3D fluid model analysis on the generation of negative hydrogen ions for negative ion source of NBI

A radio-frequency(RF) inductively coupled negative hydrogen ion source(NHIS) has been adopted in the China Fusion Engineering Test Reactor(CFETR) to generate negative hydrogen ions.By incorporating the level-lumping method into a three-dimensional fluid model,the volume production and transportation of H^(-) in the NHIS,which consists of a cylindrical driver region and a rectangular expansion chamber,are investigated self-consistently at a large input power(40 k W) and different pressures(0.3–2.0 Pa).The results indicate that with the increase of pressure,the H^(-) density at the bottom of the expansion region first increases and then decreases.In addition,the effect of the magnetic filter is examined.It is noteworthy that a significant increase in the H^(-) density is observed when the magnetic filter is introduced.As the permanent magnets move towards the driver region,the H^(-) density decreases monotonically and the asymmetry is enhanced.This study contributes to the understanding of H-distribution under various conditions and facilitates the optimization of volume production of negative hydrogen ions in the NHIS.

Experimental results of a magnetic field modification to the radio frequency driver of a negative ion source

A magnetic field produced by a current flowing through the plasma grid(PG) is one of the solutions to reduce the collisional loss of negative ions in a negative ion source, which reduces the electron temperature in front of the PG. However, the magnetic field diffused into the driver has some influence on the plasma outflowing. In order to investigate the effect of changing this magnetic field on the outflowing of plasma from the driver, a circular ring(absorber) of high permeability iron has been introduced at the driver exit, which can reduce the magnetic field around it and improve plasma outflowing. With the application of the absorber, the electron density is increased by about 35%, and the extraction current measured from the extraction grid is increased from 1.02 A to 1.29 A. The results of the extraction experiment with cesium injection show that both the extraction grid(EG) current and H-current are increased when the absorber is introduced.

Hefei utility negative ions test equipment with RF source:commissioning and first results

In order to study the key technology and physics of RF driven negative ion source for neutral beam injector in China, the Hefei utility negative ions test equipment with RF source was developed at Institute of Plasma Physics, Chinese Academy of Sciences（ASIPP）. Its negative ion source can be equipped with single or double RF drivers. There is a plasma expansion chamber with depth of 19 mm and an enhanced filter field. A three electrodes negative ion accelerator was employed to extract and accelerate the negative ions, which are plasma grid,extraction grid and ground grid. And there are several diagnostic tools for the plasma and beam parameters measurement. The characteristics of plasma generation, negative ion production and extraction were studied on the test equipment. The negative ion beam was extracted from the RF driven negative ion source for the first time. The detailed structure and main results are presented in this article.

Negative Corona Discharge Ion Source Under Ambient Conditions with Mini Line-cylinder Electrodes

A novel ambient negative corona discharge ion source with mini line-cylinder electrodes is designed. The diameters of inner and outer electrode are 0.16 and 4 mm respectively. With a special assembly method, a perfect coaxiality of the two electrodes is obtained. An injection system utilizing a temperature control technique, achieves a constant and stable concentration of the sample, which is critical to the experiment. The formulas of the corona onset voltage of line-cylinder electrodes are also introduced. The experiment results show that negative substances such as formic acid and acetic acid can be ionized under ambient conditions. When combined with micro electrical mechanical system fabricationprocess, the volume of the ion source can be reduced dramatically, but there is an undesirable surface discharge. To solve the surface discharge problem, an improved structure was designed and tested. The simplicity of the interface of the ion source makes it suitable for mass spectrometer, micro mass spectrometer, ion mobility spectrometer, and high-field asymmetric waveform ion mobility spectrometer applications.

An analysis and preliminary experiment of the discharge characteristics of RF ion source with electromagnetic shielding

Combined with two-dimensional(2D)and three-dimensional(3D)finite element analysis and preliminary experimental tests,the effects of size and placement of the electromagnetic shield of the radio-frequency(RF)ion source with two drivers on plasma parameters and RF power transfer efficiency are analyzed.It is found that the same input direction of the current is better for the RF ion source with multiple drivers.The electromagnetic shield(EMS)should be placed symmetrically around the drivers,which is beneficial for the plasma to distribute uniformly and symmetrically in both drivers.Furthermore,the bigger the EMS shield radius is the better generating a higher electron density.These results will be of guiding significance to the design of electromagnetic shielding for RF ion sources with a multi-driver.

