Hydrogen Ion Beam Research Articles

Microscopic Difference of Hydrogen Double-minimum Potential Well Detected by Hydroxyl Group in Hydrogen-bonded System

We investigate the microscopic structure of hydrogen double-well potentials in a hydrogen-bonded ferroelectric system exposed to radioactive particles of hydrogen-ion beams. The hydrogen-bonded system is ubiquitous, forming the base of organic-inorganic materials and the double-helix structure of DNA inside biological materials. In order to determine the difference of microscopic environments, an atomic-scale level analysis of solid-state 1H high-resolution nuclear magnetic resonance (NMR) spectra was performed. The hydrogen environments of inorganic systems represent the Morse potentials and wave function of the eigen state and eigen-state energy derived from the Schrödinger equation. The wave functions for the real space of the localized hydrogen derived from the approximated solutions in view of the atomic scale by using quantum mechanics are manifested by a difference in the charge-density distribution.

Laser-assisted high-energy proton pulse extraction for feasibility study of co-located muon source at the SNS

We have experimentally demonstrated the first non-intrusive 1-GeV proton beam extraction for the generation of muons with a temporal structure optimized for Muon Spin Relaxation/Rotation/Resonance (μSR) applications. The proton pulses are extracted based on the laser neutralization of 1 GeV hydrogen ion (H−) beam in the high energy beam transport of the Spallation Neutron Source (SNS) accelerator. The maximum flux of the extracted proton beam based on laser neutralization causes only 0.2% reduction of the total proton beam used for neutron production, a marked difference from the 20% reduction at other co-located muon and neutron facilities, and thus the proposed method will result in negligible impact on the SNS operation. This paper describes the development of a fiber/solid-state hybrid laser system that has high flexibility of pulse structure and output power, initial experiments on laser neutralization of H− beam and separation of H0 beam from the existing SNS accelerator beam line, conversion of H0 to proton at the SNS linac dump, and measurement results of 30 ns/50 kHz proton pulses. This system conclusively demonstrates the feasibility of laser-based proton beam extraction to power a world-leading μSR facility at the SNS.

Positive and negative hydrogen ion reflections of low-energy atomic and molecular hydrogen ion beam from HOPG and Mo surfaces.

Positive and negative hydrogen ion reflections from surfaces by injecting singly charged hydrogen ion beams show a clear difference between atomic and molecular ion injections at low energy and grazing incidence. The intensity ratio of reflected negative to positive ions H-/H+ increased as the incident beam energy per nucleon decreased only when molecular ion beams are injected. It implies that negative ions are more produced upon beam-surface interaction when molecules are injected. A possible reason was discussed in terms of difference in the negative ion production processes between atomic and molecular ions.

Ballistic formation of high-intensity low-energy gas ion beams.

The development of the method of high-intensity implantation of low-energy ions requires the design of an efficient system for generating high-intensity ion beams of various elements with a current density of tens and hundreds of milliamperes per square centimeter with ion energies not exceeding some kiloelectronvolt. This paper considers the regularities of formation of high-intensity beams of nitrogen ions and argon and mixed beams of argon and hydrogen ions in spherical and cylindrical grid systems with ballistic focusing of the ion beam. The studies were carried out with the plasma-immersion formation of repetitively pulsed ion beams with duration from units to hundreds of microseconds and a pulse frequency of up to 105 pulses/s with negative bias potentials in the range from 0.6 to 3 kV. The possibility of stable formation of gas ion beams with an ion current density of up to 0.7 A/cm2 is demonstrated.

Hydrogen ion beam transport in an energy range lower than 50 eV: Ion beam species.

Low energy beam transport in the energy range below 50 eV is studied using a compact ion source with a high temperature tungsten cathode that can be put into a vacuum system. A 2.6 cm diameter, 5.2 cm long compact ion source successfully produced more than 2.4 nA beam of H2 + ions at 50 eV beam energy. The source also supplied a stable beam of H3 + ions at 2.5 eV energy with more than 100 pA mass-separated current. The inside wall of the ion source was covered by thin sheets of titanium, nickel, and molybdenum to see if the species composition of the ion beam can be controlled by changing the ion source wall material. Usually, the H2 + ion peak was the highest in the mass spectrum, and the H2 + ion ratio (H2 +/Hn +) was measured for a source operation with hydrogen gas. The ion species ratio drifted against time, and Mo showed the most stable ion ratio.

