兰州重离子回旋加速器主场电源改造

为满足分离扇回旋加速器（SSC）对于磁场精度的需求,需对其主场电源进行改造。提出开关电源与线性电源相结合的方式作为SSC主场电源的改造方案。电源总体分为两部分,采用模块化的开关电源作为前级电压源,三极管线性调整电路作为后级模块的主电路,充分利用两种电源的优势,实现高稳定度、低纹波的电流输出,同时大幅度提升电源的功率密度和可靠性。文章介绍了电源的工作原理及改造过程,详细阐述了三极管线性放大原理以及管压降控制电路、输出电流控制电路的设计与实现,通过仿真对电路进行功能验证,最终在电源样机上进行实验测试。测试结果表明:改造后主场电源输出电流稳定度达到了±3.99×10?6,电流纹波达到了2.7×10?9,各项性能均优于改造前。     

低温辐射计紫外探测器光谱响应度测试技术研究北大核心CSCD

通过研制真空多光路切换组件,结合Y型真空比较通道、探测器真空舱,在保证超高真空环境的前提下,实现激光、紫外连续可调单色光以及真空紫外单色光3个光路的快速切换,从而以低温辐射计为基准,以紫外增强硅陷阱探测器为传递标准,实现波长115 nm~400 nm紫外探测器绝对光谱响应度的测量,实验验证绝对光谱响应度测量不确定度在115 nm~230 nm可达到0.8%~1.5%(k=2),在230 nm~400 nm可达到0.5%~1.0%(k=2)。     

Study of eddy current power loss in an RCS vacuum chamber

In a Rapid Cycling Synchrotron (RCS), power loss due to an eddy current on the metal vacuum chamber would cause heating of the vacuum chamber. It is important to study the effect for estimating eddy current induced power loss and temperature growth. Analytical formulas for eddy current power loss for various types of vacuum chambers are derived for dipole and quadrupole repectively. By using the prototype of dipole of CSNS/RCS, an experiment was done to test the analytical formula. The derived formulas were applied to calculating the eddy current power loss on some special structures of an RCS vacuum chamber.     

A high current electron switch with deep volume charge compensation

The current switching by means of a gas-filled electron switch has been studied experimentally and theoretically. The switch showed complete controllability under deep volume charge compensation conditions. The switched current density was an order of magnitude higher than the current density of a similar vacuum switch     

Theoretical basis of the design of magnetic field generator for DCvacuum circuit breakers

The magnetic field generator (MFG) for producing the transverse magnetic field switching off the direct current in the vacuum chamber is presented. The method of calculating generator coils inductance for different geometrical dimensions and various systems of coils connections, assuming the maximization of the magnetic flux density value in the contact gap and the maximization of the vacuum chamber switching ability, is presented. The possibilities of MAG program for designing magnetic field generators is described     

Sculpting the vacuum in a photonic band gap micro-chip

We describe the engineering of the electromagnetic vacuum in a 2D–3D photonic bandgap (PBG) hetero-structure. This facilitates the development of novel active devices and the observation of novel quantum electrodynamic phenomena. We consider a specific architecture suitable as an all-optical micro-transistor capable of novel ultra-fast response with low switching power requirements. This relies on a unique collective atomic switching and population inversion achieved by coherent resonant pumping in a suitably engineered vacuum. Specific waveguide architectures within the 3D PBG micro-chip provide local density-of-states (LDOS) peaks near their cutoff frequency. These provide “building blocks” for electromagnetic vacuum engineering without recourse to conventional high Q-factor micro-cavities. For the all-optical micro-transistor, a fork shape LDOS within the micro-chip is desirable, using trimodal waveguide architecture. We delineate the functional robustness of these architectures to disorder caused by manufacturing errors within the PBG micro-chip.     

一种用于弧流电源的新型打坑电路设计

作为中性束注入加热系统的核心设备,弧流电源的性能至关重要。打坑电路是弧流电源的重要组成部分,其动态响应特性及稳定性决定了弧流电源的性能。提出了一种用于弧流电源的新型打坑电路解决方案,能在150 μs内快速实现大电流的跌落和恢复,并且跌落和恢复过程中基本无过冲,用于转移的电子开关(比如IGBT)在开关过程中过电压小,可靠性高,吸收电路容易实现。该方案可以很好地替代传统的弧流电源打坑电路。     

