Much of the research and development work for the High-Luminosity LHC (HL-LHC) aims to protect the accelerator’s fragile components from the detrimental effects of high luminosity, such as radiation and increased heat. The installation of the “MKI-Cool” LHC kicker magnet (MKI), the first of a series of eight, during this year-end technical stop marks another successful milestone in this endeavour: a water-cooled toroidal ferrite cylinder will lower the projected heat load deposited onto the kicker magnet yokes to allow the HL-LHC to operate well.
The LHC’s two kicker systems, each made up of four magnets and pulse generators, are found at the intersection of the LHC ring and its two transfer lines that funnel particles from the SPS. As their name suggests, kicker magnets give each injected bunch a kick to put it on the LHC orbit. As the kick must leave the circulating LHC beam untouched, each magnetic field pulse lasts only 8 microseconds: kicker magnets must be swift and precisely timed.
These specs make kicker magnets particularly vulnerable to their harsh environment: while the highly energetic LHC beam whizzes through the magnet’s aperture, the MKI cannot be completely shielded from the beam-induced heating, as a shielding would interfere with its high-frequency magnetic field pulse. In addition, the high-voltage pulse required precludes any water-cooling of the MKI yoke, which constitutes a serious hurdle as the yoke loses its magnetic properties above the critical temperature of 125 °C. Under these conditions, with dysfunctional kickers, mis-kicked particles would cause quenches in the LHC superconducting magnets. Measures have already been taken to avert this risk in the current accelerator, but they would not suffice to guard the magnets from the expected four-fold increase of the heat load in the context of higher luminosity.
The MKI-Cool system is an ingenuous solution thought up by the Accelerator Beam Transfer group (SY-ABT) to sustainably protect the kicker magnets. A toroidal ferrite cylinder is mounted upstream of the MKI-Cool aperture to absorb a significant portion of the beam-induced heating, thus reducing the heating of the magnet’s yoke. In addition, the ferrite cylinder is cooled using water (hence the name, MKI-Cool). The MKI-Cool ferrite yoke is expected to stay below a temperature of 100 °C, even with high-luminosity beams.
The first MKI-Cool was installed at LHC Point 8 on 11 January, replacing a standard MKI. Once the LHC is restarted, the interaction of the particle beam with the MKI-Cool will test the technology’s performance. Provided this test yields positive results, the seven remaining MKI-Cools will be installed before the start of HL-LHC operations.