Cluster ion source for external injection and high capacity filling of light elements into the relativistic heavy ion collider electron beam ion source.

An advanced Electron Beam Ion Source (EBIS) is the primary ion source to supply highly charged ion beams of different elements to the Relativistic Heavy Ion Collider (RHIC) and to the NASA Space Radiation Laboratory (NSRL). Intense beams of highly charged ions of various elements of the periodic table, ranging from helium to uranium, have been demonstrated since EBIS became operational in 2010. EBIS routinely provides ion beams to RHIC and NSRL quasisimultaneously with about 1 s switching time between different ion species. Such unique flexibility and rapid switching between ion species are based on external injection of singly charged ions into the EBIS trap either in "fast" or "slow" injection modes. At present, a Laser Ion Source (LIS) provides most of the ion species of solid materials using the "fast" injection mode into the EBIS trap and a Hollow Cathode Ion Source (HCIS) provides most of the ion species of gaseous elements using the "slow" injection mode into the EBIS trap. Gas injection into the EBIS trap is also possible and has been used but imposes some restrictions for the simultaneous generation of highly charged ions such as Au32+ ions for RHIC and ions of gaseous species for NSRL. Because light ions have relatively high velocity inside the EBIS trap, efficient injection of hydrogen and helium ions and filling of the EBIS trap to high capacity is difficult from either LIS or HCIS. To overcome this restriction and enhance EBIS operational capability, we suggest injecting beams of hydrogen and helium cluster ions into the EBIS trap. Required parameters of cluster ion beam injection into the EBIS trap are estimated, and advantages of such an injection are highlighted. A cluster ion source with required high intensity is visible and will be designed, built, optimized, and tested.

Breakdown Oscillations of the ISIS H− Penning Ion-Source Hydrogen–Cesium Discharge

The ISIS Penning ion source is a pulsed dc discharge surface plasma source delivering a 55-mA beam of negative hydrogen ions (H−) in 250- ${ mu }\text{s}$ pulses to the ISIS accelerator for neutron and muon physics at 50-Hz pulse repetition rate. The H− ions are extracted from the hydrogen–cesium discharge sustained by a current-regulated pulsed power supply delivering a current of 50–60 A. The discharge exhibits an ignition transient that requires the pulselength to be prolonged to 700 ${ mu }\text{s}$ to extract a clean H− beam pulse. The current and voltage fluctuations during the breakdown oscillation enhance the sputtering damage of the ion-source cathodes, thus contributing to the lifetime limitation of the device. It has been hypothesized that the breakdown oscillations are due to cesium dynamics causing the surface work function and electron emission from the cathode surfaces to fluctuate periodically. Experiments with the ISIS H− Penning ion source, reported here, reveal that the breakdown oscillations are primarily driven by the discharge power supply and its auxiliary circuits, whereas cesium dynamics have only a minor effect on the ignition transient. The conclusion is derived from careful characterization of the discharge current–voltage characteristics, optical emission measurements combined with a 0-D model, and comparison of different discharge geometries. Engineering solutions to mitigate the breakdown oscillations are presented and the potential effect of the applied modifications on the molybdenum cathode erosion by cesium sputtering is estimated.

Operation of RF-driven negative hydrogen ion source in China Spallation Neutron Source.

The China Spallation Neutron Source started delivering neutron beams to users in March 2018. To upgrade the beam power to 500 kW and improve the performance of the ion source, an RF-driven negative hydrogen (H-) ion source is under development. The source has a silicon nitride ceramic plasma chamber surrounded by a 4.5-turn antenna. The plasma is ignited by a pulsed DC spark gap and then driven by a 2 MHz solid-state amplifier with a repetition rate of 25 Hz. The commissioning of the source started in January 2019. When uncesiated, it produced about 20 mA beam at an RF power of 32 kW and pulse width of 450 μs. This paper describes the configuration of the ion source, several peculiar technologies used in it, and the first negative hydrogen (H-) ion beam extraction.

