[Clas12_first_exp] RC notes

[burkert]

Dear all,

  I brief update on the current run.

The beam came to Hall B around 3pm, and tuning went quickly. Two Moller 
measurements were performed with HWP IN / OUT. The average polarization 
turned out to be ~85.1%, just above our self imposed value of 85% below 
which we wanted to do a mini spin dance.

Since no mini-spin dance was necessary the beam was brought quickly to 
the Faraday cup at 5nA and good quality beam  and well defined BPM 
coordinated were established.

Next we did the mini luminosity scan with 300MeV threshold and 
determined the trigger and data rates and R1 occupancies. At 75nA we 
have ~4% occupancies in R1 chambers, ~650MB/s and 30kHz rate at 89.5% L.T.

  We are currently running a low current run until midnight with 150MeV 
threshold and 10nA. From midnight until 8am, we will run 200-MeV 
threshold and 35nA beam current.

In summary, we have already established, after few hours of beam, that 
running at 75nA is possible with similar background as at 45nA with the 
FT-OFF as measured with in the 7.5GeV run.

Your friendly RC, Volker