Issues in the plasma wall interactions in RFX

Valisa, M.; Bartiromo, R.; Bettella, D.; Carraro, L.; Costa, S.; Martin, P.; Martini, S.; Pasqualotto, R.; Puiatti, M. E.; Scarin, P.; Sattin, F.; Telesca, G.; Zanca, P.; Zaniol, B.

doi:10.1016/s0022-3115(00)00545-6

Cited by 7 publications

(7 citation statements)

References 12 publications

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“…On average the influx depends linearly on the density with a value of 3 × 10 21 m −2 s −1 for a density of 2.5 × 10 19 m −3 (figure 8(a)) which corresponds to an average global particle confinement time (τ P ) of about 2 ms, while the maximum τ P is about 3 ms. In the same plasma current range (>800 kA) on RFX about 40% of particle influx [18] came from a region close to the m = 1 LM. Due to the strong wall interaction and the poor particle confinement in RFX the global influx was independent of density with a value of ≈6 × 10 21 m −2 s −1 (figure 8(b)) two times higher than in RFX-mod VS.…”

Section: Particle Transportmentioning

confidence: 92%

“…The deformation affects transport introducing non axial-symmetric effects locally modifying both the density profile and the influx from the wall. Due to the plasmawall interaction, density profiles close to the locking position have a steeper edge gradient than at other toroidal positions [17] and particle influx is higher [18]. Controlling the edge radial magnetic field by VS greatly reduces the deformation amplitude [7], but the effect is still present.…”

Section: Particle Transportmentioning

confidence: 99%

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Transport and confinement studies in the RFX-mod reversed-field pinch experiment

Innocente

Alfier²,

Carraro³

et al. 2007

Nucl. Fusion

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In the modified RFX experiment (RFX-mod) external magnetic field coils and a close fitting thin conductive shell control radial magnetic fields. In the so-called virtual shell (VS) operation, radial field zeroing at the thin shell radius is stationary provided by the feedback-controlled coils. First experiments on RFX-mod proved the capability of the active scheme to steadily reduce the radial magnetic field. Furthermore it has been found that such edge magnetic field control extends its beneficial effects to the whole plasma. With respect to the old RFX, where magnetohydrodynamic modes amplitude was controlled by the use of a passive thick conductive shell, a stationary 2- to 3-fold reduction of the B r field amplitude in the core is obtained. The reduction of field fluctuations positively reflects on confinement. In fact, a strong reduction of the loop voltage is observed and correspondingly a 3-fold increase in pulse length is achieved by using the same poloidal flux swing. Temperature and particle measurements confirm the improved confinement properties of the VS operation. With a lower ohmic input power, higher electron temperature and lower particle influx are measured. Particle and heat transport have been studied by means of a 1D code. Local power balance was used to compute the heat conductivity profile: for the VS discharges a lower conductivity over a significant region of the plasma is found. The improved properties of RFX-mod VS operation provide a better confinement scaling in terms of plasma current. The results show that compared with the thick shell configuration, a significant confinement improvement can be obtained under stationary conditions by actively controlling the plasma magnetic boundary.

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Section: Particle Transportmentioning

confidence: 92%

Section: Particle Transportmentioning

confidence: 99%

Transport and confinement studies in the RFX-mod reversed-field pinch experiment

Innocente

Alfier²,

Carraro³

et al. 2007

Nucl. Fusion

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“…Though local field errors introduced by the insulating poloidal gap (allowing for the penetration of the magnetic field) were reduced by a local active control system, LMs still produced a large radial displacement of ≈2 cm [567], determining power loads locally as high as ≈100 MW m −2 in the region where the bulge intercepted the wall [80]. This was associated to local enhancement of electron density and density fluctuations, suggesting a continuous ionization and loss of neutrals, and to increased transport and impurity influxes [568]. Carbon and oxygen influxes from the LM region were estimated to be of the order of 20%-40% of the total; however, tomographic measurements of total radiation showed that, due to the relatively small region of interaction, the radiation enhancement produced by LM was a fraction of the total input power of the order of ≈10%, leading to the conclusion that the main loss term is due to the local increase of transport and particle fluxes [80].…”

Section: Effect Of Magnetic Topology On Plasma-wall Interactionmentioning

confidence: 99%

The reversed field pinch

et al. 2021

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This paper reviews the research on the reversed field pinch (RFP) in the last three decades. Substantial experimental and theoretical progress and transformational changes have been achieved since the last review (Bodin 1990 Nucl. Fusion 30 1717–37). The experiments have been performed in devices with different sizes and capabilities. The largest are RFX-mod in Padova (Italy) and MST in Madison (USA). The experimental community includes also EXTRAP-T2R in Sweden, RELAX in Japan and KTX in China. Impressive improvements in the performance are the result of exploration of two lines: the high current operation (up to 2 MA) with the spontaneous occurrence of helical equilibria with good magnetic flux surfaces and the active control of the current profile. A crucial ingredient for the advancements obtained in the experiments has been the development of state-of-art active feedback control systems allowing the control of MHD instabilities in presence of a thin shell. The balance between achievements and still open issues leads us to the conclusion that the RFP can be a valuable and diverse contributor in the quest for fusion electricity.

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“…In stellarators, the locking can produce a rapid growth of the mode with a consequent drop of confinement and beta [6,7]. Wall locking has also been observed in all reversed-field pinches (RFPs) [8][9][10][11][12], where it produces a toroidally localized increase of the plasma-wall interaction [13] and of the radiated power [14] with a consequent reduction of particle confinement [15] and a possibly significant degradation of the plasma discharge [16] or a disruption. The understanding of the unlocking process can be useful for improving the plasma performances.…”

Section: Introductionmentioning

confidence: 99%

The tearing mode locking–unlocking mechanism to an external resonant field in EXTRAP T2R

Frassinetti

Fridström

Menmuir

et al. 2014

Plasma Phys. Control. Fusion

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The tearing mode (TM) locking and unlocking process due to an external resonant magnetic perturbation (RMP) is experimentally studied in EXTRAP T2R. The RMP produces a reduction of the natural TM velocity and ultimately the TM locking if a threshold in the RMP amplitude is exceeded. During the braking process, the TM slows down via a mechanism composed of deceleration and acceleration phases. During the acceleration phases, the TM can reach velocities higher than the natural velocity. Once the TM locking occurs, the RMP must be reduced to a small amplitude to obtain the TM unlocking, showing that the unlocking threshold is significantly smaller than the locking threshold and that the process is characterized by hysteresis. Experimental results are in qualitative agreement with a model that describes the locking-unlocking process via the balance of the electromagnetic torque produced by the RMP that acts to brake the TM and the viscous torque that tends to re-establish the unperturbed velocity.

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Issues in the plasma wall interactions in RFX

Cited by 7 publications

References 12 publications

Transport and confinement studies in the RFX-mod reversed-field pinch experiment

Transport and confinement studies in the RFX-mod reversed-field pinch experiment

The reversed field pinch

The tearing mode locking–unlocking mechanism to an external resonant field in EXTRAP T2R

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