Seed electrons needed in discharge are mainly provided by Penning ionizations between metastable molecules. This regime results in a low ionization level, which makes the discharge in N_2 being close to a Townsend discharge. 放电所需的种子电子主要由亚稳态之间潘宁电离提供,这种机理使放电的电离水平较低,导致氮气中的放电只能是汤生放电。