An instrument for measuring the momentum flux from atomic and charged particle jets

We have developed an instrument to measure the momentum flux from an intense plasma stream for which the standard techniques used for low-pressure gases (<10 Torr) at room temperature are unsuitable. With a response time of < 50 ms, this device, a plasma momentum meter, can measure forces of 10 ^-5-10³ N onto surfaces of different materials immersed in dense plasmas (n≳10¹²cm^-3). Such forces are transmitted predominantly by ionic and neutral species, with 10's of eV's of kinetic energy, are accompanied by high heat fluxes, and are pulsed. The momentum flux onto a biasable target plate is transferred via a suspended quartz tube onto a sensitive force transducer, a capacitance-type pressure gauge. This protects the transducer from thermal damage, arcing, and sputtering. An absolute force calibration of the PMM to 1% accuracy has been made and is described. A flat carbon target has been used in measurements of the momentum flux of He, Ne, Ar, and Kr plasmas produced in a magnetized linear plasma device.