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A moving atmospheric-pressure nonthermal-equilibrium argon plasma bullet was investigated by emission spectrum and plasma current. Moving plasma changes spatially and temporally. Therefore, it is necessary to consider the time variation of plasma in measurement. Thus, the validity of the electron density estimated by the two types of optical and electrical measurement methods was examined. The electron density and temperature are estimated from the analysis of continuum spectrum (CS). Moreover, the electron density was also estimated from the relationship between the current and the propagation velocity of the plasma luminescence. The plasma current was estimated from the power-line currents with and without plasmas. The propagation velocity of the plasma luminescence was measured by applying the time-of-flight (ToF) method on the observed emission intensity. The electron density estimated from the analysis of CS is comparable to that estimated from the effective peak plasma current. Consequently, the analysis of CS is applicable to a moving plasma bullet.

Backward wave oscillators (BWOs) have a slow-wave structure (SWS) with periodically corrugated walls. To increase the operation frequency and the power handling capability, the SWS is oversized with the diameter larger than the free-space wavelength of output electromagnetic wave. Generally, the slow wave becomes a surface wave concentrated on the corrugation of oversized SWS. Excited surface waves are converted into radiating waves at the ends of SWS, leading to BWO radiations1. There exists an alternative mechanism to radiate electromagnetic waves in periodic structures, i.e., Smith-Purcell (SP) mechanism which directly excites radiating waves2. Original SP radiation was a spontaneous emission. SP radiation more intense than the original one was demonstrated based on the stimulated emission, in which self-bunching of electron beam due to the backward-wave interaction plays an essential role3.

Summary form given only. Recently, plasma techniques under atmospheric pressure circumstances have been adapted for industrial, medical and biological applications. Atmospheric pressure plasmas, such as a plasma jet are typically produced using an arc discharge and a dielectric barrier discharge (DBD). The arc discharge produces a high-temperature plasma, whereas DBD produces a low-temperature plasma, which results in less thermal damage to materials. Atmospheric pressure plasma of DBD is generated intermittently using dielectric, rate gas and metal electrode by applying radio frequency and high voltage1. When it is used a quartz tube as a dielectric, plasma is released to the atmosphere. A plasma plume is a small bulletlike volume of plasma traveling at unusually high velocities2. We have studied a generation of high density plasma jet using focused plasma jets3. However, the detailed properties of the plasma current and density were still not estimated. In this work, we use helium plasma jet produced using a quartz tube and copper foil electrodes where a low frequency (~13 kHz) and a high voltage (-6 ~ +9 kV) are applied. The measurement of plasma current is used by a current probe. The plasma drift velocity is measured indirectly by the drift velocity of luminous bullet on the time of flight method. The plasma cross-section is estimated on the photographs. The plasma density is evaluated from these measurements values. The dependences of plasma current and density on the helium gas flow rate are examined. Detail experimental results and discussion will be presented at the conference.