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Photoemissive Detectors
Published in Antoni Rogalski, Zbigniew Bielecki, Detection of Optical Signals, 2022
Antoni Rogalski, Zbigniew Bielecki
The gain of a PMT is a function of the applied voltage. Typical emission curves for several materials as a function of incident electron energy are shown in Figure 6.9. The secondary emission process depends on the incident energy of the primary electron, as the number of electrons generated with sufficient energy to escape from the surface increases. If the penetration of accelerated electrons to the dynode is very deep (more than several atoms), the likelihood of secondary electrons escaping a classical dynode becomes low. An optimum bias voltage can, therefore, be found that trades off electron energy with dynode penetration to achieve maximum gain. A NEA dynode is not very likely to trap secondary electrons once these electrons are excited to the conduction band, however. Therefore NEA dynodes show nearly linear increase in gain with applied voltage, what is shown in Figure 6.9 for GaP(Cs).
High-Power Vacuum Devices
Published in Jerry C. Whitaker, The RF Transmission Systems Handbook, 2017
Free electrons can be produced in a number of ways. Thermonic emission is the method normally employed in vacuum tubes. The principle of thermonic emission states that if a solid body is heated sufficiently, some of the electrons that it contains will escape from the surface into the surrounding space. Electrons are also ejected from solid materials as a result of the impact of rapidly moving electrons or ions. This phenomenon is referred to as secondary electron emission because it is necessary to have a primary source of electrons (or ions) before the secondary emission can be obtained. Finally, it is possible to pull electrons directly out of solid substances by an intense electrostatic field at the surface of the material.
Vacuum Tube Principles
Published in Jerry C. Whitaker, Power Vacuum Tubes, 2017
In all electron tubes, electrons striking the plate may, if moving at sufficient speed, dislodge other electrons [3]. In two- and three-electrode types, these dislodged electrons usually do not cause problems because no positive electrode other than the plate itself is present to attract them. These electrons, therefore, are drawn back to the plate. Emission caused by bombardment of an electrode by electrons from the cathode is called secondary emission.
Historical Developments and Recent Advances in High-power Magnetron: A Review
Published in IETE Technical Review, 2022
Patibandla Anilkumar, Dobbidi Pamu, Tapeshwar Tiwari
In 1991, Richard R. Smith was experimented on an L-band magnetron of 1.1 GHz at RMS power of 2.4 GW and achieved a limit of impedance collapse at the end of the pulse compared to S-band and X-band relativistic magnetrons [20]. The behavioural characteristics of anode-cathode interactions must be thoroughly investigated. George E. Dombrowski [21] pointed to the improvement of the efficiency of the magnetron by suppressing the secondary emission of the electrons in the anode-cathode gap. In 1998, Jin-Jun Feng et al. [22] designed a long anode magnetron (LAM) that produces high-order axial modes and presented different strapping connections and output plate designs by MAFIA software. Pulse shortening and lower efficiency are the challenges to the relativistic magnetron. In 1998, Saveliev [23] had designed and experimented with different cathodes to increase efficiency without compromising pulse shortening.
Numerical simulation of air DBD under standard atmospheric pressure
Published in Radiation Effects and Defects in Solids, 2022
Xiaobing Wang, Chenyang Zhu, Lu Wang, Jinqiu Liu, An Jin
After discharging for a period of time, the discharge is stable. Under the influence of an alternating electric field, electrons accumulate near the sheath of the anode and cathode. At the same time, with the addition of electron secondary emission reaction, the smaller the escape work of the cathode material, the ions impact the surface of the material to excite more electrons, and more electrons participate in the ionization, excitation and collision process, resulting in the increase of electron density, with the maximum value of about 1 × 1018 1 m−3. At this time, the continuous accumulation of electron energy makes the excitation cross-section of the electron decrease, the excitation process is relatively weakened, and the electron density decreases, so the electron density forms a blank area between the cathode and anode.
New Compact Neutron Generator System for Multiple Applications
Published in Nuclear Technology, 2020
A recent innovation is a negative ion–based compact neutron generator that produces a 100% monatomic D− ion beam.1 In this case, all secondary emission electrons produced by the incident ion beam will return back to the positively biased target electrode. The absence of back-streaming electrons greatly enhances the efficiency for neutron production and provides significantly better operational reliability. Further, since there are no stable negative molecular deuterium ions, a pure atomic D− ion beam is extracted from the source and the fusion reactions at the target will occur at the full acceleration energy. It has also been demonstrated that the surface charging voltage, due to a negative ion beam impinging on a nonconducting target surface, is only several volts.2 This effect allows thick oxide-based lithium or boron targets for the D-7Li or D-10B reaction to be used, and further, prevents the D− ion beam from being deflected away from the target electrode.