1. NATIONAL RESEARCH CENTER “KURCHATOV INSTITUTE”
EX/10-2
3D structure of density fluctuations in T-10 tokamak and new approach for current profile estimation.
Vershkov V.A., Buldakov M.A., Subbotin G.F., Shelukhin D.A., , Melnikov A.V., Eliseev L.G.,Khabanov F.O.,Drabinsky M.A., Sergeev D.S., Myalton T.B., Trukhin V.M., Gorshkov A.V., Belbas I.S., Asadulin G.M.
FEC 2018 1 1 1 1 1

2. Mainly OH discharges were investigated
NATIONAL RESEARCH CENTER “KURCHATOV INSTITUTE”
Motivation: Confirmation of different density fluctuation types and complete characterization of their properties with correlation reflectometry and Heavy Ion Beam Probe (HIBP) diagnostics
Experimental setup
Mainly OH discharges were investigated
Two independent reflectometers and HIBP diagnostic with 5 slits were used
Antenna system and two independent
reflectometers enables to measure:
Poloidal correlations ( rotation and dimensions)
Radial amplitude distributions at 4 poloidal angles (0, 60, 120 and 180 degrees)
Radial correlations at 4 poloidal angles
Long Range Correlations ( LRC ) along the field line at LFS and HFS
5 channel HIBP measured density and potential fluctuations at 5 adjacent points), providing:
Poloidal correlations
LRC correlations between Reflectometry and HIBP 2 2 2 2 2

3. Two techniques for Long Range Correlations (LRC) measurements
NATIONAL RESEARCH CENTER “KURCHATOV INSTITUTE”
Two techniques for Long Range Correlations (LRC) measurements
Measurements of the delays between reflectometry signals at different radii in a series of reproducible discharges
Measurements with several antenna pairs at fixed radius.
Simultaneously measured:
Resonant radius
Local Magnetic shear 3 3 3 3 3

4. NATIONAL RESEARCH CENTER “KURCHATOV INSTITUTE”
Fluctuation Types
previous types classification was confirmed : Broad Band (BB), Stochastic Low Frequencies (SLF) и High и Low Frequency Quasi-Coherent fluctuations (HFQC and LFQC).
For the first time 5-channel HIBP diagnostic also fully confirmed those types.
Poloidal correlation reflectometry
Poloidal correlation HIBP 4 4 4 4 4

5. NATIONAL RESEARCH CENTER “KURCHATOV INSTITUTE”
ВВ characteristics
Poloidal correlation length much less 2 cm; correlation length along field line much less then 2.5 m. LRC with BB was never seen.
Autocorrelation time about 2.5 µs corresponds to poloidal dimension less then 1 cm.
Radial correlation length is about 1 cm at 00, 600 и 1200 At1800 abrupt decrease at the distances less then 1 mm was confirmed.
BB amplitude at HFS lower then at LFS in a factor of 3.
So, BB exited locally at each poloidal angle and poloidal asymmetry is connected with the source strength. 5 5 5 5 5

6. Characteristics of Quasi-Coherent Fluctuations (QC)
NATIONAL RESEARCH CENTER “KURCHATOV INSTITUTE”
Characteristics of Quasi-Coherent Fluctuations (QC)
LFQC and HFQC have in core kpol×ρi values 0.3 и 0.7 respectively. Amplitude of LFQC minimal in the gradient part of the column. HFQC is maximal in that region. This properties are typical for ITG and TEM turbulence.
Autocorrelation function has oscillating structure
Typically smooth maximum of LFQC in experiments with peripheral ECRH transforms initially to a set of peaks and finally degenerates to a single mode structure with m=19. So QC arise due to excitation of rational modes with high m. 6 6 6 6 6

7. Long Range Correlation of QC at LFS with reflectometry
NATIONAL RESEARCH CENTER “KURCHATOV INSTITUTE”
Long Range Correlation of QC at LFS with reflectometry
The delays between signals of independent reflectometers in two ports separated 900 toroidally were measured at LFS in discharges with currents 200 and 250 kA.
Two experimental runs with simultaneous reversal of current and toroidal field were made in order to sustain the trace of magnetic line.
Zero delays were observed at the same resonant radius for both magnetic configurations. This may evidence that the amplitude of QC is constant along the magnetic line.
The resonant radius shifted outward at higher current in accordance with widening of the current profile. 7 7 7 7 7

8. HF and LF QC were observed in spectra of both diagnostics
NATIONAL RESEARCH CENTER “KURCHATOV INSTITUTE”
Long Range Correlation of QC at LFS between reflectometry and HIBP
For the first time LRC were measured at LFS between Reflectometry and HIBP
HF and LF QC were observed in spectra of both diagnostics
High LRC correlation values was measured for HF and LF QC 8 8 8 8 8

