Metal-hydride Cathode Research Articles

PENNING-TYPE H– ION SOURCE WITH METAL HYDRIDE CATHODE IN PULSATING REGIME

The features of H– ion emission from gas-feed-free Penning-type ion source with metal hydride cathode have been studied in pulsating regime. The metal hydride cathode provided local injection of hydrogen in activated state and impacts on Penning discharge ability to emit H– ions in the longitudinal direction. For stimulation of pre-excited hydrogen desorption from metal hydride the voltage pulse (4.5 kV, τ ≈ 15 µs) was performed against the background constant voltage of 6 kV on the anode of the discharge. The H– ion current of about 0.2 mA was obtained.

MODULATION OF NEGATIVELY CHARGED PARTICLE FLUX FROM PENNING DISCHARGE WITH METAL HYDRIDE CATHODE

The features of modulation of negatively charged particle flux extracted along the magnetic field from Penning discharge with metal hydride cathode have been investigated. The separation of negative ions from coextracted electrons was performed by an electromagnetic filter with efficiency not worse than 90 %. It is shown that electrons in the extracted flow are deeply modulated with the frequency of the diocotron instability of the anode layer, while negative ions are not. An increase in the interelectrode distance and anode length resulted in a more pronounced expression of this effect due to the minimization of the influence of the magnetic field of the filter on the discharge.

The emission of H− ions from Penning-type ion source with metal hydride cathode in pulsating regime

The operation in pulsating regime of gas-feed-free Penning-type H− ion source with metal hydride cathode and extraction in the longitudinal direction has been investigated. Hydrogen is stored in metal hydride in atomic state followed by the formation of rovibrationally excited H2* molecules due to the process of nonequilibrium desorption. It impacts on a Penning discharge ability to emit negative hydrogen ions in the longitudinal direction and provides local gas injection to the discharge without any external gas supply. The AC power input of 65 W during τ≈15 μs was performed against the background DC one of 5 W. The extracted axial flux of charged particles was separated in an electromagnetic filter followed by the registration of H− current. The H− ion current of about 0.22 mA was obtained. In the DC regime it was only 5uA, which is order of magnitude below the current obtained with the present pulsating regime of source implementation.

The Plasma Parameters of Penning Discharge with Negatively Biased Metal Hydride Cathode at Longitudinal Emission of H– Ions

The enhancement of negative ion production in a volume Penning based source could be performed by the application of metal hydride cathode. Hydrogen isotopes are stored there in a chemically bound atomic state and desorbed from the metal hydride under the discharge current impact. Highly vibrationally / rotationally excited molecules H2* are formed by recombination of H-atoms at the metallic surface, which then can be easily converted to H– by dissociative electron attachment without the pre-excitation of a H2 molecule in plasma. Changing the discharge properties opens the way of source design simplification by negative ions extraction along the external magnetic field in comparison with traditional volume sources, where the extraction is performed perpendicular to magnetic field. The separation of negative ions from the extracted in longitudinal direction flux of charged particles was performed by an electromagnetic filter basing on numerical calculations of particles trajectories. The dependence of electron temperature and plasma density on the bias potential is carried out by Langmuir probe method. The measurement of electron energy was performed by an electrostatic energy analyzer. It was shown that the yield of H– ions depends on the electrical bias on the metal hydride cathode with strong dependences on the plasma electrons temperature. The estimation of the bias potential versus Te was performed under the assumption of electron Boltzmann distribution near the cathode. The presence of additional groups of electrons with higher energies distorts the behavior of H– current, but generally the experimental results are in good agreement with estimation based on the physics behind the Boltzmann distribution. The optimum for the effective extraction of H– ions was revealed, when the metal hydride cathode had been electrically biased at -20V and higher, and plasma density reaches the maximum value to 2×109 cm-3.

AN ATTEMPT FOR INCREASING THE EFFICIENCY OF PENNING SOURCE OF Н- IONS WITH A METAL HYDRIDE CATHODE

The possibility of increasing the current of negative hydrogen ions extracted in the longitudinal direction from a Penning discharge with a metal hydride cathode by reducing the anode-cathode distance is shown. The features of Н– ions emission have been revealed depending on the electric shift on the metal hydride cathode and the external magnetic field. The power parameters of the electromagnetic filter have been optimized for the separation of negative ions from the extracted flux of charged particles. The current of H– ion beam was obtained at the level of 16 μA with hydrogen supply only from the metal hydride cathode and at the level of 0.1 mA at external supply from the balloon.

