A study of pulsed high voltage driven hollow-cathode electron beam sources through synchronous optical trigger

In this study,a pulsed,high voltage driven hollow-cathode electron beam sources through an optical trigger is designed with characteristics of simple structure,low cost,and easy triggering.To validate the new design,the characteristics of hollow-cathode discharge and electron beam characterization under pulsed high voltage drive are studied experimentally and discussed by discharge characteristics and analyses of waveform details,respectively.The validation experiments indicate that the pulsed high voltage supply significantly improves the frequency and stability of the discharge,which provides a new solution for the realization of a high-frequency,high-energy electron beam source.The peak current amplitude in the high-energy electron beam increases from 6.2 A to 79.6 A,which indicates the pulsed power mode significantly improves the electron beam performance.Besides,increasing the capacitance significantly affects the highcurrent,lower-energy electron beam more than the high-energy electron beam.

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.

Feasibility study of the photonuclear reaction cross section of medical radioisotopes using a laser Compton scattering gamma source

In recent years,the gap between the supply and demand of medical radioisotopes has increased,necessitating new methods for producing medical radioisotopes.Photonuclear reactions based on gamma sources have unique advantages in terms of producing high specific activity and innovative medical radioisotopes.However,the lack of experimental data on reaction cross sections for photonuclear reactions of medical radioisotopes of interest has severely limited the development and production of photonuclear transmutation medical radioisotopes.In this study,the entire process of the generation,decay,and measurement of medical radioisotopes was simulated using online gamma activation and offline gamma measurements combined with a shielding gamma-ray spectrometer.Based on a quasi-monochromatic gamma beam from the Shanghai Laser Electron Gamma Source(SLEGS),the feasibility of this measurement of production cross section for surveyed medi-cal radioisotopes was simulated,and specific solutions for measuring medical radioisotopes with ultra-low production cross sections were provided.The feasibility of this method for high-precision measurements of the reaction cross section of medical radioisotopes was demonstrated.

Development of plasma sources for Dipole Research EXperiment(DREX)

Dipole Research EXperiment（DREX） is a new terrella device as part of the Space Plasma Environment Research Facility（SPERF） for laboratory studies of space physics relevant to the inner magnetospheric plasmas. Adequate plasma sources are very important for DREX to achieve its scientific goals. According to different research requirements, there are two density regimes for DREX. The low density regime will be achieved by an electron cyclotron resonance（ECR） system for the ‘whistler/chorus＇ wave investigation, while the high density regime will be achieved by biased cold cathode discharge for the desired ‘Alfvén＇ wave study. The parameters of ‘whistler/chorus＇ waves and ‘Alfvén＇ waves are determined by the scaling law between space and laboratory plasmas in the current device. In this paper, the initial design of these two plasma sources for DREX is described. Focus is placed on the chosen frequency and operation mode of the ECR system which will produce relatively low density ‘artificial radiation belt＇ plasmas and the seed electrons, followed by the design of biased cold cathode discharge to generate plasma with high density.

Anode Plasma Influence on Breakdown Formation in Explosive-Emission Electron Sources

Breakdown formation in the explosive-emission sources is related to the interelectrode gap filling with the cathode and anode plasma generated at the anode and in the gap under the beam influence. Under conditions of saturation of the cathode plasma emissive ability as well as when the measures on the emission boundary stabilization are taken, the anode plasma has the deciding part in the formation of the electron source breakdown. The paper presents the results of the anode plasma investigations obtained to solve the problem of the electron beam length increase in the explosive-emission sources. The data concerning the gas release from the anode, the mechanism of the anode plasma formation and the anode plasma influence on the parameters of the generated electron beam are presented as well.

Formation of a Quasi-Stationary Discharge in the Explosive-Emission Electron Sources

Formation of a quasi-stationary discharge or quasi-stationary emission mode in the explosive-emission electron sources is related to the current limitation resulting from the emissive ability saturation of cathode plasma with its expansion. The paper shows that in the process of the discharge current stabilization in the explosive-emission sources with the point- or blade-type emitters the essential role belongs to the electron beam space charge. Availability of the space charge results in limitation of the current growth velocity at the initial discharge phase and, hence, restricts the emissive ability of the cathode plasma and contributes to its saturation. In the vacuum diodes with multiemitter cathodes, the space charge availability increases the cathode operation stability and can provide obtaining of quasi-stationary beam current values or close to them resulting in formation of a plasma emission surface at the cathode close to the continuous one.

Discharge Stabilization and Obtaining of Quasi-Stationary Electron Beams in Explosive-Emission Sources

Quasistationary discharge mode setting in the explosive-emission sources is related to the saturation of the cathode plasma emissive ability resulting in the decrease of the velocity of plasma propagation into the interelectrode gap. It was shoran previously that the electron beam space charge providing the current rise slowing-down is of great importance in the process of the discharge mode stabilization. The paper considers a possibility of the discharge protraction at the expense of decrease of the ion charge order in the plasma composition and application of the directed plasma flows. The data concerning obtainig of micro- and millisecond electron beams in the explosive-emission sources are presented as well.

