Installation of MKICool magnets in Pt. 8 completed!

By Giorgia Favia, Tobias Stadlbauer & Thomas Kramer for SY-ABT

The LHC is equipped with two injection kicker (MKI) systems for deflecting the incoming particle beams onto the LHC’s orbits. Each system, located at Point 2 (MKI2) and Point 8 (MKI8), consists of four MKI magnets.

The MKIs employ a large amount of ferrite to generate the required pulsed field homogeneity and magnitude. Since the yoke is directly exposed to the beam it is susceptible to beam induced heating. To mitigate this, the MKIs incorporate a 3-meter-long alumina chamber that provides mechanical support and electrical insulation for beam screen conductors. These conductors shield the yoke from high-frequency beam-induced effects.

At the higher beam intensities expected for the High Luminosity (HL) LHC, the conventional beam screens are insufficient to provide the necessary reduction in beam coupling impedance to keep the beam induced heating at acceptable levels. This has led to a major upgrade: the MKICool project which features an improved Cr₂O₃ coated alumina chamber, the integration of a water cooled “RF damper” as well as other smaller performance improvements.

The RF damper is a small ferrite loaded copper cavity designed to redistribute a significant proportion of the beam induced power losses, thereby reducing the residual power deposition in the MKI magnet.

Achieving an effective thermal interface between copper and ferrite is a complex challenge. Special efforts are still being made to improve the heat transfer between these surfaces, maximizing the thermal contact conductance (TCC).

The high secondary electron yield (SEY) of alumina (~9) used for the beam screen chambers causes electron cloud formation. To mitigate the dynamic vacuum activity and the risk of breakdown, surface conditioning is required after operational restarts and when beam parameters are increased. To prevent an MKI magnet from being a limiting factor in LHC operation, the SEY of the alumina tube’s inner surface has been significantly reduced by applying a magnetron sputtered Cr₂O₃ coating.

The first MKICool (MKI8D) was installed at Point 8 during EYETS 2022/23, followed by a second one (MKI8C) during EYETS 2023/24. Figure 2 shows the measured temperatures of the MKI magnets at their upstream end during LHC operation in early 2024. The upstream temperature increase of the MKICool is only 30% of that observed with the previous design, confirming the effectiveness of the upgrade.

Significant efforts have been made to further improve component qualification and performance during the upgrade to ensure smooth conditioning and reliable operation. The ABT team, supported by CERN colleagues, has worked hard to ensure the timely preparation and installation of the third and fourth MKICool magnets at Point 8 during YETS 2024/25.

This major milestone completes the upgrade of the entire injection point 8. The full MKI upgrade in point 2 will be completed during Long Shutdown 3.