An electrical discharge is the passage of electrical current through a material which normally does not conduct electricity. Consider, for example, a simple experiment which we have all experienced. If we hold two wires a few millimeters apart, and connect each to one pole of a battery, no perceptible electrical current flows through the air, because the air is insulating. However if these wire were connected to a high voltage source of several thousand volts, sparks will fly. The normally insulating air was transformed into a conductor, a process called electrical breakdown, and the sparks which we would see are a form of an electrical discharge. Normally air consists of neutral molecules of nitrogen, oxygen, and other gases, in which electrons are tightly bound to atomic nuclei. During the breakdown process, some of the negatively charged electrons are separated from their host atoms, leaving them with a positive charge. The negatively charged electrons, and the positively charged atoms (known as positive ions) are then free to move separately under the influence of the applied voltage. Their movement constitutes an electrical current. The collection of ions and electrons is known as a plasma, and one of its more important properties is that a plasma can conduct electrical current.

There are several types of electrical discharges: The Corona: is a 'partial' discharge occurring when a highly inhomogeneous electric field is imposed. Typically, there is a very high electric field adjacent to a sharp electrode, and a net production of new electron-ion pairs occurs in this vicinity. The Corona typically has a very low current, and very high voltage. The Glow Discharge typically has a voltage of several hundred volts, and currents up to 1 A. A small electron current is emitted from the cathode by collisions of ions, excited atoms, and photons, and then multiplied by successive electron impact ionization collisions in the cathode fall region. The Arc is a high current, low voltage discharge, where electron emission from the cathode is from thermionic and/or field emission. Electrical discharges can also by excited by RF, microwave, or laser radiation, with or without electrodes.


The mission of the Electrical Discharge and Plasma Laboratory is to investigate the basic physics of electrical discharges and plasmas, and to develop technological applications for these phenomena. The laboratory carries out its mission through a combination of theoretical and experimental investigations.


The main focus of the laboratory's research effort is a particular form of electrical discharge known as the vacuum arc, and the utilization of the plasma produced by the vacuum arc to form thin films and metallurgical coatings. The vacuum arc is a high current, low voltage discharge between a pair of electrodes located in a vacuum chamber. The electrical current is carried by a plasma produced by ionizing material which the arc evaporates from the electrodes. The plasma is formed as an energetic jet, which can be directed with magnetic fields. A coating will form on any surface which intercepts part of the plasma jet, in a process known as vacuum arc deposition. The vacuum arc also produces a spray of molten metal droplets from the cathode surface, which can degrade the quality of electronic and optical thin films. These droplets can be removed from the plasma beam by obstructing the direct path between the cathode and the substrate, and using a magnetic field to direct the plasma beam around the obstruction, in a process known as filtered vacuum arc deposition.

Smaller research programs study other discharges. Pulsed Air Arc Deposition applies high current, low voltage pulses between a source electrode and a workpiece, and forms a metallurgical coating of the source material on the workpiece. The Corona is a high voltage, low current discharge between a pointed and planar electrode, which appears as a nuisance on high voltage transmission lines, but can be utilized for chemical synthesis, material processing, and charge transfer in photocopiers.


The laboratory is a joint facility of the Fleishmann Faculty of Engineering, and the Faculty of Exact Sciences of Tel Aviv University. The lab is directed alternately by Prof. R.L. Boxman of the Department of Interdisciplinary Studies, Faculty of Engineering, and Prof. S. Goldsmith, of the School of Physics and Astronomy, Faculty of Exact Sciences. The current director (2002) is Prof. Goldsmith. The lab personnel includes some 19 staff and students, plus a number of collaborators from other laboratories. Five of the senior researchers, and two of the graduate students, are recent immigrants from the former Soviet Union, which was formally the world leader in electrical discharge research and applications.


The lab is located in Room 451 of the Wolfson Building of Mechanical Engineering on Rechov Klauzner, on the engineering campus of Tel Aviv University in Ramat Aviv. The lab is equipped with four vacuum arc experimental set-ups, where each one includes a vacuum system, arc chamber, and arc power supply. System 1 is mounted on a marble optical table and includes a 0.5 m monochrometer equipped with a CCD television camera, VCR, frame grabber, and computer, for collecting and analyzing optical spectra emitted by the arc. System 2 includes a 1 kA vacuum arc gun, and a quarter torus macroparticle filter, and is used for studying filtered vacuum arc deposition. System 3 is a triple cathode vacuum arc deposition system, which facilitates that study of multi-component, multi-layer, and graded vacuum arc coatings. System 4 is a 60 cm wide rectangular system, which has a mechanized carriage for transporting 40x40 cm substrates past rectangular plasma sources, and is used for applying uniform coatings on flat panels. The lab also has mass spectroscopy equipment, and optical microscope, and instrumentation for measuring coating thickness.

Facilities of both the Faculty of Engineering, and the Faculty of Exact Sciences, are available for research projects conducted by the lab, including computer facilities, work shops, and electronics repair and fabrication labs. The lab is an affiliate of the Tel Aviv University Materials Research Center and the Nano Science and Technology Center, and has access to their materials characterization facilities, including x-ray diffraction, electron microscopy, and x-ray photoelectron spectroscopy, as well as access to the Metallurgy Laboratory and The micro-fabrication Laboratory of the Faculty of Engineering.

For further information or specific inquiries, contact:
Prof. R.L. Boxman, Director
Electrical Discharge and Plasma Laboratory
Tel Aviv University
POB 39040
Tel Aviv 69978
Fax: +972-3-641-0189
Tel: +972-3-640-7364
e-mail: boxman@eng.tau.ac.il


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