Dispersion and betatron matching into the linac

In high-energy linear colliders, the low-emittance beam from a damping ring has to be preserved all the way to the linear accelerator (LINAC), in the LINAC and to the interaction point. In particular, the ring-to-LINAC (RTL) section of the SLAC Linear Collider (SLC) should provide an exact betatron and dispersion match from the damping ring to the LINAC. A beam with a nonzero dispersion shows up immediately as an increased emittance, while with a betatron mismatch the beam forms filaments in the LINAC. Experimental tests and tuning procedures have shown that the linearized beta matching algorithms are insufficient if the actual transport line has some unknown errors not included in the model. Also, adjusting quadrupole strengths steers the beam if it is offset in the quadrupole magnets. These and other effects have led to a lengthy tuning process, which in the end improves the matching, but is not optimal. Different ideas are discussed to improve this matching procedure and make it a more reliable, faster, and simpler process.<
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