No Arabic abstract
The cw CCL being designed for the Accelerator Production of Tritium (APT) project accelerates protons from 96MeV to 211MeV. It consists of 99 segments each containing up to seven accelerating cavities. Segments are coupled by intersegment coupling cavities and grouped into supermodules. The design method needs to address not only basic cavity sizing for a given coupling and pi/2 mode frequency, but also the effects of high power densities on the cavity frequency, mechanical stresses, and the structures stop band during operation. On the APT project, 3-D RF (Ansoft Corp.s HFSS) and coupled RF/structural (Ansys Inc.s ANSYS) codes are being used to develop tools to address the above issues and guide cooling channel design. The codes predictions are being checked against available low power Aluminum models. Stop band behavior under power will be checked once the tools are extended to CCDTL structures that have been tested at high power. A summary of calculations made to date and agreement with measured results will be presented.
The vibration of components of the NLC linac, such as accelerating structures and girders, is being studied both experimentally and analytically. Various effects are being considered including structural resonances and vibration caused by cooling water in the accelerating structure. This paper reports the status of ongoing work.
This paper outlines the RF design of the CLIC (Compact Linear Collider) 30 GHz main linac accelerating structure and gives the resulting longitudinal and transverse mode properties. The critical requirement for multibunch operation, that transverse wakefields be suppressed by two orders of magnitude within 0.7 ns (twenty fundamental mode cycles), has been demonstrated in a recent ASSET experiment. The feasibility of operating the structure at an accelerating gradient of 150 MV/m for 130 ns has yet to be demonstrated. Damage of the internal copper surfaces due to high electric fields or resulting from metal fatigue induced by cyclic surface heating effects are a major concern requiring further study.
In the framework of the Eupraxia Design Study an advanced accelerator facility EUPRAXIA@SPARC_LAB has been proposed to be realized at Frascati (Italy) Laboratories of INFN. Two advanced acceleration schemes will be applied, namely an ultimate high gradient 1 GeV X-band linac together with a plasma acceleration stage to provide accelerating gradients of the GeV/m order. A FEL scheme is foreseen to produce X-ray beams within 3-10 nm range. A 500-TW Laser system is also foreseen for electron and ion production experiments and a Compton backscattering Interaction is planned together with extraction beamlines at intermediate electron beam energy for neutron beams and THz radiation production. The electron beam dynamics studies in the linac are here presented together with the preliminary machine layout.
Electrons of dark current (DC), generated in high-gradient superconducting RF cavities (SRF) due to field emission, can be accelerated up to very high energies-19 GeV in the case of the International Linear Collider (ILC) main linac-before they are removed by focusing and steering magnets. Electromagnetic and hadron showers generated by such electrons can represent a significant radiation threat to the linac equipment and personnel. In our study, an operational scenario is analysed which is believed can be considered as the worst case scenario for the main linac regarding the DC contribution to the radiation environment in the main linac tunnel. A detailed modeling is performed for the DC electrons which are emitted from the surface of the SRF cavities and can be repeatedly accelerated in the high-gradient fields in many SRF cavities. Results of MARS15 Monte Carlo calculations, performed for the current main linac tunnel design, reveal that the prompt dose design level of 25 {mu}Sv/hr in the service tunnel can be provided by a 2.3-m thick concrete wall between the main and service tunnels.
A single gap, 352 MHz superconducting reentrant cavity for 5-100 MeV beams has been designed and it is presently under construction. This development is being done in the framework of a 30 mA proton linac project for nuclear waste transmutation. Mechanical, cryogenic and rf design characteristics of such cavities will be described.