Data from: Experimental Characterization of Low-Frequency Oscillations in Electrodeless Plasma Thruster via Wall-Embedded Diagnostics (wall probe data)

Data from: Experimental Characterization of Low-Frequency Oscillations in Electrodeless Plasma Thruster via Wall-Embedded Diagnostics (wall probe data) Authors: Elpidio Lettera, Marco Riccardo Inchingolo, Jaume Navarro-Cavallé, Mario Merino Contact email: [e-mail] Date: 2026-07-01 Keywords: Electric Propulsion, Plasma Physics, Plasma Plumes, Oscillations, Electron Cyclotron Resonance Thruster Version: 1.0.0 Digital Object Identifier (DOI): 10.5281/zenodo.21107845 License: This dataset is made available under the Open Data Commons Attribution License Abstract This dataset contains the experimental data employed in the MSc Thesis: “Experimental Characterization of Low-Frequency Oscillations and Power Losses in Electrodeless Plasma Thruster via Wall-Embedded Diagnostics” The data in this repository are obtained from measurements performed on a waveguide ECR thruster prototype as described in the reference. For further information on the experimental setup please refer to the MSc Thesis (Chapter 5). Dataset description The experimental data were collected using an array of nine wall-embedded planar floating Langmuir probes installed at different azimuthal and axial positions. Further details on the probe layout and acquisition configurations are provided in the MSc Thesis (Subsection 3.1.2). The signals were acquired with an AC-coupled Yokogawa DLM5058 Mixed Signal Oscilloscope, resolving frequencies up to $5\,\ \mathrm{MHz}$. Since the diagnostic array includes nine probes and the oscilloscope provides eight input channels, the measurements were performed using two acquisition configurations. Each signal was transmitted through a $50\,\ \mathrm{\Omega}$ acquisition line including a DC-block ($f_{\mathrm{cut\text{-}off}} = 45\,\mathrm{Hz}$) and a low-pass filter ($f_{\mathrm{cut\text{-}off}} = 100\,\mathrm{MHz}$). The dataset provides the raw time-resolved signals acquired by the planar floating Langmuir probes. The post-processed Power Spectral Densities (PSD) were computed independently for each acquisition using Welch’s method. The time traces were divided into Hann-windowed segments with 50% overlap and the corresponding periodograms were averaged to obtain the PSD estimate (expressed in V^2/Hz). Azimuthal modal content was extracted via a non-uniform discrete Fourier transform (NUDFT) to accommodate the irregular angular spacing of the available probes. The traces were normalized to the maximum value across the full probe set, limiting amplitude artifacts arising from channel-to-channel gain differences among the probes. As a result, the modal power spectral density is expressed in arbitrary units (a.u.). Finally, microwave leakage power was monitored externally to the vacuum chamber using a MW leakage detector at the waveguide ECRT operating frequency of $5.8\,\ \mathrm{GHz}$. Data Files The data files are in standard Matlab .mat format. A recent version of Matlab is recommended. The dataset is organized into three main file groups: time-resolved waveforms, probe power spectral densities, and azimuthal modal analysis results. The file nomenclature follows the general structure: "WaveData_[configuration]_[mass flow rate]SCCM_[input power]W.mat", "PowerSpectralDensityData_[configuration]_[mass flow rate]SCCM_[input power]W.mat" and "ModalData_[configuration]_[mass flow rate]SCCM_[input power]W.mat". Here, [configuration] denotes the acquisition configuration (A or B), [mass flow rate] is the injected xenon mass flow rate and [input power] is the nominal input power. The acquisition configuration specifies the subset of probes recorded in each measurement. Further details on the probe layout and configuration are provided in the corresponding MSc Thesis. For the time-resolved data, each file contains the variable "WaveData", which stores the raw waveform data acquired by the planar floating Langmuir probes. Each "WaveData" variable is structured as a 3-dimensional matrix, where: The first dimension represents the time evolution of the waveform (size 50'000'000) The second dimension represents a different waveform at the same operating point (size 2) The third dimension represents each a different probe (size 8) The probes are ordered according to the probe numbering reported in the dataset documentation. Configuration A excludes probe LP2, while configuration B excludes probe LP8. For the spectral data, each file provides the variables "PowerSpectralDensityData" and its corresponding frequency vector f (in Hz). The variable PowerSpectralDensityData is structured as a 3-dimensional matrix, where: The first dimension represents frequency (size 12'500) The second dimension represents a different waveform at the same operating point (size 2) The third dimension represents each a different probe (size 8) For the azimuthal modal data, each file includes the variables "ModalData", the corresponding frequency vector f and azimuthal mode numbers vector m_theta [-2, -1, 0, +1, +2, +3]. The variable "ModalData" is structured as a 3-dimensional matrix, where: The first dimension represents frequency (size 12'500) The second dimension represents a different waveform at the same operating point (size 2) The third dimension represents the azimuthal mode number (size 6) A dedicated subset of files is additionally provided for the case corresponding to "_B_2 SCCM_80W", identified by the suffix "_tf" (e.g., "WaveData_..._tf", "PowerSpectralDensityData_..._tf", "ModalData_..._tf"). These files correspond to time-resolved acquisitions in which four waveforms were recorded at the same operating point at successive time instants, separated by 10-minute intervals. Accordingly, the second dimension of the corresponding variable has size 4, consistent with the four temporally resolved acquisitions. The file "MWLeakageData.mat" provides the microwave leakage measurements acquired at different operating conditions. The file includes the variable "MWLeakageData", structured as a 12x4 matrix, where each row corresponds to one experimental operating point. The columns are organized as follows: mp: Injected xenon mass flow rate [SCCM] Pset: Input power [W] PT: Thruster power [W] Pleak: Microwave leakage power [dBm] For each nominal operating condition, repeated measurements are listed as separate rows in the file rather than being averaged. Acknowledgments This work and the corresponding dataset were supported by the European Research Council (ERC), under the European Union’s Horizon 2020 research and innovation programme (Starting Grant ZARATHUSTRA, grant agreement No. 950466). Additional funding was provided by project PID2023-150052OB-I00, funded by MICIU/AEI/10.13039/501100011033 and by ERDF, EU.