Publications

2025

• On the use of pulsed DC bias for etching high aspect ratio features
  
  • Shi Xingyi
  • Sadighi Samaneh
  • Rauf Shahid
  • Luo Han
  • Wang Jun-Chieh
  • Kenney Jason
  • Booth Jean-Paul
  • Marinov Daniil
  • Foucher Mickaël
  • Sirse Nishant
  Journal of Vacuum Science & Technology A, American Vacuum Society, 2025, 43 (1). Inductively coupled plasmas (ICPs) containing Cl2 are widely used for plasma etching in the semiconductor industry. One common issue during plasma etching is aspect ratio dependent etching (ARDE), which is generally attributed to variation in the flux of etchant species to the bottom of features with different dimensions. Insufficient fluxes of neutral etchants to the bottom of high aspect ratio features can also result in sputtering, which tends to distort the feature profile. This article addresses two issues relevant to Cl2 ICP and plasma etching in these plasmas. First, a comprehensive set of diagnostics is used to validate a model for Cl2 ICP for gas pressure between 3 and 90 mTorr. The plasma diagnostics include microwave resonant hairpin probe-based measurements of electron density, photolysis-calibrated two-photon laser induced fluorescence measurement of Cl density, photo-detachment-based measurement of Cl− density, and laser diode absorption spectroscopy of argon metastable species to measure the gas temperature. Consistent with the experiments, the model shows that the electron density peaks near the center of the chamber at low gas pressure due to rapid diffusion. The electron density peak moves under the coils at higher pressures. Using the validated Cl2 model, we investigate ICPs with rectangular pulsed DC voltage for bias. It is shown that the Cl flux at the bottom of a trench decreases significantly with increasing aspect ratio of the trench. Neutral to ion flux ratio is therefore low at the bottom of higher aspect ratio trenches. The duty cycle of the pulsed bias waveform is found to be an effective means of increasing the neutral to energetic ion flux ratio, which should help with ARDE and sputter reduction. (10.1116/6.0003943)
  DOI : 10.1116/6.0003943
• Investigation of Filamentary and Diffuse DBD in CO₂ by Means of InSitu FTIR Absorption Spectroscopy
  
  • Bajon Corentin
  • Baratte Edmond
  • Sadi Dihya
  • Guaitella O.
  • Belinger A.
  • Dap Simon
  • Hoder T.
  • Naudé N.
  Journal of Physical Chemistry C, American Chemical Society, 2025, 129 (38), pp.16967-16976. This work investigates CO₂ dielectric barrier discharges (DBDs) at atmospheric pressure in the filamentary and diffuse regimes for the first time using in situ FTIR absorption measurements. The conversion factor of CO₂ is determined and is consistent with the results obtained for DBDs in the literature, following a power law with respect to the specific energy input in both regimes. Vibrational temperatures for CO₂ and CO molecules as well as rotational temperature are also determined within the discharge. A noticeably high vibrational temperature of CO is observed for low specific energy input (SEI). It drops abruptly when increasing the SEI which is attributed to strong vibrationalto-translational energy transfers by O atoms coming from CO₂ dissociation. Except that, the ordering of the different temperatures is similar to the results reported for other CO₂ discharges generated at lower pressures: the vibrational temperature of CO is higher than those of the different vibrational modes of CO₂. The latter are slightly higher than the rotational temperature of the gas for the diffuse mode, whereas they are almost the same for the filamentary mode. The evolution of the measured parameters as a function of the specific energy input is then discussed and a detailed comparison of the two different regimes is carried out. These data together with the knowledge of the reduced electric field in the diffuse regime, which is included in the range 120-140 Td for all conditions, can be of significant importance for further studies exploring the fundamentals of CO₂ plasma chemistry at atmospheric pressure, serving as reference for kinetic models. (10.1021/acs.jpcc.5c02224)
  DOI : 10.1021/acs.jpcc.5c02224
• Risk Assessment of the Ground Magnetic Response to the March and April 2023 Geomagnetic Storms Using Geomagnetically Induced Currents Indices
  
