Electromagnetic compatibility management for fast diagnostic design

Electromagnetic compatibility management for fast diagnostic designJ.Raimbourg a )Commissariat àl’Energie Atomique (CEA),BP 12,91680Bruyeres Le Chatel,France(Presented on 22April 2004;published 18October 2004)This article presents an overview of electromagnetic compatibility (EMC )management for fast diagnostic design.We will present and detail the classical approach in EMC.This approach can be successfully applied for installations where a single engineering entity has the authority to prescribe and enforce a certain compatibility level.Most of the time,strict application of generic standards is required for fast hertheless,the pulse perturbation must be synchronized to the fast diagnostic operation.Some “traditional”techniques,such as star-earthing and bonding cable screens at one end,have been shown to be inadequate for fast diagnostic design.Our laser facility,the LIL,will be able to focus up to 60kJ into a volume of less than 1mm 3.We have to evaluate the electromagnetic pulse (EMP )where diagnostics,cables,and oscilloscopes will be installed.We performed electromagnetic measurements inside and outside the OMEGA target chamber.The electromagnetic pulse generated by the target chamber contains very high frequency components above 1GHz.The electric field is around a few kV/m outside and goes up to 20kV/m inside the target.We designed a specific electromagnetic probe for pulse measurement with a rise time down to 100ps.An ultrashort rise time EMP bench test was built to test apparatus before installation around a target chamber.It produces an electric field higher than 5kV/m with a rise time under 100ps.©2004American Institute of Physics.[DOI:10.1063/1.1787608]I.INTRODUCTIONElectromagnetic compatibility (EMC )is “The ability of a system or equipment to function satisfactorily in its elec-tromagnetic environment without introducing intolerable electromagnetic disturbances to anything in that environ-ment.”The three elements of an electromagnetic pulse (EMP )episode are the source,the victim,and the coupling path.They are characterized by their sensitivity and bandwidth.An EMC solution can be placed at either end of the coupling path,or in between,to make the sources less emit-ting or the victim less susceptible.There are engineering constraints and cost aspects in deciding whether to put the suppression burden on the source,the victim,or the coupling mon sense dictates that the suppression should be made at/or near the source.This is not always feasible,es-pecially for diagnostic measurements where electromagnetic interference (EMI )is one of the undesirable side effects of the physical experiment.Thus,in many instances,solutions will be applied to the victim’s side or along the coupling path.II.IMMUNITY STANDARDS AND FAST DESIGN SPECIFICITYThe techniques described in IEC 61000-5-2:1997(EMC–Installation and mitigation guidelines–Earthing and cabling )principally address the mitigation achievable by re-duction of the coupling through appropriate practices on the implementation of bonding.This improves EMC in equip-ment,systems,and installations by creating a low-impedance path to the local rf reference or a low-impedance run along an existing cable.IEC 61000-6-2:1997–Immunity for industrial environ-ments applies to electrical and electronic apparatus intended for use in industrial environment.The object of this standard is to define the immunity test and level requirements for apparatus defined in the scope in relation to continuous and transient,conducted and radiated disturbances including electrostatic plying with this standard is sufficient for 90%of experiments.Most of the time,the specificity of fast diagnostic is to operate during high pulse electromagnetic environments.For this reason,the most important specific standards areIEC61000-4-2:Electrostatic discharge test;IEC61000-4-4:Electrical fast transient/burst test;IEC61000-4-5:Surge immunity test;and IEC61000-4-9:Pulse magnetic field test.The “pulse”specificity of fast diagnostic needs to take performance criteria into account The variety and the diver-sity of the apparatus within the scope of these standards make it difficult to define precise criteria for the evaluation of the immunity test results.In order for criterion to be ap-plicable,the pulse