PECULIARITIES OF ELECTROMAGNETIC FILTER OPERATION IN PENNING SOURCE WITH METAL HYDRIDE CATHODE

The paper describes a method of negative hydrogen ions separation from axial flow of charged particles extracted from Penning discharge with a metal hydride cathode. For this purpose, an electromagnetic filter has been designed basing on numerical solution of motion equations of charged particles in the filter. The optimal parameters of the filter operation were determined for the effective registration of negative hydrogen ions extracted in axial direction. Performed calculations together with experimental verification shows that there are not more than 10% electrons in the registered H– current. This model could be applied for the interpretation of any experiments with H– ions separation from an axial flow of charged particles extracted from a source with cylindrical geometry.

EFFECT OF NEGATIVE SHIFT OF METALHYDRIDE CATHODE ON THE EMISSION OF H– IONS FROM PENNING DISCHARGE

On the basis of numerical calculations, the experimental results obtained by the authors in the study of the source of negative hydrogen ions of the Penning type with a metal hydride cathode are explained. It was shown that the yield of negative ions depends on the potential at the metal hydride cathode and is determined by the temperature of the plasma electrons. The dependence of this potential on the electron temperature is calculated numerically to ensure the maximum current of negative ions

The increasing of H−current from Penning ion source with electrically biased metal hydride cathode

The possibility of the current increasing of negative hydrogen ions H− extracted in the longitudinal direction from gas-feed-free Penning type ion source with metal hydride cathode by the electric cathodes bias has been investigated. The separation of negative ions from the extracted flux of charged particles was performed by an electromagnetic filter, which consists of a magnetic coil for electron diverting and a grid under positive potential for positive ion reflection. The optimum for the effective extraction of H− ions has been determined. The H− ion current of 10 μA was obtained at an input power of 6 W.

Effect of metal-hydride hydrogen activation on longitudinal yield of negative ions from PIG

We present the results of the study of activated hydrogen, desorbed from a metal hydride cathode, effect on a PIG ability to emit negative hydrogen ions H− in the longitudinal direction. It becomes possible due to a change in the discharge properties with the further output of negatively charged particles together with positive ions along the magnetic field. The separation of negative ions from an extracted flow of charged particles was carried out by an electromagnetic filter. The efficiency of the filter was investigated and the optimal external parameters for H− ions separation were determined. The beam current of H− ions has been obtained at the level of 5 mkA at an average discharge current 2 mA and a discharge voltage 5 kV.

PIG charged particle source with hydrogen supply from a metal-hydride cathode

We present the results of an experimental investigation of a Penning-type charged-particles source with a metal-hydride cathode. The main characteristic of the experiment is internal hydrogen supply from the metal-hydride cathode under the conditions of ion-stimulated desorption; we studied its influence on the source's emissive characteristics. An additional mode of source operation was observed involving axial electron emission; the decisive effect was revealed of the desorbed hydrogen on the axial electron emission. The ion energy distribution function was measured and its dependence on the external discharge parameters was determined.

Photoelectrochemical cell for water decomposition with a hybrid photoanode and a metal-hydride cathode

The operation of a photoelectrochemical cell for hydrogen production by water decomposition under simulated sunlight (a 150W Xe lamp) with a hybrid photoanode based on a Si solar cell and TiO2 film as well as with a metal-hydride cathode based on LaNi5 alloy has been investigated. TiO2 films were produced by the chemical vapor deposition (CVD) method. A new technique of production of continuous CVD TiO2 films on semiconductor surface has been proposed. The peculiarity of this technique is a deposition of a thin (30–40nm) Ti layer on the substrate prior to a TiO2 deposition. This metal layer serves as the catalyst of following TiO2 film growth and then it is oxidized to TiO2. Continuous TiO2 films obtained by such a way protect the solar cell surface from oxidation in the electrolyte. The optimal TiO2 film thickness and structure for highest photocurrent have been determined. It has been shown that the use of the metal-hydride cathode based on LaNi5 alloy instead of a Pt cathode increases significantly (up to 50%) the solar cell efficiency. The photoconversion efficiency attained 2% with the Pt cathode and 3% with the metal-hydride cathode.