Good news: the intensity ramp is about 7–10 days ahead of schedule, although some of that extra time may be spent on extra MDs.
Bad news: the problem at 16L2 has not gone away, and seems to be identical to last year. It was responsible for 5 dumps during the scrubbing run yesterday.
As a reminder: 16L2 stands for cell 16, left of point 2. Throughout 2017 there were a number of UFO-like events located between a quadrupole and a dipole in 16L2, which at large beam intensities would initiate a steady increase in losses over the next few turns until losses at IP7 caused a dump. It is believed that these were caused by air that had accidentally entered the pipe during the pump-down after EYETS and frozen to the beam screen. Warming up the beam screen in August made the problem worse, and the eventual solution was to operate with "8b4e" beams, referring to gaps of 100ns (4 empty) after every 8 bunches in a train. This mitigated the losses but unfortunately reduced the number of bunches from 2556 to 1920.
During YETS, 16L2 was warmed to 90 K and approximately 8.5 g of gas was extracted, which, when analysed, was found to be consistent with air. However, as we saw yesterday, this doesn't seem to have eliminated the problem.
Here's the discussion in last year's thread: http://www.lhcportal.com/Forum/viewtopi ... =45#p12568
Here are some LHC reports from last year which cover the 16L2 issue and 8b4e operation:
https://home.cern/cern-people/updates/2 ... ng-nothing
https://home.cern/cern-people/updates/2 ... tion-holes
Here are some relevant (publicly-available) slides from https://indico.cern.ch/event/705545/
and https://indico.cern.ch/event/664048/con ... s/2718791/