Characterization of hydrogen plasma in a permanent ring magnet based helicon plasma source for negative ion source research

Abstract

HELicon Experiment for Negative ion source (HELEN-I) with single driver is developed with a focus on the production of negative hydrogen ions. In the Helicon wave heated plasmas, very high plasma densities (~10 !" !! ) can be attained with electron temperatures as low as ~ 1 eV in the downstream region. These conditions favor the production of negative hydrogen ions. In HELEN-I device at IPR, helicon plasma is produced using Hydrogen gas in a diverging magnetic field, created by a permanent ring magnet. RF Power (P RF ) of 800-1000W at 13.56 MHz frequency is applied to a Nagoya-III antenna to excite m = 1 helicon mode in the plasma. The plasma is confined by a multi-cusp field configuration in the expansion chamber. The transition from inductively coupled mode to Helicon mode is observed near P RF ~ 700W with plasma density ~ 10 18 m -3 and electron temperature ~ 5 eV in the driver and ~ 1eV in the expansion volume. Line integrated negative hydrogen ion density is measured in the expansion chamber by employing an Optical Emission Spectroscopy (OES) diagnostic technique using ! / ! ratio and Laser photo-detachment based Cavity Ring Down spectroscopic (CRDS) diagnostic technique. The measured value of negative hydrogen ion density is in the order of 10 16 m -3 at 6 mTorr pressure and does not vary significantly with power in the helicon mode, pressure and downstream axial magnetic field variation. The negative ion density measurements are compared with theoretically estimated values calculated using particle balance method considering different reaction rates responsible for negative hydrogen ion creation and destruction. It is to be noted that at present Caesium (Cs) is not injected in the plasma discharge to enhance ! ion density.In surface process, H-ion are produced on a low work-function surface due to surface conversion of energetic H atoms (H 0 * ) or hydrogen ions (H n + ) in the plasma [9];

Ambient Synthesis of Pt-Reactive Metal Alloy and High-Entropy Alloy Nanocatalysts Utilizing Hydrogen Cold Plasma

“…Figure b,c shows the cold plasma synthesis in process, with purple illuminance being observed as a result of hydrogen plasma generation, and the reactor temperature increased from room temperature to about 40 °C in about 10 s and further ramped and stabilized at around 200 °C with elongated reaction time. Previous investigations have discovered that a variety of active species, including H • , H – , and H 2 *, would be produced in hydrogen plasma and possess strong reducing power. − These active species would likely follow a trend of H – > H • > H 2 * in terms of reducing power, considering that the same element in a lower valence typically possesses a stronger reducing capability. Recently, a few studies reported the utilization of hydrogen plasma for synthesis of late transition-metal nanoparticles. − Although these studies focused on late transition metals, which are significantly easier to reduce than reactive metals, the successful nanoparticle synthesis under ambient conditions provides evidence for the strong reducing capability of hydrogen plasma.…”

“…In this work, we report a new, hydrogen cold plasma-enabled synthesis method for rapid and facile preparation of Pt-RMA nanoparticles under ambient conditions. This new approach utilizes in situ-generated hydrogen cold plasma that consists of energetically activated species including hydrogen anions (H – ), hydrogen radicals (H • ), and excited hydrogen molecules (H 2 *). − Particularly, H – has a low standard reduction potential of −2.3 V, which is more negative than that of many RMs and thus can simultaneously reduce Pt and RMs for their alloy formation. A variety of Pt-RMA nanoparticles, including Pt–Cr, Pt–Ta, Pt–V, Pt–Fe, and Pt–Al, are synthesized within minutes, proving rapid, facile, and effective features of this method.…”

Cavity Ring-Down Spectroscopy: Recent Technological Advancements, Techniques, and Applications

“…In addition, the dark region of the plasma plume, which is inaccessible to the optical emission spectroscopy can be easily investigated by the CRDS technique. Nevertheless, several recent reports − utilized the CRDS technique for plasma diagnostics in fusion research to measure H – and D – ion densities in negative ion sources like helicon plasma devices. The reports − employed a pulsed Nd:YAG laser operating at 1064 nm to achieve sufficient photon energy for detaching the weakly bound electron from the H – /D – ion in the process of photodetachment reaction which resulted in the absorption of a photon and a subsequent decrease in the ring-down time.…”

“…Nevertheless, several recent reports − utilized the CRDS technique for plasma diagnostics in fusion research to measure H – and D – ion densities in negative ion sources like helicon plasma devices. The reports − employed a pulsed Nd:YAG laser operating at 1064 nm to achieve sufficient photon energy for detaching the weakly bound electron from the H – /D – ion in the process of photodetachment reaction which resulted in the absorption of a photon and a subsequent decrease in the ring-down time. However, the CRDS technique provides the line-integrated measurements where ions in the laser beam path are only measured and thus does not provide the spatial distribution of ions inside the plasma device.…”

Spatial distributions of the ion flux in a capacitive hydrogen RF discharge using a hollow cathode with double toroidal grooves enclosed by magnets

“…On the other hand, negative ion sources of H − and D − have been developed by RF driven inductively coupled plasmas using hydrogen and deuterium gases with cesium vapor for neutral beam injection (NBI) in fusion experiments experimentally, [12][13][14][15][16][17] and numerically. 18,19) For these H 2 plasmas, it is needed to attain a high-density and low-temperature of electrons under a low gas pressure for high-quality processing and/or high-efficiency plasma production.…”