5:15 PM - 7:15 PM
[PCG20-P14] Effect of Mesh Grid-Plane Potential on Ion Trajectories in a Retarding Potential Analyzer
Keywords:Ionospheric ions, Retarding potential analyzer, Grid transparency, Grid-plane electric field
In this study, we are developing an ion drift velocity analyzer for sounding rockets to elucidate the coupling processes between the neutral atmosphere and the ionized atmosphere in the lower ionosphere. This instrument consists of a Retarding Potential Analyzer (RPA) and a collector electrode. Ions entering the instrument are energy-filtered by the retarding voltage applied to the mesh inside the RPA before reaching the collector electrode, where they are detected as an ion current. Performance evaluation tests of the flight model have confirmed that the acquired current data can be used to estimate ion energy, drift velocity, temperature, and density.
In this simulation, we used software to calculate the trajectories of charged particles in a region with an electromagnetic field. We analyzed the following: the percentage of ions that reach the collector electrode (ion transmission rate), the percentage of ions that collide with the mesh, and the percentage of ions whose trajectories are altered by the electric field.
A simulation space was created to model the interior of the RPA, with dimensions of 40 mm in the x-axis, 7.68 mm in the y-axis, and 7.68 mm in the z-axis. Six mesh grids (G1-G6), each with an open area ratio of 96.5%, were placed at 6 mm intervals based on the actual RPA design. A voltage ranging from 0 to 4 V was applied to G2 and G3 for ion energy analysis. The ions used in the simulation were O+ ions, considering the ionospheric environment. They were uniformly distributed in the yz-plane at x = 0 and emitted in the +x direction, with a total of 500,000 ions. The bulk velocity was set to 600 m/s, considering the rocket's ascent speed. The ion energy distribution was given as a Gaussian distribution in the range of 0–0.4 eV, approximating an ionospheric ion temperature of 600 K. Among the emitted ions, those with energies in the 0–0.01 eV range were the most abundant, accounting for 30% of the total.
1. Ratio of Ions Reaching the Collector Electrode Relative to the Mesh Open Area Ratio
When the RPA voltage was 0 V, the ion transmission rate was approximately 92.4%. In the simulation, since the six mesh grids were perfectly aligned without any misalignment, the transmission rate was higher than the expected 80.8%, which corresponds to the combined open area ratio of the six meshes. As the RPA voltage increased from 0.001 V to 0.01 V, the ion transmission rate gradually decreased from approximately 87.9% to 77.7% due to an increase in ion collisions with the mesh (discussed later) and changes in ion trajectories caused by the electric field.
2. Ratio of Ions Affected by the Electric Field
As the RPA voltage increased from 0.001 V to 0.01 V, the percentage of ions affected by the electric field gradually increased from approximately 7.20% to 21.9%. A potential gradient was formed between G1 (GND) and G2, to which the RPA voltage was applied. Ions with energy lower than the potential at any point between G1 and G2 had their trajectories deflected before reaching G2. Furthermore, among the ions influenced by the electric field, some were found to collide with the inner walls due to trajectory changes. The proportion of such ions is currently under further analysis.
3. Ratio of Ions Colliding with the Mesh
When the RPA voltage was 0 V, the percentage of ions colliding with the mesh was approximately 7.56%. As the RPA voltage increased from 0.001 V to 0.01 V, this percentage gradually increased from approximately 11.3% to 17.4%. This increase is attributed to the influence of the electric field within the mesh plane, which caused ions that would normally reach the collector electrode to have their trajectories altered, leading to collisions with the mesh.
In this presentation, we will discuss the effects of the electric field generated by the RPA voltage applied to the mesh on ion transmission rate, the ratio of ions colliding with the mesh, and ion trajectories, along with the aforementioned results.
In this simulation, we used software to calculate the trajectories of charged particles in a region with an electromagnetic field. We analyzed the following: the percentage of ions that reach the collector electrode (ion transmission rate), the percentage of ions that collide with the mesh, and the percentage of ions whose trajectories are altered by the electric field.
A simulation space was created to model the interior of the RPA, with dimensions of 40 mm in the x-axis, 7.68 mm in the y-axis, and 7.68 mm in the z-axis. Six mesh grids (G1-G6), each with an open area ratio of 96.5%, were placed at 6 mm intervals based on the actual RPA design. A voltage ranging from 0 to 4 V was applied to G2 and G3 for ion energy analysis. The ions used in the simulation were O+ ions, considering the ionospheric environment. They were uniformly distributed in the yz-plane at x = 0 and emitted in the +x direction, with a total of 500,000 ions. The bulk velocity was set to 600 m/s, considering the rocket's ascent speed. The ion energy distribution was given as a Gaussian distribution in the range of 0–0.4 eV, approximating an ionospheric ion temperature of 600 K. Among the emitted ions, those with energies in the 0–0.01 eV range were the most abundant, accounting for 30% of the total.
1. Ratio of Ions Reaching the Collector Electrode Relative to the Mesh Open Area Ratio
When the RPA voltage was 0 V, the ion transmission rate was approximately 92.4%. In the simulation, since the six mesh grids were perfectly aligned without any misalignment, the transmission rate was higher than the expected 80.8%, which corresponds to the combined open area ratio of the six meshes. As the RPA voltage increased from 0.001 V to 0.01 V, the ion transmission rate gradually decreased from approximately 87.9% to 77.7% due to an increase in ion collisions with the mesh (discussed later) and changes in ion trajectories caused by the electric field.
2. Ratio of Ions Affected by the Electric Field
As the RPA voltage increased from 0.001 V to 0.01 V, the percentage of ions affected by the electric field gradually increased from approximately 7.20% to 21.9%. A potential gradient was formed between G1 (GND) and G2, to which the RPA voltage was applied. Ions with energy lower than the potential at any point between G1 and G2 had their trajectories deflected before reaching G2. Furthermore, among the ions influenced by the electric field, some were found to collide with the inner walls due to trajectory changes. The proportion of such ions is currently under further analysis.
3. Ratio of Ions Colliding with the Mesh
When the RPA voltage was 0 V, the percentage of ions colliding with the mesh was approximately 7.56%. As the RPA voltage increased from 0.001 V to 0.01 V, this percentage gradually increased from approximately 11.3% to 17.4%. This increase is attributed to the influence of the electric field within the mesh plane, which caused ions that would normally reach the collector electrode to have their trajectories altered, leading to collisions with the mesh.
In this presentation, we will discuss the effects of the electric field generated by the RPA voltage applied to the mesh on ion transmission rate, the ratio of ions colliding with the mesh, and ion trajectories, along with the aforementioned results.