In the electromagnetic spectrum, the terahertz (THz) band is between the microwave band of electronics and the infrared band of optics, and some scholars define its frequency range as (wavelength 3mm-3nm) 2'31. Because of the special position of this band The position of the electromagnetic spectrum shows a series of special characteristics that are different from other electromagnetic radiation, so that the terahertz radiation imaging technology and the time-domain spectroscopy technology are used in security inspection, anti-stealth high-precision radar, military communications, industrial nondestructive testing, space physics He has broad application prospects in the fields of astronomy, environmental testing, chemical analysis, biomedicine, and network communications. At present, scholars from various countries have paid great attention to THz technology research and formed a research climax. The United States, Europe and Japan pay particular attention to it. Japan has ranked it as the top ten key technologies in the strategic planning of science and technology in the next decade. 131. The core of THz technology is the development of radiation source and detector technology. The research direction of THz radiation sources is concentrated in two aspects: on the one hand, it is to extend photonics, especially laser technology to low frequencies, including THz gas lasers, ultrashort laser pulse photoconductive antennas and optical rectification, nonlinear difference frequency process (DFG) and Parametric oscillator w is characterized by its ability to generate THz waves with good directivity and coherence, but with low output power, suitable for generating THz waves at frequencies above ITHz. On the other hand, it extends electronic methods to high frequencies, including vacuum electronic devices, electron cyclotrons, free electron lasers (FEL), Cherenkov radiation, storage ring synchrotron radiation, and THz quantum cascade lasers based on semiconductor technology. Among the various THz radiation sources, FEL has the outstanding advantages of high power, high efficiency, continuously adjustable wavelength in a wide range, good beam quality, fine and adjustable optical pulse time structure, etc. It is currently the method to obtain the highest output power .
FEL has been valued by some countries since the 1970s, but its development has not been smooth. The main reason is that FEL has too high requirements for the quality of electron beams. Generally speaking, the required divergence is within 0.5%, and the normalized emissivity is Around 5min.mrad. Ordinary electronic linear accelerators cannot provide such high-quality beams steadily, so until the 1990s, high-power FEL did not appear in the world. After 1995, the US efferson) aimed to explore the miniaturized and mobile FEL- The realization method of THz source.
Independently tuned dual cavity hot cathode microwave electron gun (ITC-RFGun) and equal gradient traveling wave acceleration tube. The symmetrical input coupler and the acceleration structure with the coaxial absorption load instead of the output coupler are adopted to make the field completely symmetrical and overcome the influence of the asymmetry of the field in the input and output couplers of the conventional accelerator tube on the beam emissivity. At the same time, the acceleration structure is simplified because there is no need to externally absorb the load, thereby reducing the lateral size of the accelerator, which is beneficial to the installation and maintenance of the focusing coil. The electron beam is accelerated to 5-10 MeV by the acceleration tube, enters the undulator through the 90 ° deflection magnet 1, interacts with the optical field in the optical resonant cavity and the magnetic field of the undulator, and generates a 1-3THz radiation wave. The optical resonant cavity is composed of two mirrors, and the position of one mirror is adjustable. The 60 ° deflecting iron 2 introduces the beam into the beam bin. The microwave power source is composed of 2856MHz microwave signal source, solid-state amplifier, 20MW klystron, modulator, waveguide system (power divider, phase shifter, attenuator, etc.). Fast beam current transformer (FCT) is used to measure the amount of charge, and OTR and fringe cameras are used to measure the length of the bunch.