Power Law Distributions in the Experiment for Adjustment of the Ion Source of the NBI System

The experiential adjustment process in an experiment on the ion source of the neutral beam injector system for the HT-7 Tokamak is reported in this paper. With regard to the data obtained in the same condition, in arranging the arc current intensities of every shot with a decay rank, the distributions of the arc current intensity correspond to the power laws, and the distribution obtained in the condition with the cryo-pump corresponds to the double Pareto distribution. Using the similar study method, the distributions of the arc duration are close to the power laws too. These power law distributions are formed rather naturally instead of being the results of purposeful seeking.

Characteristics of the pressure profile in the accelerator on the RF negative ion source at ASIPP

Neutral beam injection(NBI)systems based on negative hydrogen ion sources-rather than the positive ion sources that have typically been used to date-will be used in the future magnetically confined nuclear fusion experiments to heat the plasma.The collisions between the fast negative ions and neutral background gas result in a significant number of high-energy positive ions being produced in the acceleration area,and for the high-power long-pulse operation of NBI systems,this acceleration of positive ions back to the ion source creates heat load and material sputtering on the source backplate.This difficulty cannot be ignored,with the neutral gas density in the acceleration region having a significant impact on the flux density of the backstreaming positive ions.In the work reported here,the pressure gradient in the acceleration region was estimated using an ionization gauge and a straightforward 1D computation,and it was found that once gas traveled through the acceleration region,the pressure dropped by nearly one order of magnitude,with the largest pressure drop occurring at the plasma grid.The computation also revealed that the pressure drop in the grid gaps was substantially smaller than that in the grid apertures.

The research progress of an E//B neutral particle analyzer

An E//B neutral particle analyzer(NPA)has been designed and is under development at Sichuan University and Southwestern Institute of Physics.The main purpose of the E//B NPA is to measure the distribution function of fast ions in the HL-2A/3 tokamak.The E//B NPA contains three main units,i.e.the stripping unit,the analyzing unit and the detection unit.A gas stripping chamber was adopted as the stripping unit.The results of the simulations and beam tests for the stripping chamber are presented.Parallel electric and magnetic fields provided by a NdFeB permanent magnet and two parallel electric plates were designed and constructed for the analyzing unit.The calibration of the magnetic and electric fields was performed using a 50 kV electron cyclotron resonance ion source(ECRIS)platform.The detection unit consists of 32lutetium-yttrium oxyorthosilicate(LYSO)detector modules arranged in two rows.The response functions ofα,hydrogen ions(H^(+),H_(2)^(+)and H_(3)^(+))andγfor a detector module were measured with^(241)Am,^(137)Cs and^(152)Eu sources together with the 50 kV ECRIS platform.The overall results indicate that the designed E//B NPA device is capable of measuring the intensity of neutral hydrogen and deuteron atoms with energy higher than 20 keV.

A NEW ELECTRON IMPACT STORAGE ION SOURCE

A new electron impact storage ion source has been designed for time of flight mass spectrometers with a high mass resolving power and high sensitivity. Because of the storage and compressing focus of the source, the overall performance of the instrument has been improved greatly with a mass resolving power up to 3 500. The conditions of the second order of the focus are given and the storage ability is proved. The competer simulations and experiment results are given, too.

Commissioning of a high-resolution collinear laser spectroscopy apparatus with a laser ablation ion source

Collinear laser spectroscopy is a powerful tool for studying the nuclear spins,electromagnetic moments,and charge radii of exotic nuclei.To study the nuclear properties of unstable nuclei at the Beijing Radioactive Ion-beam Facility(BRIF)and the future High Intensity Heavy-ion Accelerator Facility(HIAF),we developed a collinear laser spectroscopy apparatus integrated with an offline laser ablation ion source and a laser system.The overall performance of this state-of-the-art technique was evaluated,and the system was commissioned using a bunched stable ion beam.The high-resolution optical spectra for the 4s ^(2)S_(1/2)→4p^(2)P_(3/2)(D2)ionic transition of ^(40;42;44;48)Ca isotopes were successfully measured.The extracted isotope shifts relative to ^(40)Ca showed excellent agreement with the literature values.This system is now ready for use at radioactive ion beam facilities such as the BRIF and paves the way for the further development of higher-sensitivity collinear resonance ionization spectroscopy techniques.

The Development of a Megawatt-Level High Current Ion Source

Neutral beam injection is one of the main plasma heating methods in nuclear fusion devices. In order to support the scientific study of the Experimental Advanced Superconducting Tokamak （EAST）, a megawatt-level high current ion source is designed and manufactured in the ASIPP, and the progress and preliminary test results will be presented in this paper.

