Abstract
The High Luminosity upgrade of the Large Hadron Collider (HL-LHC) aims to achieve an integrated luminosity of 200-300 fb(-1) per year, including the contribution from the upgrade of the injector chain. For the HL-LHC the larger crossing angle together with a smaller beta function at the collision point would result in more than 70% luminosity loss due to the incomplete geometric overlap of colliding bunches. To recover head-on collisions at the high-luminosity particle-physics detectors ATLAS and CMS and benefit from the very low beta* provided by the Achromatic Telescopic Squeezing (ATS) optics, a local crab cavity scheme provides transverse kicks to the proton bunches. The tight space constraints at the location of these cavities leads to designs which are axially non-symmetric, giving rise to high order multipoles components of the main deflecting mode and, since these kicks are harmonic in time, we expand them in a series of multipoles in a similar fashion as is done for static field magnets. In this work we calculate, for the first time, the higher order multipoles and their impact on beam dynamics for three different crab cavity prototypes. Different approaches to calculate the multipoles are presented. Furthermore, we perform the first calculation of their impact on the long term stability of the machine using the concept of dynamic aperture.
Highlights
The Large Hadron Collider (LHC) will undergo a major upgrade around 2026 to increase its discovery potential
The main enhancements foreseen in this scenario include new high-field and large-aperture inner triplet quadrupoles used to squeeze the beam and bring it into collision, use of crab cavities to recover head on collisions at interaction point 1 (IP1) and IP5 and various improvements in the experiments to sustain higher luminosity levels
In order to give a scale to the rf multipolar strength for LHC crab cavities (CCs) prototypes, they can be compared to the field quality of the D2 separation dipoles that are currently installed in the LHC ring in IR1 and IR2 [23]
Summary
The Large Hadron Collider (LHC) will undergo a major upgrade around 2026 to increase its discovery potential. The crab cavities should fit in between the two beam lines near the separation dipole D2 [9] This space constraint, plus the 400 MHz rf frequency requirements, forces the design to be extremely compact, breaking the axial symmetry of the cavity, and giving rise to time varying higher order multipoles. We make the first complete calculations of the multipole content of all three crab cavity designs for the LHC and make the first assessment of the expected effect on the single particle long term stability in a proton machine.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
