Development of copper beam ducts with antechambers for advanced high-current particle storage rings

There has been continuous progress at the High Energy Accelerator Research Organization (KEK) in R&D on vacuum beam ducts adaptable to future high-current particle storage rings. Here we proposed copper beam ducts with antechambers to deal with the severe issues attributed to the high beam currents. The proposed antechamber scheme can withstand intense synchrotron radiation (SR), provide a beam duct with low beam impedance, and effectively reduce the electron cloud effect (ECE) in positron/proton rings. Several trial models were manufactured by a pressing or cold-drawn method, and assembled with electron beam welding. Special vacuum components, such as connection flanges, distributed pumps, and gate valves, were customized for the beam ducts. TiN coating on the inner surface of the beam duct was also investigated as a mitigating measure for the ECE. Trial models of the copper beam ducts were installed into the KEK B-factory (KEKB), and their performances were evaluated using real positron and electron beams.     

Development of alumina ceramics vacuum duct for the 3 GeV-RCS of the J-PARC project

An alumina ceramics vacuum duct has been developed for the 3 GeV-RCS of J-PARC project at JAERI. There are two types of alumina ceramics vacuum ducts needed, one being 1.5 m long with a circular cross-section for use in the quadrupole magnet, the other being 3.5 m long with a 15°, bend with a race-track cross-section for use in the dipole magnet. These ducts could be manufactured by joining several duct segments of 0.5-0.8 m in length by brazing. The alumina ceramic ducts have copper stripes on the outside surface to reduce the duct impedance. One of the ends of each stripe is connected to a titanium flange by way of a capacitor so to interrupt an eddy current circuit. The copper stripes are produced by an electroforming method in which a stripe pattern formed by Mo-Mn metallization is first sintered on the exterior surface and then overlaid by PR-electroformed copper (periodic current reversal electroforming method). In order to reduce emission of secondary electrons when protons or electrons strike the surface, TiN film is coated on the inside surface of the ducts.     

Design of efficient lens ducts

Lens ducts have the potential to couple the output from a laser diode array efficiently into the gain medium of a solid-state laser in an end-pumped configuration. Using a ray-tracing method we investigate different design approaches of lens ducts and demonstrate the possibility to obtain an output beam with a symmetric profile that is insensitive to the small displacement from the output surface of a lens duct.     

Copper spall fracture under sub-nanosecond electron irradiation

Ultra-short powerful electron beam is a suitable tool for producing of high rate deformation in substance. In paper we present a new model of high rate fracture and use this model for numerical investigation of fracture of copper target at irradiation by sub-nanosecond electron beam. In this model, fracture is considered as a time-dependent process of nucleation and growth of opening mode cracks. The nucleation and growth rates are controlled by specific free energy of crack surface which is sole fitted parameter. Plastic deformations, both in cracks vicinity and total in substance, are described in frames of dislocation theory. For verification of the model, we performed simulations of spall fracture at plate impact and at irradiation by high-current electron beam with pulse duration of tens of nanoseconds, and reasonable agreement with experimental data has been demonstrated. Simulations of the sub-nanosecond electron beam action on target indicate that spall fracture of the irradiated target surface is possible. This fracture takes place at the enclosed energy density slightly below the value, which is sufficient for melting of irradiated substance. Fracture threshold energy density does not depend on the origin dislocation density and it increases with the increase of pulse duration. As a result, at long pulse durations (more than ten nanoseconds) the substance melts before fracture.     

抑制多级降压收集极二次电子发射的研究进展

简述了热解石墨、高纯各向同性石墨和无氧铜材料的二次电子发射特性,以及离子束表面改性对二次电子发射特性的影响。分析表明热解石墨和高纯各向同性石墨的二次电子发射系数均明显低于无氧铜的二次电子发射系数,并且通过离子束表面改性后二次电子发射系数能够得到进一步的降低。同样的,离子束表面改性后的无氧铜的二次电子发射系数也得到一定的降低,并且还有很大的发展空间。     