Measurement of ion parameters during a forced switching off ofcurrent in vacuum

This paper presents the results of ion parameters measured during a forced current commutation of a diffuse vacuum arc, aimed at evaluating the role of ions in discharges occurring rarely after the counterpulse commutation process, in a contact arrangement corresponding to a low-voltage vacuum switch. A sinusoidal half-wave current was interrupted near its amplitude of 400 A with a counterpulse of rise velocities 2.4 and 32 A/μs. In this way, a forced switching off of dc current was modeled. A retarding field analyzer was used for ion parameter measurements at the forced commutation process. Ion potentials up to 100 V were measured at the current zero moment, and the average decay times of ions after current zero were in the range from a few microseconds up to 30 μs as a function of observed ion potential. The measured values of decay times show the rather negligible role of ions in the discharge process after the counterpulse commutation in the examined contact arrangement. The rise time of the countercurrent is proposed as a factor in the successful forced current commutation under these conditions, and values up to a few amperes per microsecond of countercurrent rise velocity can be considered as the limit value     

Measurement and Statistical Simulation of Multiple Reignitions in Vacuum Switches

When the gap length of a vacuum switch at current zero is too small, successive reignitions and extinctions may occur under certain circuit conditions leading to overvoltages. This process of "virtual chopping" is more likely to happen when the contacts accidentally open shortly before current zero. In order to determine the values of the overvoltage and its probability when opening the contacts randomly, a computer program was developed which simulates the transient recovery voltage (TRV) in a single-phase circuit and determines the highest voltage for each switching operation. The moment of contact opening is simulated by pseudorandom numbers. Input data of the calculation are the circuit parameters, the reignition voltage of the gap versus time after current zero, and its capability of quenching the high-frequency current oscillation occurring after a reignition. These recovery data of the opening gap were determined experimentally for some contact materials using a special switching device in a synthetic test circuit with current injection.     

High power photoconductive switches of 4H SiC with Si3N4 passivation and n -GaN subcontact

The effect of a Si₃N₄ passivation layer on the breakdown voltage in 4H SiC high power photoconductive semiconductor switching devices has been investigated. An n⁺-GaN epitaxial layer was also used for these devices as a subcontact layer, which was between the contact metal and the high resistivity SiC bulk, to improve the ohmic contact and mitigate current spreading: the GaN subcontact layer protects the contact from damage occurring at high power levels. The Si₃N₄ passivation layer was grown by ultrahigh vacuum plasma enhanced chemical vapor deposition. By using the Si₃N₄ passivation, the dark leakage current of the devices was suppressed effectively and decreased by one order of magnitude, and the breakdown voltage of the switching devices was improved significantly from 2.9 to 5 kV without degrading the high photocurrent.     

The burning voltage of a high-current vacuum arc in a six-cap rodelectrode system

This paper studies the voltage-current characteristics of the six-gap rod electrode system and their dependence on the shape and material of the electrodes and interelectrode gap value. The investigations were carried out for currents up to 200 kA with the rate of its rise up to ~5·10⁹ A/s. A number of features were observed concerning arc-burning voltage dynamics depending on the value and rate of rise of the arc current, namely, a step-like voltage change at an initial discharge burning stage, and excitation of HF voltage oscillations for the discharge current wavefront. The duration and intensity of the unstable discharge burning phase accompanied by HF voltage oscillations depend strongly on the electrode system parameters. Power dissipated in the vacuum gaps and full dissipated energy were calculated as a function of the switching current peak. Results of the investigations give the possibility of designing a sealed-off triggered vacuum switch with minimum power losses and long service life evaluated by a transferred charge value >10⁶ C     

Bistability of single 1,5 cyclooctadiene molecules on Si(001)

The adsorption and current-induced bistability of single 1,5 cyclooctadiene molecules on Si(001) were studied in ultrahigh vacuum by low-temperature scanning tunneling microscopy (STM). After a dosage of ≈0.05 L at room temperature followed by cooling to the measuring temperature of 7 K, we find that the cyclic alkene molecule preferably adsorbs in the bridge structure with both C=C double bonds reacting with two adjacent Si dimers via [2+2] cycloaddition reaction. The time-dependent current measured upon tunneling through the adsorbed molecule at fixed STM tip height displays a switching between two current levels with the same mean residence time in each level. Higher bias and/or reduced tip height—and therefore higher current—increase the switching rate, suggesting that the reversible switching is due to inelastic electron tunneling. The observed bistability is interpreted as a dynamic interconversion between two degenerate conformations of the adsorbed molecule.     

