. Non-uniform grids in the phase space and in the velocity space are constructed to match the macroscopic parameter gradient and the form of the velocity distribution, respectively. The macroscopic parameters in the cases of different background gas densities, temperatures of tail plate and absorptivities are obtained for studying the influence of the background gas. The results show that with the increase of density of the background gas, the density and temperature of the metal vapor increase, the bulk velocities in the x and z$ direction decrease obviously in the domain far from the evaporation source, while the macroscopic parameters that are close to the evaporation source hardly change. As a result, the evaporation rate is not affected. Meanwhile, a circulation of the background gas is driven by the metal vapor, which in turn affects the diffusion of the metal vapor. Besides, as the temperature of tailing plate rises, the influence of the background gas on the macroscopic parameters of the metal vapor weakens. However, the rise of the temperature of tail plate leads the absorptivity of metal vapor to decrease, which enlarges the influence of the background gas. Therefore, it is appropriate to adjust the temperature of the tail plate based on the relationship between the absorptivity of metal vapor and the temperature. The results of theoretical calculation can serve as a reference for designing the vacuum and laser spot of the separation device.

Photoexcitation and photoionization of atoms, the central part of atom vapor laser isotope separation (AVLIS), relate to the ionization yield and isotope selectivity directly. Doppler broadening of absorption lines is one of the parameters that influence the photoexcitation and photoionization process of atoms. When evaporation temperature is high or beam equipment is absent, Doppler broadening has obvious influence on the ionization yield because most of atoms are non-resonantly excited. In this paper, we study the influences of Doppler broadening of absorption lines on a multi-step photoexcitation and photoionization process of atoms according to the facts of AVLIS. A Doppler-broadened three-level atom system with two resonant lasers is investigated. The interaction between laser field and atoms is described by a density matrix, which is calculated by fourth-order Runge-Kutta numerical method with variable steps. The results show that the ionization yield of atoms decreases with the increase of Doppler broadening of absorption lines under the same laser parameters. At a constant laser power, the ionization yield reaches its maximum value at the best laser bandwidths, which is different from that obtained without Doppler broadening, as reported in published papers. Meanwhile, the best laser bandwidth increases with the increase of Rabi frequency and Doppler broadening when other parameters are constant. Moreover, the best bandwidth of the second laser is smaller than that of the first laser in a multi-step photoionization process of atoms. Therefore, lasers should work at the best bandwidths in AVLIS for highest ionization yield. It is advantageous to make laser bandwidths slightly bigger than the best bandwidths technically for smaller fluctuation of ionization yield, owing to incoercible stochastic volatility in laser bandwidths. The ionization yield increases with the decrease of Doppler broadening, especially at the best laser bandwidths. Therefore, it is necessary to reduce Doppler broadening of atom vapor in laser ionization zone.

Flywheel energy storage is a promising technology for providing intermediate energy storage. An energy storage flywheel is supported by active magnetic bearings (AMBs) to achieve high speed running and increase energy efficiency of the energy storage system. The configuration of the flywheel rotor is complex and its rotor dynamic behavior influences the running of the AMB rotor greatly, including its strong gyroscopic effects and bending vibration modes whose frequencies are within the rotor’s operation speed range. Careful dynamic analysis was performed for the flywheel rotor. Based on the analysis results, an effective controller design for the AMBs was performed. An advanced controller with local damping enhancement and cross feedback technologies was successfully designed. The controller could well restrain the negative influence from the gyroscopic effects, suppress the bending mode vibration and achieve a stable suspension of the rotor in the whole operation speed range. Experimental results were provided and proved the effects of the analysis and the controller.

In a high speed rotor supported by active magnetic bearings, the rotor operation was greatly influenced by a large residual unbalance in the rotor and some low frequency vibration modes from the structure of the rotor system. A general dynamic balance procedure was not suitable for the rotor, an adaptive unbalance control method of active magnetic bearings called Generalized Notch Filter was used to help the rotor to run to a suitable balance speed and help the rotor to increase its dynamic balance efficiency with two different methods. In the first method, Generalized Notch Filter was used to restrain the synchronous vibration of the rotor and then identify the rotor unbalance distribution. In the second method, it was just used to decrease the vibration amplitude. Corresponding experiment results are provided. Generalized Notch Filter algorithm settled the balance problem and increased the balance efficiency.

This paper reports the design and construction status, technical challenges, and future perspectives of the proton-linac based Compact Pulsed Hadron Source (CPHS) at the Tsinghua University, Beijing, China., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan