  In order to optimize the parameters of the plasma plume for atmospheric
pressure plasma applications such as biological and industrial applications, it
is highly necessary to thoroughly understand its characteristics. In this
paper, various diagnostic techniques are discussed to characterize the
atmospheric pressure plasma plume. The major emphasis of this work is to
utilize possibly simple methods, low complexity in post data analysis and
obtain in-situ information. The parameters of the plasma plume such as spatial
variation of gas temperature, electron excitation temperature, plume velocity,
plume current, electron density are experimentally measured. In addition,
plasma discharge behavior and plume formation with various gas flow rates and
applied voltage are studied. The characterization of the above parameters is
carried out by using electrical diagnostics (voltage probe and a current
sensor), Optical diagnostics (optical emission spectroscopy (OES), fast imaging
method using ICCD camera), and thermocouple. The plasma plume/gas temperature
along the plume length is measured by using a simple K-type thermocouple and is
found to be in the range of (42.5 - 24.5) deg C. The OES is used to estimate
the electron excitation temperature of plasma plume and to identify the key
reactive species (OH, NO, N2+, O, etc.) present in the plume. ICCD camera is
utilized to capture the temporal evolution of plasma and to estimate the plume
velocity along the plume length. The current transformer is utilized to measure
the plume current along the plume length. By using the velocity and current
information, the plasma density is evaluated, and the obtained values are in
the range of (0.069-5.96)x 10^12 cm^-3. The above range of parameters and
tunable nature of our designed plasma source will be useful for the development
and optimization of plasma sources for various applications.
