SLAC, Menlo Park, California, USA
CERN, Geneva, Switzerland
It has been proposed to implement an Achromatic Telescopic Squeezing (ATS) scheme* in the high luminosity LHC lattice to reduce the beta functions at the Interaction Points (IP) up to a factor of 8. As a consequence, the nominal 4.5-km peak beta functions reached in the inner triplets at collision will be increased by the same factor. This therefore justifies the installation of new, larger aperture superconducting triplet quadrupoles. These higher beta functions will enhance the effects of the triplet quadrupole field errors leading to smaller beam dynamic aperture. To maintain the acceptable dynamic aperture, the effects of the triplet multipole field errors must be re-evaluated, thus specifying new tolerances. Such a study has been performed for the so-called “4444” collision optics of the ATS scheme, where the IP beta functions are reduced by a factor of 4 in both planes with respect to a pre-squeezed value of 60 cm at two collision points. The dynamic aperture calculations were performed using SixTrack. The impact on the triplets’ field quality is studied and presented in details.
* S. Fartoukh, “An Achromatic Telescopic Squeezing (ATS) Scheme for LHC Upgrade”, Proc. of IPAC11, p. 2088 (2011).
SLAC, Menlo Park, California, USA
The FACET (Facility for Advanced aCcelerator Experimental Tests) facility at SLAC has been under Construction since summer 2010. Its goal is to produce ultrashort and transversely small bunches of very high intensity (20kA peak current) to facilitate advanced acceleration experiments like PWFA and DLA. In June of 2011 the first electron beam was brought into the newly constructed bunch-compression chicane. Commissioning work included restarting the linac and damping ring, verifying hardware, establishing a good beam trajectory, verifying the optics of the chicane, commissioning diagnostic devices for transverse and longitudinal bunch size, and tuning up the beam size and bunch compression. Running a high-intensity beam through the linac without BNS damping and with large energy spread is a significant challenge. Optical aberrations as well as wakefields conspire to increase beam emittance and the bunch compression is quite sensitive to details of the beam energy and orbit, not unlike what will be encountered in a linear-collider final-focusing system. In this paper we outline the steps we took while commissioning as well as the challenges encountered and how they were overcome.
