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Strong pulsed emission of carbon nanotube cathode characteristics

Author: ZuoZuo
Tutor: XiaLianSheng
School: Chinese Academy of Engineering Physics
Course: Nuclear Technology and Applications
Keywords: carbon nanotube cathode intense pulsed emission plasma-induced field emission cathode outgassing linear induction accelerator
CLC: TL503.3
Type: Master's thesis
Year: 2011
Downloads: 69
Quote: 0
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Abstract


The several kA intense electron beams, extracted from the cathode, are required as radiography in linear induction accelerator (LIA) field. Usually, only the thermionic cathode and the field emission cathode have access to such the high emission current of the electron beams. Among them, a better quality beam can be easily obtained from the thermionic cathode, but the emission current density of the electron is relatively low, the cathode is short life due to an easily cathode poisoning, and the cost is expensive. The field emission cathode belongs to the cold cathode, it also emits intense electron beams under pulsed high voltage, the emission current density is relatively high, and the cathode has a longer life. The field emission cathode is widely used in intense electron beam accelerators and the high power microwave tube.The static electric field of the 2MeV LIA injector diode has been simulated by using ANSYS in this paper. Combined with the experimental results, the effects of the static electric field on the cathode emission have been analysed as using different cathode components. The pressure of the vacuum chamber has been simulated as a continuous outgassing from the cathode. The location of turbomolecular pump has an effect on the pressure distribution of the vacuum chamber.An investigation of the intense pulsed emission properties of the large area carbon nanotube (CNT) cathode on 2MeV LIA injector has been presented. The emission properties of the CNT cathode are studied through various means and devices. Some conclusions are followed:The CNT cathode has a capability of intense electron emission, the intense electron beam of 108.4A/cm2 is obtained from the cathode under the 1.6MV pulsed high voltage. The mechanism of the electron emission of the CNT cathode is plasma emission rather than ideally field emission. There is same process as the mechanism of the electron emission from the velvet and carbon fiber cathode. The effects of the cathode plasma expansion on the diode perveance and the impedance have been preliminary analysed. The CNT cathode desorbs gases from the CNTs during the emission process. There are significant CO2, N2(CO) and H2 desrobing gases from the cathode, and the source of plasma gas is clarified by the outgassing mass spectrum analysis. The cathode outgassing affects the pressure of the vacuum chamber. The amount of outgassing for the several experiments are estimated to be 0.06～0.49Pa·L, corresponding the ratio of outgassing and electron are roughly calculated to be within the range of 170～350 atoms per electron by numerical integral of pressure, this conclusion shows that the cathode plasma is weak ionization. Moreover, the characteristic turn-on time of CNT cathode of 39ns is measured, which is defined as the synthesized method of the CNT and not associated with the diode electric field.The mechanism of plasma-induced field emission has been proved by analyzing the intense electron emission properties of CNT cathode, and the process of plasma-induced field emission is clarified. Moreover, the effect of electric field on the intense pulsed emission of CNT cathode is studied, and there are comparative studies of intense electron emission properties of the velvet cathode and CNT cathode.

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CLC: > Industrial Technology > Nuclear technology > Accelerator > General issues > Accelerator structure and manufacturing process > Injection device
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