Deuterium plasma sputtering of mixed Be-W layers

Soni, Kunal; Moser, L.; Poroşnicu, C.; Antunes, Rodrigo; Arredondo, R.; Dincă, P.; Steiner, Roland; Marot, L.; Meyer, Ernst

doi:10.1016/j.jnucmat.2022.153671

Cited by 3 publications

(2 citation statements)

References 42 publications

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“…This results in ion acceleration towards the FM with an energy of e(V p − V DC ), where V p is the plasma potential, and leads to sputtering of surface deposits given the ion energy is greater than the sputtering energy threshold of the deposits. Plasma cleaning of FM deposits via CCRF discharges has been a subject of intense investigation in recent years [7][8][9][10].…”

Section: Introductionmentioning

confidence: 99%

Effect of 3 T magnetic field on RF plasma sputtering in an ITER-relevant first mirror unit

Soni

Iyyakkunnel²,

Steiner³

et al. 2022

Nucl. Fusion

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The first mirror (FM) cleaning operations in ITER are expected to be executed in presence of ∼ 3T magnetic field. In the RF plasma cleaning configuration, this would have a significant influence on the plasma properties, ion energy, angle of incidence as well as flux spatial distribution. To this end, RF discharges were excited in an ITER-sized mock-up of a first mirror unit (FMU) consisting of a powered first mirror M1 and a grounded second mirror M2 placed in a homogeneous 3T magnetic field. The plasma discharge was confined in a beam extending in the direction of the magnetic field, consequently wetting a limited portion of the FMU walls. In the DC-decoupled scheme (without λ/4 filter), this considerably influenced the self-bias voltage VDC that develops on M1. Changing the angle α between M1 normal and magnetic field, modified the plasma wetted wall area Ag and the resulting VDC varied by over two orders of magnitude. Plasma exposure experiments were also done in the DC-coupled scheme (with λ/4 filter), wherein the angle and wetted surface determined the area of the wall sputtered. Increasing α led to an increase in the sputtered wall area Ag, and consequently the wall deposition on grounded M2. However, in all the cases M1 was entirely clean with exception of edge deposits in some. In contrast, both M1 and M2 are coated with wall deposits in absence of a magnetic field and similar plasma exposure. The results show that plasma cleaning with a λ/4 filter in a 3T magnetic field at ITER could potentially prevent the parasitic wall deposition on FMs. The results also highlight the importance of FM orientation in the magnetic fields and the wetted area in their plasma cleaning in both DC-coupled as well as decoupled schemes within the ITER diagnostic systems.

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Section: Introductionmentioning

confidence: 99%

Effect of 3 T magnetic field on RF plasma sputtering in an ITER-relevant first mirror unit

Soni

Iyyakkunnel²,

Steiner³

et al. 2022

Nucl. Fusion

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“…They would thus require regular surface conditioning, which is foreseen to be achieved via an in-situ CCRF discharge cleaning system [17]. This system employs FMs as the powered electrodes to generate CCRF discharges, wherein they develop a negative self-bias and undergo ion sputtering [18][19][20][21]. However, Figure 1.…”

Section: Introductionmentioning

confidence: 99%

Ion flux–energy distributions across grounded grids in an RF plasma source with DC-grounded electrodes

Soni

Antunes

Steiner

et al. 2022

Plasma Sources Sci. Technol.

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We present an experimental investigation of the ion flux-energy distribution functions (IFEDF) obtained across grounded grids in an asymmetric capacitively coupled RF source using helium discharge. The powered electrode in the RF source is DC-grounded via a λ/4 filter, which lifts its DC potential to zero. Grids of different dimensions (hole width, thickness and geometric transparency) were used to confine the plasma, while the IFEDF of the ion beam departing the grid and reaching the reactor walls was studied using a retarding field energy analyzer. The IFEDF obtained was double-peaked, indicating the presence of fast ions arriving from the plasma source, and cold ions generated upon charge exchange collisions between the fast ions and neutrals. The flux, as well as the peak energies of the two ion groups, depended significantly on the process parameters: RF power, He pressure, the distance between grids and walls, as well as the dimensions of the grids. The results indicate that confining plasma with grids can reduce the ion flux at the walls by over 60%, significantly lowering the wall sputtering rate. This was confirmed with a dedicated long exposure plasma discharge with a gridded plasma reactor, wherein less than 1nm of Cu deposition was found on the DC-grounded powered electrode, and the surface reflectivity was preserved to pristine values. In contrast, a similar experiment in a gridless reactor resulted in Cu deposition of 35nm with a drastic drop in surface reflectivity. These studies are of great importance for the application of similar RF plasma sources with in-situ cleaning of diagnostic mirrors in fusion devices, as well as in a variety of plasma processing applications.

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Surface modification of ITER-like mirrors after one hundred cleaning cycles using radio-frequency plasma

Sanchez

Marot

Steiner

et al. 2023

Journal of Nuclear Materials

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Deuterium plasma sputtering of mixed Be-W layers

Cited by 3 publications

References 42 publications

Effect of 3 T magnetic field on RF plasma sputtering in an ITER-relevant first mirror unit

Effect of 3 T magnetic field on RF plasma sputtering in an ITER-relevant first mirror unit

Ion flux–energy distributions across grounded grids in an RF plasma source with DC-grounded electrodes

Surface modification of ITER-like mirrors after one hundred cleaning cycles using radio-frequency plasma

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