Initial experimental study of pulsed electron beam fluorescence

Abstract

The pulsed electron beam fluorescence technique for the measurement of gas specie densities along with rotational and vibrational population distributions is being developed for use in high enthalpy, chemically reacting flows. The fluorescence generated by a very high current, short duration pulse of energetic electrons is spectroscopically analyzed sufficiently early in the excitation-emission sequence to minimize the effects of collisional quenching and to avoid the subsequent large energy deposition in the gas caused by the beam's electrons. We present the results of both rotational temperature and gas density measurements in static, room temperature nitrogen at pressures between 5 and 150 mtorr. Using a pulsed electron gun as a source, 150-A electron beams with durations of tens of nanoseconds were used to excite fluorescence from nitrogen's first negative system (N 2 + B 2 Σ u - →N 2 + X 2 Σ g + ). The (0,0) band near 391 nm was observed with a 0.85-m spectrometer for determination of nitrogen rotational temperature and density. The spectrometer's exit slit was modified to enable simultaneous emission intensity measurements in portions of the (0, 0) band's P and R branches.