The next step after two decades of SUNIST
SUNIST-2 is the next-generation spherical tokamak built by the laboratory. It inherits the experience of more than twenty years of SUNIST operation and aims at a more flexible experimental programme.
Compared with the original design, small mechanical modifications were made to the supports and the box of the inner coils, and the compensation coils of the central solenoid were adjusted to meet the mechanical requirements. Several operation scenarios have been analysed, including doublet configurations and negative triangularity, which extend the range of plasma shapes available to experiments.
The machine is equipped with modern periphery systems: supercapacitor-based toroidal-field power supplies, electrolytic-capacitor banks with IGBT switches for the CS/PF coils, and both a plasma gun and electron-cyclotron waves for pre-ionization.
Design changes and operation modes
Mechanical modifications
The supports and the box of the inner coils were modified to meet mechanical requirements, and the compensation coils of the central solenoid were adjusted.
More operation modes
Several scenarios were analysed, including doublet configurations and negative triangularity, adding flexibility compared with the circular, strongly shaped SUNIST plasmas.
Construction and assembly
Construction was delayed by more than a year by COVID-19 restrictions and by the preparation of a suitable site; assembly was reported to be nearly complete at the time of ISTW 2022.
Power supplies and pre-ionization
Toroidal-field power supply
Based on supercapacitors and IGBT switches, built as a single module. The supply was under test at the time of the ISTW 2022 report.
CS / PF power supplies
Electrolytic-capacitor banks with IGBT switches provide the central-solenoid and poloidal-field currents; the system was under test.
Pre-ionization: plasma gun
A plasma gun provides pre-ionization for discharge start-up, complementing the electron-cyclotron-wave start-up studied on SUNIST.
Pre-ionization: electron-cyclotron waves
Electron-cyclotron waves add an alternative, non-invasive start-up channel, building on the ECW start-up research performed on SUNIST.
The SUNIST spherical tokamak
Read about the device that made SUNIST-2 possible: its design, parameters and two decades of operation.