# Review of Advanced Implementation of Doppler Backscattering Method in Globus-M
## 3 Application Results
### Turbulence  
The four frequency DBS system was used to study turbulence in H-mode with and without ELMs. The experiments were performed in the Globus-M spherical tokamak operated in H-mode initiated by NBI. Plasma density fluctuations as well as plasma velocity fluctuations were investigated during the transition to the ELM-free H-mode. Studies showed a decrease in both plasma density and plasma velocity fluctuation near the separatrix in the absence of ELMs [74; 75].  
A more in-depth study of turbulence during ELMs allowed us to identify two types of ELMs and two corresponding types of transition to the ELM-free H-mode [76]. Low-frequency ELMs in the Globus-M tokamak are characterized by the transition to the ELM-free regime during plasma current decrease alongside a similar change in the current density profile. This transition is associated with a decrease in the intensity of sawtooth oscillations. The level of turbulence at the periphery in this case varies only slightly, which was demonstrated by analyzing the amplitude of the complex DBS signal as demonstrated in Figure 7a. It can be assumed that the transport does not change, which is indicated by the constancy of the D\({}_{\alpha}\) level and average density.  
High-frequency ELMs are characterized by a spontaneous transition to the ELM-free regime. The peripheral turbulence amplitude decreases during this transition (as seen in Figure 7b), which was accompanied by the typical features of peripheral transport suppression: the electron density increases and D\({}_{\alpha}\) emission drops. A study of the turbulence amplitude spectra during this regime led to the discovery of quasi-coherent (QC) fluctuations in the ELM-free H-mode in the highest frequency (48 GHz) channel with a the cutoff radius of \(\rho\) = 0.6 [77]. The properties of these fluctuations were similar to the QCFs observed in I-phase (see Table 5), except for the fact that the QC fluctuations in ELM-free H-mode were not modulated by anything. They existed continuously during the period of ELM-free H-mode. Such QCFs were not detected in the spectra of the complex IQ signal. This, apparently, indicates that the poloidal scale of the fluctuations is much larger than the method resolution of \(\pi/\text{k}_{\perp}\).  
\begin{table}
\begin{tabular}{c c c} \hline
**Investigated Property** & **Range of Values** & **Notes** \\ \hline Additional heating & NBI & only observed during NBI \\ \hline \(f\), kHz & \(\sim\)99–160 & Alfvén continuum frequency gaps \(f_{\text{TAE}}=\frac{\
u_{\text{z}}}{4\pi qR}\)[68] \\ \hline Spectral peak width \(\Delta\)_f_, kHz & 80 & the decrease of the TAE frequency is related to the slowing down of the Alfven wave \\ \hline Type & continuous or burst & dependent on the injected beam parameters [69] \\ \hline t\({}_{\text{lifetime}}\) (for burst type), ms & \(\sim\)0.1–0.5 & predator-prey model [69] \\ \hline Radial electric field amplitude, kV m\({}^{-1}\) & \(\sim\)0.5–3 & the oscillations of the Alfven magnetic field are accompanied by the oscillations of the measured electric field according to [PERSON]’s equation \(\widetilde{B}_{\theta}=\frac{\widetilde{E}_{\theta}}{\text{k}_{\perp}}\)[73] \\ \hline Location \(R\), m & \(\sim\)0.50–0.56 & shift of TAE to the inner plasma regions is related to the increasing plasma current \\ \hline Toroidal number, \(n\) & 1–3 & different toroidal numbers correspond to different TAE harmonics \\ \hline \end{tabular}
\end{table}
Table 7: Properties of Alfven eigenmodes in Globus-M.