RAID, Exploring Helicon Plasmas
Photo of the RAID during operation, with the operator in first sight.
The Resonant Antenna Ion Device (RAID) is a linear device that was originally developed to investigate negative hydrogen ion (D–/H⁻) production for future neutral beam injection systems for tokamak heating. Today, on RAID we conduct studies of fundamental plasma physics of relevance for magnetically confined fusion, for the development and validation of advanced diagnostics, and for investigations of helicon wave physics. RAID is equipped with two 10kW resonant antennas to produce helicon plasmas.
The stainless-steel vacuum chamber is 1.5 m long and 40 cm in diameter. A turbomolecular pump maintains a base pressure of 1×10−4 Pa, while the neutral gas pressure during plasma operation is typically maintained between 0.1 Pa and 1.5 Pa. A dedicated gas control system allows operation with H₂, D₂, He, Ne, O₂, and Ar, with injection rates of a few tens of sccm. An axial magnetic field (up to 660 G on-axis) is provided by DC coils surrounding the vacuum vessel. Plasma generation is performed using two resonant network antennas mounted on the end flanges. The antenna systems—including RF generators, automatic T-matching networks, and transmission lines—are identical and designed to deliver up to 10 kW of RF power each. Active cooling of the alumina end tubes, end plates, and chamber walls enables steady-state operation at up to 5 kW per source in dual-antenna configuration.
Typical plasma parameters in RAID are:
- Electron density: a few 1017 to a few 1019 m−3
- Electron temperature: up to 10 eV
These conditions are well suited for volume production of negative hydrogen ions and for generating plasmas relevant to divertor regimes in magnetic confinement devices.
DIAGNOSTICS
- 3D movable Langmuir probes (ne, Te)
- 3D movable three-axis B-dot probe (magnetic field fluctuations, helicon wave characterization)
- 1D movable Langmuir probe (ne, Te)
- Microwave (110GHz) interferometer (line-averaged ne)
- Thomson scattering (ne, Te)
- Optical emission spectroscopy
- Laser-based diagnostics (LIF, TALIF, LCIF)
