Tracking Group

  Tony's Status Report
  Klaus's Status Report
  Yongguang's Status Report
  Jim's Status Report



  Qweak Simulation Forum

  Keep Out Zones a la Allena

  Previous Reports

So we've defined the LARGEST the primary collimator could POSSIBLY be based on the QTOR support structure (see rows 10 and 11 below)


What I need to do:

  I - Refine collimators
      a - Get a more realistic target attachment structure and/or design one to not interfere.

  II - Consider the detectors
      a - Refine main detector for 3 shapes/different z locations (study inelastic % vs. FOM)
      b - Check moller rates
      c - Consider size of minitorus and realistic supports
      d - Consider size of GEMs
      e - Consider size of Region III chambers

  II - Refine collimators
      a - Check the dose on the QTOR support and other "close" structures, possibly trim ep peak even more.
      b - possibly change z locations, redesign based on above considerations and summarize pros and cons

For more info, see the Primary Collimator Optimization "Live" Page.

This is a sketchy review of what has been accomplished since last meeting. It mainly focuses on areas
where we need some input and ideas from the rest of the group to proceed.

Last time, we determined the collimator cutouts (both at upstream and downstream locations) that
would allow for the scattered e-p profile to clear all main torus support structures with 2 cm to spared.

II b,c - For the two collimators mentioned above, we checked that our current standard mini-torus does not cause any interferences. It appears that it does not (for either location) and there is 2 cm to spare all around the scattered profile.

Currently for our best mini-torus, we have about 350 kHz/nA. So that would probably limit running with the region 2 chambers to around 2-3 nA. We are still working to optimize this, but I don't know if there is much more we can do.

Figure 1 - The minitorus does not seem to be interfering
                     with the acceptance for the upstream collimator.

I a, II d - As mentioned last time, it is likely that the lower theta limit may be defined by what the beampipe and shielding look like near the target. For reference, here are some lower theta angles:

     reference design: 6.38 (normal), 5.69 (extreme)
     downstream design: 6.01 (normal), 5.34 (extreme)
     upstream design: 7.52 (normal), 5.34 (extreme)

Figure 2 - Definition of extreme and normal angles. The normal minimum
and maximum angles are red; the extreme are black.

I a, II d - For the current GEM location, it looks very difficult to put an adequate amount of shielding in there to shield the GEM from electromagnetic showers started by lower angle scattered particles. I suspect we can put in enough shielding to START a pretty good shower, but not to contain it. This remains to be explored more quantitatively. Two other options are:

     a) Increasing the lower theta angle of the experiment.
     b) Moving the GEMs about 50 - 60 cm further downstream. This would mean the mini-torus would move further downstream and be even less effective (but we will explore it so we know what the tradeoff is).

Figure 3 - The region near the target, with ~50cm of space for the
                           GEMs between the target attachments and the first collimator.

I a, II d - These plots are the ep peak profiles at a z location of -584 cm for the reference collimator and upstream and downstream collimators used in the optimization.

Some Moller rates: At the current GEM location the Moller rates are about .4 kHz/nA/mm². At 10 nA this would imply about 4000 Hz/mm². Tony was quoted a desire for < 500 Hz/mm² in the recent proposal. BUT he also notes that COMPASS successfully ran (with high tracking efficiency) at ~ 10000 Hz/mm². So perhaps this is okay.

Figure 4a - reference collimator	Figure 4b - upstream collimator	Figure 4c - downstream collimator

Now is the time to carefully design the region near the target. If we are forgetting some design ideas from the past, we should get them back in there now.