# Review of Advanced Implementation of Doppler Backscattering Method in Globus-M
## 3 Application Results
### Filaments  
For the first time DBS diagnostics was implemented to study filaments [56]. Such an implementation is possible when the poloidal size of the filaments is close to \(\pi/\mathrm{k}_{\perp}\) (1-3 cm in the case of DBS on Globus-M), where \(\mathrm{k}_{\perp}\) is the wave vector of the incident wave in the cutoff region. Such filaments were discovered using DBS inside the separatrix in ELMy H-mode with NBI [31; 57] and in Ohmic H-mode with high MHD activity [58; 59]. Filaments were observed as a sequence of bursts of quasi-coherent fluctuations (BQFs) in the IQ DBS signals. The frequency of IQ signal oscillations during a burst was used to calculate the poloidal velocity of the filaments. The distance between filaments in the perpendicular direction was calculated by measuring the temporal delay between adjacent bursts. The four frequency DBS scheme allows one to estimate the radial size of filaments. The reconstruction of the location and spatial distribution of filaments in the Globus-M tokamak is presented in Figure 5.  
In total, three types of filaments were discovered. One of them is ELM filaments. They were observed during ELMs triggered by sawtooth oscillations [60] in discharges with H-mode initiated by NBI when plasma density was relatively small \(\mathrm{n_{e}}<\) 1.2 \(\times\) 10\({}^{19}\) m\({}^{-3}\)[61]. Figure 5: Side view of the magnetic surface of the Globus-M tokamak. The reconstruction of the location of filaments (I–V) at fixed time. Filaments are conventionally shown by lines directed along magnetic field lines. The arrows indicate the direction of the motion of the filaments. The rectangle denotes the location of the DBS receiving antenna [59]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Investigated Property** & **Range of Values** & **Notes** \\ \hline _f,_ kHz & 110 & similar to values on other \\ \hline Spectral peak width \(\Delta\)_f,_ kHz & 80 & tokamaks like T-10 [55] \\ \hline Type & burst & \\ \hline \(\mathrm{b}_{\mathrm{lifetime}}\), ms & 0.1–0.2 & modulated by LCO \\ \hline Location \(\rho\) & 0.65 & in the QCF location there is an \\ \hline Location width \(\Delta\rho\) & 0.1 & coefficient caused by ITG \\ \hline Mode of operation & I-phase & present only during a certain \\  & & phase of LCO \\ \hline Non-linear interaction with & & a peak of summed bicoherence at \\ turbulences & present & the QCFs frequency demonstrates \\  & & the existence of a relationship \\  & & with turbulent fluctuations \\ \hline Coherence of velocity fluctuations & 0.8 near QCFs & \\ and DBS amplitude & frequencies & \\ \hline Coherence of DBS amplitude and & less than 0.3 near \\ magnetic field fluctuations & QCFs frequencies & not of a magnetic nature \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Properties of QCFs in Globus-M. If the plasma density was higher, the waveform during ELMs ceased to resemble quasi-coherent oscillations, although the signal level increased greatly during ELMs. Apparently, this is due to the fact that the poloidal size of the filament depends on the density and, when the critical value is exceeded, it greatly differs from \(\pi/\mathrm{k_{\perp}}\). Measured parameters of ELM filaments can be found in Table 6.  
The second filament type is inter-ELM filaments. Such filaments were discovered between ELMs in discharges with H-mode initiated by NBI when plasma density was higher than the critical value \(\mathrm{n_{e}}\) = 1.5 \(\times\) 10\({}^{19}\) m\({}^{-3}\)[61]. Unlike radially elongated ELM filaments, inter-ELM filaments were located in a very narrow layer of <2 cm. Additionally, inter-ELM filaments were characterized by a smaller distance between each other and moved at lower velocities in comparison with ELM filaments (see Table 6). Unlike inter-ELM filaments, ELM filaments were accompanied by magnetic probe activity, which presumably indicates their peeling ballooning nature [62]. Inter-ELM filaments were also not accompanied by Langmuir probe activity.