Operation Mode on Pulse Modulation in Atmospheric Radio Frequency Glow Discharges

The discharge operation regime of pulse modulated atmospheric radio frequency(RF) glow discharge in helium is investigated on the duty cycle and frequency of modulation pulses.The characteristics of radio frequency discharge burst in terms of breakdown voltage, alpha(α)-gamma(γ) mode transition voltage and current are demonstrated by the discharge current voltage characteristics. The minimum breakdown voltage of RF discharge burst was obtained at the duty cycle of 20% and frequency of 400 k Hz, respectively. The α-γ mode transition of RF discharge burst occurs at higher voltage and current by reducing the duty cycle and elevating the modulation frequency before the RF discharge burst evolving into the ignition phase, in which the RF discharge burst can operate stably in the γ mode. It proposes that the intensity and stability of RF discharge burst can be improved by manipulating the duty cycle and modulation frequency in pulse modulated atmospheric RF glow discharge.     

Optimum beam duty cycle for coincidence experiments

It is argued that continuous beam is commonly thought to be ideal for a coincidence experiment because it minimizes the false coincidence rate. A false coincidence rate up to a factor of two lower can be obtained (for fixed average current) by a pulsed beam with relatively short pulses separated by the resolution time of the detector. The micropulse structure of the beam is discussed. Most RF accelerators produce a train of micropulses within a macropulse during which the RF is on. Macropulse timing is generally very long compared to resolution times, hence a macropulse structure that is continuous is desirable. An analysis is given of the errors associated with different duty cycle lengths     

高频单腔加速器的束流动力学和数值计算

文章介绍的束流动力学与高频谐振腔数值计算相结合的方法,可以简化常规束流动力学计算,也为谐振腔的优选提供了重要的判断标准。同时给出了将此方法用于高频单谐振腔加速器设计时所得到的一些主要结果。     

Study of possibilities for a spin flip in high energy electron ring HERA

In a high energy electron ring the spins of electrons become spontaneously polarized via the emission of spin-flip synchrotron radiation. By employing a radio frequency radial dipole field kicker, particle spin directions can be rotated slowly over many turns. A model which couples three dimensional spin motion and longitudinal particle motion was constructed to describe nonequilibrium spin dynamics in high energy electron storage rings. The effects of a stochastic synchrotron radiation on the orbital motion in the accelerator synchrotron plane and its influence on the spin motion are studied. The main contributions to the spin motion, the synchrotron oscillations and the stochastic synchrotron radiation, have different influence on the spin polarization reversal in different regions of the parameter space. The results indicate that polarization reversal might be obtained in high energy electron storage rings with a significant noise even with relatively small strengths of a perturbing magnetic field. The only experimental datum available agrees with the model prediction, however further experimental data would be necessary to validate the model.     

Investigation of NO removal using a pulse-assisted RF discharge

In this paper,removal of nitrogen oxide (NO) is investigated in capacitive atmospheric pressure discharges driven by both radio-frequency (RF) and trapezoidal pulsed power with a onedimensional self-consistent fluid model.The results show that the number density of NO could be reduced significantly once a short pulse of low duty ratio is additionally applied to the RF power.It is found that the process of NO removal by the pulse-modulated RF discharge could be divided into three stages:the quick reaction stage,the NO removal stage,and the sustaining stage.Furthermore,the temporal evolution of particle densities is analyzed,and the key reactions in each stage are discovered.Finally,the influence on the removal efficiency of the voltage amplitude of the pulse and the RF voltage amplitude is investigated.     

Numerical simulation of atmospheric pulse-modulated radio-frequency glow discharge ignition characteristics assisted by a pulsed discharge

A one-dimensional self-consistent fluid numerical model was developed to study the ignition characteristics of a pulse-modulated(PM) radio-frequency(RF) glow discharge in atmospheric helium assisted by a sub-microsecond voltage excited pulsed discharge. The temporal evolution of discharge current density and electron density during PM RF discharge burst was investigated to demonstrate the discharge ignition characteristics with or without the pulsed discharge. Under the assistance of pulsed discharge, the electron density in RF discharge burst reaches the magnitude of 1.87 × 10~(17) m~(-3) within 10 RF cycles, accompanied by the formation of sheath structure. It proposes that the pulsed discharge plays an important role in the ignition of PM RF discharge burst. Furthermore, the dynamics of PM RF glow discharge are demonstrated by the spatiotemporal evolution of the electron density with and without pulsed discharge. The spatial profiles of electron density, electron energy and electric field at specific time instants are given to explain the assistive role of the pulsed discharge on PM RF discharge ignition.     

