1. magnetic confinement - ENEA - Fusione

More documents

Recommendations

Info

38 1. MAGNETIC CONFINEMENT 1.2 FTU Facilities components may rise simultaneously if the non-locality of the measurement is taken into account, since it integrates the low frequency at some outer radial zone. It is also important that the low-frequency rotation remain unchanged. It is worth noting that the quasi-coherent rotation is sensitive to gradients, whereas the low-frequency is closer to that of the bulk plasma. Figure 1.33 shows the evolution of some turbulence parameters in an experiment with the injection of four deuterium pellets [1.50]. The discharge has I p =1.2 MA and B t =7.9 T. The probing Xl mode was used with a cut-off density of 2.76×10 20 m -3 . The trace of the reflected wave amplitude (fig. 1.33b) shows that reflection appears just transiently after the first pellet at t=800 ms and becomes permanent after injection of the second. This is eV/cm 104 s-1 Part in signal cm a.u. 1019 m-3 ω rotation pellets Electron density Reflection radius Broad band Low frequency the first time that poloidal correlation measurements in the Xl mode have been carried out in tokamaks, with the antennas located at the low-field side and the poloidal angle 17.5° above the equatorial plane. Such geometry results in a significant deviation of the incident wave from the perpendicular direction, due to the dependence of the refractive index on the magnetic field and on the Shafranov shift of the plasma column. This makes it impossible to measure reflections close to the centre of a plasma with a flat density profile. Thus, reliable results can be obtained only when the amplitude of the reflected wave is larger than some minimum value, as shown in figure 1.33b. The most distinctive feature is the drop of the quasi-coherent rotation velocity after the second pellet. An explanation for this could be that the reflection layer gradually moves towards the central region where the gradients are smaller due to density decay. At the same time, the low-frequency component rotates more slowly and does not show any strong variation in time. This may indicate again that this component is related to plasma rotation, whereas the quasi-coherent one depends on gradients. The simultaneous suppression of both components in the central region, as observed in these experiments, suggests a physical relation between these turbulence features and also the presence of a good confinement zone near the centre. The fully non-inductive discharges with LHCD [1.51] make it possible to reveal the fine structure of quasi-coherent turbulence. In figure 1.34 the usually smooth spectral maxima of these fluctuations split into an envelope of five peaks with a 3.1-kHz spacing in frequency. The depth of amplitude modulation shows that only the quasicoherent fluctuations are 100% modulated whereas the broadband are not. This supports the idea that the two components have different underlying physical mechanisms. Poloidal correlation measurements during the same time slice give the rotation velocity and show that the mean m number is equal to 48. Thus, the 3.1-kHz frequency step corresponds to an m number increment of three instead of one. In order to solve this problem, consider the reflection from a plasma region with a flat current profile around the q=3 surface but with a rather steep density gradient. The modes with m/n ≠3 will be far away from the reflection layer and will not be “seen” by the reflectometer. Thus, only modes with an m increment of three will be observed, in accordance with experimental data. Analysis of the bursting of the 4 2 20 10 0 20 10 0 0.5 0.0 0.2 0.0 1.0 0.5 0.0 m=2 HF Signal amplitude Reliability level LF 100 0 dT/dr 700 800 900 1000 1100 1200 Time (ms) Fig. 1.33 - Evolution of turbulence behaviour during a high-confinement phase of a pellet-fuelled discharge. [1.50] V. Pericoli Ridolfini et al. , Phys. Rev. Lett. , 82, 93 (1999) [1.51] S. Cirant et al., Mode coupling trigger of tering mides in ECV heated discharges in FTU, presented at the 18 th IAEA Conference, (Sorrento 2000), paper IAEA-CN-77/EX3/3
