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Online and FREE access to plasma physics experiments

Nukleonika
Volume 68 (2023): Issue 1 (March 2023)
By: Pedro A. Mendes Rossa,  Pavel Kuriščák,  João N. Silva,  José Veiga,  João P. S. Loureiro,  João Oliveira,  Daniel Hachmeister and  Horácio Fernandes  
Open Access
|Apr 2023

Figures & Tables

Fig. 1.

Depicted FREE architecture where the central server acts as a broker between several users and the experiments with dedicated hardware, usually comprising a Linux proxy running in a Raspberry Pi and connected to the embedded system, custom made board with a PIC (peripheral interface controller), running a native C code.

Fig. 2.

Screen capture from the main list of selected protocols, showing the available experimental protocols that can be executed in a particular apparatus.

Fig. 3.

The UI of the experiment EM cavity: (a) the configuration parameter to set your experiment, (b) the live stream of the experiment, and (c) framed by a brief description of the experiment.

Fig. 4.

Main components inside the chamber where the Langmuir probe is immersed and where the plasma is generated by a high AC voltage applied between the glow discharge molybdenum electrodes.

Fig. 5.

Common rail vacuum system serves both experiments. On the left is the Langmuir probe and on the right is the EM cavity each with its own injection system but sharing the same gas rail. Only the EM cavity is equipped with magnetic field coils.

Fig. 6.

The gas injection system was homemade with 200 μm clinical needles glued (epoxy) in the gas rail couplings.

Fig. 7.

Raw data from Langmuir probe displaying the initial electrical transient of the plasma. During the time period of the experiment, the pressure reading shows zero to identify the acquisition window.

Fig. 8.

Raw data from several sweeps displays a clear hysteresis when using a symmetrical triangular wave.

Fig. 9.

Fitting of the ion saturation region, using Eq. (2), for correction of the data set.

Fig. 10.

By doing a semi-log graph, it is evident the exact location of the exponential part of the characteristic, and despite the lack of symmetry, the slopes are very similar in both situations.

Fig. 11.

Relative intensities of the electric field (a) and magnetic field (b) from an EM wave propagating in the TM010 mode. The electric field has a maximum in the middle of the cavity where the antenna must be inserted, jeopardizing the plasma. Conversely, in (b) the maximum is close to the walls where a magnetic antenna can be positioned to avoid disturbing the plasma and leading to the adopted solution.

Fig. 12.

Hardware parts from the EM cavity: (a) spectrum analyzer used, (b) the main cavity block, (c) assembly with the plexiglass windows on the top, and (d) ionizing HV electrode mesh with partial view of the loop antennas.

Fig. 13.

Broad spectrum scan to identify the first resonant modes excited by the loop antenna.

Fig. 14.

The existence of plasma (Ar at 28 Pa) originates a drift on the resonant peak and a drop in the transmitted signal due to plasma losses and a consequent reduction in the quality factor.

Fig. 15.

Electron density in the function of the mean free path of the particles inside the chamber, as shown by data points in Table 3.

Results of multiple executions with diffrent neutral gas (Ar) pressures and the resultants frequency shift measured

Pressure injection (Pa)f (MHz)Δf (MHz)ne (×1014 m−3)
    83563.6––
  103573.610.0  8.8
  123580.817.215.2
  133584.821.218.7
  163586.422.820.2
  183584.420.818.3
  203582.518.916.7
  213580.016.414.4
  253578.414.813.1
  283574.510.9  9.6
  343572.8  9.2  8.1
  443570.0  6.4  5.7
  483568.8  5.2  4.6
  603567.2  3.6  3.2
  983566.8  3.2  2.8
1203566.8  3.2  2.8

Results of multiple executions with different neutral gas pressure (Ar) and results for the ion saturation current, and the respective calculation of the speed of sound and the density

Pressure (Pa)(μgA)isat+$\mathop {\left( {{\rm{\mu gA}}} \right)}\limits^{i_{{\rm{sat}}}^ + } $Te (eV)Cs (m/s)n (×1015 m−3)
  64−15.24.834058.9
100−14.26.339017.2
150−12.75.737116.8

Parameters obtained after the fitting shown in Fig_ 9, the ion saturation current

Slopeα(1/V)Vf (V)isat+ (μA)$i_{sat}^ + {\rm{ }}\left( {{\rm{\mu A}}} \right)$
10.9612.38−17.2
−10.4935.33−17.6
DOI: https://doi.org/10.2478/nuka-2023-0006 | Journal eISSN: 1508-5791 | Journal ISSN: 0029-5922
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Language: English
Page range: 37 - 46
Submitted on: Aug 31, 2022
|
Accepted on: Nov 16, 2022
|
Published on: Apr 3, 2023
Published by: Institute of Nuclear Chemistry and Technology
In partnership with: Paradigm Publishing Services
Publication frequency: 4 issues per year
Keywords:
Educational technology,
E-lab,
Electromagnetic cavity,
Langmuir probe,
Remote controlled experiments
Related subjects:
Chemistry,
Nuclear chemistry,
Physics,
Astronomy and astrophysics,
Physics, other

© 2023 Pedro A. Mendes Rossa, Pavel Kuriščák, João N. Silva, José Veiga, João P. S. Loureiro, João Oliveira, Daniel Hachmeister, Horácio Fernandes, published by Institute of Nuclear Chemistry and Technology
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.

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