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A gaseous plasma antenna array (PAA) is an aggregate of plasma discharges and possibly conventional metallic radiating elements, and it constitutes a promising alternative to metallic antennas for applications in which fast reconfiguration of radiation pattern, and gain is desired; such properties can be achieved by exploiting the electronic switch on/off condition of plasma discharges, and tuning of the plasma parameters. Here, the authors present a reconfigurable PAA that features a central metallic half-wavelength dipole working around 1.45 GHz, surrounded by a planar circular lattice of cylindrical plasma discharges. Customised plasma discharges have been realised, and filled with argon gas at 2 mbar so as to have a complete control on the plasma discharge properties (e.g. plasma frequency, collisional frequency). The magnitude of the reflection coefficient, and the gain pattern on the H -plane have been investigated numerically and experimentally; numerical and experimental results exhibit a good agreement and show that the central intrinsically omnidirectional antenna can provide simple beamforming capabilities upon turning on a subset of plasma discharges; as these plasma discharges are turned on, the authors have observed a maximum gain of ~5 dBi, a half-power beam width of 80°, and an angular steering resolution of ~15°.

We present 3D-VIRTUS (3-Dimensional adVanced fluId dRifT diffUsion plaSma solver), a numerical tool conceived for the evaluation of the equilibrium conditions of Helicon plasma sources, that consists of the Electro-Magnetic Module, and the FLUID Module. The first evaluates the power deposited into the plasma by the antenna that drives the discharge, and it is based on a solid numerical tool (i.e., ADAMANT). The power deposition is used by the second module to solve for the macroscopic transport of charged and neutral species by means of a fluid approach, and assuming valid the Drift-Diffusion approximation. The set of continuity, momentum, energy, and Poisson equations are solved numerically through the Finite Volume Method , and are implemented in OpenFOAM. The two modules are iterated until a converged solution is obtained. This approach allows the self-consistent evaluation of the local plasma parameters (e.g., plasma density) at equilibrium in Helicon sources that feature (i) arbitrary-shaped plasma regions, and antennas, (ii) realistic magneto-static fields generated by electromagnets or permanent magnets . The numerical accuracy of the FLUID Module has been assessed as a function of the time, and space discretization . The FLUID Module, and the 3D-VIRTUS code have been independently validated against other well-established numerical approaches and experimental measurements. Finally, 3D-VIRTUS has been exploited to investigate Helicon plasma discharges for space propulsion applications for magneto-static field values from 0 G up to 750 G.

Gaseous plasma antennas constitute a promising alternative to conventional metallic antennas for applications in which reconfigurability is desired. By tuning the plasma discharge parameters, e.g., plasma density, antenna properties can be changed dynamically. In this work we report on recent numerical investigations into the characteristics of a plasma antenna as a function of the plasma discharge parameters, viz., plasma density, and magnetostatic field. In addition, the effect of different gasses has been examined. We have used ADAMANT (Advanced coDe for Anisotropic Media and ANTennas) — a full-wave numerical tool based on integral equations — to assess the role played by plasma discharge parameters in shaping the radiation pattern, which is mainly determined by the plasma current distribution. The experimental characterization of the plasma discharge to be used as plasma antenna is briefly presented.

Gaseous plasma antenna arrays (PAA) constitute a promising alternative to conventional metallic antennas for applications in which fast reconfigurability with respect to some property (e.g., the gain, the frequency band) is desired. In STARLET (plaSma anTennA foR satelLitE navigaTion) project, reconfigurable capabilities of plasma antennas will be exploited in the design and development of a PAA for the reception of GPS and Galileo satellite signals. Here we give an account of the prelimary numerical results gathered so far.

In the framework of the ”Helicon Plasma Thruster for Space Missions AO7048” research program, a zero-dimensional numerical model is developed in order to assess the propulsive performances of the plasma thruster when fed with different molecular gases as propellants. The zero-dimensional model developed consists of detailed kinetic schemes for bulk plasma reactions and surface processes; particle in cell simulations are performed to properly describe the behaviour of the charged particles at the exhaust plume so to obtain exhaust parameters for the global model. Given a set of input parameters, such as geometry and mass flow rate, the model is able to follow the time evolution of plasma main physical quantities, such as neutral and charge densities and the electron temperature, and to calculate thruster performances. The model is then linked to the genetic algorithm optimization toolbox in Matlab environment in order to obtain high performance configurations. Propellants considered are H2, O2, N2 and N2O.