2 Independently tuned microwave electron gun ITC-RF electron gun is composed of two cavities, the first cavity is the cathode cavity, the beam is drawn out, and the second cavity is the acceleration cavity (as shown). The two cavities are fed with microwave power of different sizes and phases independently, and the sub-picosecond beam current is obtained by the velocity bunching effect. 61. Through preliminary simulation calculations, the ITC-RF electron gun is used. Main parameters Physical quantity value Working frequency / MHz First cavity highest field Second cavity highest field Cathode diameter / mm Beam length / ps Beam energy / MeV normalized beam emittance / (mm.mrad) Energy divergence / rms Total cavity length / cm 3 The main objective of the undulator design is to control the root-mean-square error of the peak value of the magnetic field so that the primary and secondary integrals of the vertical component of the magnetic field are as small as possible to control the direction and position deviation of the electron beam shift. In response to the requirements of small THz sources, a hybrid permanent magnet structure was used, with a period length of 5 cm, a period number of 25, and a deflection parameter X = 1.0. Based on the analytical model and experience, the undulator parameters were selected, and the TOSCA program was used for its end structure Three-dimensional analysis and optimization. The optimized primary integration is less than O.OlGs.m, and the secondary integration is 0.005Gs.m2. Through the numerical tracking of the electron trajectory, it is obtained that the position deviation of the electron beam at the shielding exit 400mm is less than 0.021111, and the direction deviation is 0.05111 ± 4 The optical resonant cavity adopts a hole coupling output stable spherical cavity structure, and the cavity mirror is composed of a gold-plated copper mirror. The performance of the designed FEL-THz source is simulated by FEL-dimensional simulation software FELO. FELO simulation starts with scattering noise, which can simulate the effect of different electron pulse current distribution, cavity length detuning and time jitter between electron beam clusters on FEL oscillation. 71. The main design parameters of the optical cavity are: cavity length 2.1008m, The radius of curvature of the cavity mirror is 1.4223m, the Rayleigh length is 0.625m, and the reflectivity of the cavity mirror is 95%. As shown in the simulation results, after about 400 round trips, the peak intensity of the optical pulse and the energy of the light pulse increase exponentially, about 1000 round After entering the stable area, the stable light pulse output can be obtained.
The change of the optical pulse energy with the number of return strokes at different reflectances requires that the FEL-THz source can achieve a higher cavity gain and a stable power output, and the parameters need to be optimized. We comprehensively considered the effects of different cavity mirror reflectivity, different emissivity, and different energy divergence on the energy of the FEL output light pulse. The effect of reflectance is as shown. When the reflectance is 85% and 90%, the system cannot start oscillation; when the reflectance is 98%, the system can start oscillation, and the output light pulse energy fluctuates within a small range, basically Stable output can be achieved; when the reflectivity is 95%, the system can reach a stable saturation output, which is the optimal cavity mirror reflectivity. The simulation results of different emissivity show that when the emissivity is 5, 10, 15mm.mrad, the effect on the stable output of light pulse energy is not great. Simulation results of different energy divergences indicate that the smaller the energy divergence of the electron beam, the greater the energy of the output optical pulse, and the easier it is to reach the saturation output.
5 Conclusion This paper presents a design scheme of a small FEL-THz source. Using the ITC-RF electron gun, symmetrical input coupler and coaxial absorption load instead of the acceleration structure of the output coupler reduces the size of the system. Through preliminary simulation calculations, the ITC-RF electron gun can achieve the required beam quality, the primary and secondary integration of the magnetic field of the undulator meet the requirements, and the optical resonant cavity can obtain a stable THz optical pulse output, which is a small FEL-THz source The device research laid the foundation.
This style is Bagless Vacuum Cleaner. This kind of Vacuum Cleaner has speed control in it.,so you will use it very diverse. It also has big dust cup capccity,then you can use it for a long time. Its cyclone system is multi-cyclone. Its dust cup is transparent dust container. It also has HEPA filter and multi-level filter. So it will avoid to cause secondary pollution. This design has high suction power,too. So you can use very effortlessly.
Bagless Vacuum Cleaner
Dust Cup Vacuum Cleaner, Bagless Vacuum Cleaner, Bagless Upright Vacuum Cleaner
Ningbo ChinaClean Household Appliances Manufacture Co., Ltd. , https://www.chinaclean-elec.com