Micro-effects of surface polishing treatment on microscopic field enhancement and long vacuum gap breakdown

Abstract

In this paper, three surface polishing treatments were employed to treat plate titanium electrodes, and microscopic surfaces of the electrodes after polishing were presented. Through comparing the breakdown strength of the 2.5 cm vacuum gap formed by plate titanium electrodes after the three treatments, experimental results showed that the breakdown strength was enhanced by 35% while the micro-surface roughness dropped from 3.5μm to 0.35μm. In view of that, effects of microstructural parameters after polishing on the microscopic field enhancement factor were investigated. The field-uniformity mechanism and the shield effect between micro-protrusions on the rough electrode surface were put forward and demonstrated. Based on the idea that electric field can be shield in a pit, a theoretical model was established to evaluate the maximum field enhancement factor βEmax on the micro-surface. It revealed that 1 ≤ βEmax ≤ 3.96, and βEmax had the maximum decrements of 1.96 and 2.1 both from 3.96 after the mirror polishing and the chemical polishing, respectively. When the surface roughness decreased to the scale from nm to μm, the effort on βEmax reduction through surface polishing was not effective to enhance the vacuum gap breakdown strength any more.

The effects of cathode electrodeposited polymer film on the long vacuum gap breakdown

“…Work function of the emitting surface can be enhanced by platinum electroplating on the surface, while the secondary electron emission can be suppressed by a layer of TiN coating on the surface. After the treatments mentioned above, the average breakdown field strength of vacuum gap (<10 À3 Pa) at cm range only increased by 20%-30% [7], which was far less than the anticipation. In view of the electron emission mechanism of dielectric composited cathode [11], the distribution of dielectric on the electrode surface showed important influences on the field induced electron emission and vacuum breakdown.…”

“…That's to say, E 0 decreases to a level which is 1/e r of the previous value (U 0 / w 2 ) before coating. In comparison with the mirror polishing treatment in [7], dielectric coating treatment has similar effect to decrease the surface field strength. Define the work function of the electrode-film interface as Ø w , and the field induced emission current density as j.…”

“…In the view of many researchers, the field induced electron emission from cathode is the initial inducement for vacuum gap breakdown [1][2][3]. The main determine factors of field induced electron emission include the micro-surface state [4][5][6], microscopic field strength [7] and environmental parameters [8]. The micro-surface state is comprehensively determined by many factors such as electrode melting point, grain structure, the Fermi level, adulteration, concentration of electron, surface absorption, surface cleanliness, work function and the secondary electron emission.…”

“…At present, the electrode surface roughness R z can decrease from several mm to 0.35 mm through the mirror polishing so that the field strength enhancement factor is compressed [7]. The electrode surface state can be improved by the chemical polishing as the surface oxide layer and defects are both eliminated [9,10].…”

Effect of surface modification of electrodes on charge injection and dielectric characteristics of propylene carbonate

“…Selection of appropriate electrode materials can inhibit charge injection, thus improving the insulation performance of the liquid [8]. Charge injection is related to the interfacial barrier between the electrode material and the liquid dielectric [9], which is mainly affected by the electrode material [10][11][12], the surface morphology of the electrode [13][14][15], the properties of the liquid dielectric, and the distance between the electrodes [16]. Changing the electrode surface conditions through surface modification also affects the work function of the metal electrode [17], possibly lowering the work function of the metal electrode to increase the possibility of charge injection [18][19][20].…”