The method of laser-sustained arc ignition

The method of laser-assisted vacuum arc deposition (laser-arc) was developed to effectively produce high-quality coatings, especially multilayer coatings with a reduced number of droplets. The efficiency of this method depends mainly on the ignition probability of the vacuum arc discharges. In the present work, the process of arc initiation by laser irradiation is studied and the influencing factors such as power density of laser irradiation, target material, and electrode configuration are discussed. It is shown that a high ignition probability (ρ>50%) on such coating materials at Ti, TiC, TiN, and C can be guaranteed with a laser power density of about 10⁸ W/cm², which can be achieved with a low-cost Nd-YAG pulse laser. Measurements of the plasma current preceding the arc ignition and microscopic investigations of the erosion pattern caused by the laser irradiation suggest that the process of plasma-sustained are ignition (unipolar arcing) plays an important role during the buildup phase of the vacuum arc discharge     

Application of the High-Speed Photography Technique to Study Pulsed Vacuum Arc Plasma in a Short Gap

Physics of Atomic Nuclei - We studied the process of switching a short vacuum gap, initiated by an auxiliary discharge along the surface of the dielectric by registration images using an...     

Experimental Investigation of Low-Current Vacuum Arc Instabilities

The instabilities of 50-Hz low-current vacuum arcs and chopping phenomena were investigated in a test circuit where current was limited either by a resistor or an inductance. Employing a special test method which was developed for statistical evaluation, current zeros were measured oscillographically with a time sweep of 50 to 100 ns/div for durations of ? 60 div. The effects observed are quantitatively better to assess than with other techniques. It was found that each chopping process is initiated by a partial arc extinction (which as a rule occurs within less than 10 ns). One of the dominant factors of the whole process is the speed of recovery of the contact material. Copper contacts showed a much faster recovery and thus higher chopping currents than contacts of copper-tungsten. Furthermore, that current value at which the first instability occurs was measured as weli as the corresponding chopping current. Both values were evaluated statistically. In agreement with previous findings the occurrence of the first instability turned out to be independent of the capacitance parallel to the switching gap. However, the chopping current showed a significant dependence on the capacitance, as is well known from earlier investigations.     

Efficient magnetization reversal with noisy currents

We propose to accelerate reversal of the ferromagnetic order parameter in spin valves by electronic noise. By solving the stochastic equations of motion we show that the current-induced magnetization switching time is drastically reduced by a modest level of externally generated current (voltage) noise. This also leads to a significantly lower power consumption for the switching process.     

Recovery properties of vacuum spark gaps

The authors investigated the recovery properties of a 90-kV, 15-kA multiple site, triggered vacuum spark gap. Triggering was accomplished with a multisite surface flashover plasma source with approximately 60 sites distributed over a 10 cm² area. Gap dimensions were 1-cm spacing by 7.5-cm diameter. Recovery measurements were performed utilizing an inductively recharged double pulse circuit. Under a sinusoidal recharge, the time to a 40-kV recovery occurred in 330 μs for an average current fall rate approaching 10¹⁰ A/s. These vacuum spark gap switches may provide an alternative method of high-average-power switching     

Subvacuum effects of the quantum field on the dynamics of a test particle

We study the effects of the electromagnetic subvacuum fluctuations on the dynamics of a nonrelativistic charged particle in a wavepacket. The influence from the quantum field is expected to give an additional effect to the velocity uncertainty of the particle. In the case of a static wavepacket, the observed velocity dispersion is smaller in the electromagnetic squeezed vacuum background than in the normal vacuum background. This leads to the subvacuum effect. The extent of reduction in velocity dispersion associated with this subvacuum effect is further studied by introducing a switching function. It is shown that the slow switching process may make this subvacuum effect insignificant. We also point out that when the center of the wavepacket undergoes non-inertial motion, reduction in the velocity dispersion becomes less effective with its evolution, no matter how we manipulate the nonstationary quantum noise via the choice of the squeeze parameters. The role of the underlying fluctuation–dissipation relation is discussed.     

Power absorption characteristics of an inductively coupled plasmadischarge

Power absorption characteristics of an inductively coupled discharge are investigated experimentally and compared with a two-dimensional inductive heating theory in a planar single turn antenna at high frequency (18 MHz) and low pressure (⩽50 mtorr) conditions. We measure the resistance R, which consists of vacuum resistance R_ν and the plasma resistance R_p for a given RF power of P=½I_c²R, where I_c is the coil current. The vacuum resistance is determined to be 0.44 R in our case. The plasma resistance increases as the gas pressure increases in a pressure range of 2 to 50 mtorr. Also, it increases with power. In a high-pressure range near 50 mtorr, however, it has a nearly constant value of about 0.6 Ω