We report on research studies on broadband impedance calculations of the TAN vacuum for the Large Hadron Collider (LHC). The TAN is the zero degree neutral particle absorber and contains the transition from a single vacuum beam tube to two beam tubes. Single bunch collective instability induced by broadband impedance may limit the beam intensity of the LHC. The broadband impedance of each component in the machine needs to be studied carefully, and the total impedance be controlled below certain threshold. Due to the complexity of the TAN chamber geometry, the impedance calculation has to be performed using 3D MAFIA in the time domain. To verify numerical simulation results, a few examples with simple geometries have been studied, and compared with the results obtained by analytical formula and a well-known 2D code ABCI. A 3D model for the TAN chamber is established to estimate the magnitude of longitudinal broadband impedance has been studied numerically as well and will be discussed.

We report on the development of a new technique for the measurement of the longitudinal beam profile in storage rings. This technique, which has been successfully demonstrated at the Advanced Light Source, mixes the synchrotron radiation with the light from a mode-locked solid state laser oscillator in a non-linear crystal. The up-converted radiation is then detected with a photomultiplier and processed to extract, store, and display the required information. The available choices of laser repetition frequency, pulse width, and phase modulation give a wide range of options for matching the bunch configuration of a particular storage ring. Besides the dynamic measurement of the longitudinal profile of each bunch, the instrument can monitor the evolution of the bunch tails, the presence of untrapped particles and their diffusion into nominally empty RF buckets ("ghost bunches").