9. Radial correlations and poloidal dependence of QC amplitude
NATIONAL RESEARCH CENTER “KURCHATOV INSTITUTE”
Radial correlations and poloidal dependence of QC amplitude
The amplitude of radial cross-correlation of QC at LFS did not decrease even up to radial difference of 5.5 cm. The radial correlation length decrease to 4 cm at 600 and to 0.8 cm at At HFS amplitude of QC was too low.
QC rotate at all poloidal angles in electron diamagnetic direction
Amplitude of QC for radii r/a>0.5 decrease at HFS practically to zero. 9 9 9 9 9

10. Impact of reflectometry properties on amplitude decrease of QC at HFS
NATIONAL RESEARCH CENTER “KURCHATOV INSTITUTE”
Impact of reflectometry properties on amplitude decrease of QC at HFS
Strong decrease of QC amplitude at HFS contradicts to high correlation along the magnetic field line.
Contradiction is resolved by the account of “non-locality” of reflectometry.
This explanation is supported by the observation of high amplitudes of QC at HFS in central regions with q≤1, where magnetic shear is low. LRC correlation of QC in such case reaches the value up to 0.7!
Tokamak axis 10 10 10 10 10

11. Characteristics of Stochastic Low Frequency (SLF) fluctuations
NATIONAL RESEARCH CENTER “KURCHATOV INSTITUTE”
Characteristics of Stochastic Low Frequency (SLF) fluctuations
SLF has smooth spectrum from 0 to 50 kHz.
Both reflectometry and HIBP showed that at LFS SLF rotate in opposite direction to QC. At HFS they rotate in the same direction.
So SLF always move in the direction of B×B both at LFS and at HFS. 11 11 11 11 11

12. LRC measurements of SLF at HFS with several antenna pairs
NATIONAL RESEARCH CENTER “KURCHATOV INSTITUTE”
LRC measurements of SLF at HFS with several antenna pairs
At HFS in the plasma core SLF LRC correlations reaches high value up to 0.8.
The decay of coherency with the antenna pairs away from the resonance gives the estimation of the poloidal width of SLF about 3.5 cm. The same estimation for QC gives higher value about 6.5 cm 12 12 12 12 12

13. LRC measurement of SLF at HFS by means of radial scan
NATIONAL RESEARCH CENTER “KURCHATOV INSTITUTE”
LRC measurement of SLF at HFS by means of radial scan
LRC were measured at HFS for two antenna pairs with different inclinations.
Experiments were carried out in two series with simultaneously reversed Bt and Ip.
The resonance radius for both magnetic configurations is the same for both antenna pairs. It is consistent with the hypothesis that SLF amplitude is also constant at the field line.
Resonant radius increases for the pair with lower inclination in accordance with rise of q value with radius.
At LFS SLF LRC correlations were not observed. The reason may be the high level of uncoherent BB at LFS 13 13 13 13 13

14. Radial correlations and poloidal dependence of SLF amplitude
NATIONAL RESEARCH CENTER “KURCHATOV INSTITUTE”
Radial correlations and poloidal dependence of SLF amplitude
At LFS coherency of SLF practically stays constant up to 5.5 cm.
At 600 correlation length decreases to 4.5 cm; at 1200 and 1800 to 2 cm.
In all cases the phase shift at different radial separation was zero.
In difference to QC SLF amplitude did not changed with poloidal angle. 14 14 14 14 14

15. Summary of density fluctuations characteristics
NATIONAL RESEARCH CENTER “KURCHATOV INSTITUTE”
Summary of density fluctuations characteristics
ВВ has the lowest correlation properties. Poloidal correlations are not observed at separation of 2 cm. Radial correlation length at all poloidal angles about 1 cm. Correlation length along the field line much less 2.5 m. So BB generated locally at each poloidal angle and amplitude asymmetry is connected with the source strength.
LFQC and HFQC are the result of the excitation of the modes with high m numbers with poloidal dimension typical for ITG and TEM instabilities. They are highly correlated along the magnetic field line. LRC showed that amplitude of QC modes are constant at the magnetic field line. QC have long radial correlation lengths at LFS, which decreases to HFS. Strong decrease at HFS is explained by integration properties of reflectometry at radii with significant magnetic shear.
SLF fluctuations have poloidal dimensions about 4 cm. They also have high radial correlation length at LFS, which decreases towards HFS. In difference to QC Their amplitude is constant at all poloidal angles. SLF move in [B×B] direction at LFS and at HFS. Their physics presently are not clear. 15 15 15 15 15

16. New approach for the current profile measurement
NATIONAL RESEARCH CENTER “KURCHATOV INSTITUTE”
New approach for the current profile measurement
LRC results of QC and SLF are in good agreement with the modelling in the real magnetic configuration.
Nevertheless for future applications it is preferable to use the modes with more transparent physics, like TAE modes.
All data for the current profile can be obtained just within reflectometry itself. But as TAE modes is localized radially approach with several antenna pairs should be used.
Such technique can be easily used at the reactor grade tokamaks, as reflectometry did not suffer neither from high neutron fluxes, no from deposited layers. 16 16 16 16 16

17. Thank you for your attantion
NATIONAL RESEARCH CENTER “KURCHATOV INSTITUTE”
Thank you for your attantion 17 17 17 17 17