Secondary electron emission yields from the J-PARC RCS vacuum components

The J-PARC 3 GeV rapid-cycling synchrotron (RCS) is required to provide 1 MW pulsed protons to the spallation neutron target and the 50 GeV main ring. Since the acceleration period is set at a repetition rate of 25 Hz, the eddy current effect due to such rapid repetition magnetic field is a big issue (i.e., the perturbation of the magnetic field and the heating owing to the ohmic loss) in the metal duct. Therefore, we choose the ceramics duct in the magnets in order to avoid the eddy current effect. But the total secondary electron emission yield (SEY) from the ceramics surface is larger than the metal one and there is a possibility of bringing about the beam instability by those secondary electrons. In order to reduce these undesirable electron emission from the chamber surface, titanium nitride (TiN) is coated on the inside surface of the chambers. We measured SEY from TiN coating surface with various conditions. First, we varied the nitrogen density and crystal face in the coating. Second, we exposed the samples to the oxygen and the water vapour with electron beam bombardment in order to simulate the actual conditions. We further investigate diamond-like carbon coating to search for the possibility of another coating. The results of these measurements are shown.     

电子束辐照诱导Cu超微粒子发生反应的HREM研究

用高分辨电子显微镜中的电子束对Ｃｕ超微粒子进行了连续的照射和跟踪观察，结果表明，电子束的辐照，首先使Ｃｕ发生了氧化反应，反应途径：Ｃｕ＋Ｏ２→成分为Ｃｕ和Ｏ的非晶膜→Ｃｕ的晶体氧化物：接着，新生的Ｃｕ的晶体氧化物，在电子束的继续照射下，又发生还原反应，Ｃｕ的氧化物不断地还原为Ｃｕ。在整个还原反应中，伴随着样品局部的多重又氧化还原现象交替出现。     

Comparison between Monte Carlo and analytical calculation of Clausing functions of cylindrical and conical tubes

In a previous work (J. Vac. Sci. Technol. A 21 (2003) 1452), we calculated the transmission probabilities for cylindrical and conical ducts, solving numerically the Clausing integral equation and integrating the resulting Clausing function. It is also important to obtain the Clausing function itself, because it is proportional to the distribution of molecular collisions with the walls of the system, as we show in this contribution. Besides, the density profile of the gas inside the duct can be calculated using the Clausing function, as shown by Davies and Lucas (J. Phys. D: Appl. Phys. 16 (1983) 1). We have calculated the Clausing functions for different cylindrical and conical ducts using a Monte Carlo simulation method and we have compared these results to the numerical ones, finding a very good agreement, within statistical uncertainties.     

基于DIABEAM法的电子束能量密度测试分析

为了充分发挥电子束焊接技术在航空航天领域的作用,对反映束流品质的关键因素—电子束能量密度开展了研究;基于法拉第传感原理,通过DIABEAM测试法对真空电子束焊机电子束能量密度分布进行测试分析;结果表明:电子束能量密度分布呈非对称的近高斯分布,随着聚焦电流的增加,电子束能量密度趋于发散分布,达到焦点状态时dP90区域内电子束能量密度均值最高;电子束能量密度峰值随着灯丝加热电流增加而增加,但受灯丝尺寸等因素的影响,灯丝加热电流达到稳定值后能量密度分布不变。     

Faraday cup for measuring the electron beams of TWT guns

A compact Faraday cup reported in this paper is designed to investigate the current distributions of the electron beams of Traveling Wave Tube’s guns. It consists of a 0.06 mm thick molybdenum aperture plate and a copper shield with a graphite collector inside. There are plates with different laser-cut aperture holes that were 100 μm, 50 μm, 20 μm and 10 μm in diameter for measuring electron beams with different sizes. The thermal analysis of the Faraday cup with pulse beam heating was performed and discussed in this paper. The pulse test shows that this device has fast response and small dissipation. A 0.58 beam perveance (μP) electron gun with expected minimum beam radius 1.0 mm was measured with the Faraday cup and the three-dimensional current density distribution and beam envelope were presented. The experiment results show that the design is reasonable for measuring the electron beam with a high resolution.     