Beam dynamics,RF measurement,and commissioning of a CW heavy ion IH-DTL

A 53.667 MHz CW(continuous-wave) heavy ion IH-DTL has been designed for the SSC-LINAC injector of HIRFL-CSR(Heavy Ions Research Facility at Lanzhou-Cooling Storage Ring). It accelerates ions with maximum mass-to-charge ratio of 7.0 from 143 to 295 ke V/u. Low-power RF measurement of the IH-DTL1 has been taken to investigate the RF performance and the quality of the electric field distribution on the beam axis.The measured Q_0 value and the shunt impedance are 10,400 and 198 MX/m, respectively. The electric field distributions on and around the beam axis were evaluated and compared with the design value. By a new approach,the dipole field component is also estimated. The beam dynamics simulation using measured field distribution was presented in this paper. Based on the dynamics analysis in both transverse and longitudinal phase space, the field distribution can meet the design requirement. Finally, the RF conditioning and very first beam commissioning on the IH-DTL1 were finished. The beam test results agree well with the simulation results; what's more, the property of the variable output beam energy about the separated functions DTL was verified.     

A Study on Plasma Polymerization of Acrylic Acid Using APF Plasma Focus Device

The most conventional way for polymerization of acrylic acid on different substrates is using RF devices and introducing of other devices is under way. In this work we have a new study on formation of polymer Acrylic Acid using APF plasma focus device. The formation of plasma polymer acrylic acid is discussed using results obtained from attenuated total reflectance infrared spectroscopy (ATR). The results show that after 15 shots, nitrogen pulses performed polymerization on the specimens and the main peaks of ATR spectra assured poly acrylic acid formation on SBR substrate.     

Simulation studies on two-frequency RF gun

Photocathode RF gun is widely used for particle accelerators as an electron source.When driving an RF electron gun at the fundamental frequency and a higher harmonic frequency simultaneously with proper field ratio and relative phase,it generates electron beams of ultralow emittance and a linear longitudinal phase space distribution.Such a gun provides high quality electron beam with low energy spread,small traverse emittance and high brightness.In this paper,the RF design of a 1.5 cell cavity is presented.Simulation results of beam dynamics for the two-frequency gun and a standard single-frequency RF gun are also shown in this paper.In addition,bunch compression with a two-frequency gun is explored.     

Diagnostics of Argon Inductively Coupled Plasma and Dielectric Barrier Discharge Plasma by Optical Emission Spectroscopy

1. IntroductionArgon plasma has been frequently used for mate-rial processing and film fabrication processes [1l [21 [31.The efficiency of these processes has very close rela-tion with plasma parameters [4][5], such as ion den-sity, electron temperature and ion energy dlstrlbu-tion. Lots of research has been done on the relation-ship between efficiency and availability of materialprocessing and plasma parameters [6][7].Both lCP dlscharge and DBD discharge are newtype plasma systems developed…     

Introduction to the Principles of NMR

The idea of resonance is introduced and its spectroscopic value discussed. It is shown how intrinsic nuclear spin leads to a magnetic moment and macroscopically observable magnetization. The dynamics of this magnetization and the associated relaxation mechanisms are described and the manipulation of the spin magnetization is shown.     

Time domain measurement of spin-dependent recombination – A novel defect spectroscopy method

A new defect characterization method is suggested which we call Time Domain Measurement of Spin-Dependent Recombination (TSR). Time resolved spin-dependent recombination rate changes in a semiconductor that is exposed to a strong magnetic field are measured. These rate changes are triggered by a spin resonant excitation of recombination centers and charge carriers through short and intensive microwave pulses. The coherence of the charge carrier–recombination center pair ensemble is already destroyed during the pulse by fast recombination processes of the recombining pairs. After the pulse, a slow relaxation of the recombination rate into its steady state takes place which is caused by the dissociation of the recombination partners. Unlike Electrically Detected Magnetic Resonance (EDMR) which can only detect and quantify distinct recombination centers, TSR opens access to a variety of qualitative and quantitative information about electronically active defects due to the dependence of the signal transient on the various parameters. Particularly because of the possibility to measure recombination probabilities of distinct recombination paths directly, TSR could be a promising new approach to defect spectroscopy. The feasibility of TSR is demonstrated with the dangling bond recombination path of microcrystalline silicon.     

Experimental study of a single tube high RF power amplifier for ICRF heating system

A concept of a single tube high RF power amplifier was developed for ion cyclotron range of frequency (ICRF) plasma heating system. In the concept, a tetrode was used with a grounded cathode and input power to drive a control grid of the tetrode was provided by a switching circuit. As the new amplifier arrangement can eliminate a low power (10 kW level) and an intermediate power (100 kW level) tetrode amplifiers, their high voltage DC (HVDC) power supplies, and control and monitor system for these amplifiers and HVDC power supplies in a conventional high RF power source of the ICRF heating system, this new high RF power source is more flexible on frequency change and more mechanically reliable than the conventional one. A test amplifier composed of the tetrode and a field effect transistor (FET) switching circuit was constructed. The FET switching circuit was so compact that it could be mounted close to the tetrode socket. The maximum output RF power of 8.5 kW was obtained with a plate efficiency of 82% at 70 MHz. The feasibility of the single tube high RF power amplifier was experimentally proved. The plate efficiency of 82% could not be explained by the standard class-C amplification but by high efficiency amplification under assumptions of a flat-topped plate current pattern and double resonance of an output cavity at the fundamental frequency and the third higher harmonic frequency.     

