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Special Contribution

Negative hydrogen (H

本研究では、パラジウム金属およびタングステン金属の表面近傍領域での水素Fulcher-α(d^3π^-_u→a^3Σ^+_g) Q-Branchの発光分光分析により励起分子種を調査した。広域分光計はタングステンと比較して、パラジウム表面近傍で水素プラズマの発光スペクトル強度が高いことを示した。高分解能スペクトロメーターは、Fulcher-α [v = v´]＝0-4 の回転振動線を明確に分離し、パラジウムとタングステン表面近傍の水素の発光スペクトル線から回転温度([T_rot])を計算することができた。両方の金属ターゲットについて、負バイアス電圧が増加すると回転励起温度[T_rot]が上昇する傾向が観測された。パラジウムはタングステンに比べて、水素プラズマ中でのより多くの励起分子放出を示した。, Hydrogen plasma-metal surface interactions accompany molecular excitations and de-excitations associated with particle reflection at the surfaces. Optical light emissions from molecular species of the hydrogen Fulcher-α(d^3π^-_u→a^3Σ^+_g) Q-Branch at near metal surface region of palladium and tungsten metals were investigated. A wide wavelength range spectrometer indicated a higher emission spectrum of hydrogen plasma on the surface of palladium than tungsten. Meanwhile a high-resolution spectrometer showed the distinct rovibronic lines of the Fulcher-α for electronic levels [v = v´]＝0-4 transitions. Rotational temperature, [T_rot] , were computed from the emission spectra lines of hydrogen from palladium and tungsten surfaces. The obtained temperature, [T_rot] for both metal targets showed increase at increasing negative bias voltages applied onto the target of these materials. Hydrogen plasma on palladium surface indicated higher molecular excitations than that on the tungsten surface., 抄録中の^3,^-,^＋は上付き文字、_u,_g,_rotは下付き文字、[v＝v´],[T_rot]は斜体文字

A transverse beam profile monitor that visualizes a two-dimensional beam-induced fluorescent image was developed. The monitor employs a sheet-shaped gas flow formed by a technique of rarefied gas dynamics. A simplified analysis method was developed to reconstruct the beam intensity profile from the obtained image. The developed profile monitor and the analysis method were applied to measure the J-PARC 3 MeV ${\mathrm{H}}^{\ensuremath{-}}$ beam profile. The root mean square values of the profiles were consistent with the ones obtained by a wire-scanning-type beam profile monitor. The beam loss due to the gas sheet injection was measured as a beam-current reduction. The amount of the beam current decreased in proportion to the gas sheet flux and the reduction ranged from 0.004 to 2.5%. The assembled system was capable of reconstructing a beam profile from a single shot beam pulse ($1.7\ifmmode\times\else\texttimes\fi{}{10}^{13}$ protons in $50\text{ }\text{ }\ensuremath{\mu}\mathrm{s}$).

We compared the effect of a tantalum (Ta) fresh coating with that of a Ta thin sheet covering the plasma electrode of a negative hydrogen ion source on the ratio of extracted negative hydrogen (H−) ion current to extracted electron current. Fresh Ta evaporation from a thin hot Ta filament showed about a 22 % increase of extracted H− ion current compared to the operation with a tungsten (W) hot filament. On the other hand, a thin Ta foil covering the plasma electrode decreased the extracted electron current without a large influence on H- ion current. Meanwhile, when a titanium (Ti) foil covered the plasma electrode, both the extracted H− ion current and electron current decreased substantially. With a plasma electrode bias higher than the plasma potential, the ratio of H- ion current to the electron current for the Ti covered plasma electrode exceeded 80%.

The efficiency of negative hydrogen (H−) ion surface production in an ion source should be highly dependent upon the velocity distribution of atomic hydrogen (H0) striking the extraction electrode. A measurement system to observe the change in the H0 velocity distribution functions depending upon the method to excite the plasma has been designed, built and, is having its performance improved. The system equips a rotating blade neutral beam chopper to modulate the intensity of the neutral flux passing through the skimmer that separates the downstream chamber for time-of-flight analysis from the ion source discharge. After about 45 cm free flying vacuum space an electron impact type ionizer converts neutral particles to positive ions. A magnetic deflection type mass separator guides the produced protons and molecular ions to a secondary electron multiplier detector. The system demonstrated the existence of a high-speed component in the H0 time-of-flight (ToF) spectrum when it was tested with an ECR plasma source. Although the temperature change of hydrogen atoms obtained from the ToF spectra and that of hydrogen molecules were unclear, some hint of the particle acceleration due to discharge was observed.

