用于中性束注入的大功率射频离子源激励器研制

建立了一个等离子体射频激励器,工作气体为氢气,工作气压为0.3Pa,激励器陶瓷桶直径300mm,工作频率1MHz。实现了RF等离子体激发放电,在输入射频功率16kW条件下,采用朗缪尔探针测得的等离子体密度>10¹⁸m^-3,初步建立了一个RF等离子体源实验平台。     

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A radio frequency (RF) driven negative ion source for NBI purpose was established at HUST. The main parameters include: pressure of 0.3Pa, frequency of 1MHz, ceramic cylinder diameter of 300mm. With 16kW RF power input the plasma density is greater than 10¹⁸m^-3.     

Characteristics of electron cyclotron resonance plasma formed by lower hybrid current drive grill antenna

A 3.7 GHz system, which is meant for LHCD experiments on ADITYA tokamak, is used for producing ECR discharge. The ECR discharge is produced by setting the appropriate resonance magnetic field of 0.13 T, with hydrogen at a fill pressure of about 5 × 10⁻⁵ Torr. The RF power, up to 10 kW (of which ∼50% is reflected back), with a typical pulse length of 50 ms, is injected into the vacuum chamber of the ADITYA tokamak by a LHCD grill antenna and is used for plasma formation. The average coupled RF power density (the RF power/a typical volume of the plasma) is estimated to be ∼5 kW/m³. When the ECR appears inside the tokamak chamber for the given pumping frequency (f = 3.7 GHz) a plasma with a density (n _e) ∼ 4 × 10¹⁶ m⁻³ and electron temperature ∼8 eV is produced. The density and temperature during the RF pulse are measured by sets of Langmuir probes, located toroidally, on either side of the antenna. H_α signals are also monitored to detect ionization. An estimate of density and temperature based on simple theoretical calculation agrees well with our experimental measurements. The plasma produced by the above mechanism is further used to characterize the ECR-assisted low voltage Ohmic start-up discharges. During this part of the experiments, Ohmic plasma is formed using capacitor banks. The plasma loop voltage is gradually decreased, till the discharge ceases to form. The same is repeated in the presence of ECR-formed plasma (RF pre-ionization), formed 10 ms prior to the loop voltage. We have observed that (with LHCD-induced) ECR-assisted Ohmic start-up discharges is reliably and repeatedly obtained with reduced loop voltage requirement and breakdown time decreases substantially. The current ramp-up rates also decrease with reduced loop voltage operation. These studies established that ECR plasma formed with LHCD system exhibits similar characteristics as reported earlier by dedicated ECR systems. This experiment also addresses the issue of whether ECR plasma formed with grill antenna exhibits similar behavior as that formed by single waveguide ECR antenna. Our experimental observations suggest that the characteristics of (LHCD system-induced) ECR-assisted Ohmic start-up discharges show similar properties, reported earlier with normal ECR-assisted Ohmic start-up discharges and hence LHCD system may be used as ECR system at reduced toroidal magnetic field for other applications like wall conditioning.      

Study on the RF Power Necessary to Ignite Plasma for the ICP Test Facility at HUST

An Radio‐Frequency (RF) Inductively Coupled Plasma (ICP) ion source test facility has been successfully developed at Huazhong University of Science and Technology (HUST). As part of a study on hydrogen plasma, the influence of three main operation parameters on the RF power necessary to ignite plasma was investigated. At 6 Pa, the RF power necessary to ignite plasma influenced little by the filament heating current from 5 A to 9 A. The RF power necessary to ignite plasma increased rapidly with the operation pressure decreasing from 8 Pa to 4 Pa. The RF power necessary to ignite plasma decreased with the number of coil turns from 6 to 10. During the experiments, plasma was produced with the electron density of the order of 10¹⁶m^–3 and the electron temperature of around 4 eV. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

横流CWCO2激光器电子密度的研究

用Langmuir静电探针测量5kW横流CO_2激光器放电等离子体,根据P.R.Smy流动等离子体厚鞘理论进行分析,表明在工作气压力为42Torr、放电电流为10～20A的情况下,电子密度约为(1.7～3.1)x10~(11)cm~(-3)的范围内,并沿流向成非均匀分布,其极大值出现在距阳极板上游边沿3cm处.电子的连续性方程给实验结果以解释,理论与实验较好地符合.     

