Non-axisymmetric perturbation of the plasma surface in RFX: analysis of magnetic data versus CCD images of plasma–wall interaction

Zanca, P.; Bettella, D.; Martini, S.; Valisa, M.

doi:10.1016/s0022-3115(00)00474-8

Cited by 7 publications

(6 citation statements)

References 6 publications

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“…5͒, of the plasma surface in the radial direction. 11 As demonstrated in Ref. 19, the maximum of ⌬ r () corresponds to the peak amplitude of the mϭ1 perturbation ͑i.e., to the angle ϭ 1 ͒.…”

Section: B Analysismentioning

confidence: 86%

“…[6][7][8][9][10] The slinky pattern gives rise to a toroidally localized distortion of the plasma torus which causes its outermost flux-surfaces to intersect the wall; thereby, generating a localized wall ''hot spot.'' 11 If the slinky pattern locks to the wall ͑as is always the case in RFX͒ then this hot spot can easily cause wall overheating, leading to the influx of impurities into the plasma, and the eventual termination of the discharge. Indeed, the maximum achievable plasma current in RFX is strongly limited by this effect.…”

Section: Introductionmentioning

confidence: 99%

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Phase-locking of tearing modes in the reversed field experiment

Fitzpatrick

Zanca²

2002

Physics of Plasmas

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In the reversed field experiment (RFX) [F. Gnesotto et al., Fusion Eng. Des. 25, 335 (1995)], the m=1 and m=0 tearing modes present in the plasma are observed to phase-lock together to form a highly peaked, strongly toroidally localized, pattern in the perturbed magnetic field. This pattern, which is commonly known as the “slinky” pattern, gives rise to severe edge loading problems which limit the maximum achievable toroidal current. A theory is presented which explains virtually all salient features of the RFX slinky pattern. The central premise of this theory is that at high ambient mode amplitude the various tearing modes occurring in the plasma phase-lock together in a configuration which minimizes the magnitudes of the electromagnetic torques exerted at the various mode rational surfaces. The theory successfully predicts the profiles of the edge radial and toroidal magnetic fields generated by the m=0 and m=1 modes, the phase relations between the various modes, the presence of a small toroidal offset between the peaks of the m=0 and m=1 contributions to the overall slinky pattern, and the response of the pattern to externally generated m=0 and m=1 magnetic perturbations.

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Section: B Analysismentioning

confidence: 86%

Section: Introductionmentioning

confidence: 99%

Phase-locking of tearing modes in the reversed field experiment

Fitzpatrick

Zanca²

2002

Physics of Plasmas

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“…Figure 4 shows the time evolution of the H α line at the position where modes are locked during a PPCD experiment. Since this local contribution to the total influx has been evaluated to be about 50% (both for hydrogen and impurities) [5], a strong reduction in the locking region leads to a decrease of the total H and impurity source by up to a factor of 2.…”

Section: Summary Of Experimental Observationsmentioning

confidence: 99%

“…In some cases, a spontaneous transition to an MHD spectrum dominated by a single, low n, m = 1 mode has been observed (a regime dubbed QSH for quasi-single helicity [3]). At the edge, electrostatic fluctuations are an important loss channel [4], but more than 50% of the power losses have been associated with localized plasma-wall interaction due to the non-axisymmetric magnetic perturbations caused by locked dynamo modes [5,6].…”

Section: Introductionmentioning

confidence: 99%

Analysis and modelling of the magnetic and plasma profiles during PPCD experiments in RFX

et al. 2003

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In this paper, we analyse the main features of the pulsed poloidal current drive (PPCD) technique, used in the reversed field pinch configuration to achieve improved confinement conditions. In the RFX experiment, PPCD corresponds to a decrease of the magnetic fluctuations, to a peaking of the temperature profile, and to a reduced transport and plasmawall interaction. A three-dimensional MHD nonlinear code and one-dimensional time-dependent transport models have been applied to study the effect of PPCD on the magnetic and plasma profiles. The three-dimensional MHD simulations show that the external inductive drive pinches and peaks the current profile driving the configuration through a transient phase, where the spontaneous turbulent dynamo action is quenched. The one-dimensional transport codes indicate that the experimental profile modifications associated with PPCD are consistent with a reduction of the stochastic transport.

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“…The power load on the portion of the wall wetted by the helix is of the order of 5 MW m −2 . However, when a back-transition from the QSH to the chaotic state occurs and modes are locked to the wall, the extension of the interaction region shrinks further [13], and the power load can locally increase up to tens of MW m −2 . Therefore, it is mandatory to protect the vacuum vessel against such strong local interactions.…”

Section: Introductionmentioning

confidence: 99%

Wall conditioning and density control in the reversed field pinch RFX-mod

et al. 2013

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In the reversed field pinch RFX-mod at the highest plasma current of 2 MA, when error fields are not effectively feedback controlled, localized thermal loads up to tens of MW m−2 can be produced. The graphite tiles withstand such high power loads, but the high hydrogen retention makes density control extremely difficult. Several wall conditioning techniques have been optimized in the last campaigns, including helium glow discharge cleaning and wall boronization by diborane glow discharges. More recently, lithium conditioning has been applied for the first time in a reversed field pinch by the evaporation technique. The main results are discussed in this paper. Lithization leads to important operational advantages: a significant improvement of the density control is obtained. Densities up to n/nG ≈ 0.5 can be produced in a controlled way. At the same value of input power, plasmas at higher densities can be sustained. However, due to the short particle confinement time, such densities are reached with high rates of gas puffing and the resulting profiles at high density are edge peaked. A lithium multipellet injector, to be applied in order to obtain a more uniform deposition, has been tested.

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Non-axisymmetric perturbation of the plasma surface in RFX: analysis of magnetic data versus CCD images of plasma–wall interaction

Cited by 7 publications

References 6 publications

Phase-locking of tearing modes in the reversed field experiment

Phase-locking of tearing modes in the reversed field experiment

Analysis and modelling of the magnetic and plasma profiles during PPCD experiments in RFX

Wall conditioning and density control in the reversed field pinch RFX-mod

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