Focused electron beam transport through a long narrow metal tube at elevated pressures in the forevacuum range

We present here our investigations of the features of focused electron beam transport in free space at elevated pressures of a few pascals.We have explored the effect of the beam accelerating voltage,operating gas pressure,and magnetic focusing upon the trajectory of beam electrons in the crossover region,in particular on the beam convergence and divergence angles.It is shown that for the forevacuum pressure range of 2-5 Pa explored,a distinctive feature of the propagation of a focused electron beam with a current of up to 20 mA at an accelerating voltage of 10-20 kV is the difference in the angles of convergence(before the focus)and divergence(after the focus).Whereas at a low pressure of 2 Pa the divergence angle is smaller than the convergence angle,as the pressure increases the divergence angle increases and for pressures greater than 5 Pa the divergence angle is greater than the convergence angle.The results obtained were used in experiments on electron beam transport through a long narrow metal tube with a diameter of 5.8-9.2 mm and length of 10-30 cm.We show that for a 30 cm long tube of 7.5 mm diameter,the focused beam transmission can exceed 70%.

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.

Factors Influencing the Electron Yield of Needle-Ring Pulsed Corona Discharge Electron Source for Negative Ion Mobility Spectrometer

A simple negative ion mobility spectrometer （IMS） is designed and used to investi- gate the factors that influence the number and efficiency of electrons generated by the needle-ring pulsed corona discharge electron source. Simulation with Ansoft Maxwell 12 is carried out to analyze the electric field distribution within the IMS, and to offer the basis and foundation for analyzing the measurement results. The measurement results of the quantities of electrons show that when the drift electric field strength and the ring inner diameter rise, both the number of ef- fective electrons and the effective electron rate are increased. When the discharge voltage becomes stronger, the number of effective electrons goes up while the effective electron rate goes down. In light of the simulation results, mechanisms underlying the effects of drift electric field strength, ring inner diameter, and discharge voltage on the effective electron number and effective electron rate are discussed. These will make great sense for designing negative ion mode IMS using the needle-ring pulsed corona discharge as the electron source.

Structure and Mechanical Properties of CrN Thick Films Deposited by High-Rate Medium-Frequency Magnetron Sputtering

A home-made electron source assisted medium-frequency （MF） magnetron sputter- ing system was used to deposit thick CrN films on silicon and tungsten carbide substrates at various nitrogen flow rates with a fixed total pressure （0.3 Pa） and MF power （11.2 kW）. Result from scanning electron microscopy showed that the deposited CrN films have clear columnar struc- ture, and X-ray diffraction revealed a preferred orientation of CrN （200） for samples prepared at a rate of N2/（N2＋Ar） below 60%, whereas those prepared at higher N2/（N2＋Ar） rate are dom- inated by Cr2N. Deposition rates up to 12.5 μm/h were achieved and the hardness of the CrN coatings were in a range of 11 GPa to 18 GPa.

Study of electron-extraction characteristics of an inductively coupled radio-frequency plasma neutralizer

Inductively coupled radio-frequency（RF） plasma neutralizer（RPN） is an insert-free device that can be employed as an electron source in electric propulsion applications.Electron-extraction characteristics of the RPN are related to the bulk plasma parameters and the device＇s geometry.Therefore,the effects of different electron-extraction apertures and operational parameters upon the electron-extraction characteristics are investigated according to the global nonambipolar flow and sheath model.Moreover,these models can also be used to explain why the electron-extraction characteristics of the RPN strongly depend upon the formation of the anode spot.During the experimental study,two types of anode spots are observed.Each of them has unique characteristics of electron extraction.Moreover,the hysteresis of an anode spot is observed by changing the xenon volume-flow rates or the bias voltages.In addition,the rapid ignited method,gas-utilization factor,electron-extraction cost and other factors that need to be considered in the design of the RPN are also discussed.

Three dimensional photovoltaic fibers for wearable energy harvesting and conversion

As the development of smart electronics, self-powered sources have been attracting increasing attention.This review summarizes research progress of photovoltaic fibers and their integrated power sources with multi-stage energy conversion. Recent development of three dimensional photovoltaic fibers is glanced with special attention to structure design and materials of typical photovoltaic types（inorganic, organic,dye/quantum dot sensitized and perovskite solar cells）. The application of carbon materials in fiber energy is focused as it is a hot topic recently. The hybrid energy systems based on fiber solar cells and fiber supercapacitors, fiber batteries and fiber nanogenerators are summarized together with hybrid energy textiles. This review provides a macroscopic view of novel energy fibers and will attract research interest in flexible/wearable fiber electronics and energy textiles.

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

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.

