Ultra Fast Beam Loss Mechanisms at the LHC and their Detection for Use in Machine Protection

At the Large Hadron Collider (LHC) high intensity proton beams are accelerated up to 7 TeV resulting in 362 MJ of stored energy in each beam. Losses of high ener- getic beam particles lead to energy deposition in the accelerator components. The deposition of a fraction of the total beam energy over a short time in the accelerator components can cause quenches in the superconducting magnets and in the worst case result in structural damage. Therefore, the beam losses are carefully monitored all along the LHC. When the beam losses, and thus the energy deposition, exceeds pre-defined limits the beam dumping system is triggered to extract the beams in a controlled manner within 270 µs. During the LHC operation losses were observed that occur in time scales below the reaction time of the beam dumping system. In order to protect the LHC from these losses the loss amplitudes have to be reduced. Therefore, it is important to under- stand the loss mechanisms causing these ultra fast losses. The time structure of these ultra fast beam losses cannot be resolved by the regular beam loss monitoring system. In the scope of this thesis diamond based beam loss monitors (dBLMs) were installed at the LHC, which provide nanosecond resolution and cover a wide range of loss amplitudes. These detectors were used to perform high resolution measurements of the ultra fast beam losses in order to identify the underlying loss mechanisms. The results presented in this thesis include characterisation experiments of the in- stalled dBLMs and the analysis of several scenarios of ultra fast beam losses during the LHC operation. The losses during beam injection, which were limiting the LHC operation in 2015 and 2016, will be discussed in great detail. Mitigation techniques based on this analysis were implemented in the LHC operation and allowed to reduce the injection losses by one order of magnitude.