New optics of the BT/BTM transfer line for horizontal emittance measurements

The measurement of horizontal emittances of LHC type beams in the PSB measurement line (BTM) is seriously hampered by the contribution of the dispersion and the momentum spread to the beam size. In order to determine emittances, the measured beam sizes must be corrected. Since the dispersion and the momentum spread are known only with limited precision, systematic errors may occur. This note descibes a new setting of the BT/BTM transfer line from the Booster to the measurement line, proposed to reduce the effect of the dispersion and the momentum spread on emittance measurements. The theoretical design is presented and compared to the setting used now in operation. Comparative measurements with the operational and new setting clearly demonstrate the improvement.