CERN
Development of a Longitudinal Beam Distribution Monitor for LHC
ESR: Adam Jeff (adam.jeff@quasar-group.org)
Supervisor: Thibaut Lefevre (thibaut.lefevre@cern.ch)
The Large Hadron Collider (LHC) at CERN is the world’s largest particle accelerator. It is designed to accelerate and collide protons or heavy ions up to center-of-mass energies of 14 TeV for protons.
Knowledge of the longitudinal distribution of particles is important for various aspects of accelerator operation, in particular to check the injection quality and to characterize the development of ghost bunches before and during the physics periods. In order to study ghost bunches at levels very much smaller than the main bunches, a longitudinal profile measurement with a very high dynamic range is needed.
With this project a new detector, the LHC Longitudinal Density Monitor (LDM) has been developed. It is a single-photon counting system measuring synchrotron light by means of an avalanche photodiode detector. The unprecedented energies reached in the LHC allow synchrotron light diagnostics to be used with both protons and heavy ions.
A prototype monitor has been developed and was installed during the 2010 LHC run. The longitudinally profile of the whole beam has now been successfully measured with a resolution close to the target of 50 ps. On-line correction for the effects of the detector dead time, pile-up and after pulsing allowed a dynamic range of 105 to be achieved.
Development of Transverse Beam Distribution Monitor for LINAC4
ESR: Benjamin Cheymol (benjamin.cheymol@cern.ch)
Supervisor: Federico Roncarolo (federico.roncarolo@cern.ch)
Linac4 is a rather new project at CERN. Its aim is to build a high current H- linac as replacement of the current proton linac as the first stage of the LHC injectors. This new machine will require improved instrumentation as the beams will be so powerful that imperfections in the functioning will cause real damage to the machine. In low energy linacs transverse profile monitors are usually based on interceptive techniques. Typically, a foil or a wire are inserted in the beam path and secondary signals like light or electrical currents, generated by the interaction between the beam and the obstacle, are detected and used in the computation of the particles distribution.
In this project, a monitor based on a set of parallel wires is being developed for the measurement of the profiles of the Linac4 high intensity H- beams. In addition, a system for the measurement of the beam emittance for the whole energy range from the source to 160 MeV is being developed.
Development of Time-resolved Spectrometry and Emittance Measurements on a High Current Electron Beam
ESR: Maja Olvegaard (maya.olvegaard@cern.ch)
Supervisor: Thibaut Lefevre (thibaut.lefevre@cern.ch)
The CLIC Test Facility 3 (CTF3) is an international collaboration at CERN that aims at demonstrating the feasibility of a 3TeV e+-e- Collider, based on the so-called “two-beam acceleration scheme”. The CTF3 provides high current (28 A), high frequency (12 GHz) electron beams which are used to generate high power radiofrequency pulses at 12 GHz by decelerating the electrons in resonant structures.
A Test Beam Line (TBL) has been built up to prove the efficiency and the reliability of the RF power production with the lowest level of particle losses. As the beam propagates along the line, its energy spread grows up to 80% which makes this beam unique. For instrumentation, this unusual characteristic implies the development of new and innovative techniques. One of the most important tasks is to measure the beam emittance and its energy spread with a good resolution. For this purpose the performances of the already existing devices had to be improved or modified significantly. Time resolved spectrometry has been performed with a time resolution better than a nanosecond. In addition, investigations into new OTR screen materials and shapes are being carried out.
Electro-Optical Techniques for the Measurement of Charged Particle Beam Longitudinal Profiles
ESR: Rui Pan (rui.pan@cern.ch)
Supervisor: Thibaut Lefevre (thibaut.lefevre@cern.ch)
Another big challenge in the CTF3 and CLIC projects is to provide accurate measurements of the longitudinal beam profile with a time resolution of better than 20 fs. One of the most promising devices would be based on electro-optical techniques. This project is being realized in close collaboration between CERN and the ultrafast electro-optics diagnostics group based jointly at Dundee University and STFC Daresbury Laboratory, which has an international reputation in the measurement of femtosecond relativistic electron beam bunches. These measurements were pioneered by the group, and have evolved into a range of techniques involving terahertz optical pulses, non-linear optics and ultrashort electron beam transport systems.
In the frame of the project, the limits of these electro-optic techniques are being pushed, requiring significant advances in both the theoretical and experimental aspects of the problem, and consequently extensive work on new optical materials and laser techniques.