亚毫米间隙负直流电晕放电Trichel脉冲特性

Trichel pulse characteristics of negative DC corona discharge in submillimeter gap

为了研究亚毫米间隙下Trichel脉冲放电特性及机理,搭建100~500μm电极间距的针-板电极放电系统,并配备光学采集系统观测负电晕放电过程,探究亚毫米间隙下电极间距及针尖曲率对伏安特性曲线、Trichel脉冲幅值频率和放电平均电流等的影响。亚毫米间隙空气电晕放电发展到锯齿波阶段过程中不存在无脉冲过渡阶段,在放电锯齿波阶段,亚毫米间隙负电晕放电发展到Trichel脉冲锯齿波阶段后难以过渡到辉光放电阶段,脉冲波形呈现伴有基底电流的锯齿波形式。针-板电极间隙越小,发生电晕放电所需的针尖曲率半径就要越小,但过小曲率半径的针尖电极会使板电极附近的电场高度发散,导致板前电晕放电保持较高的净电荷密度和碰撞电离率。在亚毫米间隙的针-板电极空气放电过程中,当电晕放电发展至板电极即将产生辉光放电时,板前电晕仍保持较高的碰撞电离率并产生二次电子,但针尖电晕还没有达到空气辉光放电所需要的发生电子雪崩的阈值。因此,与毫米级相比,在即将发生的辉光放电之前,电晕放电产生几十微安的基底电流,电晕放电向辉光放电转换过程变短甚至消失。

In order to reveal Trichel pulse characteristics and mechanism of discharging air-gap in sub-millimeter scale,the needle-plate electrode discharge platform controllable in 100-500μm air-gaps was specifically built up with a fluorescence acquisition equipment to fulfill the real-time observation of nega-tive corona discharge process and test the voltage-current characteristic curves,the amplitude and wave-form of Trichel pulse,and the impulse frequency and discharge average current.It is demonstrated that the complanate transition stage without pulse currents will not appear when corona discharge transits to glow discharge in the air discharge developing process of needle-plate electrodes in sub-millimeter gap.In sawtooth wave stage,the corona discharge coexist with glow discharge,being accompanied by arising cur-rents through plate electrode.The smaller air-gap of needle-plate electrode requires a shorter radius of needle-tip curvature to ionize air molecules and thus generate corona discharge by the adequately concen-trated electric field near needle electrode.Meanwhile,for the needle electrode with a too small radius of tip curvature,the electric field persists in high divergence to produce a high net charge density and colli-sion ionization rate near plate electrode.When the corona discharge in sub-millimeter air-gap approaches the surface of plate electrode to be subsequently followed by engendering glow discharge,the corona front near plate electrode maintains high rates of collision ionization and secondary electron excitation,while the tip corona has not reached the threshold of electron avalanche required for air glow discharge.There-fore,before the upcoming glow discharge,the corona discharge generates electric current with dozens ofμA through plate electrode,and the conversion stage from corona discharge to glow discharge becomes vague or even disappears.