Attenuation of electron gun generated surges in an electron beam evaporation system using ferrite beads Namita Maiti a, * , U.D. Barve a , Shakti Kumar Mishra b , M.S. Bhatia a , A.K. Das a a Laser & Plasma Technology Division, Bhabha Atomic Research Centre, Mumbai 400 085, Maharastra, India b Technology Development Division, Bhabha Atomic Research Centre, Mumbai 400 085, Maharastra, India article info Article history: Received 1 January 2012 Received in revised form 17 April 2012 Accepted 17 April 2012 Keywords: Electron gun Surge suppression Spectral analysis Ferrite beads abstract Vacuum breakdown is a very common problem during the operation of any electron gun, more so for e- guns used for vacuum evaporation. This not only spoils the coating or welding job but also causes damage to the electronics of the power system. This paper discusses an approach to attenuate the breakdown current near the gun itself, so that the surge does not propagate to cause any detrimental effect on the power source and thereby on the job. In this paper, ferrite beads on both the feed lines have been used to suppress the high frequency content and reduce the amplitude of the breakdown signal. An induction coil sensor has been designed to monitor the breakdown signal. The high frequency surge in the MHz range could be attenuated to a lower range of KHz by use of ferrite bead. A detailed quantitative analysis of the breakdown signal has been presented in this paper. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Electron beam evaporation offers better control over evapora- tion rate and less probability of contamination [1]. Coatings produced by such a system have good surface finish and improved metallurgical properties. One of the central issues in development of an electron beam evaporation based system is the design of the electron gun to reduce process interruptions due to breakdown. Besides process degradation, this phenomena poses threat to the feeding power source and associated control electronics. Breakdown can occur due to various reasons such as, 1) quality of material chosen for the gun electrodes, 2) inter-electrode distance, 3) outgassing of the material at high temperature, 4) degassing from molten metal. Breakdown especially occurs when the pres- sure inside the vacuum chamber increases. More specifically, as the material in the crucible evaporates, positive metal vapor ions may be generated, which may go back to the emitter along the same path taken by the electron beam causing erosion in the emitter [2]. All these factors sometimes make it difficult to ascertain the reli- able high voltage performance of the electron gun. To overcome the breakdown problem, one tries to maintain the electric field as uniform as possible. Safe limit is followed while choosing the inter- electrode gap and also the creepage path of the insulator. Electrode profiles are modified to maintain the electric field at acceptable level. After following all the necessary high voltage related guide- lines, the breakdown reduces considerably. Work along these lines have been reported [2e9] from time to time. The investigation reported in [3] prevents arcing in the gun by providing an improved electrostatic field, an improved magnetic field and an improved insulation on high voltage leads. The improved electrostatic and magnetic field guides the electron beam to the crucible with a minimum divergence. If the energy density exceeds a certain level, dense plasma forms. When the plasma reaches the gun region, intensive ion bombardment of the cathode starts causing high voltage gap breakdown. In an axial gun, reported in [4], the gun is shielded from the magnetic field with the help of a magnetic flange. These approaches are possible in an axial e-gun. For a transverse e-gun, grounded metallic shield as reported in [5] has been used to prevent establishing a discharge by utilizing the concept of ‘dark space’. A metallic shield is installed around all of the HV elements. The spacing between the shield and the HV elements is less than the dark space at a pressure 0.13 Pa or more. The dark space is also filled with controlled Argon gas such that the system chamber and the dark space can be effectively isolated. The reactive coating of desirable properties can be achieved in the pressure range of 10 À1 Pae10 À2 Pa. At this high pressure the elec- tron gun does not operate reliably due to high voltage flashover. In order to overcome this problem the substrate chamber is isolated from gun chamber using a bifurcation plate [6]. On this bifurcation plate, aperture is provided for beam emergence from the gun * Corresponding author. Tel.: þ91 22255594401. E-mail addresses: nmaiti@barc.gov.in, namita_sunil@yahoo.com (N. Maiti). Contents lists available at SciVerse ScienceDirect Vacuum journal homepage: www.elsevier.com/locate/vacuum 0042-207X/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.vacuum.2012.04.028 Vacuum 86 (2012) 1810e1814