perturbation must be synchronized to the fast diagnostic operation.We have seen that,most of the time,we only require strict application of standards.But physical experiments can cause very high electromagnetic interferences.In this case,we use a standard test,only modified.For example,the elec-trostatic discharge generator produces high electric field lev-els (few kV/m )in a ring around the discharge point.This is similar to target chamber radiation but in a small area.Wea )Electronic mail:joel.raimbourg@cea.frREVIEW OF SCIENTIFIC INSTRUMENTS VOLUME 75,NUMBER 10OCTOBER 20040034-6748/2004/75(10)/4234/3/$22.004234©2004American Institute ofPhysicsalso use a surge immunity test generator to simulate induced current from a capacitor bank discharge in a laser.III.SOURCE IDENTIFICATIONUsually,current,voltage and rise time characteristics are sufficient for EMC source identification.But sometimes,measurements are necessary.We illustrate this approach with an example:EMC on plasma diagnostics in a 10–60kJ class laser.A.Radiated EMI measurementOur laser facility,the LIL (Ligne d’Integration Laser ),will be able to focus up to 60kJ into a volume of less than a mm 3.We had to evaluate the electromagnetic pulse (EMP )inside and outside the target chamber where diagnostics,cables,and oscilloscopes will be installed.We performed experiments at the OMEGA laser facility at the University of Rochester,NY .It generates 30kJ of UV light with a 1ns duration.To estimate immunity level needed for instrumentation,we measured the electromagnetic field generated inside and out-side of the target chamber.We designed specific electromag-netic probes for this experiment.There was a 1cm 2magnetic loop with a Moebius design to achieve a rise time down to 100ps.The probe was con-nected to a 10m high frequency cable and a 3GHz oscillo-scope ͑TDS 694C ͒.B.ResultsThe electromagnetic pulse (Fig.1)generated by the tar-get chamber contains very high frequency components above 1GHz (Fig.2).Outside,the field decreases with the inverse of the distance with 4kV/m at 1m from the wall.Inside the chamber,we measured an electric field of up to 20kV/m.With high level,high frequency field,we had to design spe-cific radiation bench tests.IV.RADIATED EMI TEST A.EMI bench testWe used two different bench tests to generate a high radiation field.Our goal was to test diagnostic equipment before installing them close to a target chamber.The first main test is a strip line initially designed for nuclear electromagnetic pulse simulation.It is able to pro-duce free radiated field up to 100kV/m with 3ns risetime.FIG.1.H field radiated in the targetchamber.FIG.2.H field radiated in the target chamber (spectral density ).FIG.3.Ultrashort rise time EMP bench test.Rev.Sci.Instrum.,Vol.75,No.10,October 2004Plasma diagnostics 4235To increase equivalent frequency,we built an ultrashort rise time EMP bench test (Fig.3).A high voltage and fast rise time generator is connected to a double ridge guide an-tenna.It produces electric field higher than 5kV/m with rise time under 100ps.B.Oscilloscope under an ultrashort rise time fieldThe previous bench tested a TDS 694C oscilloscope.Two channels were connected to a RG58cable (single braid ),a SHF8cable (double braid )and a 50⍀terminal.The two others were only connected with their caps.The high level,short rise time electric field induced parasite level from 10mV (short cap )to 200mV (cable )(Fig.4).V.SINGLE POINT/MULTIPLE POINT GROUNDINGThe OMEGA laser facility is single point grounded.For EMI measurements,we first needed to insulate the BNC feedthrough connector located in the target chamber wall.Our first measurements showed the EMI field plus a strange large pulse a few hundred nanoseconds later (step 1).The second pulse could have been ion impact from the target to the probe.We removed the insulation on each BNC connector.This reduces the level of the pulse (step 2).Next,we put a glass screen to filter ions in front of the H field probe.We changed low EMC immunity BNC connectors for SMA connectors and we chose a higher EMC immunity cable with two braids (step 3).Figure 5shows the results of these three steps and clearly indicates that it was an EMIproblem.FIG.4.Parasites induced by radiatedEMP.FIG.5.Single point vs multiple point grounding effect.4236Rev.Sci.Instrum.,Vol.75,No.10,October 2004J.Raimbourg。