Numerical Study on Characteristics of Argon Radio-Frequency Glow Discharge with Varying gas Pressure

A one-dimensional fluid simulation on argon rf glow discharge with varying linearly gas pressure from 1 Torr to 100 Tort is performed. The model based on mass conservation equations for electron and ion under diffusion and mobility approximation, and the electron energy conservation equation is solved numerically by finite volume method. The numerical results show that a uniform plasma with high density can be obtained from rf glow discharge with varying gas pressure, and the density of plasma becomes higher as the gas pressure varies from 1 Tort to 100 Tort. It is also shown that in the range of the gas pressure from 1 Tort to 100 Tort with the slower rate of varying gas pressure, higher density of plasma can be obtained.     

Experimental study of a plasma-filled backward wave oscillator

Experimental studies of a plasma-filled X-band backward-wave oscillator (BWO) are presented. Depending on the background gas pressure, microwave frequency upshifts of up to 1 GHz appeared along with an enhancement by a factor of 7 in the total microwave power emission. The bandwidth of the microwave emission increased from ⩽0.5 GHz to 2 GHz when the BWO was working at the RF power enhancement pressure region. The RF power enhancement appeared over a much wider pressure range in a high beam current case (10-100 mT for 3 kA) than in a lower beam case (80-115 mT for 1.6 kA). The plasma-filled BWO has higher power output than the vacuum BWO over a broader region of magnetic guide field strength. Trivelpiece-Gould modes (T-G modes) are observed with frequencies up to the background plasma frequency in a plasma-filled BWO. Mode competition between the T-G modes and the X-band Tm₀₁ mode prevailed when the background plasma density was below 6×10¹¹ cm^-3 . At a critical background plasma density of ≃8×10¹¹ cm^-3 power enhancement appeared in both X-band and the T-G modes. Power enhancement of the S-band in this mode collaboration region reached up to 8 dB. Electric fields measured by the Stark-effect method were as high as 34 kV/cm while the BWO power level was 80 MW. These electric fields lasted throughout the high-power microwave pulse     

Experimental results of helicon sources

Helicon plasma sources are known as efficient generators of uniform and high density plasma.A helicon plasma source was developed for the investigation of plasma stripping and plasma lenses at the Institute of Modern Physics, CAS.In this paper, the characteristics of helicon plasma have been studied by using a Langmuir four-probe and a high plasma density up to 3.9×10~(13)/cm~3 has been achieved with the Nagoya type Ⅲ antenna.In the experiment, several important phenomena were found: (1) for a given magnetic induction intensity, the plasma density became greater with the increase of RF power; (2) helicon mode appeared at RF power between 300 W and 400 W; (3) the plasma density gradually tended to saturation as the RF power increased to the higher power; (4) a higher plasma density can be obtained by a good match between the RF power and the magnetic field distribution.The key issue is how to optimize the matching between the RF power and the magnetic field.Moreover, some tests on the extraction of ion beams were performed, and preliminary results are given.The problems which existed in the helicon ion source will be discussed and the increase in beam density will be expected by extraction system optimum.     

Power dependence of the reflection coefficient at lower hybrid heating

Due to the ponderomotive action of the radiofrequency (RF) field at the plasma edge, conditions for minimizing the power reflection coefficient R² can change considerably with increasing RF power. Dependences of R² on the unperturbed edge plasma density and on the RF power density are computed for a series of illustrative examples.In conclusion, we recall that the present theory is, strictly speaking, valid for long grills consisting of many waveguides.     

The Hydrogen Dissociator

A performance analysis is presented for the hydrogen dissociator used in hydrogen masers to provide a beam of atomic hydrogen. An analysis of the discharge characteristics yields relations for electron temperature as a function of vessel size and gas pressure and for plasma density as a function of power input. Also a relation between ion impact energy at the wall and electron temperature is derived. For a typical dissociator (2" diameter, 0.1 Torr hydrogen pressure, and 4 watt input power) these relationships yield an electron temperature of 39,000°K, a plasma density of 1011 cm-3 and an ion impact energy of 20 volts. The dissociation rate is calculated using published cross-sections. Assuming a recombination rate of 4 × 10-3, the analysis yields an atomic hydrogen density of about 1014 cm-3, a degree of dissociation of 2%, and an atomic beam flux of 1.3 × 1018 cm-2 × sec-1 for the example quoted. This beam flux is in good agreement with estimated values for hydrogen masers. A coefficient for performance ? is derived for the hydrogen dissociator, defined as the ratio of atomic beam flux to discharge power consumption. It is shown that ? is a function of the electron temperature and has a maximum at 87,000°K. It is concluded from this analysis that the discharge in presently used hydrogen dissociators is well optimized given the pressure constraints of the system.     

