Experimental investigation of hypervelocity plasma jets generated with a coaxial arc device

A new coaxial plasma generator has been developed. It provides hypervelocity plasma pulses for aerosol formation purposes. Plasma ignition and acceleration inside the plasma generator strongly determine subsequent particle formation and growth processes and are therefore intended to be studied within the frame of this work. The first part of the paper describes the experimental set-up. Special emphasis is drawn to the plasma generator which basically consists of a coaxial electrode assembly with two high pressure gas injections to supply different reactive and/or inert gases. The plasma is initiated and sustained by the surge current of a capacitor bank (60 /spl mu/F with charging voltage up to 15 kV). The discharge characteristics (typical several 10 kA) can be modified by a pulse forming variable inductance and by the settings of the gas injection (e.g. type of gas, pressure of gas, trigger delay). The second part of the paper deals with the experimental investigation of the plasma jet itself. Since plasma ignition and acceleration inside the electrode assembly initiate the whole process chain-including particle formation-special focus is laid on measuring plasma parameters. Standard electrical measurements of current and arc voltage are performed to investigate the energy coupling. Short time photography provides information on arc generation and on acceleration of the jet. Optical emission spectroscopy is carried out to gain information on the composition on the plasma. It permits to derive a first estimation of plasma temperature and of electron density.