One of the methods used to produce ions of metals and metal oxides is through extracting them from a magnetron sputter-type ion source. Metal nanoparticles, such as zinc oxide (ZnO), can be deposited using this method. However, low-energy conditions are required to prevent damage to the substrate. The extraction of ions from a differentially pumped, reactive magnetron sputtering source with a pulsed, conduit-type extraction electrode is investigated, with Zn as the metal target and argon and water vapor as discharge support and reactive gases, respectively. The use of water vapor has been shown to improve the properties of ZnO, through hydrogen doping. Using a quadrupole mass analyzer, the species produced from the ion source were detected and identified. Ar, H2O, H3O, and Zn ions were extracted using the pulsed extraction electrode, and the intensity of the extracted ions were found to be frequency dependent. Extraction of ions were observed starting from-40 V extraction potential using a Faraday cup, and the ion beam current appeared to increase in proportion to the extraction voltage. A mechanism for realizing ion extraction using an alternating extraction potential is proposed.

Doppler-spectroscopy study of hydrogen atoms reflected from a fuzzy tungsten (W-fuzz) surface was performed to investigate the effects of the W surface morphology upon the hydrogen particle reflection in low energy region less than 300 eV. The reflected atoms from the W-fuzz surface contributed to a tail part of Hα spectra measured in the vicinity of the surface negatively biased in a magnetized hydrogen plasma. Time evolution of the spectral intensity exhibited an increase of the hydrogen particle reflection coefficient correlated to the continuous removal of the porous fuzz structure due to the hydrogen-plasma bombardment. The initial particle reflection coefficient of hydrogen atoms from the porous W-fuzz surface was 50% lower in comparison to a smoother W surface following the removal of the fuzz structure.

A thermal cracking cell that served as the atomic hydrogen source for hydrogen attachment/abstraction dissociation (HAD) analysis has an intrinsic problem to produce a beam of atoms reactive against heated tungsten capillary. A plasma excited by 2.45 GHz microwave discharge can deliver reactive species to a quadrupole ion trap confining analyte ions without excessive heating of the radical source components. The radical (H•) production performance of the developed source was evaluated by optical emission spectroscopy and H• attachment reaction to fullerene ions. The source exhibited the H• attachment rate as high as a thermal cracking source forming H• in the high temperature tungsten capillary to induce fragmentation processes preserving post-translational modifications. Water vapor was introduced to the source to confirm the stability to generate oxygen containing radicals, which were found present in the water vapor plasma together with atomic hydrogen. Injection of radicals from a water vapor plasma s...

Spectroscopy study of reflected hydrogen atoms from a W surface under plasma bombardment was performed by measuring the $\text{H}\alpha $ emission spectra. The contribution from the reflected hydrogen atoms was confirmed at the outermost part of the Doppler-broadened $\text{H}\alpha $ spectra by suppressing the background light from the atomic and molecular excitations in the plasma. A mechanism of the collisional excitation with an H2 molecule is proposed to explain the excitation of the reflected atoms to the $n=3$ level in the region outside of the plasma column, where the background signal from the plasma was largely reduced. The measured spectra were compared with the reconstructed spectral profiles by Monte Carlo simulations using the atomic collision amorphous target code. This paper presents a promising method to collect fundamental data related to the recycling of hydrogen atoms near the edge region of fusion devices in the energy range below a few 100 eV.

Selected students' paper

We developed a small-size electron gun capable of producing electrons with kinetic energy less than few tens of eV to investigate the slowing down and transport mechanisms of electrons in hydrogen negative ion source plasmas. The maximum extractable beam current density reached 36 μA/cm2 for 1 eV beam energy in a preliminary experiment. Although the present electron current density is still insufficient compared with our target value, 1 mA/cm2, we have found some hints to realize larger beam current density from the electron gun through this study. The measured beam profile along the electron beam axis has shown that the electron beam could travel approximately 7 mm from the electron gun in vacuum. The Particle-In-Cell (PIC) simulation explained the measured beam profile well and indicated that the electron beam has an energy spread as small as 0.1 eV compared to the 1 eV mean energy. The PIC simulation showed a discrepancy from the measurement in the dependence of the electron beam current on the beam extraction voltage of the electron gun. It implies that we should introduce a more realistic filament structure inside the electron gun in the PIC simulation in order to study the transport of low energy electrons more precisely.