  • Amaechi Paul O
  • Messanga Honore
  • Grodji Frank O
  • Akala Andrew
  • Despirak Irina
  • Ngwira Chigomezyo M
  • Oyeyemi Elijah
  • Amory-Mazaudier Christine
  Space Weather: The International Journal of Research and Applications, American Geophysical Union (AGU), 2025, 23 (4), pp.e2024SW004324. We analyzed the solar origin and ground response during the severe geomagnetic storms (GSs) of 23–24 March (GS1) and 23–24 April 2023 (GS2) using Geomagnetically Induced Currents Indices (GIC indices) computed from geomagnetic field data. The GSs were initiated by erupting filaments and associated slow (fast) halo coronal mass ejections on 20 March (21 April) 2023. GS1 was also influenced by coronal hole high speed streams (CR HSSs) while substorm onsets drove the most intense GIC X (GIC Y ) of 86 (70) in Abisko, Sweden. GS2 was marked by strong negative Bz in a sheath and magnetic cloud with larger GIC indices of 84 (69) driven by magnetic pulsations, as evident at Abisko. This posed a moderate risk to power networks in Sweden. The threat however, reached only a low/moderate risk level in Boulder during the Sudden Impulse (SI)/main phase of GS1. For GS2, a low risk level was attained in Vernadsky and Eyrewell. As expected, at low latitude, GIC indices constituted a very low risk to ground infrastructures during both storms. The results also revealed longitudinal features with larger GIC indices in Boulder (Vernadsky) during the GS1 (GS2), and a North South Asymmetry characterized by a higher risk level in the northern (southern) hemisphere at the American longitude. Additionally, this study provides evidence that the equatorial electrojet can enhance GIC indices at the magnetic equator in the presence of sufficiently strong dH/dt. Finally, we relate GIC indices at high latitudes to the CR HSS on 23 March, and a magnetic cloud during the recovery phase on 24 April 2023. (10.1029/2024SW004324)
  DOI : 10.1029/2024SW004324
• Hybrid simulations of Mercury’s global dynamics and the interplanetary ions’ precipitation fluxes under different interplanetary conditions
  
  • Cazzola E.
  • Fontaine D.
  • Modolo Ronan
  Astronomy & Astrophysics - A&A, EDP Sciences, 2025, 701, pp.A209. Aims. We aim to quantify the impact of different interplanetary conditions met by Mercury along its orbit between its aphelion (~0.47 AU) and perihelion (~0.31 AU) on the Hermean environment, including the rate of solar-wind ion precipitation onto the surface.Methods. We performed a set of 3D global hybrid simulations (kinetic ions and fluid electrons) with interplanetary conditions taken from recent statistics from observations on board the Parker Solar Probe and MESSENGER missions in such a way as to represent an average scenario at both the aphelion and perihelion positions, and in the cases of a slow (250 km/s) and fast (450 km/s) solar wind.Results. The results are in general agreement with empirical models. However, we have found that the subsolar stand-off distances of magnetopause and bow shock, respectively, in the range of 1.0–1.4 RM and 1.3–2.0 RM, are relatively shorter than global statistical averages of, respectively, 1.45 and 1.96 RM. We also observe a local time (LT) asymmetry in the cusp’s location, with the northern cusp located in the post-noon sector centred around 13–14.3 LT and the southern cusp located in the pre-noon sector centred around 9–10.7 LT. Noticeably, the southern cusp region takes the shape of a parallelogram extended from southern middle latitudes in the pre-noon sector to equatorial latitudes in the post-noon sector. We suggest that these effects could result from the orientation of the interplanetary magnetic field along the Parker spiral, which is characterised by an almost radial orientation with a small duskward component. (10.1051/0004-6361/202553953)
  DOI : 10.1051/0004-6361/202553953
• Refining the modeling strategy for anomalous electron transport in fluid simulations of Hall thrusters via insights from PIC simulations
  
  • Petronio Federico
  • Alvarez Laguna Alejandro
  • Guillon Martin Jacques
  • Bourdon Anne
  • Chabert Pascal
  Physics of Plasmas, American Institute of Physics, 2025, 32 (7), pp.073513. Modeling anomalous transport in fluid simulations is a fundamental challenge for developing efficient and robust fluid simulation tools for Hall thrusters. This paper investigates optimal strategies for modeling anomalous transport in such simulations. Using the particle-in-cell (PIC) benchmark (BM) setup of Charoy et al., we demonstrate that various terms in the electron momentum equation can be readily identified. In particular, we show that the assumption of expressing the rate of change of the electron momentum due to instability as proportional to the momentum itself does not hold under these simulation conditions. Subsequently, we present two fluid simulations that replicate the conditions of the PIC BM setup. The first employs the conventional empirical anomalous collision frequency approach. While this model provides generally satisfactory results, it fails to capture specific plasma characteristics. The second fluid model adopts a data-driven approach to represent the anomalous force terms in the momentum equation. This approach furnishes significantly improved results, suggesting that although the anomalous collisionality framework provides meaningful outcomes, it can be effectively replaced by more advanced techniques. (10.1063/5.0274535)
  DOI : 10.1063/5.0274535
• Fast gas heating and peculiarities of temperature measurements by optical emission spectroscopy in nanosecond surface dielectric barrier discharge
  
