arXiv subjects
Publications and source records attributed to V. F. Khan.
The key feature of the improved coupling design in the Damped Detuned Structure (DDS) is focused on the four manifolds. Rectangular geometry slots and rectangular manifolds are used. This results in a significantly stronger coupling to the manifolds compared to the previous design. We describe the new design together with its wakefield damping properties.
A Damped Detuned Structure (DDS) for CLIC main linac has been proposed as an alternative to the present baseline design which is based on heavy damping. A first prototype, CLIC_DDS_A, for high power tests has been already designed and is under construction. It is also foreseen to design a further prototype, CLIC_DDS_B, to test both the wakefield suppression and high power performances. Wakefield calculations for DDS are, in the early design stage, based on single infinitely periodic cells. Though cell-to-cell interaction is taken into account to calculate the wakefields, it is important to study full structure properties using computational tools. In particular this is fundamental for defining the input parameters for the HOM coupler that is crucial for the performances of DDS. In the following a full analysis of wakefields and impedances based on simulations conducted with finite difference based electromagnetic computer code GdfidL will be presented.
The main accelerating structures for the CLIC are designed to operate at an average accelerating gradient of 100 MV/m. The accelerating frequency has been optimised to 11.994 GHz with a phase advance of 2π/3 of the main accelerating mode. The moderately damped and detuned structure (DDS) design is being studied as an alternative to the strongly damped WDS design. Both these designs are based on the nominal accelerating phase advance. Here we explore high phase advance (HPA) structures in which the group velocity of the rf fields is reduced compared to that of standard (2π/3) structures. The electrical breakdown strongly depends on the fundamental mode group velocity. Hence it is expected that electrical breakdown is less likely to occur in the HPA structures. We report on a study of both the fundamental and dipole modes in a CLIC_DDS_HPA structure, designed to operate at 5π/6 phase advance per cell. Higher order dipole modes in both the standard and HPA structures are also studied.
A damped detuned structure for the main X-band linacs of CLIC is being investigated as an alternative design to the present baseline heavily damped structure. In our earlier designs we studied detuned structures, operating at 11.994 GHz, with a range of dipole bandwidths in order to ensure the structure satisfies beam dynamics and rf breakdown constraints. Here we report on the development of a damped and detuned structure which satisfies both constraints. Preparations for high power testing of the structure are also discussed
We report on suppression of long-range wakefields in CLIC accelerating structures. Strong detuning and moderate damping is employed. In these initial design studies we focus on the CLIC_G structure and enforce a moderate Q of 300 and 500. We maintain a dipole bandwidth of approximately 1 GHz as specified from breakdown constraints in a modified structure, CLIC_DDS. The circuit model, which facilitates a rapid design of manifolds slot-coupled to the main accelerating cells, is described.
The present design of the main accelerating structure for CLIC is based on heavy damping (WDS) with a Q of ~10. The wakefield suppression in this case entails locating the damping materials in relatively close proximity to the accelerating cells. Herein we present an alternate design for the main accelerating structures. We detune the lowest dipole band by prescribing a Gaussian distribution to the cell parameters and consider moderate damping Q~500 to prevent the recoherence of the modes; in this case the damping materials can be located at an extended distance from the accelerating structure. The procedure to achieve a well-damped wakefield is described. Results are presented elucidating the various designs including the current one which is being developed to incorporate r.f. breakdown, pulse surface heating and beam dynamics constraints.