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.

A magnetic quadrupole lens system coupled to a 30° bending deflection magnet was designed and constructed to realize a beam focusing of Xe+ ions with the energy less than 200 eV. Compared to a triplet electrostatic quadrupole lens system, the quadrupole doublet magnetic lens system showed a larger beam transmission, indicating the mitigation of the space charge in the beam transport region free of the electrostatic field. The misalignment of the magnetic field axis was observed probably due to a slow change in magnetization of magnetic materials to construct the magnetic circuit of the quadrupole lens. A countermeasure to realign the beam axis by coupling the permanent magnets to trim coil electromagnets is proposed.

A miniature sized duoplasmatron ion source mountable on a standard 34 mm diameter copper gasket flange was designed, and its performance was tested. A hollow cathode exited a stable discharge in the anode through a 3 mm diameter orifice of the intermediate electrode with less than 10 W discharge power for Ar. The extracted ion beam current was larger at a smaller discharge current and was maximum at 5 mA below, where the discharge became unstable. A Faraday cup located 200 mm downstream of the extractor detected 1 µA beam current at 5 mA discharge current with 390 V discharge voltage and 2 kV extraction potential. The source required higher discharge voltage for operation of hydrogen gas.

A compact ion source that produces hydrogen plasma with an electron cyclotron resonance (ECR) configuration combined with a 2-stage extraction system with a single aperture of 6 mm diameter has been designed and built to study the performance of different materials as the plasma electrode (PE) of a negative hydrogen ion source. The source has the capability to electrically bias the PE with respect to the ECR plasma. The first experiment with low ECR power input (less than 40 W) was carried out. The PE of the C12A7 electride showed the largest H- current among aluminum, molybdenum, and the C12A7 electride.

When the working gas of a negative ion source is changed from hydrogen to its isotope, deuterium, an ‘isotope effect’ is observed; namely, several plasma characteristics such as the electron energy distribution, the atomic fraction and the spectra of rovibrationally excited molecules change. The understanding of the effect becomes more important, as research and development aiming at ITER power level operation is being challenged with feeding deuterium to the ion sources. As a historical review of the effort to develop hydrogen/deuterium negative ion sources, several types of negative ion sources designed for the neutral beam plasma heating are described: double charge exchange sources, volume sources and surface-plasma sources. The early results with volume sources operated with and without cesium are introduced. The characteristics of the source charged with deuterium are compared to those of the source charged with hydrogen. The isotope effect did not appear pronounced as the negative ion density was measured in a small source but became more pronounced when the plasma source size was enlarged and the discharge power density was increased to higher values. Surface plasma sources were optimized for deuterium operation but could not achieve the same performance as a source operated with hydrogen at the same power and pressure. The lower velocity of negative deuterium ions leaving the low work function surface seemed to limit the production efficiency. Fundamental processes causing these differences in negative ion source operation are summarized. After explaining the current status of negative ion source research and development, the acquired knowledge is utilized to the development of large negative ion sources for nuclear fusion research and to the development of compact negative ion sources for neutron source applications.

Lipids, a class of biomolecules, play a significant role in the physiological system. In this study, gas-phase hydroxyl radicals (OH·) and atomic oxygens (O) were introduced into the collision cell of a triple quadruple mass spectrometer (TQ-MS) to determine the positions of the double bond in unsaturated phospholipids. A microwave-driven compact plasma generator was used as the OH·/O source. The reaction between OH·/O and the precursor ions passing through the collision cell generates product ions that correspond to the double bond positions in the fatty acyl chain. This double bond position specific fragmentation process initiated by the attachment of OH·/O to the double bond of a fatty acyl chain is a characteristic of oxygen attachment dissociation (OAD). A TQ-MS incorporating OAD, in combination with liquid chromatography, permitted a high throughput analysis of the double bond positions in complex biomolecules. It is important to know the precise position of double bonds in lipids, since these molecules can have widely different functionalities based on the position of the double bonds. The assignment of double bond positions in a mixture of eight standard samples of phosphatidylcholines (phospholipids with choline head groups) with multiple saturated fatty acyl chains attached was successfully demonstrated.

