Carbon Nanotubes (CNTs) as Electron Emitters for Plasmas Operating in Subatmospheric pressure under DC and Pulsed Fields
Type of Degreedissertation
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Subatmospheric pressure is defined as the pressure from several milliTorr to several hundred Torr. The plasmas operated in subatmospheric pressure have the advantages of easier construction and stable operation. The efficiency of the emitter electrons is critical in the performance of the plasma devices. After accelerated in the electric field between the cathode and the anode, the seed electrons play a significant role in the ionization processes. In this dissertation, two specific types of plasma devices are operated at subatmospheric pressure. The first is a in-house built microplasma device with different cathode geometry. The second is a pseudospark switch based on plasma ignition. Microplasma devices have caught many research interests with the advantages of smaller size, lower power and gas consumption and operation from subatmospheric to atmospheric pressure compared to the traditional plasma devices. In this work, the hollow cathode geometry is adopted in the microplasma devices' design. Different cathode materials, including carbon nanotubes (CNTs) as emitters, are used in the devices. CNTs are known for their excellent field emission characteristics, which makes them a good candidate as the source of seed electrons in the design. The second device is a pseudospark plasma switch. Pseudospark switches have been applied in pulse power application as the fast closing switches, with hold-off voltage as high as 10 kV. The cathode geometry is hollow, so hollow cathode discharge is formed to increase the charge carrier density. Pseudospark switches need a trigger element where the seed electrons are employed to initiate ionization. In our work, CNTs are used as trigger that supplies the seed electrons. CNTs used as the electron emitter material are fabricated by chemical vapor deposition (CVD) method. The CNTs are synthesized under different growth conditions, including sputtering time, sputtering pressure, type of catalysts, growth time, and growth temperature. The plasma devices are assembled and tested under subatmospheric pressure in-house in the vacuum chamber. The test experiments are carried out in different background gas, and different operating pressures. Voltage-current characteristics are recorded to study the properties of the plasma. The mathematical simulation are discussed later to study the properties of the plasma in detail.
- Dissertation_Huirong Li_v6.pdf