Formative Time Lags in Nitrogen, Oxygen and Dry Air in Crossed Electric and Magnetic Fields

Formative time lags in nitrogen, oxygen, and dry air are measured with and without a magnetic field over a range of gas pressures (0.05 ¿ p ¿ 20.2 torr, 5 kPa to 2 MPa, electric field strengths (1.8×104 ¿ E ¿ 60×104 V m-1) and magnetic field strengths (85×10-4 ¿ B ¿ 16×10-2 Tesla). For experiments below the Paschen minimum, the electrodes are designed to ensure that breakdown occurs over longer gaps and for experiments above the Paschen minimum, a coaxial cylindrical system is employed. The experimental technique consists of applying pulse voltages to the gap at various constant values of E/p and B/p and measuring the time lags from which the formative time lags are separated. In the gases studed, formative time lags decrease on application of a magnetic field at a given pressure for conditions below the Paschen minimum. The voltages at which the formative time lags remain the same without and with magnetic fields are determined, and electron molecule collision frequencies (v/p) are determined using the Effective Reduced Electric Field [EREF] concept. With increasing ratio of E/p in crossed fields, v/p decreases in all the three gases. Measurements above the Paschen minimum yield formative time lags which increase on application of a magnetic field. Formative time lags in nitrogen in E×B fields are calculated assuming an average collision frequency of 8.5×109 sec-1 torr-1. It is concluded that the EREF concept can be applied to explain formative time lags in E×B fields.