In this Tutorial, surface and double charge exchange negative ion sources for producing negative ion beams of different ion species will be described. The need for negative ions as the beam particles of tandem Van de Graaf accelerators and that for charge exchange injection of hydrogen negative ions into high-energy proton accelerators requires the development of these ion sources, which are then enlarged to generate ampere level broad beams to heat up, after neutralization, the fusion experiment plasmas confined in magnetic field. The physical mechanisms leading to the formation of various negative ion species, such as hydrogen, helium, alkali metals, and halogens will be presented, and the ion source designs are analyzed based on the knowledge of fundamental processes related to negative ion formation and destruction. The use of negative ion sources in accelerators, nuclear fusion research, technology, and medicine will also be presented.

A duoplasmatron type ion source with a hollow cathode has been designed and the beam extraction performance under various discharge conditions tested. An ion beam extracted from a hydrogen plasma showed a clear peak of C 2 H 2 + in the mass spectrum with the source operation H 2 gas pressure of 5.2×10−3 Pa in the downstream of the extraction aperture, 20 mA discharge current, 616 V discharge voltage and 1 kV extraction voltage. Hydrogen plasma confinement in the beam extraction region of the ion source seems necessary to enhance molecular ion beam extraction from the source.

Electrostatic probes were utilized as tools to measure the space-charge-neutralization by a plasma flood gun (PFG). Thought the probes did not show ordinary current voltage characteristics in a dilute plasma in the ion beam propagation region, a clear shift of the local potential was identified with the method. The effectiveness of the PFG for the space-charge-neutralization was found dependent upon the distance from the PFG.

Aluminum nitride ion beams were extracted from a plasma sputter type ion source with an actively cooled Al sputter target. The Al target holds permanent magnets to form a magnetron magnetic field geometry and excites plasma by the applied 13.56 MHz RF voltage. The extracted ion beam current decreased as the temperature of the target increased due to plasma operation. The active air cooling of the target decreased the temperature to stabilize the intensity of the ion beam current. The active cooling also reduced the amount of dusts formed in the source during the plasma operation.

A negative hydrogen ion source delivers more beam current when Cs is introduced to the discharge, but a continuous operation of the source reduces the beam current until more Cs is added to the source. This behavior can be explained by adsorption and ion induced desorption of Cs atoms on the plasma grid surface of the ion source. The interaction between the ion source plasma and the plasma grid surface of a negative hydrogen ion source is discussed in correlation to the Cs consumption of the ion source. The results show that operation with deuterium instead of hydrogen should require more Cs consumption and the presence of medium mass impurities as well as ions of the source wall materials in the arc discharge enlarges the Cs removal rate during an ion source discharge.

Gas-phase hydrogen radicals were introduced into a quadrupole ion trap containing singly charged phospholipids to obtain structural fragmentation patterns in tandem mass spectrometry (MS/MS). Saturated and unsaturated phosphatidylcholines were used as a model phospholipid, whose chain-length ranges between 16 and 24. The MS/MS spectrum yielded a continuous series of fragment ions with a mass difference of 14 Da, representing the saturated fatty acyl chains. The fragment ions corresponding to the double-bond position within a single fatty acyl chain showed a characteristic mass difference of 12 Da. The detection of these diagnostic product ions enabled the structural analysis of double-bond isomers of phospholipids. To further investigate the potential of radical-induced dissociation for the isomeric analysis of phospholipids, gas-phase hydroxyl radicals, and triplet oxygen atoms were employed in tandem mass spectrometry. The methylene bridges adjacent to the double-bond positions were selectively dissociated, accompanied by oxidation of the double bonds. Tandem mass spectrometry incorporating multiple radical species facilitates the structural analysis of isomeric phospholipids.

長方形プラズマ源内で2.45 GHzのマイクロ波と永久磁石による磁場によってArプラズマを生成した。 ラングミュアプローブのアレイによって電子密度と電子温度の2次元空間分布を測定した。永久磁石の配列は電子密度と電子温度の分布に影響し、一方マイクロ波のアンテナと磁石の距離を変えるとマイクロ波の反射が変化した。均一なプラズマ形状になる最適な磁場の構造を議論した。, A power supply network at 2.45 GHz frequency coupled to a field produced by permanent magnets excited an Ar plasma in a rectangular-shape long-slot plasma source. Data measured with an array of Langmuir probe were utilized to construct the two dimensional spatial distribution of electron density and temperature. The arrangement of permanent magnets affected the distribution while the distance of the microwave antenna to the magnets changed the power reflection of the system. Structure of the magnetic field suitable to form homogeneous plasma is discussed.

