Abstract
In the CERN LHC, optics transitions are mainly required to control the beam size at the four experimental interaction points. The current method, based on linearly-interpolated optics functions over a small set of matched optics and parabolic time-domain segments, introduces non-zero beta-beating and it is not optimal in time. This contribution presents an alternative approach, based on continuously-matched optics solutions distributed in time domain by using a realistic model of the superconducting circuits, which optimises the overall process duration. This method requires a change in the paradigm used in the control system and it is proposed for the future High Luminosity LHC (HL-LHC) runs.
Highlights
The LHC [1] and the HL-LHC [2, 3] lattice is composed of 8 arcs and 8 insertion regions (IR) for the two counter rotating beams (Beam 1 and Beam 2)
Each IR is equipped with a large number of individually-powered quadrupole (IPQ) circuits (324 in total for the 8 insertions)
The final solution has been obtained by optimising the transition of each individual insertion, merging the insertions after matching their individual timings and generating the complete optics sets to perform the global chromatic correction
Summary
The LHC [1] and the HL-LHC [2, 3] lattice is composed of 8 arcs and 8 insertion regions (IR) for the two counter rotating beams (Beam 1 and Beam 2). Four IRs (IR1, IR2, IR5, IR8) host the main experiments (ATLAS, ALICE, CMS, LHCb) and the remaining ones (IR3, IR4, IR6, IR7) provide the momentum cleaning, RF and instrumentation, beam dump, and β-cleaning functionalities, respectively. Optics transitions are needed since optics constraints at injection (e.g. aperture and transfer-line matching) are very different from experimental conditions at flat top (e.g. low-β at the interaction point (β∗)). Each IR is equipped with a large number of individually-powered quadrupole (IPQ) circuits (324 in total for the 8 insertions). Each arc is equipped with independent main circuits and trim circuits for each beam (48 circuits in total). In the present [4] and future operations, almost all quadrupole circuits change their momentum-normalised strength during the energy ramp and at flat top ( to other circular colliders [5]). This paper reviews the strategy used currently to implement the optics transitions and proposes a new method to be applied in the HL-LHC to overcome some of the present limitations
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