In this work we illustrate the design of a thrust balance, to be employed for the experimental characterization of low power helicon plasma thrusters developed at the Center for Aerospace Studies and Activities (CISAS) “G. Colombo” of the University of Padua. The nominal thrust level of the propulsive systems to be tested is estimated between 1 and 20 mN. The measurement of millinewton-range thrusts in presence of RF emissions magnetic fields from the thruster poses several engineering challenges as: (i) an highly sensible system is required, capable of detecting the low thrust levels produced by the thrusters with sufficient accuracy and stability; (ii) the necessity of feeding RF power to the thruster mounted on the balance imposes to deal with RF disturbances on the measurement systems and RF heating of the power line and of the mechanical structure of the balance; (iii) the magnetic field can interact with elements of the balance, hampering the measurement. We considered all these aspects with careful theoretical analyses, supported by experimental validation of the envisioned solutions. The work was thus structured as follow: (i) definition of the physical principles related to the measurement of millinewton-range thrusts in an RF environment; (ii) definition and preliminary characterization of the mechanical configuration of the system; (iii) definition of the measurement chain, in terms of mechanical interfaces, sensors, RF shielding and data handling, (iv) analysis of system criticalities; (v) design and experimental validation of the critical technologies involved in the system; (vi) detailed design of the thrust balance.

The physics involved in the coupling, propagation and absorption of RF helicon waves (electronic whistler) in low temperature Helicon plasma sources is investigated by solving the 3D Maxwell-Vlasov model equations using a WKB asymptotic expansion. The reduced set of equations is formally Hamiltonian and allows for the reconstruction of the wave front of the propagating wave, monitoring along the calculation that the WKB expansion remains satisfied. This method can be fruitfully employed in a new investigation of the power deposition mechanisms involved in common Helicon low temperature plasma sources when a general confinement magnetic field configuration is allowed, unveiling new physical insight in the wave propagation and absorption phenomena and stimulating further research for the design of innovative and more efficient low temperature plasma sources. A brief overview of this methodology and its capabilities has been presented in this paper.

This paper is focused on the description of simulation codes developed to design a helicon plasma thruster for a small satellite under development in the research project Helicon plasma hydrazine combined micro (HPH.com) conducted within the 7th Framework Program of the EU by a European consortium.

Radiofrequency magnetized cylindrical plasma sources are proposed for the development of space thrusters, whose thrust efficiency and specific impulse depend on the power coupled into the plasma. At this stage of research, emphasis has been on the absorption of Whistler wave energy by non-uniform plasmas but not much on the role played by the magneto-static confinement field, considered uniform, constant and aligned with the axis of the source. We present RAYWh (RAY-tracing Whistler), a three-dimensional (3D) ray-tracing solver for electromagnetic propagation and power deposition in cylindrical plasma sources for space plasma thrusters, where actual magnetic confinement configurations along with plasma density profiles are included. The propagation and absorption of Whistler waves are investigated by solving the 3D Maxwell-Vlasov model equations by a Wentzel-Kramers-Brillouin (WKB) asymptotic expansion. The reduced set of equations for the wave phase and for the square amplitude of the electric field is solved numerically by means of a modified Runge-Kutta algorithm. Unexpected cut-offs, resonances, radial reflections, mode conversions and power deposition profile of the excited waves are found, when realistic confinement magnetic fields are considered. An analysis of the influence of axial wavenumbers and the axial length of the system on the power deposition is presented. © 2014 IOP Publishing Ltd.

We have designed and tested a thrust stand conceived for the characterization of RF plasma thrusters. The balance has been employed in the development of small-medium size HPT prototypes, therefore it allows for an high number of tests per day with an accuracy within the 10%. The balance relies on the counterbalanced-type pendulum concept, which allows to achieve high sensitivity while maintaining a low overall size of the system; the displacement is measured by means of an high-accuracy laser interferometer put outside the vacuum chamber. The system can be calibrated with both a calibration mass, before the test, and an electro-magnetic device, during the test session. We have verified the linear behavior of the instrument and we have developed a dedicated algorithm in order to correct the thermal drifts of the balance. We have compared the stand measurements with the thrust estimations derived from Faraday probe measurements within the plasma plume, verifying that the two estimates are in agreement within 20%.