Anisotropic emission in laser-produced aluminum plasma in ambient nitrogen

We report on the dynamical expansion of pulsed laser ablation of aluminum in ambient pressure of nitrogen using images of the expanding plasma. The plasma follows shock model at pressures of 0.1 Torr and drag model at 70 Torr, respectively, with incident laser energy of 265 mJ. The plasma expansion shows unstable boundaries at 70 Torr and is attributed to Rayleigh-Taylor instability. The growth time of Rayleigh-Taylor instability is estimated between 0.09 and 4 μs when the pressure is varied from 1 to 70 Torr. The pressure gradients at the plasma-gas interface gives rise to self-generated magnetic field and is estimated to be 26 kG at 1 Torr ambient pressure using the image of the expanding plasma near the focal spot. The varying degree of polarization of Al III transition 4s ²S_1/2-4p ²P°_3/2 at 569.6 nm gives rise to anisotropic emission and is attributed to the self-generated magnetic field that results in the splitting of the energy levels and subsequent recombination of plasma leading to the population imbalance.     

Measurement of neutral gas temperature in inductively coupled plasmas

Dependence of the neutral gas temperature on the gas pressure and discharge power in an inductively coupled plasma source has been investigated using optical emission spectroscopy. Both nitrogen and argon plasmas have been studied separately. In the case of argon plasma, about 5% nitrogen was added to the total gas flow as an actinometer. The maximum temperature was found to be as high as 1850 K at 1 Torr working pressure and 600 W radiofrequency power. The temperature increases almost linearly with the logarithm of the gas pressure, but changes only slightly with the discharge power in the range of 100–600 W. In a nitrogen plasma, a sudden increase in the neutral gas temperature occurs when the gas pressure is increased at a given discharge power. This suggests a discharge-mode transition from the H-mode (high plasma density) to the E-mode (low plasma density). In the H-mode, the gas temperature is proportional to the logarithm of the gas pressure, as in the argon plasma. However, the gas temperature increases almost linearly with the discharge power, which is in contrast to the case of argon plasma. The electron density in the nitrogen plasma is about 10% of that in the argon plasma. This may explain the observation that the nitrogen neutral temperature is always lower than the argon neutral temperature under the same discharge power and gas pressure.     

上海光源储存环高频功率源

上海光源(SSRF)是一台能量为3.5GeV的中能第三代光源. 储存环的设计束流是300mA, 总的束流功率约625kW, 借鉴国际先进经验, 从THALES等公司引进500MHz 300kW (CW)高频发射机(包括速调管和相应的PSM型电源)及350kW (CW)环流器等作为三套高频功率源的主体, 一一供给三套超导高频腔, 加速电子以补偿其同步辐射以及其他功率损耗. 近一年来我们完成了储存环高频厅和其水冷、风冷、配电系统的建设, 4台速调管的制造厂验收测试, 三套发射机的就位安装和调试, 第一套发射机的现场验收测试, 第一台环流器的安装和高功率验收测试, 第一套高频功率源的高功率传输系统在不同反射相位下的满功率老炼. 第二、三套发射机的现场验收测试正在进行中, 预计10月份全部完成. 迄今为止所有的验收项目均达到技术指标. 本文简要地叙述了SSRF高频功率源的选型、技术指标、设计方案、总体布局, 重点介绍了现场验收测试的结果.     

Radial inhomogenity of plasma parameters in a low-pressure inductive RF discharge

This work is devoted to systematic investigation into the radial dependence of the plasma parameters of a low-pressure inductive radio-frequency (RF) discharge on pressure within a wide range of 0.8–1 Torr. Experimental results that were obtained under the considered pressures make it possible to analyze the patterns of the changes in plasma parameters upon both a nonlocal mode of discharge and a transition from a nonlocal to local mode of the RF power input. Discharges in helium, neon, argon, and krypton were considered. Experimental data were compared to the results of the numerical simulation of the inductive RF discharge using the particle-in-cell (PIC) method.     

Plasma parameters in a dual-camera low-power inductive RF discharge with an external magnetic field

The results from studying a dual-camera inductive radio-frequency (RF) discharge that was placed in an external magnetic field are presented. The operating conditions were as follows: an argon pressure of 5 × 10^–5–6 × 10^–2 Torr, an external magnetic field strength of 0–60 G, and an RF generator power supply of 25–300 W. During the experiment the resonant RF power consumption and the correspondence between the local power-consumption maxima and spatial maxima of the plasma concentration as a function of the external magnetic field were observed. The comparison of the experimental results with the results of the mathematical simulation indicates that the resonant character of the discharge is associated with the excitation of helicons and Trivelpiece–Gould waves.     

