A Response Matrix Approach to Skew-Sextupole Correction in the LHC at Injection

To date, no dedicated attempt has been made to correct the skew-sextupole (𝑎3 ) 3𝑄𝑦 resonance in the LHC at injection. This topic has recently gained interest, following investigation of the emittance growth during the LHC energy ramp due to third-order islands. The LHC is equipped with skewsextupole correctors in the experimental insertions, intended for local compensation at top energy, and with families of skew-sextupole magnets in the arcs, intended for chromaticcoupling correction (but not optimally placed for 3𝑄𝑦 compensation). Simulation studies were performed to assess whether these correctors could compensate 3𝑄𝑦 in the LHC at injection via a response matrix approach, based on values at the BPMs. Corrections for 3𝑄𝑦 could be found within magnet powering limitations, but required significantly increased corrector strength compared to chromatic-coupling compensation.