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From: KURIKI Masao
Email: masao.kuriki@kek.jp
Date: 27 Mar 2005
Time: 10:02:52 PM
I agree with Susanna's idea about the bunch spacing: 2820 bunches (Nominal parameter set) with a "safe" T_dr and 5640 bunches (Low Q parameter set) with the minimum achievable value of T_dr. It is very important and difficult issue to determine how much is the safe and shortest bunch spacing. The fast kicker experiment will provide such important information for T_dr. The experiment has been just started at KEK-ATF and we got a preliminary result. I have already presented this result at DESY (KEK-DESY meeting)and Marc Ross will (did?) give the same result in US soon, but let me describe it here anyway. In this experiment, the beam stored in ATF-DR is kicked by a strip line electrode. The rise time determined by the propagation time in the electrode and the rise time of the pulser is expected to be 2.5ns. The kick is observed as the betatron motion amplitude with a multi-turn BPM. By scanning the induced betatron amplitude with the kicker fire timing, approximately 3ns rise time was observed on the kick temporal profile. The accuracy of the measurement is currently limited, but it is going to be better. Anyway, the rise time which will be established by this experiment, can be considered to be the "minimum T_dr" and it is around 3ns. By assuming 6ns safe T_dr and 3ns minimum T_dr, the total length of DR can be 6km according to Susanna's approach. As Susanna pointed out, there are several possibilities for the DR layout. For example, 6km Dogbone DR and 2 x 3km ring DR. 6km Dogbone has advantage for the shorter (additional) tunnel length, 2km , but the difference is only 1km from the 3km ring layout. Another layout is possible for 6km Dogbone with a separate tunnel from the main linac. In this case, tunnel length will be 4km, but no concern for the stray field, commissioning, construction, availability, etc.