1. MAGNETIC CONFINEMENT 39 Coherency Cross-phase Amplitude π a.u. 1.0 0.5 0.0 1 0 1.0 -1 0.5 0.0 -100 -50 0 50 100 Frequency kHz Fig. 1.34 - Turbulence spectrum in a discharge with full LH current drive. The quasi-coherent and lowfrequency components show a peaked structure. Fig. 1.35 - Comparison of MHD and turbulence properties in a discharge with 2/1 island ECRH stabilisation. Fig. 1.36 - Temperature time trace in discharges with BT scan used for the diagnostics comparison. [1.52] D. Frigione et al. , Nucl. Fusion 41, 11, 16131 (2001) Frequency m=2, kHz Amplitude m=2, a.u. ωrotation 104 s-1 4 3 2 1 0 1.5 1 0.5 0 5 4 3 4 2 0 4 2 0 2 1 0 a) b) c) 800 T ece a) b) c) 850 T ece /T sc T sc B tor Time (ms) 1.2 FTU Facilities harmonics in time shows that they behave stochastically and are not correlated. Therefore the conclusion in this case is that each harmonic is just an independent excitation of the helical mode with high values of m numbers. Important information was obtained in experiments with m=2, n=1 stabilisation by ECR heating [1.52]. Figure 1.35 shows a comparison of frequency (fig. 1.35a) and amplitude (fig. 1.35b) variation of the m=2, n=1 mode measured with magnetic probes and an O-mode reflectometer. The good agreement is clearly seen. The angular velocities of the m=2 mode and the quasicoherent and low-frequency components are compared in figure 1.35c. The rotation of the quasi-coherent component is practically equal to or sometimes transiently higher than that of the 900 Reflectometer Magnetic probes ECRH Reflectometer Magnetic probes MHD LF HF 950 0 0.5 1 1.5 2 Time (s) m=2 mode and does not change after its stabilisation. The lowfrequency component rotates slightly more slowly and does not vary after the m=2 stabilisation either. Comparison of ECE and Thomson scattering temperature measurements After upgrading of the Thomson scattering (TS) system and realignment of the ECE optics, with a consequent re-calibration of the Michelson interferometer, the electron temperature measurements performed with the two diagnostics were no longer in agreement. To understand which of the two measurements was correct, some toroidal field ramps were analysed to see if the discrepancy depended on the magnetic field or on the temperature itself. In the first case, the error could be attributed to the ECE optics as the emitted spectrum moves at different frequencies when the magnetic field is changed, if there is an error in the calibration. In the second case, the error can only be due to the TS system since the Michelson measurements are far from saturation. In the following it is shown that the discrepancy depends strongly on the magnetic field and, hence, is to be attributed to the ECE diagnostics. The result of a single toroidal field ramp is shown in figure 1.36. The ECE
Page 1 and 2: ITALIAN AGENCY FOR NEW TECHNOLOGIES
Page 3 and 4: 1. MAGNETIC CONFINEMENT 09 1.1 Toka
Page 5 and 6: 3.6 Remote Handling 81 3.6.1 IVROS
Page 7: 5.3 Theory 123 5.3.1 Interaction of
Page 10: partner in this respect, the Instit
Page 14 and 15: 10 1. MAGNETIC CONFINEMENT 1.1 Toka
Page 32 and 33: 28 1. MAGNETIC CONFINEMENT 1.2 FTU
Page 46 and 47: 42 1. MAGNETIC CONFINEMENT 1.3 Plas
Page 54 and 55: 50 1. MAGNETIC CONFINEMENT 1.4 FT3
Page 56 and 57: 52 1. MAGNETIC CONFINEMENT 1.4 FT3
Page 58 and 59: 54 1. MAGNETIC CONFINEMENT 1.5 PROT
Page 63 and 64: 2. IGNITOR PROGRAM 59 2.1 Introduct
Page 65: 2. IGNITOR PROGRAM 61 2.3 Engineeri
Page 70 and 71: 66 3. FUSION TECHNOLOGY 3.2 First W
Page 72 and 73: 68 3. FUSION TECHNOLOGY 3.3 Vacuum
Page 74 and 75: 70 3. FUSION TECHNOLOGY 3.4 Magnets
Page 80 and 81: 76 3. FUSION TECHNOLOGY 3.5 Neutron
Page 86 and 87: 82 3. FUSION TECHNOLOGY 3.6 Remote
Page 88 and 89: 84 3. FUSION TECHNOLOGY 3.7 Materia
Page 90 and 91: 86 3. FUSION TECHNOLOGY 3.7 Materia
Page 92 and 93:
88 3. FUSION TECHNOLOGY 3.7 Materia
Page 94 and 95:
90 3. FUSION TECHNOLOGY 3.8 Liquid
Page 96 and 97:
Page 98 and 99:
Page 100 and 101:
Page 102 and 103:
98 3. FUSION TECHNOLOGY 3.9 Thermal
Page 104 and 105:
100 3. FUSION TECHNOLOGY 3.10 Inter
Page 106 and 107:
102 3. FUSION TECHNOLOGY 3.12 Safet
Page 108 and 109:
Page 110 and 111:
Page 112 and 113:
Page 114:
Page 118 and 119:
114 4. MISCELLANEOUS 4.3 Partecipat
Page 120 and 121:
116 4. MISCELLANEOUS 4.4 Advanced S
Page 122 and 123:
118 4. MISCELLANEOUS 4.5 Optical Me
Page 124:
120 4. MISCELLANEOUS 4.8 Cryogenics
Page 128 and 129:
124 5. INERTIAL CONFINEMENT 5.3 The
Page 130 and 131:
Page 132 and 133:
Page 137 and 138:
PUBLICATIONS, CONFERENCES AND REPOR
Page 139 and 140:
Page 141 and 142:
Page 143 and 144:
Page 145 and 146:
Page 147 and 148:
Page 149:
Page 154 and 155:
150 ABBREVIATIONS AND ACRONYMS EC E
Page 156 and 157:
152 ABBREVIATIONS AND ACRONYMS LHC
Page 158:
154 ABBREVIATIONS AND ACRONYMS WDS
show all

1. magnetic confinement - ENEA - Fusione

Create successful ePaper yourself

Delete template?

Save as template?