Physics and engineering design of 400 keV H- accelerator for negative ion based neutral beam injection system in China.

A research project of the China Fusion Engineering Test Reactor (CFETR) Negative ion-based Neutral Beam Injection (NNBI) prototype has been started in China. The objectives of the CFETR NNBI prototype are to produce a negative hydrogen ion beam of >20 A up to 400 keV for 3600 s and to attain a neutralization efficiency of >50%. In order to identify and optimize the design of the negative ion accelerator, a self-consistent model has been developed to consider all key physics and engineering issues (electric and magnetic fields, background gas flow, beam optics, beam-gas interaction, secondary particle trajectories, power deposition on grids, heat removal design, and mounting pattern). This paper presents the primary results by applying the self-consistent model to the current design of the 400 keV H- accelerator of the CFETR NNBI prototype.

Extending the pulse length of the ISIS H− Penning ion source

The ISIS Penning ion source can routinely produce a 55 mA beam of negative hydrogen ions in 250 µs pulses at 50 Hz repetition rate. Extending the beam pulse length to 2 ms requires eliminating the 15%–30% droop of the current observed in long pulse operation and benefits from the suppression of discharge breakdown oscillations otherwise forcing to prolong the pulse length to 2.2 ms or longer. The droop can be compensated by ramping the discharge current during the pulse, whereas the discharge oscillations are suppressed by modifying the ancillary circuit of the pulsed arc power supply.

The mechanism of negative and positive hydrogen ions production on the Ni surface

The studies about surface production of hydrogen negative ions play an important role in many technologies. In the present paper, a low energy molecular hydrogen ion beam was irradiated to the porous Ni sheet. It was found that negative atomic hydrogen ions were detected at the back of the porous Ni sheet when the energy of incident ion beam was lower than 180 eV. When the energy of the incident ions increased, the positive ions dominated at the back of the porous Ni sheet. The production of negative hydrogen on Ni surface can't be explained by comparing the electron affinity of Ni and H. The charge transferring during the process of H atoms reflected from Ni surface was calculated by using constrained DFT (cDFT). The results show the production of negative hydrogen on Ni surface may well be due to heterogeneous electron density on the Ni surface. However, the influence of incident energy on the production of negative and positive hydrogen ions is unable to be explained by cDFT. The problem may be solved by using TDDFT which is able to capture the transfer of energy to electrons during the collision between atoms.

Physical design of the neutralizer for CFETR negative ion based neutral beam injection prototype

A research project of the CFETR Negative ion based Neutral Beam Injection (NNBI) prototype has been started in China. The objectives of the CFETR NNBI protype are to produce a negative hydrogen ion beam of >20 A to 200–400 kV for 3600 s and to attain a neutralization efficiency of >50%. Thus, a neutral beam power of >2 MW is foreseen onto the calorimeter (i.e., beam dump). A gas neutralizer is applied inside the beamline of CFETR NNBI prototype, to achieve the neutralization of negative ion beam through the charge-exchange collisions with the gas target. The most critical issues for the gas neutralizer are to balance the contradictive requirements of high neutralization efficiency, low gas inflow, and low heat load. During the physical design of the neutralizer for CFETR NNBI prototype, two proposals have been considered and studied in detail. One has single beam channel and other one has two narrow channels separated by a panel. The narrow channel design is benefic to decrease gas conductance, and thus reduce the required gas inflow to attain the maximal neutralization efficiency. However, the inserted panel will restrict the extraction area of the beam source, where the aperture columns corresponding to the panel should be masked to avoid the direct beam interception. But the leading edge of the inserted panel will still suffer a high thermal load due to the stray particles from the beam source. A 3D model of the whole beamline of CFETR NNBI prototype has been developed to study the gas flow and the beam transport in the beamline. Based on this model, these two neutralizer designs have been evaluated in detail, in terms of the relation between neutralization efficiency and gas inflow, and the power load on the neutralizer components.

