First Results from an Event Synchronized -- High Repetition Thomson Scattering System at Wendelstein 7-X

TL;DR

This paper presents the initial results of a novel high-repetition-rate Thomson scattering system at Wendelstein 7-X, capable of synchronized, rapid measurements of plasma parameters during dynamic events.

Contribution

It introduces an upgraded Thomson scattering diagnostic with kilohertz sampling and event synchronization, enabling detailed time-resolved plasma measurements.

Findings

Achieved up to twelve measurements per burst with adjustable timing

Demonstrated synchronization with plasma events such as pellet injection

Captured fast electron density and temperature evolution

Abstract

The Wendelstein 7-X (W7-X) Thomson scattering (TS) diagnostic was upgraded to transiently achieve kilohertz sampling rates combined with adjustable measuring times. The existing Nd:YAG lasers are employed to repetitively emit "bursts", i.e. multiple laser pulses in a short time interval. Appropriately timing burst in the three available lasers, up to twelve evenly spaced consecutive measurements per burst are possible. The pulse-to-pulse increment within a burst can be tuned from 2 ms to 33.3 ms (500 kHz - 30 Hz). Additionally, an event trigger system was developed to synchronize the burst Thomson scattering measurements to plasma events. Exemplary, a case of fast electron density and temperature evolution after cryogenic H2 pellet injection is presented in order to demonstrate the capabilities of the method.