Electromagnetic compatibility management for fast diagnostic design

This paper presents an overview of electromagnetic compatibility (EMC) management for fast diagnostic design. In research centers, we often use prototypes or very specific diagnostics which exist in very few small number. Technical specifications are close to physical limits or hard to reach. It takes a considerable effort to put them in working order. Often, there is no real expertise on EMC. However, electromagnetic interference (EMI) could ruin the system. At best, it will decrease the signal to noise ratio. In the worst cases, the diagnostic will not work or could be destroyed. Generally, EMI occurs when an electrical disturbance from either natural phenomena (electrostatic discharge, lightning, and so on) or electronic equipment causes an undesired response in another piece of equipment. EMC is just the opposite of EMI; that is, EMC is said to exist when no equipment or system causes EMI to other equipment or systems. The three elements of an EMI episode are the source, the victirn, and the coupling path. 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. We illustrate this approach with an example: EMC on plasma diagnostics in a 10 - 60 kiloJoule class laser. Up to now, all the diagnostics developed for laser produced plasmas have mainly been designed without taking into account the direct effects of radiated energies emitted by the plasma itself on the diagnostic active components. Our laser facility, the LIL, will be able to focus up to 60 kJ into a volume of less than 1 mm(3). We have 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. We designed a specific electromagnetic probe for pulse measurement with a rise time down to 100 ps. We will discuss problems induced by the grounding approach and show how to cope with them.