The development of data acquisition and processing application system for RF ion source

As the key ion source component of nuclear fusion auxiliary heating devices, the radio frequency （RF） ion source is developed and applied gradually to offer a source plasma with the advantages of ease of control and high reliability. In addition, it easily achieves long-pulse steady-state operation. During the process of the development and testing of the RF ion source, a lot of original experimental data will be generated. Therefore, it is necessary to develop a stable and reliable computer data acquisition and processing application system for realizing the functions of data acquisition, storage, access, and real-time monitoring. In this paper, the development of a data acquisition and processing application system for the RF ion source is presented. The hardware platform is based on the PXI system and the software is programmed on the LabVIEW development environment. The key technologies that are used for the implementation of this software programming mainly include the long-pulse data acquisition technology, multi- threading processing technology, transmission control communication protocol, and the Lempel-Ziv-Oberhumer data compression algorithm. Now, this design has been tested and applied on the RF ion source. The test results show that it can work reliably and steadily. With the help of this design, the stable plasma discharge data of the RF ion source are collected, stored, accessed, and monitored in real-time. It is shown that it has a very practical application significance for the RF experiments.

Energy properties and spatial plume profile of ionic liquid ion sources based on an array of porous metal strips

An ionic liquid ion source(ILIS)is a kind of high brightness ion source capable of providing high-speed positive or negative ion beams.This paper presents a miniaturized ILIS based on an array of porous metal strips.The porous emitter array,integrated with seven 10 mm long strips,is fabricated using wire electrical discharge machining(WEDM)combined with electrochemical etching.The assembled ILIS is 30 mm×30 mm×17.5 mm in size and weighs less than 25 g.A series of experiments,including anⅠ-Ⅴcharacteristic test,a retarding potential analyzer(RPA)test,and a spatial plume distribution test,have been conducted in vacuo to characterize the performance of the ILIS.Results show that the emitted current is up to about 800μA and ion transparency is as high as 94%.Besides,RPA curves reveal that the total fragmentation rate of the emitted particles accounts for 48.8%in positive mode and 59.8%in negative mode.Further,with the increase in applied acceleration voltage,the voltage loss rises while the energy efficiency decreases.It is also found that the plume perpendicular to the strips has a higher divergence than the one parallel to the strips.A numerical simulation by COMSOL reveals that the electric field distribution between the two electrodes results in such a spatial plume profile.

Laser ion source for heavy ion inertial fusion

The proposed heavy ion inertial fusion(HIF)scenarios require ampere class low charge state ion beams of heavy species.The laser ion source(LIS)is recognized as one of the promising candidates of ion beam providers,since it can deliver high brightness heavy ion beams to accelerators.The design of LIS for the HIF depends on the accelerator structure and accelerator complex following the source.In this article,we discuss the specifications and design of an appropriate LIS assuming two major types of the accelerators:radio frequency(RF)high quality factor cavity type and non-resonant induction core type.We believe that a properly designed LIS would satisfy the requirements of both types,while some issues need to be verified experimentally.

Diagnosing the Fine Structure of Electron Energy Within the ECRIT Ion Source

The ion source of the electron cyclotron resonance ion thruster （ECRIT） extracts ions from its ECR plasma to generate thrust, and has the property of low gas consumption （2 seem, standard-state cubic centimeter per minute） and high durability. Due to the indispensable effects of the primary electron in gas discharge, it is important to experimentally clarify the electron energy structure within the ion source of the ECRIT through analyzing the electron energy distribution function （EEDF） of the plasma inside the thruster. In this article the Langmuir probe diagnosing method was used to diagnose the EEDF, from which the effective electron temperature, plasma density and the electron energy probability function （EEPF） were deduced. The experimental results show that the magnetic field influences the curves of EEDF and EEPF and make the effective plasma parameter nonuniform. The diagnosed electron temperature and density from sample points increased from 4 eV/2 ×10^16 m-3 to 10 eV/4×10^16 m-3 with increasing distances from both the axis and the screen grid of the ion source. Electron temperature and density peaking near the wall coincided with the discharge process. However, a double Maxwellian electron distribution was unexpectedly observed at the position near the axis of the ion source and about 30 mm from the screen grid. Besides, the double Maxwellian electron distribution was more likely to emerge at high power and a low gas flow rate. These phenomena were believed to relate to the arrangements of the gas inlets and the magnetic field where the double Maxwellian electron distribution exits. The results of this research may enhance the understanding of the plasma generation process in the ion source of this type and help to improve its performance.

Diagnosis of Hydrogen Plasma in a Miniature Penning Ion Source by Double Probes

Parameters of hydrogen plasma in a miniature Penning discharge ion source, including the electron temperature and the electron density, were measured by using double probes. The results indicate that the electron density increases and the electron temperature decreases with the increase in gas pressure and the discharge current. The electron temperature is about 5 - 9 eV and the electron density is 6.0× 10^13 ～ 1.2 × 10^14 m^-3 while the discharge current is in a range of 50 - 120 μA.

