TeV Energy Superconducting Linear Accelerator Research Articles

Higher-order mode-based cavity misalignment measurements at the free-electron laser FLASH

At the Free-Electron Laser in Hamburg (FLASH) and the European X-Ray Free-Electron Laser, superconducting TeV-energy superconducting linear accelerator (TESLA)-type cavities are used for the acceleration of electron bunches, generating intense free-electron laser (FEL) beams. A long rf pulse structure allows one to accelerate long bunch trains, which considerably increases the efficiency of the machine. However, intrabunch-train variations of rf parameters and misalignments of rf structures induce significant trajectory variations that may decrease the FEL performance. The accelerating cavities are housed inside cryomodules, which restricts the ability for direct alignment measurements. In order to determine the transverse cavity position, we use a method based on beam-excited dipole modes in the cavities. We have developed an efficient measurement and signal processing routine and present its application to multiple accelerating modules at FLASH. The measured rms cavity offset agrees with the specification of the TESLA modules. For the first time, the tilt of a TESLA cavity inside a cryomodule is measured. The preliminary result agrees well with the ratio between the offset and angle dependence of the dipole mode which we calculated with eigenmode simulations.

Design study of an optical cavity for a future photon collider at ILC

Hard photons well above 100 GeV have to be generated in a future photon collider which essentially will be based on the infrastructure of the planned International Linear Collider (ILC). The energy of near-infrared laser photons will be boosted by Compton backscattering against a high-energy relativistic electron beam. For high effectiveness, a very powerful laser system is required that exceeds today's state-of-the-art capabilities. In this paper a design of an auxiliary passive cavity is discussed that resonantly enhances the peak-power of the laser. The properties and prospects of such a cavity are addressed on the basis of the specifications for the European TeV Energy Superconducting Linear Accelerator (TESLA) proposal. Those of the ILC are expected to be similar.

Multipacting phenomenon at high electric fields of superconducting cavities

Recently multipacting (MP) recalculation of the TeV Energy Superconducting Linear Accelerator (TESLA) resonator was performed. In addition to the normal MP which occurs at a peak electric field of around 40MV/m for the TESLA cavity, another type of multipacting with resonant electron trajectory that is far from the equator is also seen. It occurs at a gradient around 60MV/m to 70MV/m. This result seems to explain some experimental observations.

Beam monitors for TESLA based on diamond strip detectors

For TeV energy superconducting linear accelerator (TESLA), it is foreseen to measure the beam profile with so-called wire scanners. A thin carbon fiber is moved through the beam and the number of scattered secondary particles is measured in correlation to the position of the wire. From this, a beam profile can be calculated as an average over many bunches of the beam. With strip detectors made from diamond, the beam profile can be measured online for single bunches. With two perpendicular arrays of strips on the front and the back side of the detector, the beam profile can also be measured in the X and Y direction. If fast electronics are used and the bunches are not too short, even a longitudinal profile in the Z direction can be obtained. We successfully tested a diamond detector in a heavy ion beam with bunches of up to 3/spl middot/10/sup 10/ O/sup 6+/ ions and in a beam of 10/sup 10/ electrons in bunches with a length of 300 /spl mu/m, as planned for TESLA. The fluence of 10/sup 15/ e/sup -//cm/sup 2/ or more by one of the bunches foreseen for TESLA corresponds to the irradiation a vertex detector receives during ten years of large hadron collider. The results of our measurements will be presented and discussed.

Particle transverse autophasing in weak focusing linear accelerators

The transverse autophasing conditions in high-energy linear accelerators with weakly focusing lattice have been studied. A solution has been developed which does not require an additional correlated energy spread in the beam along the linear accelerator. The main features of the solution are that the focusing lattice is not scaled along the linac and the autophasing regime is provided only by initial correlated energy spread. The matching of the amplitudes of dispersive and wakefield terms (the autophasing regime) in equation of motion is accomplished by accelerating the bunch behind the crest of the radio-frequency wave at the low-energy part of the linac. The analytical study is confirmed by particle tracking simulations in TeV Energy Superconducting Linear Accelerator (TESLA).

Comparison of Boundary Integral Formulations for Field Computation in Axisymmetric Resonators

In this paper several boundary integral formulations for the computation of electromagnetic fields in axisymmetric RF resonators are derived and their numerical stability is studied. The geometry may be an open (with magnetic ends) or closed cavity resonator with perfectly conducting walls or a segment of a waveguide having a dielectric window. It is found that the proper choices of integral formulation and test functions are essential in order to maintain the numerical stability of a solution as the discretization is made denser. Numerical results are presented for three simple geometries which allow analytical solutions, and as an application of the method to practical problems, the TESLA accelerating cavity and the coaxial input coupler with a ceramic window are considered. TESLA (TeV Energy Superconducting Linear Accelerator) is an international linear collider research and development project based on superconducting accelerator structures.