We present an extensive study into the influences that the magnitudes of the applied electric (E) and magnetic (B) fields have on collisionless plasma discharges of xenon, krypton, and argon. The studies are performed in a 2D radial-azimuthal configuration with perpendicular fields’ orientation. The dependency of the dynamics of E×B discharges on the strength of electromagnetic field and ion mass has not yet been studied in a manner that distinguishes the role of individual factors. This has been, in part, due to significant computational cost of conventional high-fidelity particle-in-cell (PIC) codes that do not allow for practical extensive simulations over broad parameter spaces. Also, the experimental efforts have been limited by aspects such as the measurements’ spatiotemporal resolution and the inability to independently control individual discharge parameters. The computationally efficient reduced-order PIC scheme allows to numerically cast light on the parametric variations of various aspects of the physics of E×B discharges, such as high-resolution spatial-temporal mappings of plasma instabilities. In this part I, we focus on the effects of the E-field intensity. We demonstrate that, across all the studied propellants, the E-field’s intensity determines two distinct plasma regimes characterized by different dominant instability modes. At relatively low E-field magnitudes, the Modified Two Stream Instability (MTSI) is dominant. At relatively high E-field magnitudes, the MTSI is mitigated, and the Electron Cyclotron Drift Instability (ECDI) becomes dominant. Consequent to the change in the plasma regime, the radial distribution of the axial electron current density and the electron temperature anisotropy vary.