Hydrogen ion reflection properties have been investigated following the injection of H+, H2+ and H3+ ions onto a polycrystalline W surface. Angle- and energy-resolved intensity distributions of both scattered H+ and H− ions are measured by a magnetic momentum analyzer. We have detected atomic hydrogen ions reflected from the surface, while molecular hydrogen ions are unobserved within our detection limit. The reflected hydrogen ion energy is approximately less than one-third of the incident beam energy for H3+ ion injection and less than a half of that for H2+ ion injection. Other reflection properties are very similar to those of monoatomic H+ ion injection. Experimental results are compared to the classical trajectory simulations using the ACAT code based on the binary collision approximation.

ナノクリルスタルフィルムは、純水素のECRプラズマ中でカーボンターゲットの前にシリコン基板を設置することにより作られる。そして、開口部に繋がれた四重極質量分析計により、カーボンターゲット表面に生成された分子の種類の分布を観察した。その結果、測定された気体の質量分布は、発生した炭化水素が化学スパッタリングによって生成されたものであることをはっきりと示した。また、マイクロウェーブアンテナの位置は、電気的なバイアスと同様にカーボンターゲットから生成される分子の種類に影響を与え、これらのパラメータは薄膜蒸着の状態を制御するのに利用することができる。, Nano-diamond thin film has been successfully prepared by placing a Si substrate in front of a carbon target in pure hydrogen electron cyclotron resonance plasma. A quadrupole mass analyzer coupled to an orifice monitored the molecular species distributions produced at the surface of the carbon target. The measured mass distribution of the gas had clearly indicated that the observed hydrocarbon emission was due to chemical sputtering of hydrocarbon. The position of the microwave antenna as well as the electrical bias affected the molecular species from the carbon target, and these parameters can be utilized as the tuning knobs to control the film deposition condition.

A compact ion source with the extraction energy less than 300 eV has been developed to study low-energy ion reflection from a metal surface. Extraction characteristics of atomic and molecular hydrogen ion beams were investigated by changing the wall materials of the discharge chamber to Ti, Ni, Mo, and stainless steel. The discharge chamber surface of the stainless steel produced the currents of 45 nA H+ and 550 nA H2+ beams. The latter current corresponds to particle flux of 1100 pnA(particle nanoamperes) of protons. The 300 eV H3+ ion beam with the Ti surface formed the particle flux of 1300 pnA of protons. The production of hydrogen atom particle flux was more efficient in the order from Ti, Mo, stainless steel to Ni. The 50 eV/u and 630 pnA of protons were extracted for the H3+ ion beam with the Ti surface.A compact ion source with the extraction energy less than 300 eV has been developed to study low-energy ion reflection from a metal surface. Extraction characteristics of atomic and molecular hydrogen ion beams were investigated by changing the wall materials of the discharge chamber to Ti, Ni, Mo, and stainless steel. The discharge chamber surface of the stainless steel produced the currents of 45 nA H+ and 550 nA H2+ beams. The latter current corresponds to particle flux of 1100 pnA(particle nanoamperes) of protons. The 300 eV H3+ ion beam with the Ti surface formed the particle flux of 1300 pnA of protons. The production of hydrogen atom particle flux was more efficient in the order from Ti, Mo, stainless steel to Ni. The 50 eV/u and 630 pnA of protons were extracted for the H3+ ion beam with the Ti surface.

Carbon cluster ion beams were produced utilizing a monoplasmatoron ion source with carbon cold hollow cathodes. Changing the gas injection position of the hollow cathode caused the difference in intensities and species of extracted ions. The pure carbon cluster ion beams were successfully produced at about 36 Pa Ar gas pressure in the ion source, 70 mA discharge current, 1 kV extraction voltage and focusing by an electrostatic lens system. The source operation was often limited by discharge extinction, possibly attributable to a rapid discharge pumping.

