02 December 2007

RHIC Startup:

Stochastic cooling was on for the stores last night, but it appears that it doesn't have much of an effect on the lifetime.  Both experiments complain that when the cooling gets turned on, it produces a large burst of noise.  It appears that the Yellow lifetime is governed by something other than beam beam interactions.  Todd is concerned about the vertical chromaticity in Yellow.  There needs to be a chromaticity measurement in Yellow.  Vincent doesn't want to do the measurement with 59 bunches in the machine.  Try to do a 6x6 store for the measurement, if we can get the right people in.  If we have a large non-linear chromaticity in Yellow, that may prevent us from fixing the linear part.  Thomas wants to make sure that the BBQ is on.  It is suspect, and so should be shut off until it can be checked.  What does the vertex distribution look like?  It should make a big difference in how large the interaction vertex is.  The most recent store looks like it had several kinks in the vertexing efficiency, as if the cooling either came on or went off during the fill.  The chromaticity needs to be very small in order for the cooling to work without large losses.  The machine is unstable with negative chromaticity causing emittance growth.  There was a store with good Yellow lifetime on 30 Nov, so try reloading the stones from that store and see if the store repeats. 

There is currently a 59 bunch store being set up, so we will call in Vadim, and when he is in, we will dump the store and refill with 6 bunches.