Electric propulsion (EP) is the norm for Electric Orbit Raising (EOR) and in-orbit station-keeping. Hall Effect Thrusters (HET) and Gridded Ion Thrusters (GIT) are mature technologies, but their reliance on fragile neutralizers and susceptibility to component erosion motivate the development of alternative concepts. Electron Cyclotron Resonance (ECR) thrusters could offer long-life, electrodeless plasma sources. While xenon remains the reference propellant, its limited availability drives up cost, thus iodine has emerged as an attractive substitute with similar performance at lower cost. Unlike noble gases, iodine features coupled atomic-molecular chemistry (I, I_2, I^+, I_2^+ , I^−) with multiple inelastic channels and incomplete cross-section coverage. Predictive modeling of ECR performance must capture strong axial gradients and disparate advection-chemistry time scales, making purely temporal or purely spatial models insufficient. This work, done at ONERA, develops a one-dimensional spatiotemporal multi-species fluid model for iodine- fed ECR thrusters. To do so, reaction cross sections are assembled to compute rate coefficients; then the methodology is validated on a quasi-1D helicon discharge with noble gases; the framework is then adapted to ECR operation; and finally extended to iodine. The formulation advances heavy-species mass and momentum together with an electron energy balance, enforcing quasi-neutrality through an ambipolar closure. A proof-of-concept is implemented using an IMEX scheme with reduced iodine chemistry. Simulations show ambipolar electric fields accelerating ions. This field is governed by the electron pressure gradient which, in turn, is shaped by the ECR layer, where Te peaks. Including ion recombination into neutrals at the wall increases ionization and utilization but enhances collisional drag, lowering exhaust velocity and revealing a utilization-specific impulse trade-off. For a nominal case (10 W, 0.25 mg·s^−1 I_2 flow), the model predicts performance consistent with typical measured values (Isp ∼ 10² s, sub-mN thrust) and highlights actionable levers such as ECR-layer placement and wall recycling.
La propulsione elettrica (EP) è lo standard per l’Electric Orbit Raising (EOR) e il mantenimento in orbita. Gli Hall Effect Thrusters (HET) e i Gridded Ion Thrusters (GIT) sono tecnologie consolidate, ma la dipendenza da neutralizzatori fragili e l’erosione dei componenti spingono allo sviluppo di concetti alternativi. I propulsori a risonanza ciclotronica elettronica (ECR), basati su riscaldamento a microonde senza elettrodi, promettono sorgenti di plasma longeve ed elettrodeless. Sebbene lo xeno sia il propellente di riferimento, la sua scarsità ne aumenta il costo; lo iodio emerge quindi come sostituto con prestazioni simili a costi inferiori. A differenza dei gas nobili, lo iodio presenta chimica atomico-molecolare accoppiata (I, I_2, I^+, I_2^+ , I^−), numerosi canali inelastici e sezioni d’urto incomplete. La modellizzazione predittiva delle prestazioni ECR deve quindi descrivere forti gradienti assiali e scale temporali distinte di advezione e chimica, rendendo inadeguati modelli solo temporali o solo spaziali. Questo lavoro, svolto all’ONERA, sviluppa un modello fluido multi-specie monodimensionale spaziotemporale per propulsori ECR a iodio. Le sezioni d’urto sono raccolte per calcolare i coefficienti di reazione; la metodologia è validata su una scarica elicon quasi-1D con gas nobili, poi adattata al regime ECR ed estesa allo iodio. La formulazione integra massa e quantità di moto delle specie pesanti con un bilancio energetico elettronico, imponendo la quasi-neutralità tramite chiusura ambipolare. Un proof-of-concept è implementato con schema IMEX e chimica ridotta. Le simulazioni mostrano campi elettrici ambipolari che accelerano ioni, governati dal gradiente di pressione elettronica modellato dallo strato ECR, dove Te massimizza. La ricombinazione ionica alle pareti aumenta ionizzazione e utilizzo, ma rafforza l’attrito collisionale riducendo la velocità di scarico, rivelando un compromesso tra utilizzo e impulso specifico. Per un caso nominale (10 W, 0.25 mg·s−1 di flusso di I_2), il modello predice prestazioni coerenti con valori tipici misurati (Isp ∼ 10² s, spinta sub-mN) e identifica leve operative come posizione dello strato ECR e riciclo alle pareti.
Numerical study of the composition of an Iodine plasma
Soule, Yannice
2024/2025
Abstract
Electric propulsion (EP) is the norm for Electric Orbit Raising (EOR) and in-orbit station-keeping. Hall Effect Thrusters (HET) and Gridded Ion Thrusters (GIT) are mature technologies, but their reliance on fragile neutralizers and susceptibility to component erosion motivate the development of alternative concepts. Electron Cyclotron Resonance (ECR) thrusters could offer long-life, electrodeless plasma sources. While xenon remains the reference propellant, its limited availability drives up cost, thus iodine has emerged as an attractive substitute with similar performance at lower cost. Unlike noble gases, iodine features coupled atomic-molecular chemistry (I, I_2, I^+, I_2^+ , I^−) with multiple inelastic channels and incomplete cross-section coverage. Predictive modeling of ECR performance must capture strong axial gradients and disparate advection-chemistry time scales, making purely temporal or purely spatial models insufficient. This work, done at ONERA, develops a one-dimensional spatiotemporal multi-species fluid model for iodine- fed ECR thrusters. To do so, reaction cross sections are assembled to compute rate coefficients; then the methodology is validated on a quasi-1D helicon discharge with noble gases; the framework is then adapted to ECR operation; and finally extended to iodine. The formulation advances heavy-species mass and momentum together with an electron energy balance, enforcing quasi-neutrality through an ambipolar closure. A proof-of-concept is implemented using an IMEX scheme with reduced iodine chemistry. Simulations show ambipolar electric fields accelerating ions. This field is governed by the electron pressure gradient which, in turn, is shaped by the ECR layer, where Te peaks. Including ion recombination into neutrals at the wall increases ionization and utilization but enhances collisional drag, lowering exhaust velocity and revealing a utilization-specific impulse trade-off. For a nominal case (10 W, 0.25 mg·s^−1 I_2 flow), the model predicts performance consistent with typical measured values (Isp ∼ 10² s, sub-mN thrust) and highlights actionable levers such as ECR-layer placement and wall recycling.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/243579