A Global Enhanced Vibrational Kinetic Model for High-Pressure Hydrogen RF Discharges

Abstract

A global enhanced vibrational kinetic model (GEVKM) is developed for multitemperature, chemically reacting hydrogen plasmas in inductively coupled cylindrical discharges for low-to high-pressure regimes. The species in a GEVKM are ground-state hydrogen atoms H and molecules H 2 , 14 vibrationally excited hydrogen molecules H 2 (v), v = 1 − 14, electronically excited hydrogen atoms H(2) and H(3), groundstate positive ions H + , H + 2 , and H + 3 , ground-state negative ions H − , and electrons e. The GEVKM involves volume-averaged steady-state continuity equations for the plasma species, an electron energy equation, a total energy equation, a heat transfer equation to the chamber walls, and a comprehensive set of surface and volumetric chemical processes governing vibrational and ionization kinetics of hydrogen plasmas. The GEVKM is verified and validated by comparisons with previous numerical simulations and experimental measurements of a negative hydrogen ion source in the low-pressure (20-100 mtorr), low-absorbed-power-density (0.053-0.32 W/cm 3 ) regime and of a microwave plasma reactor in the intermediate-to high-pressure (1-100 torr), high-absorbed-power-density (8.26-22 W/cm 3 ) regime. The GEVKM is applied to the simulation of a highcurrent negative hydrogen ion source (HCNHIS). The HCNHISconsists of a high-pressure (20-65 torr) radio-frequency discharge chamber in which the main production of high-lying vibrational states of the hydrogen molecules occurs, a bypass system, and a low-pressure (0.1-0.4 torr) negative hydrogen ion production region where negative ions are generated by the dissociative attachment of low-energy electrons to rovibrationally excited hydrogen molecules. The discharge pressure and negative hydrogen ion current predicted by the GEVKM compare well with the measurements in the HCNHIS.

Benchmarking and validation of global model code for negative hydrogen ion sources

“…The interactions of neutrals with the walls include the wall recombination of ground-state H atoms into molecules, the wall quenching of excited states of H atoms, 26 and the de-excitation of vibrationally excited hydrogen molecules. 44,45 The rate coefficient , s wall k is given as 46…”

“…Even if the sets of volume reactions considered are not exactly the same, the reactions significantly affecting the plasma parameters are the same between these two models. Additional heavy-particle collisions included in GEVKM 26 increases and then tends to saturate with increasing pressure. Figure 1(b) shows H e nn − ratio as a function of pressure, and an excellent agreement is achieved between the two models.…”

“…Recently, Averkin et al proposed a high current negative hydrogen ion source (HCNHIS). 25,26 The HCNHIS consists of a high-pressure RF discharge chamber where high vibrational states of molecular hydrogen are mainly generated. The plasma and gas flow in the discharge chamber is controlled (reduced) by a series of bypass tubes and enters through a nozzle into a low-pressure negative hydrogen ion production chamber, where H − ions are produced mainly by DA process.…”

“…All i  are the ratios of the volume-averaged to center densities. For cylindrical chamber, they are given as26…”

Πειραματική Μελέτη Της Παραγωγής Αρνητικών Ιόντων Η- Από Πλάσμα Κυκλοτρονικού Συντονισμού Ηλεκτρονίων

“…Ζ αλάπηπμε πεγψλ θαη ζπζηεκάησλ εμαγσγήο αξλεηηθψλ ηφλησλ γηα ηε δεκηνπξγία δεζκψλ κεγάιεο δηάξθεηαο θαη πςειήο ηζρχνο απνηειεί ζθνπφ πνιιψλ εξεπλεηηθψλ ηδξπκάησλ ζχληεμεο φπσο ην IPP ζην Garching ηεο Γεξκαλίαο [25], ην Consorzio RFX ζηελ Ηηαιία [26], θαζψο θαη ηα JAEA [27,28] θαη NIFS [29] ζηελ Ηαπσλία. Δλ ησ κεηαμχ, ε θπζηθή ησλ πεγψλ αξλεηηθψλ ηφλησλ απνηειεί ην αληηθείκελν έξεπλαο ηφζν πεηξακαηηθψλ [30][31][32][33] φζν θαη ζεσξεηηθψλ [34][35][36][37][38][39] εξγαζηψλ παγθνζκίσο.…”