An improved beam screen for the lhc injection kickers

Abstract

The two LHC injection kicker magnet systems must produce a kick of 1.3 T.m with a flattop duration variable up to 7860 ns, and rise and fall times of less than 900 ns and 3000 ns, respectively. Each system is composed of two resonant charging power supplies (RCPSs) and four 5 Ω transmission line kicker magnets with matched terminating resistors and pulse forming networks (PFNs). A beam screen is placed in the aperture of the magnets: the screen consists of a ceramic tube with conductors on the inner wall. The conductors provide a path for the image current of the, high intensity, LHC beam and screen the ferrite against Wake fields. The conductors initially used gave adequately low beam coupling impedance however inter-conductor discharges occurred during pulsing of the magnet: an alternative design was discharge free at the nominal operating voltage but the impedance was too high for the ultimate LHC beam. This paper presents the results of a new development undertaken to meet the often conflicting requirements for low beam coupling impedance, fast magnetic field risetime and good high voltage behaviour. High voltage test results and thermal measurements are also presented. Large Hadron Collider Project AbstractThe two LHC injection kicker magnet systems must produce a kick of 1.3 T.m with a flattop duration variable up to 7860 ns, and rise and fall times of less than 900 ns and 3000 ns, respectively. Each system is composed of two resonant charging power supplies (RCPSs) and four 5 Ω transmission line kicker magnets with matched terminating resistors and pulse forming networks (PFNs). A beam screen is placed in the aperture of the magnets: the screen consists of a ceramic tube with conductors on the inner wall. The conductors provide a path for the image current of the, high intensity, LHC beam and screen the ferrite against Wake fields. The conductors initially used gave adequately low beam coupling impedance however inter-conductor discharges occurred during pulsing of the magnet: an alternative design was discharge free at the nominal operating voltage but the impedance was too high for the ultimate LHC beam. This paper presents the results of a new development undertaken to meet the often conflicting requirements for low beam coupling impedance, fast magnetic field risetime and good high voltage behaviour. High voltage test results and thermal measurements are also presented.

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

“…3, to further reduce the electric field, and thus decrease the probability of electrical breakdown, the conductive wires have graded lengths at the upstream end. The vacuum gap and graded lengths were introduced in 2013 [30] and are part of the so-called post-LS1 design. In the LHC, all the injection kicker magnets have such a design.…”

“…4), whereas the lowest voltage is induced on the screen conductor closest to the GND busbar (#13): Figure 6 shows the maximum induced voltage for each of the 24 screen conductors (red curve with circular markers), as well as the difference in the maximum induced voltage between two neighboring screen conductors (green curve with triangular markers). Voltage breakdowns, along the surface of the alumina tube, between neighboring screen conductors or between screen conductors and the metallic cylinder, are a concern during operation of the LHC MKI and issues have occurred [30,31]. Hence, extensive studies were carried out to optimize the HV performance of the LHC MKI [30,32,33].…”

“…Voltage breakdowns, along the surface of the alumina tube, between neighboring screen conductors or between screen conductors and the metallic cylinder, are a concern during operation of the LHC MKI and issues have occurred [30,31]. Hence, extensive studies were carried out to optimize the HV performance of the LHC MKI [30,32,33].…”

Source of horizontal instability at the CERN Proton Synchrotron Booster

“…Beam-coupling impedance reduction techniques have been implemented for the MKI kickers [46] used for injection into the CERN LHC rings. A 3 m long alumina tube was manufactured with 24 slots on its inside diameter [47,48], where beam screen conductors are inserted. The design of the upstream end of the beam screen, unintentionally resulted in an open-ended half-wavelength resonator.…”

Challenges and Plans for Injection and Beam Dump

“…The screen consists of a ceramic tube with conductors lodged in grooves in the inner wall. To limit longitudinal beam coupling impedance, while allowing a fast magnetic field rise-time, the conductors are connected to the standard LHC vacuum chamber at one end and are capacitively coupled to it at the other end [7]. In the original design the extruded ceramic tube had 24 nickel-chrome (80/20) conductors, each 0.7 mm × 2.7 mm with rounded corners, inserted into slots.…”