Alignment of the Thomson scattering diagnostic on NSTX

The Thomson scattering diagnostic can provide profile measurement of the electron temperature, T-e, and density, n(e), in plasmas. Proper laser beam path and optics arrangement permits profiles T-e(R) and n(e)(R) measurement along the major radius R. Keeping proper alignment between the laser beam path and the collection optics is necessary for an accurate determination of the electron density. As time progresses the relative position of the collection optics field of view with respect to the laser beam path will invariably shift. This can be kept to a minimum by proper attention to the physical arrangement of the collection and laser-beam delivery optics. A system has been in place to monitor the relative position between laser beam and collection optics. Variation of the alignment can be detected before it begins to affect the quality of the profile data. This paper discusses details of the instrumentation and techniques used to maintain alignment during NSTX multi-month experimental campaigns.