Development of high $\beta^*$-optics for ALICE

This thesis describes a feasibility study for a special optical configuration in Insertion Region 2 (IR2) of the Large Hadron Collider (LHC), which is host of the ALICE detector. This configuration allows the study of elastic and diffractive scattering during LHC high-intensity proton operation, in parallel to the nominal physics studies in all LHC experiments at the design energy of 7 TeV per beam. Such measurements require the instal- lation of additional Roman Pot (RP) detectors in the very forward region, at longitudinal distances of 150 m to 220 m from the Interaction Point (IP). Apart from being adjusted for a specific betatron phase advance between the IP and the RP detectors, such a configuration must be optimized for the largest possible $\beta^*$ -value, to be sensitive for the smallest possible four-momentum transfer $|t|$. A value of $\beta^*$ = 18 m is compatible with a bunch spacing of 25 ns, considering the LHC design emittance of N = 3.75 μm rad, and a required bunch-bunch separation of $12 \sigma$ at the parasitic bunch encounters. An optical configuration with $\beta^*$ = 18 m and a matched betatron phase advance between IP and RP ($\Delta \psi_{x,y}$= 0.34) has been calculated. The optics are studied for their compatibility with the constraints imposed by the LHC. A crossing angle of $\theta_C$ = 300 $\mu$rad is matched for the optical configuration. The adjustment of the IP-RP phase advances leads to a significant reduction of the phase advance across the IR, so external compensation methods must be applied. In high-intensity operation of the LHC, the phase advance compensation must be applied between IP1 and IP5. However, detailed strategies on these compensations must still be worked out. The detector acceptance for scattered protons is calculated, based on different assumptions for the measurement parameters. The 50% acceptance threshold for the measurement of elastic events is moved from $|t|_{50\%}$ =13 GeV$^2$ with the nominal ALICE optics, to a value of $|t|_{50\%}$ = 0.44 GeV$^2$ with the matched $\beta^*$ = 18 m optics. The most optimistic boundary conditions lead to an acceptance threshold of $|t|_{50\%}$ =0.24 GeV$^2$ , whereas the most pessimistic scenario leads to $|t|_{50\%}$ = 0.78 GeV$^2$ . Remaining studies are outlined, and scenarios with different beam conditions are discussed.