Where is my pulse M Paschen please help

Where is my pulse ? M. Paschen, please help ! L. Ducimetière, with voluntary and involuntary contribution from ABT colleagues L. Ducimetière - ABT Group Meeting 01/06/2018 2

Outline The facts ZDFA 2018 MKBH 2003 The investigation Why does this happened ? The Paschen curve Can we profite from that ? L. Ducimetière - ABT Group Meeting 01/06/2018 3

ZDFA, the ELENA fast Deflector ZDFA is a fast pulsed electric field separators used for the two extraction. It works at ± 6. 25 k. V L. Ducimetière - ABT Group Meeting 01/06/2018 4

ZDFA, the ELENA fast Deflector ZDFA is a fast pulsed electric field separators used for the two extraction. It works at ± 6. 25 k. V Broken switches or simultaneous short circuit of both electrodes ? L. Ducimetière - ABT Group Meeting 01/06/2018 5

MKBH, the LHC beam dump dilution kicker magnet MKBH is a fast pulsed electro-magnet used for diluting (horizontally) the extracted beam before the dump. It works at 27 k. V, 25 k. A Sudden short circuit at the entrance of the magnet ? L. Ducimetière - ABT Group Meeting 01/06/2018 6

MKBH, the LHC beam dump dilution kicker magnet MKBH is a fast pulsed electro-magnet used for diluting (horizontally) the extracted beam before the dump. It works at 27 k. V, 25 k. A Sudden short circuit at the entrance of the magnet ? L. Ducimetière - ABT Group Meeting 01/06/2018 7

The investigation ionisation of residual gas Both ZDFA and MKB operate under vacuum but can also be pulsed and tested up to full voltage in air. • At time of the incident, both devices were under pumping (around 10 -3 mbar) • Similar strange short circuit phenomena have been reported • • in the SPS electrostatic septa ZS while the vacuum was leaking • During under-vacuum bake-out with mains voltage (lamp or resistor) L. Ducimetière - ABT Group Meeting 01/06/2018 8

The Paschen curve The Paschen's Curve gives the breakdown voltage, between two electrodes in a gas as a function of pressure x gap length (1 Torr ≈ 1. 3 mbar) Condition for ionisation : The electron shall have a minimum amount of energy (ionisation potential) Left side : Insignificant ionization. Electrons might gain lots of energy, but have fewer ionizing collisions Right side : Too many collisions. Electrons loose energy in the many collisions and need more voltage to ionize the gas L. Ducimetière - ABT Group Meeting 01/06/2018 9

Can we profite from that ? yes, … Septa and Kickers: devices using Ultra High Vacuum as HV insulator. Maximises the beam aperture. SF 6 at high pressure: used in HV pulse forming Lines and transmission cables, and magnet entry boxes Thyratrons: widely used as HV switches for kickers. Magnetron sputtering: Ti deposition in LHC MKD ceramic chambers Cr 2 O 3 deposition for low SEY in MKI ceramic sreen tube WARNING: Dangerous area for devices designed for air or UHV, even at mains voltage L. Ducimetière - ABT Group Meeting 01/06/2018 10