Edge Thomson scattering diagnostic on COMPASS tokamak: Installation, calibration, operation, improvements

Abstract

The core Thomson scattering diagnostic (TS) on the COMPASS tokamak was put in operation and reported earlier. Implementation of edge TS, with spatial resolution along the laser beam up to ∼1/100 of the tokamak minor radius, is presented now. The procedure for spatial calibration and alignment of both core and edge systems is described. Several further upgrades of the TS system, like a triggering unit and piezo motor driven vacuum window shutter, are introduced as well. The edge TS system, together with the core TS, is now in routine operation and provides electron temperature and density profiles.

High resolution Thomson scattering on the COMPASS tokamak—extending edge plasma view and increasing repetition rate

“…Since the beginning, it was designed to have two separate collection optics (both sharing one laser beam); one observing the edge plasma -1 - region with high resolution (~a/100), the second extending the measured profiles to the middle of the plasma. The first measurements used only the core TS lens, the edge lens was installed later [9]. Couple of modifications and upgrades were done on the system since its installation.…”

“…The available port for the edge TS was directed to the core plasma (figure 2), which made the optical design of the collection lens challenging [9]. The resulting edge TS system worked, but the available field of view proved to limit the variability of plasma scenarios to only those, where the pedestals were well covered.…”

“…The old lens was designed for the adverse geometry of the old edge TS port [9]. It consisted of 7 lens elements, some of them made of high refractive index glass SF6 to reach the required field of view far from the tokamak port axis.…”

Contribution to the multi-machine pedestal scaling from the COMPASS tokamak

“…COMPASS is equipped with a set of high resolution diagnostics for measurements in the plasma edge [13]. The most important one for these studies is the high resolution Thomson scattering (HRTS) [14,15], which allows to measure the edge profiles with a spatial resolution of ~2-3 mm (~a minor /100), which is sufficient to well resolve the pedestal. HRTS uses two 1.5 J Nd:YAG lasers with a repetition rate of 30 Hz each.…”

Contribution to fusion research from IAEA coordinated research projects and joint experiments

“…Compass-D, Alcator C-Mod, T-10, Globus-M, START, RTP, TEXT, TJ-2, Uragan-2M, Uragan-3 and others have (or had) extended research programmes, wellequipped with sophisticated diagnostics and powerful heating systems. Figure 3 shows results from very advanced Thomson scattering diagnostics on COMPASS, IPP-AS Prague [30,31], and comparison of Thompson scattering (TS) measurements with very high core and edge resolution with reflectometry and Langmuir probes (LPs). Similar diagnostics on C-Mod, T-10 and Globus-M allows detailed investigation of the tokamak transport.…”