Direct-on-barrier copper electroplating on ruthenium from the ionic liquid 1-ethyl-3-methylimidazolium dicyanamide

The "direct-on-barrier" electroplating of copper on ruthenium from a 1 mol dm⁻³ solution of CuCl in the ionic liquid 1-ethyl-3-methylimidazolium dicyanamide, [C₂mim][N(CN)₂], is reported. Continuous layers of copper with a preferential Cu(111) orientation were obtained from this electrolyte. The copper coatings were investigated by top view scanning electron microscopy (SEM), X-ray diffraction (XRD), and focused ion beam transmission electron microscopy (FIB-TEM). The nucleation density was both theoretically and experimentally evaluated by the Scharifker-Hills model and transmission electron microscopy, respectively. The direct plating of copper on resistive substrates for advanced interconnects and package is a promising new application of ionic liquids.     

Fabrication of nanosized metallic copper by electrochemical milling process

Using a copper oxide powder of micrometer size as the starting electrode material in CuO/Li cells, copper oxide (CuO) can be electrochemically reduced into metal particles of smaller sizes in a controllable way. A novel electrochemical milling (ECM) method is developed for a “top–down” synthesis of nanometer-scaled metal particles. X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM) were employed to characterize the structure of copper particles obtained by the electrochemical reduction. The influences of CuO precursors, current density, and operating temperature on the final products were also studied. It is found that the latter two factors had pronounced effects on the obtained copper products.     

Metallurgical characterization of arc-conditioned carbon coating on copper electrodes

During arc discharge between two parallel electrodes, the electrode surface is eroded by the arc. Carbon coating of the electrode surface often results in a decreased erosion. The surface structure of the arc-conditioned carbon-coated copper electrode was metallurgically characterized by the use of (1) scanning electron microscopy and (2) Auger in-depth profiling. Two different types of a.c. conditioning with varying pulse characteristics were studied.It was found that the peak current density, the pulse duration and the total number of pulses were the most important parameters in determining the metallurgical structure of the conditioned electrode surface. The vapor arcs which were produced by pulses with a high current density and short pulse duration were most effective in compacting the carbon coating and promoting good adhesion between the carbon and the copper electrode. The compaction and the adhesion are effected by a high ionic beam pressure on the cathode reaching up to 1000 atm.A lower degree of carbon penetration was effected when surface melting was produced by thermionic arcs which have a lower current density and longer pulse duration. In this case, carbon adhesion is due to the mechanical entrapment of carbon powder in the thin molten copper layer produced on the electrode surface by the arcs.     

Experimental investigation of the efficiency of a high-voltage glow discharge as a source of a beam of run-away electrons

To determine the energetic efficiency of the formation of the run-away electron beam in a highvoltage glow discharge, we measure the temperature of the electron beam generator. According to the measurements, the energetic efficiency (the part of the input discharge power carried away by the beam) was 50–70% at the generator supply voltage of 4.4 kV and it increased up to ~85% at ~8 kV. The measurements were performed for the discharge in helium with copper, steel, molybdenum, and lanthanum hexaboride cathodes.     

Enhancement of the low-temperature catalytic graphitization of polyacrylonitrile by incorporating Cu nanostructures as plasmonic photocatalyst

Journal of Materials Science - Here, we systematically investigate the chemical process of low-temperature catalytic graphitization of polyacrylonitrile (PAN) by using roughened copper (Cu)...     