Surface production of negative hydrogen (H-) ions due to hydrogen atom impact has been confirmed in the actual ion source operating condition. Three types of atomic sources injected beams of atomic hydrogen (H0) into a cesiated/uncesiated hydrogen plasma confined in a small multicusp ion source. Hydrogen atoms produced by a thermal cracking and a microwave capacitively coupled plasma (CCP) sources decreased the amount of H− ions under the uncesiated conditions. Injection of hydrogen atoms from the thermal cracking source enhanced the H− ion current corresponding to the surface production at the plasma grid under the cesiated condition. Meanwhile, the H− ion enhancement by low temperature H0 injection from microwave discharge plasma was less pronounced. A series of experiments concluded that the electrons in high energy tails of the velocity distribution functions of produced hydrogen atoms from the CCP source and that from the thermal cracking source are capable to realize H− surface production.Surface production of negative hydrogen (H-) ions due to hydrogen atom impact has been confirmed in the actual ion source operating condition. Three types of atomic sources injected beams of atomic hydrogen (H0) into a cesiated/uncesiated hydrogen plasma confined in a small multicusp ion source. Hydrogen atoms produced by a thermal cracking and a microwave capacitively coupled plasma (CCP) sources decreased the amount of H− ions under the uncesiated conditions. Injection of hydrogen atoms from the thermal cracking source enhanced the H− ion current corresponding to the surface production at the plasma grid under the cesiated condition. Meanwhile, the H− ion enhancement by low temperature H0 injection from microwave discharge plasma was less pronounced. A series of experiments concluded that the electrons in high energy tails of the velocity distribution functions of produced hydrogen atoms from the CCP source and that from the thermal cracking source are capable to realize H− surface production.

A change in negative hydrogen (H-) ion current extracted from a cesiated H− ion source was observed by injecting an amplitude modulated hydrogen atomic beam. A 2.45 GHz microwave power excited hydrogen plasma for injecting atoms to the plasma grid of a multicusp H− ion source. Under a cesium-free condition, the atom injection increased the extracted H− ion current by nearly 50 %. The extracted H− ion current reached 2.5 times the initial value when a small amount of cesium was introduced to the ion source. The microwave plasma injection to the cesiated ion source decreased the extracted H− ion current by 13 %. The poor H− ion production by the atom injection can be attributed to a low temperature of the hydrogen atoms produced by the microwave plasma source.

In the Japan Proton Accelerator Research Complex (J-PARC), peak H− current of several tens of mA is produced from a cesiated hydrogen plasma generated by a solid-state radio-frequency (RF) amplifier with the frequency of 2 MHz. In case of the high-intensity H- beam extracted from the ion source, the plasma density in the source chamber is so high that the ion sheath around the beam extraction area follows the RF oscillation. Because the ion plasma frequency defined by the ion density is much higher than the driving frequency. The potential fluctuation of the plasma is combined with the driving RF electric field and causes motion of charged particles in the plasma. As a result, the H- beam extracted from the source plasma also fluctuates. The beam current signal from a Faraday cup was measured by a spectrum analyzer. A powerful frequency component at 2 MHz which is the same as that of the RF amplifier was also observed after the acceleration of a radio-frequency quadrupole (RFQ) linac located downstream of the ion source.

For an unique experimental approach to study low-energy electron transport in a plasma, a “sub” filament was introduced in a volume-produced, DC filament-driven hydrogen negative ion (H−) source as an additional electron source. The sub-filament engages in the special task which introduces additional electrons into the plasma with controlling injection energies. Transports of the additional electrons are observed by the difference of the electron density profiles with and without the electron introduction. The experimental result here indicates that the electron transport is strongly restricted by the filter magnetic field. On the other hand, analysis with Particle-In-Cell simulation seems to imply that the restriction by the magnetic field can be changed by the controlling electron energy in the sub-filament experiments for the research of the electron transport.For an unique experimental approach to study low-energy electron transport in a plasma, a “sub” filament was introduced in a volume-produced, DC filament-driven hydrogen negative ion (H−) source as an additional electron source. The sub-filament engages in the special task which introduces additional electrons into the plasma with controlling injection energies. Transports of the additional electrons are observed by the difference of the electron density profiles with and without the electron introduction. The experimental result here indicates that the electron transport is strongly restricted by the filter magnetic field. On the other hand, analysis with Particle-In-Cell simulation seems to imply that the restriction by the magnetic field can be changed by the controlling electron energy in the sub-filament experiments for the research of the electron transport.

