Achromatic telescopic squeezing scheme and application to the LHC and its luminosity upgrade

Abstract

A novel optics concept, the achromatic telescopic squeezing (ATS) scheme has been invented in the context of the Large Hadron Collider (LHC) upgrade studies, and chosen as the baseline scheme for the optics and layout of the recently approved high luminosity LHC project (HL-LHC). This scheme offers an extremely powerful and flexible machinery in order to strongly reduce à in a symmetric or asymmetric way (i.e. without necessarily imposing the same à in both planes), while perfectly controlling the chromatic aberrations induced, namely the linear and nonlinear chromaticities, the off-momentum beating, and the spurious dispersion from the large crossing angle which is required at small à in the particular case of the (HL)-LHC. The initial motivations of the scheme will be reviewed, followed by a detailed description of its fundamental theoretical foundations. An effective construction of ATS optics will be given and its main features illustrated in the case of the LHC and HL-LHC.

Pile up management at the high-luminosity LHC and introduction to the crab-kissing concept

“…The ambitious performance target for ATLAS and CMS cannot be met without pushing to the extreme both the optics, namely β Ã [2], and the nominal parameters of the LHC beam [3,4]. It relies as well on a number of very challenging new equipments and key innovative technologies, such as: (i) new larger aperture super-conducting magnets in order to preserve the transverse acceptance of the two high-luminosity insertions at low β Ã [5,6], and (ii) crab-cavities which are high-frequency RF transverse deflectors, ensuring quasi-head-on collisions at the interaction point (IP) despite of the crossing angle, hence preserving the luminosity gain with 1=β Ã (see [7] which introduced the crab-crossing concept, and [8] for proposing it as an ingredient for upgrading the LHC performance).…”

The HL-LHC Machine

“…These parameters coupled together imply larger aperture insertion magnets (triplet magnets, D1, D2 and Q4, Q5 magnets), lower operating temperatures for some of the insertion magnets (e.g. Q4 and Q5) and the exploitation of a novel optics matching scheme ATS [2] that utilizes the neighboring arcs for matching the insertion optics to the rest of the machine, requiring some upgrades in the non-experimental insertions (e.g. additional Q5 in IR6).…”

“…Note that due to RF beam loading the abort gap length must not exceed the 3 μs design value. 2 An intensity loss of 5% distributed along the cycle is assumed from SPS extraction to collisions in the LHC. 3 A transverse emittance blow-up of 10 to 15% on the average H/V emittance in addition to the 15% to 20% expected from intra-beam scattering (IBS) is assumed (to reach the 2.5 μm/3.0 μm of emittance in collision for 25 ns/50 ns operation).…”

Collider Beam Physics

“…The final focusing quadrupoles introduce a large chromaticity which must be corrected by sextupoles in dispersive regions placed either locally ("compact final focus" [33]), semi-locally ("modular final focus" [34]) or in the collider arcs (for which the ATS scheme is a particularly powerful example [35]). Residual higher-order chromatic aberrations are important, and so is the field quality of the triplet quadrupoles and the separation dipoles, which are located in the regions with the largest beta functions of the collider.…”