Subject: Erratum to 3/18 RFA meeting report From: Jim Crittenden Date: Thu, 20 Mar 2008 12:37:29 -0400 To: David Rubin CC: Jerry Codner , Shlomo Greenwald , Mark Palmer , Joe Calvey , Jesse Livezey Shlomo noticed that 90 eV electrons were surviving the 100 V potential drop in the Vgrid=-100v Vcoll=20v model, which should not happen. The reason turned out to be that I was starting the electrons 0.01" outside of the beampipe wall, so they were missing the first 20 v of the potential drop. In the meantime I also refined the mesh to give a more accurate field in the tracking region. The corrected values for the transparency through the 14-degree cone grid holes are: 90 eV: 0% 100 eV: 26.3% 110 eV: 44.6% 200 eV: 38.7% I have updated the plots of trajectories 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 -- Jim ======================================================== James Crittenden Tel. (607) 255-9424 Wilson Synchrotron Laboratory Fax (607) 255-8062 Cornell University Ithaca, New York 14853-8001 ======================================================== Jim Crittenden wrote: > 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 > ======================================================== > > > > > >