New techniques for plasma density profiling

Two new techniques for the measurement of plasma density profiles are presented. The two approaches are aimed at simultaneously overcoming uncertainties due to the Abel inversion and plasma irreproducibility. The first technique combines standard heterodyne interferometry with rapid spatial scanning. The Abel inversion problem is addressed by the very high spatial resolution obtainable, while the plasma irreproducibility is overcome by multiple framing in a single discharge. The technique requires only a single detector channel and is applicable over a wide range of parameters. The apparatus has been built and successfully bench tested. The second technique, currently in the design stage, is based on Thomson scattering of a short laser pulse. With a wavepacket small compared to the plasma, the nondispersed scattered light pulse shape is essentially the plasma profile. Additionally, the short light pulse allows time of flight discrimination against instrumental scatter. With very modest pulse energy, the scattered power greatly exceeds the plasma radiation and signal statistics determine the detection quality.