Vacuum system for the 3-GeV RCS in J-PARC

The 3-GeV RCS (rapid cycling synchrotron) in the J-PARC (Japan Accelerator Research Complex) project accelerates a proton beam of 0.333 mA up to 3 GeV. At 25-Hz repetition rate, the RCS generates a high-power beam of 1 MW. In such an accelerated proton beam, neutrons as well as gamma rays are generated. The cumulative energy dose will be of the order of 100 MGy over 30 years of operation. So as to minimize the radiation exposure during maintenance, it is necessary to construct a vacuum system with reliable components which have a long life in such a high level of radiation. In addition, it is necessary to keep the operating pressure of the beam in ultra high vacuum to suppress pressure instability. Thus we should think not only of the outgassing mainly due to ion-induced desorption but also of the pumping efficiency. Based on the above, the vacuum system was designed as follows: The ring is divided by isolation valves into 6 sections (3 straight and 3 arc sections), which can be pumped down independently. To avoid any eddy current loss, ceramic ducts are used in the bending and focusing magnets. These ducts are connected to titanium ducts placing the Ti bellows between. Here, we adopt pure Ti as a material for the ducts and bellows because of its small residual radioactivity. The ring is evacuated with 20 ion pumps (0.7 m³/s) and 24 turbomolecular pumps (TMPs) (1.3 m³/s), which are attached to the Ti ducts. The TMPs are used not only for rough pumping but also for evacuation during the beam operation. Especially a collimator system for localizing beam losses in a restricted area is evacuated with the TMPs, because the outgassing from this region will probably be the greatest. In addition, the straight sections for beam injection and extraction are pumped down mainly by the TMPs. Each arc section is pumped by 4 ion pumps and 2 TMPs. To realize the above system, we developed components such as large aperture ceramic ducts and TMPs with high radioactive resistance, as well as several kinds of heat treatment to reduce the outgassing. Finally, we realized the UHV without baking in the RCS and the beam operation has been successful to date.     

Effect of filament heating current on electron beam of directly heated strip-type electron gun

The method of Electron Beam-Physical Vapour Deposition (EB-PVD) for handling large substrates is well established in the metallurgical industry, where sweeping axisymmetric electron guns or multiple pencil guns are routinely used to cover a large target area. The non-uniformity in current density in those methods can be overcome, to a large extent, by using the strip-type electron gun. In this paper, we propose to use an AC-heated strip-type electron gun to cover large target areas. The magnetic field generated by the alternating filament current oscillates the beam in a direction parallel to the filament length, thereby eliminating the need for applying an external electric or magnetic field for sweeping the beam. The non-uniformity in the current density within the strip electron beam, arising due to finite length of the filament, is reduced by the use of dummy filaments on both ends of the active filament. These results are supported by electron trajectory simulations.     

Evaluation of the optical properties of epitaxial lateral overgrown gallium nitride on sapphire and the role of optically active metastable defects using cathodoluminescence and photoluminescence spectroscopy

Photoluminescence (PL) and cathodoluminescence (CL) measurements on a variety of GaN samples confirm earlier reports that epitaxial lateral over-growth (ELOG) results in improved material quality. Depth profiling of epitaxial lateral over-growth samples, reported here for the first time using variable energy electron beam excitation, shows that there is a substantial reduction in defect density away from the interface, and that the barriers to defect propagation are very effective. In addition to the normal yellow emission generally observed for GaN, we find intense blue emission, already assigned to a metastable defect, in some materials. Using a rapid scanning interferometer, we study the changes in the luminescence spectrum as a function of time and at a range of temperatures. We suggest possible explanations for the complex nature of the metastability displayed by the defect responsible for the blue band.     

Titanium flanged alumina ceramics vacuum duct with low impedance

We successfully developed alumina ceramics vacuum ducts for the 3GeV-RCS of J-PARC at JAERI. This duct has titanium flanges and exterior RF shield to reduce duct impedance. The temperature of titanium flange became 45 °C due to eddy current heating under dipole magnet operation. The longitudinal duct impedance was sufficiently small for stable beam acceleration as shown by impedance measurement by the coaxial method. It was found that the radiation damage of the capacitor used for the RF shield of this duct was small, because the capacitance decreased only by 7% after a gamma-ray irradiation of 30 MGy. This duct is usable for the 3GeV-RCS of J-PARC.     

Annular structures formed in a beam of ions during their collective acceleration in a system with dielectric anode

We have studied the collective acceleration of protons and deuterons in an electron beam emitted from plasma formed at the surface of a dielectric anode insert. The experiments were performed with a pulsed electron accelerator operating at an accelerating voltage up to 1 MV, current amplitude up to 40 kA, and pulse duration of 50 ns. Reduction of the accelerating voltage pulse front width and optimization of the diode unit and drift region ensured the formation of several annular structures in the electron beam. As a result, up to 50% of the radioactivity induced in a copper target was concentrated in a ring with 4.5-cm diameter and 0.2-cm width. The formation of high energy density in these circular traces and the appearance of an axial component of the self-generated magnetic field of the electron beam are related with the increasing efficiency of acceleration of the most intense group of ions.