Dependence of resonance condition on pressure in an RF resonancemethod

The plasma density is shown as functions of pressure and magnetic flux density in an RF resonance method using the XPDP1 simulation code. The RF resonance method has the unique feature that a strong electric field in bulk controls the plasma density. Owing to the balance between the electric field decrease and the collision rate increase, the plasma density in the RF resonance method has a peak with respect to pressure. The plasma density with respect to the magnetic flux density depends on the condition of the RF resonance method, and the dependence is strong at low pressure because of the strong resonance. Sheath thickness is the most important parameter that determines the strength of the resonance induced. It is shown that the sheath thickness s is related to the plasma density n as a function of ns, obtained from a dispersion relation at constant external parameters. The magnetic flux density which induces the strong resonance is determined from sheath thickness. The plasma density in the RF resonance method can be predicted from discharge parameters using the relation between plasma density and sheath thickness     

Transients and efficient generation of electron beams in the pulsed wide-aperture glow discharge

The quasi-continuous wide-aperture glow discharge in helium at pressures from 1.2 to 6.0 Torr is studied. It is found that electron beam generation efficiency η is higher than 96% in the pressure range 1.2–3.0 Torr at voltages from 1.0 to 2.6 kV. The maximum power was ≈ 0 kW at 6 Torr and a voltage across the discharge gap of 2.6 kV. Under these conditions, the beam generation efficiency is about 80%. The pressure and voltage dependences of main parameters of the discharge are explained from the standpoint of its photoemission nature.     

Optical characterization of atmospheric‐pressure plasma needle

The atmospheric‐pressure plasma needle is a promising source that can be used efficiently for different industrial applications. A radio frequency (RF) (13.56 MHz) generator was used to generate a He–O₂/Ar mixture plasma. The ground‐state oxygen atomic density [O] was calculated as a function of discharge parameters by “actinometry”. The Ar‐I (2p₁ → 1s₂) line at 750 nm and the O‐I (³P → ³S) line at 844 nm were used to estimate the [O] atomic density. The rotational temperature T _R of He–O₂/Ar mixture was measured from the rotational levels of the “first negative system” (FNS) by using the “Boltzmann plot”. The effect of discharge parameters on the atomic oxygen density [O] and the gas temperature was monitored. These results show that [O] density increases with RF power and O₂ concentration, but decreases with the gas flow rate. Whereas the gas temperature increases with increase in the input RF power, it decreases with increase in the gas flow rate and O₂ concentration in the mixture. Since the [O] atomic density contributes to plasma‐based biomedical applications, the proposed optimum conditions for plasma‐based decontamination of heat‐sensitive materials in the present study are 0.6% oxygen, 500 sccm flow rate, and 26 W RF power.     

Power absorption corresponding to ion losses in parallel-plate RFdischarges

A simple model of a symmetric parallel-plate RF discharge is studied to illustrate how such discharges may absorb power from an RF power supply in order to sustain DC power losses corresponding to the steady acceleration of ions through the sheaths. The motions of the sheath boundaries over one period are derived assuming that the current density varies sinusoidally. One finds that the sheath thickness increases discontinuously at one sheath whenever the plasma contacts the opposing electrode. This implies that the external power supply delivers an electron pulse from the electrode at higher potential to the electrode at lower potential, so that some power is being absorbed in a pulsed fashion. The power absorbed by the discharge is also calculated for the portions of the RF cycle where the current varies sinusoidally. It is found that power is supplied by the discharge in this phase of the RF cycle, with the energy coming from the deflating sheaths. It is further shown that the sum of the pulsed power absorption and smooth power generation, averaged over one RF period, is equal to the DC ion power losses arising from ions falling through the time-averaged sheath potentials     

HL-2A 装置低杂波系统高功率速调管调试

建立了低杂波系统调试平台,在此平台上对4 只TH2103A 型高功率速调管及传输线主要部件进行了短脉冲调试,对每只速调管运行参数进行了优化和标定。在50kV/20A 的束电流条件下,速调管工作脉冲脉宽为30ms,4 只速调管输出功率分别为449kW、417kW、460kW 和450kW。测试数据和调试结果为下一步在HL-2A 装置上建设低杂波系统、开展物理实验等提供了重要的参考数据。