| 1. |
- Alfier, A., et al.
(författare)
-
Energy confinement in high current RFX-mod plasmas
- 2007
-
Ingår i: 34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts. - 9781622763344 ; , s. 415-418
-
Konferensbidrag (refereegranskat)
|
|
| 2. |
- Annibaldi, Silvia Valeria, et al.
(författare)
-
Excitation of beta-induced Alfvén eigenmodes in the presence of a magnetic island
- 2007
-
Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 49:4, s. 475-483
-
Tidskriftsartikel (refereegranskat)abstract
- Observation of magnetic activity in several discharges in the Frascati Tokamak Upgrade has revealed high-frequency oscillations that accompany the development of large magnetic islands in ohmic plasmas. The frequency of these oscillations is one order of magnitude above the typical island rotation frequency and one order of magnitude below the toroidicity-induced gap of the shear-Alfvén continuum. By writing a precise dispersion relation, we interpret these modes as beta-induced Alfvén eigenmodes, i.e. Alfvén eigenmodes located in the low frequency gap which is caused by finite compressibility.
|
|
| 3. |
- Annibaldi, Silvia Valeria, et al.
(författare)
-
Strong transport reduction in the helical core of the reversed-field pinch
- 2007
-
Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 14:11, s. 112515-
-
Tidskriftsartikel (refereegranskat)abstract
- An explanation of the strong heating observed in the core of a reversed-field pinch in the quasi-single-helicity state is presented. A magnetic island is formed, in which the heat transport coefficient is much smaller than in the surrounding chaotic sea, because of the formation of well defined magnetic surfaces. The values of the thermal conductivity obtained with the M1TEV [F. Porcelli , Phys. Rev. Lett 82, 1458 (1999)] two-dimensional transport code are in very good agreement with the estimates of the ion diffusion coefficient inside the island, given by a Hamiltonian guiding center code. Moreover, the values of thermal conductivity are in the tokamak range, and are consistent with the peak temperatures measured in the Reversed Field eXperiment [P. Sonato , Fusion Eng. Des. 66-68, 161 (2003)] at Consorzio RFX, Padova, Italy. The effect of the island width and the different powers deposited inside the island on the final temperature peak are also investigated.
|
|
| 4. |
- Martin, P., et al.
(författare)
-
Overview of RFX-mod results
- 2009
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 49:10, s. 104019-
-
Tidskriftsartikel (refereegranskat)abstract
- With the exploration of the MA plasma current regime in up to 0.5 s long discharges, RFX-mod has opened new and very promising perspectives for the reversed field pinch (RFP) magnetic configuration, and has made significant progress in understanding and improving confinement and in controlling plasma stability. A big leap with respect to previous knowledge and expectations on RFP physics and performance has been made by RFX-mod since the last 2006 IAEA Fusion Energy Conference. A new self-organized helical equilibrium has been experimentally achieved ( the Single Helical Axis-SHAx-state), which is the preferred state at high current. Strong core electron transport barriers characterize this regime, with electron temperature gradients comparable to those achieved in tokamaks, and by a factor of 4 improvement in confinement time with respect to the standard RFP. RFX-mod is also providing leading edge results on real-time feedback control of MHD instabilities, of general interest for the fusion community.
|
|
| 5. |
- Tuccillo, A. A., et al.
(författare)
-
Overview of the FTU results
- 2009
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 49:10
-
Tidskriftsartikel (refereegranskat)abstract
- Spontaneous increases in plasma density, up to similar to 1.6 times the Greenwald value, are observed in FTU with lithized walls. These plasmas are characterized by profile peaking up to the highest obtained densities. The transport analysis of these discharges shows a 20% enhancement of the energy confinement time, with respect to the ITER97 L-mode scaling, correlated with a threshold in the peaking factor. It has been found that 0.4 MW of ECRH power, coupled at q = 2 surface, are sufficient to avoid disruptions in 0.5 MA discharges. Direct heating of magnetic islands produced by MHD modes determines current quench delay or avoidance. Supra-thermal electrons generated by 0.5 MW of lower hybrid power are sufficient to trigger precursors of the electron-fishbone instability. Evidence of spatial redistribution of fast electrons, on the similar to 100 mu s typical mode timescale, is shown by the fast electrons bremsstrahlung diagnostic. From the presence of new magnetic island induced accumulation points in the continuous spectrum of the shear Alfven wave spectrum, the existence of new magnetic island induced Alfven eigenmodes (MiAE) is suggested. Due to the frequency dependence on the magnetic island size, the feasibility of utilizing MiAE continuum effects as a novel magnetic island diagnostic is also discussed. Langmuir probes have been used on FTU to identify hypervelocity (10 km s(-1)), micrometre size, dust grains. The Thomson scattering diagnostic was also used to characterize the dust grains, present in the FTU vacuum chamber, following a disruption. Analysis of the broad emitted light spectrum was carried out and a model taking into account the particle vaporization is compared with the data. A new oblique ECE diagnostic has been installed and the first results, both in the presence of lower hybrid or electron cyclotron waves, are being compared with code predictions. A time-of-flight refractometer at 60 GHz, which could be a good candidate for the ITER density feedback control system, has also been tested.
|
|
