Interaction region design driven by energy deposition

The European Strategy Group for High Energy Physics recommends to study collider designs for the post-LHC era. Among the suggested projects there is the circular 100 TeV proton-proton collider FCC-hh. Starting from LHC and its proposed upgrade HL-LHC, this paper outlines the development of the interaction region design for FCC-hh. We identify energy deposition from debris of the collision events as a driving factor for the layout and draft the guiding principles to unify protection of the superconducting final focus magnets from radiation with a high luminosity performance. Furthermore, we offer a novel strategy to mitigate the lifetime limitation of the first final focus magnet due to radiation load, the Q1 split.

Figure 1

Layout of the LHC interaction region.

Figure 2

$\beta$ functions of the scaled LHC lattice with $L^{*}=46\mathrm{m}$ for ${\beta }^{*}=0.8\mathrm{m}$. The $\beta$ function in the dispersion suppressors are scaled as well and will be adapted to the arc lattice.

Figure 3

Magnet cross sections: quadrupole (top) and orbit corrector (bottom).

Figure 4

Peak power densities (top) and peak doses (bottom) for the first lattice compared with LHC and HL-LHC for horizontal crossing. The horizontal axes were chosen to overlap similar magnets in the LHC and FCC lattices. The crossing angles were $285\mu \mathrm{rad}$ for LHC, $590\mu \mathrm{rad}$ for HL-LHC and $86\mu \mathrm{rad}$ for FCC.

Figure 5

Peak power densities (top) and peak doses per $3000{\mathrm{fb}}^{-1}$ (bottom) for the $L^{*}=36\mathrm{m}$ lattice for different shielding thicknesses at $70\mu \mathrm{rad}$ vertical half crossing angle and assuming 100 mm coil aperture.

Figure 6

Interaction region with $L^{*}=36\mathrm{m}$ and ${\beta }^{*}=0.3\mathrm{m}$.

Figure 7

Minimum ${\beta }^{*}$ of the $L^{*}=36\mathrm{m}$ lattice for beam star clear requirements of $12–21\sigma$. The baseline goal of ${\beta }^{*}=1.1\mathrm{m}$ poses no problem from the aperture point of view. The “ultimate” goal of ${\beta }^{*}=0.3\mathrm{m}$ can barely be reached with uniform apertures. With individual apertures, the baseline can be reached or exceeded within a beam stay clear of up to $\approx 17\sigma$.

Figure 8

${\beta }^{*}$ reach of the $L^{*}=61\mathrm{m}$ lattice for beam stay clear requirements of $12–21\sigma$. The reachable ${\beta }^{*}$ is very similar to the one of the $L^{*}=36\mathrm{m}$ lattice with individual apertures. Note that the triplet magnets in the $L^{*}=61\mathrm{m}$ all have similar gradients, so all apertures are the same.

Figure 9

Comparison of the peak doses per $3000{\mathrm{fb}}^{-1}$ for the $L^{*}=36\mathrm{m}$ and the $L^{*}=61\mathrm{m}$ lattices with 15 mm shielding.

Figure 10

Minimum ${\beta }^{*}$ for the $L^{*}=36\mathrm{m}$ lattice (top) and $L^{*}=61.5\mathrm{m}$ (bottom) lattice analytically scaled in length, scaling factor and resulting $L^{*}$ (top horizontal axis). Markers show ${\beta }_{\min }^{*}$ values obtained with MAD-X aperture calculations. The green vertical lines indicate the nonscaled value.

Figure 11

Detector and interaction region layout leading to the $L^{*}=45\mathrm{m}$ lattice. The IP is located at (0,0).

Figure 12

Beam stay clear of the $L^{*}=45\mathrm{m}$ lattice for different values of ${\beta }^{*}$. Allowing a beam stay clear of only $12\sigma$, the aperture allows a ${\beta }^{*}$ down to 0.05m. Alternatively, the ultimate baseline goal of ${\beta }^{*}=0.3\mathrm{m}$ leaves a beam stay clear of $42\sigma$, allowing thicker shielding. The beam stay clear was calculated with 15 mm of shielding in every magnet.

Figure 13

Peak dose distributions per $3000{\mathrm{fb}}^{-1}$ for the $L^{*}=45\mathrm{m}$ scenario with and without spectrometer. The strong early deflection of the debris due to the spectrometer leads to a significant peak dose increase, most notably in Q1.

Figure 14

Peak dose distributions $L^{*}=45\mathrm{m}$ for vertical crossing with a shielding thickness of 55 mm for an integrated luminosity of $3000{\mathrm{fb}}^{-1}$. The massive increase in shielding reduced the dose by a factor of 10.

Figure 15

Change of the optics from unsplit (dark) to split (light) Q1 for $r_{\mathrm{g}}=1.2$ and 1.5, each with $\lambda =0.3,1.0,3.0$. No rematching was performed.

Figure 16

Qualitative sketch of the peak dose in the Q1. The horizontal axis extends over the length of Q1(a/b) shown at the top. The black line describes the peak dose for an unsplit Q1. The expected changes for splitting Q1 are shown by the dashed red and green lines.

Figure 17

Peak doses of the triplet with unsplit and split Q1. For an optimized Q1 split (V2), the maximum peak dose is reduced by about 33% with respect to the unsplit 20 mm shielding case.

Figure 18

Minimum dynamic apertures for the IR lattices with $L^{*}=36\mathrm{m},45\mathrm{m}$, and 61 m with ${\beta }^{*}=0.3\mathrm{m}$. The crossing angles were turned off.

Figure 19

Minimum dynamic apertures for the $L^{*}=45\mathrm{m}$ lattice with ${\beta }^{*}=0.3\mathrm{m}$.

Figure 20

Minimum dynamic apertures for the $L^{*}=45\mathrm{m}$ lattice with ${\beta }^{*}=0.3\mathrm{m}$ for different local multipolar corrections.