A Secondary Ion Energy Analyzer for Measuring the Degree of Compensation of the Ion Beam Space Charge

This paper describes an analyzer of the energy of secondary slow ions, which is used to measure the degree of compensation of the spatial charge of a hydrogen ion beam in a low energy beam transport channel (LEBT) to the input of an accelerator with high-frequency quadrupole focusing. The electrostatic analyzer with a retarding field has increased accuracy due to the use of a double analyzing grid. The results of measuring the degree of compensation of the space charge of a hydrogen ion beam with a pulse current of 60 mA and an energy of 400 keV are presented. The analyzer also allows non-disturbing measurements of the radial size of the ion beam.

Validating fast-ion wall-load IR analysis-methods against W7-X NBI empty-torus experiment

The first neutral beam injection (NBI) experiments in Wendelstein 7-X (W7-X) stellarator were conducted in the summer of 2018. The NBI system is used to heat the magnetically confined plasma by neutralising an accelerated hydrogen ion beam and directing it into the plasma, where the resulting energetic ions release their energy to heat the plasma. The modelling of the NBI fast ion experiments has commenced, including estimation of the shine-through and the orbit-losses. The stellarator has a wide-angle infra red (IR) imaging system to monitor the machine plasma facing component surface temperatures. This work validates the NBI model “Beamlet Based NBI (BBNBI)” and the newly written synthetic IR camera model. The validation is accomplished by comparing the measured and the synthetic IR camera measurements of an experiment where the NBI was injected into the vacuum vessel without a plasma. A good qualitative and quantitative match was found. This agreement is further supported by spectroscopic and calibration measurements of the NBI and and IR camera systems.

Achievement of ITER-relevant accelerated negative hydrogen ion current densities over 1000 s at the ELISE test facility

The neutral beam heating system for the future international fusion experiment ITER will be based on radiofrequency driven ion sources delivering a large (≈1 × 2 m) and homogeneous negative hydrogen or deuterium ion beam of severals tens of amperes for up to 1 h. Such beams have never been produced before and a dedicated R&D process has been ongoing for more than two decades. An important intermediate step is the size scaling test facility ELISE (Extraction from a Large Ion Source Experiment) with its half-ITER size ion source. Recently, ELISE has fulfilled its first main aim, demonstrating hydrogen ITER-relevant accelerated negative ion current densities over 1000 s, at the required filling pressure of 0.3 Pa, with an electron–ion ratio below one and a beam homogeneity better than 90%. The measures identified as essential for achieving such pulses are the introduction of external permanent magnets and internal potential rods as well as a dedicated caesium conditioning technique.

Measurements of beam current density and space potential in a highly focused ion beam of extremely low energy

Using an electrostatic double probe, profiles of the ion beam current density, electron density, and electron temperature were measured in the background plasma that appears by injecting a hydrogen ion beam into low-pressure hydrogen gas in a propagation chamber. The hydrogen ion beam is extracted using concave-shaped electrodes at extremely low energies (Eib = 60–120 eV). Focusing of the beam occurs when Eib exceeds a certain threshold. One probe electrode P3 is far from the beam source and is set in the shadow of another electrode in the beam trajectory. The ion saturation current in P3 is then estimated without considering the beam contribution. The measured electron densities are much larger than those of the ion beam density, the electron temperatures are very low (<1 eV), and the ion beam current densities exhibit fairly good agreement with those measured by Faraday cups. The profiles of the space potential are also estimated by measuring the potential of P3 with respect to ground with a voltage divider having an extremely high resistance. The space potentials obtained are quite low at <10 eV with focusing and ∼23 eV without focusing. The data with and without focusing are compared and conditions for focusing are examined. Focusing achieved through additional electron beam injection in the ground electrode is also examined. The results obtained indicate that a large electron source is required to balance the ion charges. Secondary electron emissions and/or small electron beam injection are effective sources.

