A phase contrast imaging-interferometer system for detection of multiscale electron density fluctuations on DIII-D

Area of Science:

• Plasma physics
• Fusion energy research
• Diagnostic techniques

Background:

• Heterodyne interferometry measures low-k electron density fluctuations.
• Phase contrast imaging (PCI) measures high-k electron density fluctuations.
• Simultaneous measurement of diverse fluctuation scales is crucial for understanding plasma behavior.

Purpose of the Study:

• To report the first implementation of a combined phase contrast imaging-interferometer diagnostic.
• To enable simultaneous measurement of electron density fluctuations across a broad spatiotemporal bandwidth.
• To facilitate advanced studies of plasma instabilities and magnetohydrodynamics (MHD).

Main Methods:

• Utilized a single 10.6 μm probe beam.
• Employed two distinct interference schemes and two detectors.
• Integrated measurements with existing DIII-D diagnostics for core-localized studies.

Main Results:

• Achieved simultaneous measurement of electron density fluctuations from 10 kHz to 5 MHz and 0 cm^-1 to 20 cm^-1.
• Enabled simultaneous observation of ion- and electron-scale instabilities.
• Facilitated core-localized, low-n MHD studies previously inaccessible.

Conclusions:

• The combined PCI-interferometer is a powerful new diagnostic for plasma turbulence.
• Its design is suitable for harsh environments and limited space in future fusion devices.
• This diagnostic advances the capability to study complex plasma phenomena in fusion research.