Subject:
Followup to today's RFA meeting
From:
Jim Crittenden <critten@lepp.cornell.edu>
Date:
Tue, 18 Mar 2008 17:00:48 -0400
To:
David Rubin <DLR@CESR10.LNS.CORNELL.EDU>, Jerry Codner <gcodner@lepp.cornell.edu>, Shlomo Greenwald <sg@lepp.cornell.edu>, Mark Palmer <map36@cornell.edu>, Joe Calvey <jrc97@cornell.edu>, Jesse Livezey <jal245@cornell.edu>

The results for the Opera electric field and electron tracking calculations
which I showed in today's meeting can be found here (slides1-10):
http://www.lepp.cornell.edu/~critten/cesrta/talks/18mar08/

In the meantime, I have addressed two questions which were raised at
the meeting:
1) For the 10 eV e- in the 45-degree grid hole model, how much of the
   focusing comes from the 50v on the collector?
   The original slide is here:
      http://www.lepp.cornell.edu/~critten/cesrta/talks/18mar08/slide8.pdf
   Setting the collector voltage to zero gives this comparison:
      http://www.lepp.cornell.edu/~critten/cesrta/talks/18mar08/rfa_super18_vc0_10ev_2.pdf

    A little more than half the focusing comes from the collector voltage.
    Notice also that this collector voltage results in the tracks beginning to leave their
    linear trajectories and start bending toward the collector.

2) For Shlomo's measurements with Vg=-100v Vc=20v, how does the grid transparency
   depend on electron energy?
   For this purpose I chose the model with the smallest nonzero grid hole angle (14 degrees).
   As requested, I calculated transparencies for 90, 100, 110, and 200 eV electrons.
   The trajectories can be seen here:
    http://www.lepp.cornell.edu/~critten/cesrta/talks/18mar08/rfa_super22_vg-100_vc20_90ev_2.pdf
    http://www.lepp.cornell.edu/~critten/cesrta/talks/18mar08/rfa_super22_vg-100_vc20_100ev_2.pdf
    http://www.lepp.cornell.edu/~critten/cesrta/talks/18mar08/rfa_super22_vg-100_vc20_110ev_2.pdf
    http://www.lepp.cornell.edu/~critten/cesrta/talks/18mar08/rfa_super22_vg-100_vc20_200ev_2.pdf

    The transparency values are:
          90 eV:  46.1%
         100 eV:  41.5%
         110 eV:  40.0%
         120 eV:  38.1%

Next steps to be contemplated & executed:
  1)  Refine the mesh to improve the unphysical field anomaly we observed near the beampipe wall,
       where some field appeared to leak into the wall.
   2) Superpose a dipole magnetic field of 5G directed along the axis of the RFA.
   3) Introduce the wiggler beampipe hole pattern.

All comments welcome.

-- Jim

p.s. The results for superposed fields described in my mail message on March 13 were wrong due
      to an oddity in Opera v12.003 which I have informed Vector Fields about.
      I have deleted them from the web page.
      The results reported on March 12 remain legitimate.

========================================================
James Crittenden                   Tel. (607) 255-9424
Wilson Synchrotron Laboratory      Fax  (607) 255-8062
Cornell University
Ithaca, New York 14853-8001
========================================================