Drift waves and ion temperature gradient instabilities in the large linear device SPEKTRE

The objective of this work is to linearly investigate the plasma instabilities that will be observed in the linear SPEKTRE device, currently being assembled at Institut Jean Lamour. Two configurations are considered. In the first configuration, the magnetic field is set to 0.1 T with no ion temperature gradient (ITG), resulting in the observation of only collisional drift waves (DW). In the second configuration, the magnetic field is set to 0.44 T, and ions can be heated using an ion cyclotron radiofrequency heating (ICRH) system to establish an ITG. Under these conditions, two major types of instabilities may be observed: collisional DW and ITG instabilities. ITG instabilities become more unstable than DW when the ratio of the characteristic lengths of the ion temperature to ion density profiles η=ΩT*/Ωn*>2.6. The observation of such a transition between the two types of instabilities will be possible on this machine using the ICRH system. The azimuthal mode number m of the most unstable mode is significantly larger for helium plasma compared to argon plasma. Furthermore, for the plasma parameters considered in both configurations, a fluid model is often sufficient to accurately describe DW, while a kinetic model is required to accurately describe ITG instabilities. There is a 30% difference between the ITG instability growth rates predicted by the fluid model and those predicted by the kinetic model.