An improvement of high voltage power supply for pseudospark discharge

An analysis of the high voltage power supply removing the Pulse Forming Line (PFL) is presented in this paper. This is an important improvement to make a desktop free electron laser with about one meter length instead of an original device length of 5.5 meters and to realize other applications of the new beam source of pseudospark discharge at high voltage of 200kV and a current of 2kA.     

A Guided Field for Raman Free Electron Laser Could Be Removed with New Beam Source

A guided field is an important part for focusing the intense beam in Raman free electron laser. A new electron beam source with high brightness of 10¹²A/(m rad)² based on a pseudospark discharge was developed [1]. Numerical simulation showed that the guided field for compact free electron lasers could be removed using the new beam source. An electron beam with 12 kA current and 300 kV voltage was obtained. Self-pinch effect of high current beam was observed, the beam propagates 75 cm with constant diameter of 1.5 mm without guided field.     

高功率强流密度低发射度高亮度赝火花电子束产生

由修改了的脉冲线加速器驱动的、高功率(200kV)、高电流密度、低发射度、高亮度赝火花放电电子束在15pa氮气中产生。束流强度2.2kA,脉宽400ns,束径1mm的电子束从阳极口射出,可在中性氮电离通道中传输20cm。在阳极下游5cm处,电子束相继打穿紧密粘贴在一起的酸敏纸和0.05mm厚的铜箔,分别留下0.6mm和0.3mm的穿孔。依据箍缩平衡条件算出该处的高能电子束的归一化发射度和亮度分别是23πmm mrad和8×10¹⁰A/(m²rad²)。对同一酸敏纸连续轰击10次给出1.6mm穿孔表明它具有好的重复性。观察工作60枪后的放电室发现,各种电极和绝缘子表面几乎未见任何破坏性烧蚀痕迹。实验证明,赝火花电子束的束质量比冷阴极电子束的束质量要好得多。 关键词：     

Influence of the hollow cathode dimensions on the electron beamcurrent in a pseudospark discharge

Investigations on the electron beam current of a free running pseudospark discharge are presented. A single gap system with hollow cathodes of different dimensions is used. The filling gases are argon and helium. The electron beam signal consists of a first pulse with currents of several hundreds of mA and a main pulse with currents up to 20 A. A variation of length and diameter of the hollow cathode significantly influences the pressure range in which a free running pseudospark discharge exists and the peak current of both electron beam pulses. Plasma formation and electron beam generation are studied by high speed photography. The experimental results give some information on the discharge mechanisms that is integrated in a qualitative model of the pseudospark discharge     

不用导引磁场的虚火花束源拉曼自由电子激光器的数值计算

采用非线笥模型对拉曼自由电子激光器进行数值模拟,发现虚火花束源自由电子激光器苛以去掉导引磁场,用小周期摇摆器,实现器件的小型化和高功率。     

Laser action ofnd 8(n + 1)s 2 −nd 9(n + 1)p transitions in HgIII,Cull and AgII

A mechanism of the laser action of 5d ⁸ 6s ² –5d ⁹ 6p HgIII transitions is proposed. The explanation is based on atomic constants of the transitions and the predominant role of direct electron excitation of the upper laser level. The kinetic models of electron beam and hollow cathode discharge sources are calculated. The theoretical estimations are compared with experimental data and possible laser transitions are also proposed. The role of electron impact excitation in the formation of inverse population for two-electron transitions in CuII and AgII obtained in hollow cathode discharges is discussed.     

Discrete scale invariance and ln(B) periodic quantum oscillations in topological semimetals

The Panda X-4T experiment, a 4-ton scale dark matter direct detection experiment, is being planned at the China Jinping Underground Laboratory. In this paper we present a simulation study of the expected background in this experiment. In a 2.8-ton fiducial mass and the signal region between 1-10 keV electron equivalent energy, the total electron recoil background is found to be 4.9 × 10~(-5) kg~(-1) d~(-1) keV~(-1). The nuclear recoil background in the same region is 2.8 × 10~(-7) kg~(-1) d~(-1) keV~(-1). With an exposure of 5.6 ton-years, the sensitivity of Panda X-4 T could reach a minimum spin-independent dark matter-nucleon cross section of 6 × 10~(-48) cm~2 at a dark matter mass of 40 Ge V/c~2.     

