Measurement of θ-Pinch End Loss Using a Gas Laser Interferometer

A He–Ne gas laser interferometer has been used to make plasma density measurements outside the central plasma core of a θ-pinch plasma. At the θ-pinch coil midplane, the average plasma density is less than the sensitivity of the interferometer, that is, less than 5 × 1013cm−3. Outside the ends of the coil line densities (particles per cm of tube length) of the order of 1015cm−1 are measured. When compared with previous data from the same θ pinch, a streaming velocity out the coil ends in the neighborhood of the ion thermal velocity is obtained.