KEK, Ibaraki
SLAC, Menlo Park, California
Fermilab, Batavia
INFN/LASA, Segrate (MI)
DESY, Hamburg
In an attempt at demonstrating an average field gradient of 31.5 MV/m as per the design accelerating gradient for ILC, a program called S1-Global is in progress as an international research collaboration among KEK, INFN, FNAL, DESY and SLAC. The design of the S1-G cryomodule began at May 2008 by INFN and KEK. The S1-Global cryomodule was designed to contain eight superconducting cavities from FNAL, DESY and KEK, and to be constructed by joining two half-size cryomodules, each 6 m in length. The module containing four cavities from FNAL and DESY was constructed by INFN. Four KEK cavities have been assembled in the 6 m module which KEK fabricated. All major components were transported to KEK from INFN, FNAL and DESY in December 2009. The assembly of the two 6-m cryomodules started from January 2010 in a collaborative work of FNAL, DESY, INFN and KEK. The construction of the S1-G cryomodule will complete in May, and the cool-down of the S1-G cryomodule is scheduled from June 2010 at the KEK-STF. In this paper, the construction and the cold tests of the S1-Global cryomodule in the worldwide research collaboration will be presented.
SLAC, Menlo Park, California
CERN, Geneva
KEK, Ibaraki
Cavity pulsed heating experiments have been conducted at SLAC National Accelerator Laboratory in collaboration with CERN and KEK. These experiments were designed to gain a better understanding on the impact of high power pulsed magnetic fields on copper and copper alloys. The cavity is a one port hemispherical cavity that operates in the TE013-like mode at 11.424 GHz. The test samples are mounted onto the endcap of the cavity. By using the TE013 mode, pulsed heating information can be analyzed that is based only on the impact of the peak magnetic field which is much bigger in value on the test sample than on any other place in the cavity. This work has shown that pulsed heating surface damage on copper and copper alloys is dependent on processing time, pulsed heating temperature, material hardness, and crystallographic orientation and that initial stresses occur along grain boundaries which can be followed by pitting or by transgranular microfractures that propagate and terminate on grain boundaries. The level of pulsed heating surface damage was found to be less on the smaller grain samples. This is likely due to grain boundaries limiting the propagation of fatigue cracks.
SLAC, Menlo Park, California
With the growing demand for FEL light sources, cost issues are being revaluated. To make the machines more compact, higher-frequency room-temperature linacs are being considered, in particular, ones using C-band (5.7 GHz) rf technology where 40 MV/m gradients are possible. In this paper, we show that an X-band (11.4 GHz) linac using the technology developed for NLC/GLC can provide an even lower cost solution. In particular, stable operation is possible at gradients of 100 MV/m for single bunch operation, and 70 MV/m for multibunch operation. The concern of course is whether the stronger wakefields will lead to unacceptable emittance dilution. However, we show that the small emittances produced in a 250 MeV, low bunch charge, LCLS-like S-band injector and bunch compressor can be preserved in a multi-GeV X-band linac with reasonable alignment tolerances.
SLAC, Menlo Park, California
The superconducting cavities and interconnects in the 12 km long linacs of the International Linear Collider (ILC) are designed to operate at 2K where cooling costs are very expensive. Thus it is important to ensure that any additional cryogenic heat loads are small in comparison to those from static losses and the fundamental 1.3 GHz accelerator mode. One potential heat source is the higher order modes (HOM) excited by the beam. Such modes will be damped by specially designed HOM couplers that are attached to the cavities (for trapped modes), and by 70K ceramic dampers that are located in each of the eight or nine cavity cryomodules (for propagating modes). Brute force calculations of the higher frequency, non-trapped modes excited in a string of cryomodules is limited by computing capacity. We present, instead, an approach that combines scattering matrix and wakefield calculations to study the effectiveness of the dampers in limiting the heat deposited in the 2K cryogenic system.