Electrical breakdown | EPFL Graph Search

In electronics, electrical breakdown or dielectric breakdown is a process that occurs when an electrically insulating material (a dielectric), subjected to a high enough voltage, suddenly becomes a conductor and current flows through it. All insulating materials undergo breakdown when the electric field caused by an applied voltage exceeds the material's dielectric strength. The voltage at which a given insulating object becomes conductive is called its breakdown voltage and, in addition to its dielectric strength, depends on its size and shape, and the location on the object at which the voltage is applied. Under sufficient electrical potential, electrical breakdown can occur within solids, liquids, or gases (and theoretically even in a vacuum). However, the specific breakdown mechanisms are different for each kind of dielectric medium. Electrical breakdown may be a momentary event (as in an electrostatic discharge), or may lead to a continuous electric arc if protective devices

DC Breakdown in gases for complex geometries from high vacuum to atmospheric pressure

Ralph Schnyder

This thesis presents an experimental investigation and a numerical simulation of breakdown in a ring assembly. Previous works are mostly limited to breakdown in simple geometries such as parallel plates or pin-to-plate. Here we discuss the effect of more complex geometries for DC breakdown in gases over a large pressure range from high vacuum to atmospheric pressure. The breakdown voltage versus pressure curves shows a similar shape as Paschen curves but with a wide flat plateau between the low and high pressure thresholds. The low pressure threshold determines the limit between gas and vacuum discharges. Additional optical emission spectroscopy confirms the presence of two different kinds of discharges: Gas and vacuum dis- charges. Moreover the global shape of the gas breakdown voltage curve in the ring assembly has been fully understood by a complementary numerical simulation. Fur- ther current-voltage study showed that voltage only is the most significant factor for breakdown and that current determines the kind of discharge after breakdown. As the breakdown voltages are lower for gas discharges than for vacuum discharges, a numerical simulation model for gas breakdown using a fluid model was developed in order to support the experimental conclusions. Starting as simple as possible with par- allel plates (1 mm and 100 mm gap width representing approximatively the shortest and longest electric field path length in the ring assembly geometry) and extending to double gap and multi-gap geometries, an understanding of the overall shape of the breakdown voltage versus pressure curve is established: The high (low) pressure thresholds of gas discharge are determined by the shortest (longest) electric field path length in a complex geometry. Moreover, the availability of multiple path lengths leads to a breakdown voltage minimum over a wide range of intermediate pressure because breakdown can occur in the most favorable gap. Finally, the numerical simulation in the ring assembly shows the importance of parameters such as the secondary electron emission coefficient which play a major role in determining the breakdown voltage value.

EPFL2013

Helical beam screen for the Future Circular Collider for hadrons injection kicker magnets

Agnieszka Chmielinska

The Future Circular Collider for hadrons (FCC-hh) is the proposed high-energy frontier particle collider, which is expected to enable proton-proton collisions at a center-of-mass energy of 100 TeV. The specifications for the FCC-hh injection kicker system are very challenging. To provide fast magnetic field rise and fall times, and low ripple during the flat-top, ferrite loaded transmission line type magnets will be used. To limit the beam coupling impedance, a suitable beam screen will be placed in the aperture of each kicker magnet. Due to issues associated with the "conventional" beam screen design, used in the injection kickers magnets of the Large Hadron Collider (LHC), such as high voltage (HV) breakdowns and yoke heating problems, we have developed a novel concept of a helical beam screen. The fundamental advantage of the new design, in comparison to the conventional beam screen, is a significant reduction of the maximum voltage induced on the screen conductors, thus a greatly reduced probability of an electrical breakdown of the beam screen. In addition, the longitudinal beam coupling impedance of the helical beam screen is optimized to reduce power deposition in the kicker magnet. Furthermore, the helical beam screen allows a reduction of the maximum transverse beam coupling impedance of the kicker system. Detailed numerical simulations, theoretical studies and experimental results demonstrate that a new design is a promising solution not only for the FCC-hh, but also for existing machines.

2020

New spiral beam screen design for the FCC-hh injection kicker magnet

Agnieszka Chmielinska

The injection kicker system for the Future Circular Collider (FCC-hh) must satisfy demanding requirements. To achieve low pulse ripple and fast field rise and fall times, the injection system will use ferrite loaded transmission line type magnets. The beam coupling impedance of the kicker magnets is crucial, as this can be a dominant contribution to beam instabilities. In addition, interaction of the high intensity beam with the real part of the longitudinal beam coupling impedance can result in high power deposition in the ferrite yoke. This gives a significant risk that the ferrite yoke will exceed its Curie temperature: hence, a suitable beam screen will be a critical feature. In this paper, we present a novel concept a spiral beam screen. The fundamental advantage of the new design is a significant reduction of the maximum voltage induced on the screen conductors, thus decreased probability of electrical breakdown. In addition, the longitudinal beam coupling impedance is optimized to minimize power deposition in the magnet.

IOP PUBLISHING LTD2019

DC Breakdown in gases for complex geometries from high vacuum to atmospheric pressure

Ralph Schnyder

EPFL2013