Negative hydrogen (H−) ion density near the plasma electrode (PE) depends upon the materials which are absorbed the PE surface. Tungsten and tantalum were compared as adsorbates on the PE by means of evaporation from the filaments made of these elements in a hydrogen discharge plasma. The difference of the filament material against the plasma electrode bias voltage showed different characteristics of the extraction current and that of the H− ion current. For the tantalum filament operation, the photodetachment signal showed a dependence upon the PE bias similar to the one for the extraction current, while the tungsten filament operation indicated a plateau near the anode potential. In this paper, the possible reasons for observing the difference between W and Ta filament operations are discussed.

Key issues to fabricate a beam extraction system of a H− source with a plasma electrode (PE) made from C12A7 electride which has low work function were studied. Preliminary study of the H− extraction using a compact ECR ion source reveals, that high H− current can be extracted from a source without PE bias of high voltage. A bucket type with ECR source is being designed. Beam simulation for the extraction through the designed electrodes has been carried out using the OPERA code. It predicts that the optimum perveance is 0.6 mA/kV1.5, optimum acceleration to extraction voltage ratio Vacc/Vext is 4, with the minimum beam divergence of 9 mrad, which are enough to demonstrate the capability to produce a high H− current density.Key issues to fabricate a beam extraction system of a H− source with a plasma electrode (PE) made from C12A7 electride which has low work function were studied. Preliminary study of the H− extraction using a compact ECR ion source reveals, that high H− current can be extracted from a source without PE bias of high voltage. A bucket type with ECR source is being designed. Beam simulation for the extraction through the designed electrodes has been carried out using the OPERA code. It predicts that the optimum perveance is 0.6 mA/kV1.5, optimum acceleration to extraction voltage ratio Vacc/Vext is 4, with the minimum beam divergence of 9 mrad, which are enough to demonstrate the capability to produce a high H− current density.

Tantalum was compared with tungsten as filament material for negative ion extraction in the discharge of hydrogen and deuterium. For hydrogen discharge, tantalum filament operation showed about 40 % increase of negative hydrogen ion current and decrease of co-extracted electron current by 10 % against tungsten filament operation. Tantalum filament operation with deuterium indicated lower intensity of co-extracted electron current compared with tungsten while negative deuterium ion current showed slightly higher intensity. Dependence of extracted currents upon the plasma electrode bias voltage was linked to the local plasma parameters measured by a Langmuir probe. The effects due to the filament materials in hydrogen and deuterium plasmas are discussed.Tantalum was compared with tungsten as filament material for negative ion extraction in the discharge of hydrogen and deuterium. For hydrogen discharge, tantalum filament operation showed about 40 % increase of negative hydrogen ion current and decrease of co-extracted electron current by 10 % against tungsten filament operation. Tantalum filament operation with deuterium indicated lower intensity of co-extracted electron current compared with tungsten while negative deuterium ion current showed slightly higher intensity. Dependence of extracted currents upon the plasma electrode bias voltage was linked to the local plasma parameters measured by a Langmuir probe. The effects due to the filament materials in hydrogen and deuterium plasmas are discussed.

The consumption rate of cesium (Cs) for negative hydrogen (H-) ion source increases when the source operation gas is changed from hydrogen to deuterium. There was observed a clear indication that a deuterium discharge erodes Cs atoms on the plasma grid (PG) surface to increase work function and the co-extracted electron current. We have proposed a model, that the enhanced sputtering yield of Cs from the PG due to deuterium ions, which carries more kinetic energy to Cs adsorbed on the surface directly or indirectly, is the main reason for this fast dissipation of Cs. Introduction of helium (He) into discharge can verify the enhanced sputtering effect due to the lager mass ions in the source discharge. Comparing the effect due to seeded Cs before and after the He injection into discharge through Cs OES signals as well as the H- density measured with cavity ring-down method, the sputtering/evaporation enhancement due to He is estimated. Neutral atoms and positive ions in the He discharge should cause enhanced sputtering like deuterium, while the system does not generate neutron under the induction of acceleration voltage to diagnose the extracted negative ion beam. Plasma parameters of the H2 and He plasmas are investigated by diagnostics tools installed on NIFS-RNIS (National Institute for Fusion Science, Research and development Negative Ion Source) together with H- density measurement by cavity ring down. Enhanced consumption rate of Cs is compared with proposed sputtering yield data to predict the rate for deuterium operation of negative ion sources.