Practical 2.45-GHz microwave-driven Cs-free Hˉ ion source developed at Peking University

A practical 2.45-GHz microwave-driven Cs-free H^- source was improved based on the experimental H^- source at Peking University（PKU）. Several structural improvements were implemented to meet the practical requirements of Xi＇an Proton Application Facility（XiPaf）. Firstly, the plasma chamber size was optimized to enhance the plasma intensity and stability. Secondly, the filter magnetic field and electron deflecting magnetic field were enhanced to reduce co-extracted electrons. Thirdly, a new two-electrode extraction system with farther electrode gap and enhanced water cooling ability to diminish spark and sputter during beam extraction was applied. At last, the direct H^- current measuring method was adopted by the arrangement of a new pair of bending magnets before Faraday cup（FC） to remove residual electrons. With these improvements, electron cyclotron resonance（ECR） magnetic field optimization experiments and operation parameter variation experiments were carried out on the H^- ion source and a maximum 8.5-mA pure H^- beam was extracted at 50 kV with the time structure of 100 Hz/0.3 ms. The root-mean-square（RMS） emittance of the beam is 0.25 Π·mm·mrad. This improved H^- source and extraction system were maintenance-free for more than 200 hours in operation.

Interaction between plasma and electromagnetic field in ion source of 10 cm ECR ion thruster

Through diagnosing the plasma density and calculating the intensity of microwave electric field,four 10 cm electron cyclotron resonance(ECR)ion sources with different magnetic field structures are studied to reveal the inside interaction between the plasma,magnetic field and microwave electric field.From the diagnosing result it can be found that the plasma density distribution is controlled by the plasma generation and electron loss volumes associated with the magnetic field and microwave power level.Based on the cold plasma hypothesis and diagnosing result,the microwave electric field intensity distribution in the plasma is calculated.The result shows that the plasma will significantly change the distribution of the microwave electric field intensity to form a bow shape.From the boundary region of the shape to the center,the electric field intensity varies from higher to lower and the diagnosed density inversely changes.If the bow and its inside lower electric field intensity region are close to the screen grid,the performance of ion beam extracting will be better.The study can provide useful information for the creating of 10 cm ECR ion source and understanding its mechanism.

Ion source effect on the bond length of ^4HeH^＋

The bond length of ^4HeH^＋ resulting from collision-induced destruction is measured at 1.4420 MeV using the Coulomb Explosion Technique. The measured bond length of ^4HeH^＋ is 0.094±0.003nm. The bond length of ^4HeH^＋ obtained with our radio frequency （RF） ion source is larger than that obtained with a duoplasmatron ion source at Argonne National Laboratory （ANL）, but the bond lengths of H^＋2 and H^＋3obtained separately by ANL and by us with the two different ion sources are consistent with each other, which implies that there exists an ion source effect on the bond length of ^4HeH^＋. The main reason why the 4^4HeH^＋ bond lengths obtained by the two different ion sources are different is also discussed.

Mechanical Analysis and Measurements of a Multicomponent NbTi/Cu Superconducting Magnets Structure for the Fully Superconducting Electron Cyclotron Resonance Ion Source

A fully superconducting electron cyclotron resonance （ECR） ion source （SECRAL ID is currently being built in the Institute of Modern Physics, Chinese Academy of Sciences. Its key components are three superconducting solenoids （Nb-Ti/Cu） and six superconducting sextupoles （Nb-Ti/Cu）. Different from the conventional supercon- ducting ECR magnetic structure, the SEC17AL Ⅱ includes three superconducting solenoid coils＇ that are located inside the superconducting sextupoles. The SECRAL Ⅱ can significantly reduce the interaction forces between the sextupole and the solenoids, and the magnets can also be more compact in size. For this multi-component SECRAL Ⅱ generating its self field of -8 T and being often exposed to the high self field, the mechanical analysis has become the main issue to keep their stress at 〈200 MPa on coils. The analytical and experimental results in mechanics are presented in the SECRAL Ⅱ structure. To improve the accuracy and efficiency of analysis, according to the composite rule of micromechanics, the equivalent uniform windings are used to simulate the epoxy-impregnated Nb-Ti/Cu coils. In addition, using low temperature strain gauges and a wireless fast strain acquisition system, a fundamental experiment on the based on our analysis, the stresses and deformations optimized. strains developments of a sextupole is reported. Finally, for its assembly of each SECRAL Ⅱ coil will be further