Discharge and emission parameters of a plasma electron source based on a discharge in crossed E × H fields with various cathode materials

The possibility of using a plasma electron source (PES) with a discharge in crossed E × H field for compensating the ion beam from an end-Hall ion source (EHIS) is analyzed. The PES used as a neutralizer is mounted in the immediate vicinity of the EHIS ion generation and acceleration region at 90° to the source axis. The behavior of the discharge and emission parameters of the EHIS is determined for operation with a filament neutralizer and a plasma electron source. It is found that the maximal discharge current from the ion source attains a value of 3.8 A for operation with a PES and 4 A for operation with a filament compensator. It is established that the maximal discharge current for the ion source strongly depends on the working gas flow rate for low flow rates (up to 10 ml/min) in the EHIS; for higher flow rates, the maximum discharge current in the EHIS depends only on the emissivity of the PES. Analysis of the emission parameters of EHISs with filament and plasma neutralizers shows that the ion beam current and the ion current density distribution profile are independent of the type of the electron source and the ion current density can be as high as 0.2 mA/cm² at a distance of 25 cm from the EHIS anode. The balance of currents in the ion source-electron source system is considered on the basis of analysis of operation of EHISs with various sources of electrons. It is concluded that the neutralization current required for operation of an ion source in the discharge compensation mode must be equal to or larger than the discharge current of the ion source. The use of PES for compensating the ion beam from an end-Hall ion source proved to be effective in processes of ion-assisted deposition of thin films using reactive gases like O₂ or N₂. The application of the PES technique makes it possible to increase the lifetime of the ion-assisted deposition system by an order of magnitude (the lifetime with a Ti cathode is at least 60 h and is limited by the replacement life of the deposited cathode insertion).     

高亮度虚火花电子束发射度的测量

介绍了对一台脉冲线加速器驱动虚火花放电装置产的电子束发射度的测量工作。在十隙虚火花放电室中育以１５Ｐａ的氮气，产生能量为约２００ｋｅＶ，束流２０００Ａ，直径为１ｍｍ和高亮度电子束。在距阳极５ｃｍ处测得电子束的均方根发射度εｒｍｓ≈４８ｍｍ．ｍｒａｄ，规一化发射率εｎ≈４７ｍｍ．ｍｒａｄ。     

Short-pulse, high-brightness X-ray production with the PLEIADES Thomson-scattering source

PLEIADES is a compact, tunable, high-brightness, ultra-short-pulse, Thomson-scattering X-ray source. Picosecond pulses of hard X-rays (10–200 keV) are created by colliding an ultra-relativistic (20–100 MeV), picosecond-duration electron beam with a high-intensity, sub-picosecond, 800-nm laser pulse. Initial operation of this source has produced 78-keV X-rays with 10⁶ photons per pulse using a 57-MeV, 0.3-nC, 50-m rms width electron beam and a 180-mJ, 15-m rms width laser pulse. The angular distribution, energy, and energy spectrum of the source are found to agree well with theory and simulations. Source optimization is expected to increase X-ray output to between 10⁷ and 10⁸ photons per pulse with a peak brightness approaching 10²⁰ photons/s/0.1% bandwidth/mm²/mrad². PACS 41.50.+h; 07.85.Fv; 41.75.Ht; 42.62.-b     

Investigation on the pseudospark electron beam and its applicationfor the generation of soft X-rays

An investigation on the pseudospark electron beam is presented in this paper. Time-integrated and time-resolved pictures of the X-rays generated by the electron beam are taken with a special X-ray pinhole camera. They show the spatial and temporal development of the pseudospark electron beam. Time-integrated pictures indicate spatial instabilities of the electron beam caused by a bent or broadened electron beam due to space charge effects. The results of the time-resolved measurements show X-ray emission only during two short periods at the very beginning of the discharge before the beam current reaches its maximum. Only during these periods does the electron beam contain high-energy electrons. In between these two periods the energy of the beam electrons decreases because of a space-charge-limited beam transport     

Wide-aperture electric-discharge XeCl lasers

Experimental investigations have been performed for aXeCl laser with the active region aperture equal to 6.5×7 and 15×15 cm. To pump the laser, two types of generator were used: a generator connected in a double-loop circuit with a peaking capacitor and a multichannel spark gap switch and a magnetic thyratron generator. The working mixtureNe−Xe−HCl was preionized with soft x rays and a low-current electron beam, providing an initial electron density ranging from 10⁶ to 5·10¹³ cm⁻³. Conditions in which a homogeneous space discharge is initiated have been studied. It has been investigated how the degree of ionization of the gas and the aperture of the active region affect the discharge and lasing characteristics of the laser. The laser efficiency reaches 4% with an energy of ≈ 6 J extracted from one liter of the active region. Institute of High-Current Electronics, Siberian Division of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 54–59, April, 2000.     

