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Incoherent Light Sources
Published in Daniel Malacara-Hernández, Brian J. Thompson, Advanced Optical Instruments and Techniques, 2017
Among other mechanisms that can produce light, there is the electron de-excitation in gases. An electron is excited by an electron or ion collision, which is achieved by the following means: Thermal electron emission by a hot cathode. A heating incandescent filament emits some electrons, which statistically overcome the metal's work function. In the presence of an electrical potential, the electron is accelerated and, by collision, new ions are produced. This method is used to start a discharge.Secondary emission. Several electrons are emitted from a metal that is struck by a colliding electron. Once a discharge begins, it is maintained by continuous ion bombardment. This mechanism is responsible for the arc maintaining in arc sources.Field emission. A strong electrical field applied in a relatively cold cathode can be high enough for electrons to be emitted from the metal. This mechanism is used to start the discharge in an initially cold lamp.
Available Lamp (or Burner) Technologies
Published in Willy J. Masschelein, Rip G. Rice, Ultraviolet Light in Water and Wastewater Sanitation, 2017
Willy J. Masschelein, Rip G. Rice
The hot cathode type is based on thermoionic emission of electrons from a structured electrode system composed of coiled tungsten wires coated and embedded with alkaline earth oxides: CaO, BaO, or SrO. On heating, the oxide coatings build up a layer of metal (e.g., barium) and at about 800°C enough electrons are discharged to get the emission started. At normal operation regime, the temperatures of the electrodes reach 2000°C. Hot cathode lamps operate at low voltage ranges, (e.g., with voltages of the mains [220 V in Europe]). The cathode possibly can be brought to the necessary discharge temperature in a way similar to that of fluorescent lighting lamps. A typical example of the electrical feed scheme of the hot cathode lamp type is shown in Figure 11.
Light Sources & Components
Published in Samuel Mills, Fundamentals of ARCHITECTURAL LIGHTING, 2018
Fluorescent lamps operate on a principal of a hot-cathode. There are two types of cathodes, hot and cold. The cold-cathode method is found in light sources like neon lamps. The hot-cathode is a coiled tungsten filament impregnated with electron-emissive materials. The operating temperatures are about 950°C for hot-cathode and 150°C for cold-cathode. With fluorescent lamps at this temperature electrons are emitted with a small wattage loss at each cathode. The voltage drop at the cathodes for cold-cathode lamps is higher than hot-cathode. This results in higher wattage loss, more heat, and lower lamp efficiency. These small diameter lamps are used for signs and other bent shapes and offer instant starting.
Conceptual Design of Control System for the Prototype RF-Driven Negative Ion Source at ASIPP
Published in Fusion Science and Technology, 2022
Y. Z. Zhao, C. D. Hu, Q. L. Cui, S. H. Song, Y. H. Xie, W. Liu
Neutral beam injection (NBI) is an effective method for fusion plasma heating and current driving.1,2 For the future China Fusion Engineering Test Reactor3,4 (CFETR), a NBI system is required in terms of a deuterium beam with beam energy of 1 MeV, beam power of 20 MW, and off-axis injection. At such a high beam energy level, a stable giant negative ion source is essential to attain an allowable neutralization efficiency. At present, two NBI systems have been constructed on the Experimental Advanced Superconducting Tokamak (EAST). Each EAST NBI with two hot cathode bucket ion sources can deliver 2- to 4-MW beam power with 50- to 80-keV beam energy in 10- to 100-s pulse lengths.5 Future fusion reactors (ITER, CFETR) are equipped with high-power and long-pulse NBI. When the beam energy is greater than 100 keV, the neutralization efficiency of the positive ion source decreases sharply, while the neutralization efficiency of the negative ion source remains at 60% to 70%. At the same time, compared with the hot cathode bucket ion source, the radio frequency (RF) ion source has a long lifetime and no tungsten contamination, which is better suited for long-pulse operation.6–8 Based on these two reasons, a NBI system based on a RF negative ion source has become the development trend of NBI technology.
Simulation and monetization of collateral airborne infection risk improvements from ultraviolet germicidal irradiation for coil maintenance
Published in Science and Technology for the Built Environment, 2018
Joseph Firrantello, William Bahnfleth
The value of ηUVGI depends on several parameters. Table 3 lists the design parameters and assumptions made in sizing coil UVGI systems for the 554 distinct air systems in the study buildings. UVGI surface and air irradiance calculations were performed using view factor methods developed by Kowalski (2003; analogous to those used by radiative heat transfer) and implemented with proprietary software. The value of k was set to 0.0002996 cm2/µJ, the median of species-averaged virus values tabulated by Kowalski (2003). Lamp output variation was modeled using Equation 8 (Lau et al. 2009) which applies to a typical hot cathode, standard output, cylindrical germicidal lamp in crossflow. The derating factor accounts for variation in output due to cooling (“wind chill”) as a function of air temperature and velocity. High output lamps are typically used in these applications, and purport to have more favorable derating characteristics versus standard output lamps for high air speeds and low temperatures. Equations developed for a high output, twin-tube lamp show similar behavior (Lau 2009) to Equation 8, but its geometry is not cylindrical, and a direct comparison cannot necessarily be made. In the absence of more specific lamp derating relations, Equation 8 may be considered conservative. where fUV is the UV output derating factor, Tair is the air temperature [°C], and Uair is the average airstream velocity [m/s].
Past, present, and the future of the research and commercialization of CVD diamond in China
Published in Functional Diamond, 2022
Another technique for diamond film deposition worthy of mentioning is the DC Hot Cathode Plasma CVD (or PACVD (Plasma Assisted CVD)). It was established in China in the 1990s by Jilin University [17,18]. This technique is capable of large area diamond film deposition with a reasonably high quality at high growth rate. This technology is fully developed both in China and in Korea. Korea is now actually the leading country both in the deposition area as well as the film quality [19].