Conducted Noise Studies of High Voltage Pulsed Power Supply for Copper Vapor Laser – A Case Study P.K. Agrawal, B.P. Das, S.V. Nakhe Laser System Engineering Division Department of E & C Engineering. Laser System Engineering Division RRCAT, Indore, Madhya Pradesh, I I T- Guwahati, Assam RRCAT, Indore, Madhya Pradesh, Abstract- Studies on conducted noise were carried out on high voltage pulsed power supply, thyratron heater unit and thyratron trigger unit used for Copper vapor laser. This paper presents conducted noise generated by heater unit, trigger unit and high voltage pulsed power supply at different conditions. The effect of laser discharge on conducted noise generated by thyratron heater unit and trigger unit is also presented here. I. INTRODUCTION The issue of electromagnetic compatibility (EMC) is very important in high voltage pulse power systems. Intra system electromagnetic interference (EMI) may attain high amplitudes to the extent that satisfactory operation of the high voltage pulse power supply becomes difficult to achieve and this is particularly true when there are mismatched loads on the power supply like gas discharge loads [1]. Systematic studies on conducted and radiated EMI generated in such systems under varying conditions are vital to implement proper EMI mitigation techniques in these systems. All gas laser using pulsed electrical excitation fall under the category of the mismatched loads as mentioned earlier. Copper vapour laser is one of the gas discharge lasers operated from high voltage pulse power supply and used in wide applications. Some studies reported earlier [2] discuss the radiated noise generated by Copper Vapour Laser (CVL) system with very limited experimental work and that too without defining working conditions of the laser. This work does not cover conducted EMI from the High Voltage Pulsed Power Supply (HVPPS). In references [3]-[5], different techniques implemented for control electronics for EMI environment of CVL are illustrated but EMI measurement with the CVL system is not dealt with. In yet another work [6] some of the simulated conducted EMI studies on CVL are presented considering only power circuit. The objective of this paper is to study the effect of laser discharge load on thyratron Heater Power Supply (HPS), Trigger Power Supply (TPS) and the CVL power supply unit. The heater & trigger power supply are basically SMPS operating units from 230 V mains supply. HPS is required to maintain the gas pressure in thyratron & TPS is used for grid biasing and trigger pulses to the thyratron. The paper shows the difference in conducted noise generated by HPS and TPS when used with and without laser discharge. This paper also present the total conducted noise generated by (HVPPS) to all the input line. The setup used for conducted noise measurement is as per CISPR 11 and hence data is used as pre-compliance testing. The measurement is done by using Line Impedance Stabilization Network (LISN) and spectrum Analyser (SA). The measured conducted noise is then compared to the European standard EN55011 Class A (average). The HVPPS is applied to CVL which is an inherently a pulsed laser and requires average input average power ~ 5.5 kW, high output voltage ~ 20 kV, fast pulse rise time < 100 ns at pulse repetition rate of 5 -10 kHz. The power supply uses hydrogen thyratron (CX1535) as main switch and requires heater and trigger power supply for its operation. CVL is a strong source of radiated and conducted of EMI because of high voltage, high current & fast switching of pulses in the mismatched load. As electrically noisy source may pollute the input lines which are connected to many control electronic circuitry proper measurements of conducted noise are carried out to evaluate effectiveness of mitigation technique and to achieve better electromagnetic compatibility of power supply. II. HIGH VOLTAGE PULSED POWER SUPPLY Figure 1 Block diagram of HVPPS and laser load The HVPPS consist of high voltage dc power supply, pulse generating circuit, thyratron heater power supply, thyratron trigger power supply and gas-vacuum control unit. The block diagram of complete laser system with power supply is as shown in figure 1. A. High Voltage DC Power Supply Variac HV Step Up Transformer 3-phase Rectifier Pulse Generating circuit Heater Unit Trigger Unit R Y B N Y N HVDC (0-10kV) Heat Exchanger Laser Head Gas & Vacuum control unit B N Water Oil HV Cable R N