Production of YBa2Cu3O7−x superconducting thin films by pulsed pseudospark electron beam evaporation

Thin-film superconducting YBa₂Cu₃O_7–x layers have been produced in a single-step process by pulsed electron beam evaporation from a stoichiometric 1-2-3 target. The films were produced at the 100 surface of SrTiO₃ substrates heated to a temperature of approximately 1000 K in a pure oxygen atmosphere of about 10 Pa total pressure. After deposition the films were cooled in situ within 20 minutes to ambient temperature. At present, the films are polycrystalline and show a T_c,zero of 83 K with a transition width of 3–5 K. Critical current densities of 7·10⁴ A/cm² at 4.2 K and zero magnetic field have been achieved. The pulsed electron beams used in these experiments are produced by a pseudospark discharge; the estimated energy density deposited at the target surface by the electron beam is of the order of 4 J/cm².     

Fast electron energy deposition in aluminium foils: Resistive vs. drag heating

The high current electron beam losses have been studied experimentally with 0.7 J, 40 fs, 6 10¹⁹ Wcm^-2 laser pulses interacting with Al foils of thicknesses 10-200 μm. The fast electron beam characteristics and the foil temperature were measured by recording the intensity of the electromagnetic emission from the foils rear side at two different wavelengths in the optical domain, ≈407 nm (the second harmonic of the laser light) and ≈500 nm. The experimentally observed fast electron distribution contains two components: one relativistic tail made of very energetic (T _h ^tail ≈ 10 MeV) and highly collimated (7° ± 3°) electrons, carrying a small amount of energy (less than 1% of the laser energy), and another, the bulk of the accelerated electrons, containing lower-energy (T _h ^bulk=500 ± 100 keV) more divergent electrons (35 ± 5°), which transports about 35% of the laser energy. The relativistic component manifests itself by the coherent 2ω₀ emission due to the modulation of the electron density in the interaction zone. The bulk component induces a strong target heating producing measurable yields of thermal emission from the foils rear side. Our data and modeling demonstrate two mechanisms of fast electron energy deposition: resistive heating due to the neutralizing return current and collisions of fast electrons with plasma electrons. The resistive mechanism is more important at shallow target depths, representing an heating rate of 100 eV per Joule of laser energy at 15 μm. Beyond that depth, because of the beam divergence, the incident current goes under 10¹² Acm^-2 and the collisional heating becomes more important than the resistive heating. The heating rate is of only 1.5 eV per Joule at 50 μm depth.     

Neutralization of an ion beam from the end-Hall ion source by a plasma electron source based on a discharge in crossed E × H fields

The possibility of using a plasma electron source (PES) with a discharge in crossed E × H field for compensating the ion beam from an end-Hall ion source (EHIS) is analyzed. The PES used as a neutralizer is mounted in the immediate vicinity of the EHIS ion generation and acceleration region at 90° to the source axis. The behavior of the discharge and emission parameters of the EHIS is determined for operation with a filament neutralizer and a plasma electron source. It is found that the maximal discharge current from the ion source attains a value of 3.8 A for operation with a PES and 4 A for operation with a filament compensator. It is established that the maximal discharge current for the ion source strongly depends on the working gas flow rate for low flow rates (up to 10 ml/min) in the EHIS; for higher flow rates, the maximum discharge current in the EHIS depends only on the emissivity of the PES. Analysis of the emission parameters of EHISs with filament and plasma neutralizers shows that the ion beam current and the ion current density distribution profile are independent of the type of the electron source and the ion current density can be as high as 0.2 mA/cm² at a distance of 25 cm from the EHIS anode. The balance of currents in the ion source-electron source system is considered on the basis of analysis of operation of EHISs with various sources of electrons. It is concluded that the neutralization current required for operation of an ion source in the discharge compensation mode must be equal to or larger than the discharge current of the ion source. The use of PES for compensating the ion beam from an end-Hall ion source proved to be effective in processes of ion-assisted deposition of thin films using reactive gases like O₂ or N₂. The application of the PES technique makes it possible to increase the lifetime of the ion-assisted deposition system by an order of magnitude (the lifetime with a Ti cathode is at least 60 h and is limited by the replacement life of the deposited cathode insertion).     

