Beam density distribution measurement method based on Faraday cup with a micro aperture for high power density electron beams
-
摘要: 电子束焊机中的电子束具有功率密度高（106～108 W/cm2）、焦斑尺寸小（几百微米）的特点。其束流密度分布是一项重要的束流品质参数，对焊接工艺研究具有重要意义。然而，传统的电子束密度测量方法（比如荧光成像法）在如此高的功率密度下无法使用。研究了一种基于水冷微孔法拉第杯与高频束流扫描相结合的测量方法。在电子束焊机偏转线圈上加高频（1～10 kHz）信号，使电子束在较大尺寸范围内扫描，从而降低电子束沉积在法拉第杯表面的功率密度，避免法拉第杯表面被烧毁。可用于真空腔体中的水冷微孔法拉第杯是经过特别设计的，通过水冷带走电子束损失在法拉第杯的表面上的热量。法拉第杯表面有一个数十微米尺寸的微孔。当电子束周期性地经过微孔时，少量电子束通过微孔会进入法拉第杯，形成电信号并经过集成在法拉第杯中的放大器放大后被采集。电子束功率密度分布可由采集到的时域内的电流信号进行重建得到。实验证明，该方法可以准确测量电子束焊机中高功率密度电子束的密度分布，同时具有约23 μm的成像精度。Abstract: The electron beam in the electron beam welding machine has the characteristics of high-power density (106−108 W/cm2) and small focal spot size (several hundreds micrometers). Its beam density distribution is an important beam quality parameter and is of great significance to welding process research. However, traditional electron beam density measurement methods, such as fluorescence imaging, cannot be used at such high-power densities. We studied a measurement method based on a combination of a water-cooled Faraday cup with a micro aperture and high-frequency beam scanning. Adding a high-frequency (1−10 kHz) signal to the deflection coil of the electron beam welding machine causes the electron beam to scan within a larger size range, thereby reducing the power density of the electron beam deposited on the surface of the Faraday cup to avoid being burned. Water-cooled Faraday cups that can be used in vacuum chambers are specially designed to take away the heat deposited by the electron beam on the surface of the Faraday cup through water cooling. There is a micro aperture with a size of tens of micrometers on the surface of the Faraday cup. When the electron beam passes through the micro aperture periodically, a small amount of the electron beam passes through the aperture and enters the Faraday cup, forming an electrical signal that is amplified by an amplifier integrated in the Faraday cup and then collected. The electron beam power density distribution can be reconstructed from the collected current signal in the time domain. Experiments have shown that this method can accurately measure the density distribution of high power density electron beams in electron beam welding machines, while having an imaging accuracy of about 23 μm.
-
图 1 电子束焊机束流功率密度测量系统示意图
Figure 1. Schematic diagram of electron beam welding machine beam power density measurement system
图 2 法拉第杯上电子束偏转轨迹示意图
Figure 2. Schematic diagram of electron profile trajectory on Faraday cup
-
[1] Schultz H. Electron beam welding[M]. Cambridge: Woodhead Publishing, 1994. [2] Birnie J V. An introduction to electron beam welding[J]. Physics in Technology, 1976, 7(3): 116-122. doi: 10.1088/0305-4624/7/3/I03 [3] Ahmed N. New developments in advanced welding[M]. Cambridge: Woodhead Publishing, 2005. [4] Sun Z, Karppi R. The application of electron beam welding for the joining of dissimilar metals: an overview[J]. Journal of Materials Processing Technology, 1996, 59(3): 257-267. doi: 10.1016/0924-0136(95)02150-7 [5] Meier J W. Recent advances in electron beam welding technology[J]. Welding Journal, 1963, 42(12): 963-968. [6] Arata Y, Tomie M, Terai K, et al. Shape decision of high energy density beam[J]. Transactions of JWRI, 1973, 2(2): 130-146. [7] Arata Y. Evaluation of beam characteristics by the AB test method[D]. Ohio/USA: ASM International, 1986. [8] Siekman J G, Schoenmakers T M B, Eindhoven K N, et al. New microprobe techniques for measuring the current distribution in an electron beam used for welding[J]. Journal of Physics E: Scientific Instruments, 1975, 8(5): 391-395. doi: 10.1088/0022-3735/8/5/017 [9] Maternia Z, Radzimski Z, Borkowicz Z. Method of measuring the profile of a fine-focused electron beam by using a semiconductor detector[J]. Journal of Physics E: Scientific Instruments, 1984, 17(6): 447-450. doi: 10.1088/0022-3735/17/6/007 [10] Wójcicki S, Mladenov G. A new method of experimental investigation of high-power electron beam[J]. Vacuum, 2000, 58(2/3): 523-530. [11] Koleva E, Vutova K, Wojcicki S, et al. Use of radial distributions of the beam current density for evaluation of beam emittance and brightness[J]. Vacuum, 2001, 62(2/3): 105-111. [12] Dilthey U, Goumeniouk A, Böhm S, et al. Electron beam diagnostics: a new release of the diabeam system[J]. Vacuum, 2001, 62(2/3): 77-85. [13] Dilthey U, Boehm S, Dobner M, et al. Comparability, reproducibility and portability of the electron beam technology using new tools of the DIABEAM measurement device[J]. Welding in the World, 1997, 39(3): 124-129. [14] Dilthey U, Weiser J. Investigations of EB characteristics and their influences on the weld shape[J]. Welding in the World, 1997, 39(2): 89-98. [15] Dilthey U, Weiser J. Study of the tool electron beam-part 1: comparison between the Arata test and Diabeam measurement[J]. Welding Cutting, 1995(47): 339-345. [16] Peng Yong, Wang Kehong, Zhou Qi, et al. Beam quality test technology and devices of electron beam welding[J]. Vacuum, 2011, 86(3): 261-266. doi: 10.1016/j.vacuum.2011.06.017 -
下载:
点击查看大图
图(9)
计量
- 文章访问数: 131
- HTML全文浏览量: 40
- PDF下载量: 25
- 被引次数: 0