  • Zhang Bin
  • Kreyder Geoffrey
  • Popov Nikolay
  • Shcherbanev Sergey
  • Starikovskaia Svetlana
  Plasma Sources Science and Technology, IOP Publishing, 2025, 34 (9), pp.095010. The aim of this work is the experimental and theoretical study of nanosecond Surface dielectric barrier discharge (SDBD) parameters in atmospheric pressure air. Measurements of electric current and delivered energy, ICCD images of the discharge at all stages of its evolution, and gas heating in the discharge and near afterglow are performed. The paper presents the results of 2D numerical modeling of the nanosecond SDBD. The results of the calculations are compared with measured data on the dynamics of current, energy input and gas heating. Special attention is paid to the study of the spatial structure of the discharge, in particular, to the distribution of gas temperature and the second positive system emission intensity in the direction perpendicular to the surface of the dielectric. It is shown that the results of temperature measurements in SDBD using optical emission spectroscopy technique are severely influenced by this spatial structure. The parameters of a probe discharge of smaller amplitude, which is formed by a reflected pulse 500 ns after the main discharge, are also calculated. The possibility of using the second diagnostic pulse to measure the gas temperature in the afterglow discharge is discussed. (10.1088/1361-6595/ae00ef)
  DOI : 10.1088/1361-6595/ae00ef
• Survey of the edge radial electric field in L-mode TCV plasmas using Doppler backscattering
  
  • Rienäcker S
  • Hennequin P
  • Vermare L
  • Honoré C
  • Coda S
  • Labit B
  • Vincent Benjamin
  • Wang Y
  • Frassinetti L
  • Panico O
  Plasma Physics and Controlled Fusion, IOP Publishing, 2025, 67 (6), pp.065003. A Doppler backscattering (DBS) diagnostic has recently been installed on the Tokamak à Configuration Variable (TCV) to facilitate the study of edge turbulence and flow shear in a versatile experimental environment. The dual channel V-band DBS system is coupled to TCV’s quasi-optical diagnostic launcher, providing access to the upper low-field side region of the plasma cross-section. Verifications of the DBS measurements are presented. The DBS equilibrium v ⊥ profiles are found to compare favorably with gas puff imaging (GPI) measurements and to the E r inferred from the radial force balance of the carbon impurity. The radial structure of the edge E r × B equilibrium flow and its dependencies are investigated across a representative set of L-mode TCV discharges, by varying density, auxiliary heating and magnetic configuration. (10.1088/1361-6587/add0e0)
  DOI : 10.1088/1361-6587/add0e0
• Phase transition from turbulence to zonal flows in the Hasegawa–Wakatani system
  
  • Guillon P L
  • Gürcan Ö D
  Physics of Plasmas, American Institute of Physics, 2025, 32 (1). The transition between two-dimensional hydrodynamic turbulence and quasi-one-dimensional zonostrophic turbulence is examined in the modified Hasegawa–Wakatani system, which is considered as a minimal model of β-plane-like drift-wave turbulence with an intrinsic instability. Extensive parameter scans were performed across a wide range of values for the adiabaticity parameter C describing the strength of coupling between the two equations. A sharp transition from 2D isotropic turbulence to a quasi-1D system, dominated by zonal flows, is observed using the fraction of the kinetic energy of the zonal modes as the order parameter, at C≈0.1. It is shown that this transition exhibits a hysteresis loop around the transition point, where the adiabaticity parameter plays the role of the control parameter of its nonlinear self-organization. It was also observed that the radial particle flux scales with the adiabaticity parameter following two different power law dependencies in the two regimes. A simple quasi-linear saturation rule which accounts for the presence of zonal flows is proposed, and is shown to agree very well with the observed nonlinear fluxes. Motivated by the phenomenon of quasi-one dimensionalisation of the system at high C, a number of reduction schemes based on a limited number of modes were investigated and the results were compared to direct numerical simulations. In particular, it was observed that a minimal reduced model consisting of 2 poloidal and 2 radial modes was able to replicate the phase transition behavior, while any further reduction failed to capture it. (10.1063/5.0242282)
  DOI : 10.1063/5.0242282
• Milestone in predicting core plasma turbulence: successful multi-channel validation of the gyrokinetic code GENE
  
  • Höfler Klara
  • Görler Tobias
  • Happel Tim
  • Lechte Carsten
  • Molina Pedro
  • Bergmann Michael
  • Bielajew Rachel
  • Conway Garrard
  • David Pierre
  • Denk Severin
  • Fischer Rainer
  • Hennequin Pascale
  • Jenko Frank
  • Mcdermott Rachael
  • White Anne
  • Stroth Ulrich
  Nature Communications, Nature Publishing Group, 2025, 16 (1), pp.2558. On the basis of several recent breakthroughs in fusion research, many activities have been launched around the world to develop fusion power plants on the fastest possible time scale. In this context, high-fidelity simulations of the plasma behavior on large supercomputers provide one of the main pathways to accelerating progress by guiding crucial design decisions. When it comes to determining the energy confinement time of a magnetic confinement fusion device, which is a key quantity of interest, gyrokinetic turbulence simulations are considered the approach of choice – but the question, whether they are really able to reliably predict the plasma behavior is still open. The present study addresses this important issue by means of careful comparisons between state-of-the-art gyrokinetic turbulence simulations with the GENE code and experimental observations in the ASDEX Upgrade tokamak for an unprecedented number of simultaneous plasma observables. (10.1038/s41467-025-56997-2)
  DOI : 10.1038/s41467-025-56997-2