Influence of magnetic fields on negative corona discharge currents

The mechanism of magnetically enhanced negative corona discharges was studied by comparing the influences of two different magnetic fields on the negative corona discharge current. In the magnetically enhanced corona discharge, a local magnetic field is formed near the discharge electrode by using the small permanent magnets, and the corona discharge currents are enhanced because the Larmor movements of free electrons enhance the ionizations of the gas molecules in the ionization region. It is assumed that the increase of the discharge currents attributes to only the enhanced ionization process in the small ionization region, and is not relevant to the lengthening trajectory of free electrons in the wide drift inter-electrode region. In the enhanced ionization-region magnetic field, the mechanism of magnetically enhanced corona discharges was explained and the relative increase of the discharge current could exceed 150%. However, in a weakened ionization-region magnetic field, the mechanism of magnetically enhanced corona discharges was inconspicuous and the relative increase of the discharge current could only reach about 25%. It is predicted that after the magnetic field of magnetically enhanced negative corona discharges had been fixed, the relative increases of the discharge current for varied mean electric fields in the inter-electrode region could have a maximum value, according to the mechanism of magnetically enhanced negative corona discharges. The above predication was completely validated by the current experiment data. In addition, the optimum combinations between the electric field and the magnetic field were obtained. In order to reach the largest relative increase of the discharge current under 4 kV/cm mean electric field intensity in the inter-electrode region for a practical electrostatic precipitator, the optimum magnetic field with a magnetic flux density of about 0.43 T at the edges of magnetic st rings should be selected.