Characteristics of cesium-free negative hydrogen/deuterium ion source by sheet plasma

The use of negative ion sources without Cs seeding is desired in neutral beam injectors of fusion experiments. We have designed a magnetized-sheet plasma that produces negative ions by volume production without Cs seeding. The developed system was experimentally tested on steady-state hydrogen and deuterium plasmas. The negative hydrogen ion beam was extracted by a two-grid extraction system located at the periphery of the sheet plasma. The negative hydrogen/deuterium ions were successfully extracted from the sheet plasma. The current densities of the ion beams increased with increasing discharge current. At an extraction voltage of 7 kV and a discharge current of 80 A, the approximate current densities of the negative hydrogen and deuterium ion beams were 3.8 and 1.2 mA/cm2, respectively.

Modeling of H/D isotope-exchange in crystalline beryllium

Abstract A reaction-diffusion model with surface occupation dependent desorption [D. Matveev et al., Nucl. Instr. Meth. B 430 (2018) 23–30] has been updated to handle multiple hydrogen species to simulate hydrogen/deuterium isotope-exchange experiments performed on polycrystalline beryllium samples under ultra-high vacuum laboratory conditions. In the experiments subsequent exposures of a sample to hydrogen and deuterium ion beams in direct and reverse implantation order were followed by thermal desorption spectroscopy measurements under a constant heating rate of 0.7 K/s. The recorded signals of masses 2 to 4 (H2, HD and D2) indicate that the second implanted isotope dominates clearly the low temperature release stage ( ≈ 450 K), while both isotopes show a comparable contribution to the high temperature desorption stage ( ≈ 700 K) with only minor effect of the implantation order attributed to a slightly deeper penetration of deuterium compared to hydrogen. Simulations of the implantation and subsequent thermal desorption of hydrogen isotopes are performed to assess the atomic processes behind the isotope-exchange. Simulations were performed under the assumption that the low temperature release stage is attributed to hydrogen/deuterium atoms retained on effective open surfaces (e.g. interconnected porosity) represented in the simulations by a surface with an effective surface area exceeding the nominal exposed surface area by a factor up to 100. Kinetic de-trapping from vacancies with multiple trapping levels and enhanced desorption at surface coverages close to saturation are addressed in the model as possible mechanisms promoting the isotope-exchange. Simulation results suggest the applicability of the model to describe isotope-exchange processes in crystalline beryllium and give a qualitative explanation of the observed experimental facts.

Plasma-immersion formation of high-intensity gaseous ion beams

The symbiosis of plasma-immersion extraction of ions and their subsequent ballistic focusing in the hemisphere geometry of the focusing system was used to form a high intensity nitrogen, argon, and hydrogen ion beams. The gas-discharge plasma was formed using a hot-cathode-arc discharge source. The regularities of the formation of high-intensity ion beams of various gases from according to the pressures of the working gases, the plasma density depending dependence on the bias potential amplitudes in the range of 0.9–2.4 kV, frequencies in the range of 10–100 kHz and pulse durations in the range of 2–80 μs were investigated. The possibility of the stable forming of axially symmetric gas ion beams with a current density of up to hundreds of mA/cm2 was shown. Nitrogen ion beams with a maximum current density of 0.7 A/cm2 at the ion current of 0.6 A were obtained. Studies at nitrogen pressures in the range of 0.3–1.8 Pa revealed that a decrease in the gas pressure during the generation of a gas-discharge plasma caused a significant increase in the ion current amplitude at the collector.

Thermo-mechanical analysis of unidirectional carbon-carbon composite for thermal imaging diagnostic of a particle beam

Unidirectional carbon fiber-carbon matrix (CFC) composite tiles can be used to diagnose the main features of a particle beam such as its power, divergence and uniformity. The diagnostic calorimeter STRIKE will be used with such an aim for the negative hydrogen ion beam produced by the ITER ion source prototype SPIDER, which is in operation at Consorzio RFX (Padova, Italy) since 2018.In the present work, a transient non-linear parametric finite element model developed in ANSYS and already validated on the basis of data collected in other test facilities, is used to predict the operational limits of STRIKE, i.e. at which performance (in terms of beam power, divergence and pulse duration) SPIDER may operate when the beam is dumped onto STRIKE. Powerful long lasting pulses in fact, may induce cracks in the tiles, affecting the heat transfer and thus limiting their diagnostic capability. The effects of different configurations for the STRIKE setup on the thermo-mechanical stresses are also discussed.