High Voltage Measurements on a Prototype Pfn for the Lhc Injection Kickers

Two LHC injection kicker magnet systems must produce a kick of 1.3 T.m each with a flattop duration of 4.25 μs or 6.5 μs, a rise time of 900 ns, and a fall time of 3 μs. The ripple in the field must be less than ±0.5%. The electrical circuit of the complete system has been simulated with PSpice[3]. The model includes a 66 kV resonant charging power supply (RCPS), a 5 Ω pulse forming network (PFN), a terminated 5 Ω kicker magnet, and all known parasitic quantities. Component selection for the PFN was made on the basis of models in which a theoretical field ripple of less than ±0.1% was attained. A prototype 66 kV RCPS[1,6] was built at TRIUMF and shipped to CERN. A prototype 5 Ω system including a PFN[2], thyratron switches, and terminating resistors, was built at CERN. The system (without a kicker magnet) was assembled as designed without trimming of any PFN component values. The PFN was charged to 60 kV via the RCPS operating at 0.1 Hz. The thyratron timing was adjusted to provide a 30 kV, 5.5 μs duration pulse on a 5 Ω terminating resistor. Measurement data is presented for the prototype PFN, connected to resistive terminators. A procedure has been developed for compensating the probe and oscilloscope amplifier calibration errors. The top of the 30 kV pulse is flat to ±0.3% after an initial oscillation of 600 ns total duration. The post-pulse period is flat to within ±0.1% after approximately 600 ns from the bottom of the falling edge of the pulse. A calculation was performed in which a measured 27.5 kV pulse with a 5.5 μs flattop was fed into a PSpice model of a kicker magnet with a 690 ns delay length. The resultant predicted kick rise time, from 0.2% to 99.8%, is 834 ns and the fall time 2.94 μs, for a field pulse with a flattop of 4.69 μs and a ripple of less than ±0.2%.