600kV强流毫微秒脉冲加速器中的前切割与后聚束系统

介绍了６００ｋＶ强流微秒脉冲加速器中束流脉冲化系统的物理设计、工艺结构特点、粒子动力学计算、聚束腔的静态特性调整与测量、高频功率发射系统以及载束实验结果。     

325 MHz高功率波导窗设计研究

为了使漂移管加速结构运行更加稳定,传输功率可更好地馈入质子直线加速器中,本文对漂移管加速结构的波导窗进行设计与研究。利用微波仿真软件CST对波导窗的结构进行计算,并通过改善匹配结构对射频参数进行分析及优化。通过仿真结果计算频率带宽、电场分布及功率损耗。最终对波导窗进行热分析,通过公式计算所需冷却水的流量。结果表明,该波导窗可应用于325 MHz加速结构中。     

Acceleration of heavy ions with a new RF system at HIMAC synchrotron

A fast three-dimensional scanning irradiation method is under development at the Heavy Ion Medical Accelerator in Chiba (HIMAC) as the next stage of heavy ion cancer therapy. This method requires highly accurate control of the beam size, energy, and intensity. To improve the accelerated beam’s quality, a new scheme for the synchrotron RF system has been developed. The new system adopts a periodic time clock system (T-clock) instead of an ordinary B-clock system. The new T-clock system is synchronized with a power line frequency of 50 Hz for synchronization with the synchrotron power supply. An ordinary B-clock system results in error pulses owing to the small analog signal of the magnetic field of the main dipole magnet, and the errors cause dipole oscillation of the beam in the RF bucket. Using the new T-clock generator at 192 kHz, we have observed an improvement in the acceleration efficiency and bunch shape compared to the B-clock generator.     

质子直线加速器控制系统硬件的扩充和改进

本文介绍了北京35.5 MeV质子直线加速器控用系统扩充时遇到的两个问题及解决办法。1.采用普通CAMAC A/D插件,稍加修改用来采集脉冲电流幅值,可节省复杂而昂贵的采样保持器。2.为了使出来脉冲严格和市电50 Hz同步以保证加速器的束流稳定,研制出一种基准定时脉冲产生器NIM插件,既可满足严格与市电同步,又能方便地任意设置出束周期。     

RADI—A RF source size-scaling experiment towards the ITER neutral beam negative ion source

IPP Garching is currently developing a negative hydrogen ion RF source for the ITER neutral beam system. The source demonstrated already current densities in excess of the ITER requirements (>200 A/m² D⁻) at the required source pressure and electron/ion ratio, but with only small extraction area and limited pulse length. A new test facility (RADI) went recently into operation for the demonstration of the required (plasma) homogeneity of a large RF source and the modular driver concept.The source with the dimension of 0.8 m × 0.76 m has roughly the width and half the height of the ITER source; its modular driver concept will allow an easy extrapolation in only one direction to the full size ITER source. The RF power supply consists of two 180 kW, 1 MHz RF generators capable of 30 s pulses. A dummy grid matches the conductance of the ITER source. Full size extraction is presently not possible due to the lack of an insulator, a large size extraction system and a beam dump.The main parameters determining the performance of this “half-size” source are the negative ion and electron density in front of the grid as well as the homogeneity of their profiles across the grid. Those will be measured by optical emission and cavity ring down spectroscopy, by Langmuir probes and laser detachment. These methods have been calibrated to the extracted current densities achieved at the smaller source test facilities at IPP for similar source parameters. However, in order to get some information about the possible ion and electron currents, local single aperture extraction with a Faraday cup system is planned.     

基于模拟贝努里试验的随机脉冲发生器的实现

利用EPLD器件模拟了n维贝努里试验,通过改变其参数,得到符合二项分布、泊松分布以及高斯分布的随机脉冲。当信号满足泊松分布时,脉冲平均计数率可达100kHz,最小时间间隔为100ns。对电路分别作了一定时间内脉冲计数统计分布检验和脉冲时间间隔分布检验,证明在时间特性上可用于仿真一般核信号源。     

Beam Dynamics Study for CYCIAE-100

To meet the need of the installation of the RF cavities, the hill gap is increased from 5 cm to 6 cm in the central region, and from 4 cm to -5 cm at the outer region so as to provide space for the RF liner. In the meantime, the space between the hills in the central region brings an easier engineering design of the centering coils. However, for such kind of compact machine, the fringe field at both sides of the sector magnet is quite important for the vertical focusing. So, the basic geometry is studied again and the field distribution is produced for beam dynamics study.