Pseudospark produced pulsed electron beam for material processing

An intense pulsed electron beam produced by a pseudospark discharge is used for material processing. The electron beam propagates in a self-focused manner in the background gas. Hardly 12 ns after the beginning of the discharge the fraction of space charge neutralization is about 96%. To sustain the neutralization effect high energy electrons (E <500 keV) are accelerated in radial direction at the beam head, due to strong electric field gradients. At current maximum the beam pinches due to its own magnetic field. At peak current of 400 A and charging voltage up to 16 kV power density reaches 10⁹ W/cm ² on the target surface. Some results of copper thin films are presented. Due to the high expansion velocity of 10⁴ m/s of the ablated target material a copper-matrix has been masked     

A CW DCN waveguide laser of high volumetric efficiency

This paper describes a CW submillimeter waveguide laser operating on 190 and 195 μm DCN lines with high volumetric efficiency. The laser cavity is a 3.2 cm inner diameter, 70 cm long, Pyrex tube with plane reflectors (one of them is a copper mesh) against its ends. After optimization of various parameters (such as the N₂:CD₄:He gas mixture, the pressure and the discharge current, the wall temperature and the output coupling), this laser, with only 57 cm long active discharge, delivers 8.4 and 7.6 mW on the 190 and 195 μm lines, respectively, for the EH₁₁ mode. This represents volumetric powers of 75 and 65 μW cm^-3. The free space propagation of the EH₁₁ fundamental mode was found to be as for a gaussian beam, and the absorption of the laser beam in the atmosphere was also measured.     

Low energy ion beams by laser interaction

We developed an ion accelerator with a double accelerating gap system supplied by two power generators of different polarity. The ions were generated by laser ion source technique. The laser plasma induced by an excimer KrF laser, freely expanded before the action of accelerating fields. After the first gap action, the ions were again accelerated by a second gap. The total acceleration can imprint a maximum ion energy up to 160 keV per charge state. We analysed the extracted charge from a Cu target as a function of the accelerating voltage at laser energy of 9, 11 and 17 mJ deposited on a spot of 0.005 cm². The peak of current density was 3.9 and 5.3 mA for the lower and medium laser energy at 60 kV. At the highest laser energy, the maximum output current was 11.7 mA with an accelerating voltage of 50 kV. The maximum ion dose was estimated to be 10¹² ions/cm². Under the condition of 60 kV accelerating voltage and 5.3 mA output current the normalized emittance of the beam measured by pepper pot method was 0.22 π mm mrad.     

一种非拦截式束流强度测量方法的研究

介绍了用圆柱型容性感应探针进行非拦截式束流强度测量的方法。该方法利用测量束流相宽和中心相位的感应探针同时进行束流强度的监测, 以满足HIRFL束流诊断的在线测控要求;说明了采用数字示波器测量束流感应信号并从中提取束团相宽及束流强度等信息的原理。介绍了测量系统装置及虚拟仪器技术在本系统中的应用,并给出了初步实验结果和测量精度的分析。     

Predicted emittance and brightness of the pseudospark electron-beam

The emittance and brightness of the electron beam generated during the hollow cathode phase of pseudospark operation are calculated using the two-dimensional hybrid fluid-particle model previously developed to study the time and space development of the plasma in a pseudospark discharge. Two distinct energy components exist in the electron beam; a high-energy component with an energy equivalent to the full discharge voltage and another, broad, low-energy component. In the 100 ns following breakdown and for the conditions of the calculations, the emittance of the high energy component decreases by an order of magnitude and the brightness of the high energy component reaches almost 10¹⁰ A/m² rad². This work demonstrates the feasibility of using the model to guide the optimization of the pseudospark electron beam properties and shows that the optimum beam properties are achieved after the plasma has filled the hollow cathode and begun to expand radially in the main gap