Passive magnetic shielded spin polarized electron source with optical electron polarimeter

A new GaAs（100） spin polarized electron source with an optical polarimeter, which is employed in the field of polarized electron and gas atom collision, is presented in detail. The apparatus is passive-magnetic-shielded by a box and a cylinder made of nickel-iron-molybdenum soft magnetic alloy without Helmholtz coil arrangement. And a uniformly distributed residual magnetic field of less than 5 × 10^-7T is obtained near the collision area. The spin polarized electron beam is transmitted and focused onto collision point from photocathode by a set of electron optics with more than 25% transmission 95 cm distance through an 1 mm diameter aperture. Construction and operation of the apparatus, such as vacuum and magnetic shielding system, photocathode, laser optics, electron optics and polarimeter are discussed. The polarization of the spin polarized electron beam is determined to be 30.8 ±3.5% measured with a He optical polarimeter.

A PHOTOEMISSIVE MONOENERGETIC ELECTRON SOURCE FOR CALIBRATING THE BETA－MAGNETIC SPECTROMETER

A new kind of electron source, the photoemissive monoenergetic electron source has been invented for calibrating the beta--magnetic spectrometer. It produceselectrons in the form of simulating a radioactive monoenergetic electron source andcan be made in any shape and size according tO the demands of experimentS. In thispaper, the principles and basic constructions of the photoemissive monoenergeticelectron source are described, the resultS of calibrating our 2’l’x bead--magneticspectrometer with a single strip arc shaped photoemissive monoenergetic electronsource are listed, a new way for determining resolution function of experimentslsystem in the research of neutrino rest mass has been posed and one of its actualapplications is also given.

Study of temporal evolution of emission spectrum in a steeply rising submillimeter burst

The temporal evolution of a spectrum during a steeply rising submillimeter（THz） burst that occurred on 2003 November 2 was investigated in detail for the first time.Observations show that the flux density of the THz spectrum increased steeply with frequency above 200 GHz.Their average rising rates reached a value of 235 sfu GHz^（-1）（corresponding to spectral index α of 4.8） during the burst.The flux densities reached about 4 000 and 70 000 sfu at 212 and 405 GHz at the maximum phase,respectively.The emissions at 405 GHz maintained such a continuous high level that they largely exceeded the peak values of the microwave（MW） spectra during the main phase.Our studies suggest that only energetic electrons with a low-energy cutoff of~ 1 MeV and number density of ~ 10~6-10~8 cm^（-3） can produce such a strong and steeply rising THz component via gyrosynchrotron radiation based on numerical simulations of burst spectra in the case of a nonuniform magnetic field.The electron number density N,derived from our numerical fits to the THz temporal evolution spectra,increased substantially from 8 ×10~6 to 4 × 10~8 cm^（-3）,i.e.,the N value increased 50 times during the rise phase.During the decay phase it decreased to 7 ×10~7 cm^（-3）,i.e.,it decreased by about five times from the maximum phase.The total electron number decreased an order of magnitude from the maximum phase to the decay phase.Nevertheless,the variation in amplitude of N is only about one time in the MW emission source during this burst,and the total electron number did not decrease but increased by about 20%during the decay phase.Interestingly,we find that the THz source radius decreased by about 24%while the MW source radius,on the contrary,increased by 28%during the decay phase.

Understanding hydrogen plasma processes based on the diagnostic results of 2.45 GHz ECRIS at Peking University

Optical emission spectroscopy（OES）, as a simple in situ method without disturbing the plasma, has been performed for the plasma diagnosis of a 2.45 GHz permanent magnet electron cyclotron resonance（PMECR） ion source at Peking University（PKU）. A spectrum measurement platform has been set up with the quartz-chamber electron cyclotron resonance（ECR） ion source [Patent Number： ZL 201110026605.4] and experiments were carried out recently. The electron temperature and electron density inside the ECR plasma chamber have been measured with the method of line intensity ratio of noble gas. Hydrogen plasma processes inside the discharge chamber are discussed based on the diagnostic results. What is more, the superiority of the method of line intensity ratio of noble gas is indicated with a comparison to line intensity ratio of hydrogen. Details will be presented in this paper.

Influence of Cathode Plasma on Breakdown Formation in Plasma-Anode Explosive-Emission Source

Breakdown formation in an explosive-emission electron source is related to the interelectrode gap filling with plasma propagating from the cathode and formed at the anode and in the interelectrode gap under the electron beam action. Plasma anode is used to increase the beam current density. Preliminary interelectrode gap filling with plasma in the explosive-emission source decreases the influence of uncontrolled plasma arrival from the anode on the diode processes, promotes current density increase and duration of generated electron beams. The paper considers the influence of the cathode geometry on the breakdown formation in the plasma-anode explosive-emission electron source. The data on obtaining of microsecond electron beams with current density of 30 A/cm^2 and 1.5-2 kA/cm^2 are presented.