SHMS MC Working Group

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Meetings

SHMS Characteristics

  • Drawings of magnets:
    • [Side view drawing ] of the SHMS Q3 and Dipole with distances. The far left cross hair in the drawing is the x_hut=y_hut=z_hut=0 point from which the detector positions are measured in the hut. The distance from the dipole center to the "zero" point projected perpendicular to the mechanical center axis of the dipole is 3.65m as shown on an annotated drawing with the calculation. [Plot] of detector distances from the "zero" point. (From Mike Fowler on Sept 12th, 2011)
    • [Drawing ] with measurements of the dipole entrance flange. [3d picture ] of the dipole entrance.
  • [Summary table ] of the SHMS magnets field properties. From Steve Lassiter file magnet_summary.doc on Sept 9th 2011.
  • Horizontal bender magnet dimensions (Mike Fowler on Sept 12th, 2011): [Top view] , [3-D view], a few more views of the H bender from 2010, top view, top view at the smallest spectrometer angle, front face view, side view, side sectional view, top sectional view, view of aperture
  • Dipole apertures used in the MC model: The following figures describe how to calculate the parameters required to describe the dipole apertures in the MC. The dipole effective length is divided into 8 equal segments and the aperture center and inclinations are calculated at each of these segments. The inclinations angles are shown in angles, and the drift distances and offsets of the center of the aperture with respect to the central trajectory are shown in table of offsets (20 cm drop) and (26 cm drop)

SNAKE

Field maps of magnets

  • The Horizontal Bender
    • The integral field needed for 3 deg bend is 1.9211 Tm.
    • From map file, MSU_Bender.map, the maximum integral field along a straight path is 1.92929 Tm with B_max=2.4768 T giving L_eff= 0.7789m. So need a factor of 0.996 to scale map toget field for 3deg bend.
  • Dipole
    • The integral field needed for 18.4 deg bend is 11.783 Tm for integration along the path of the particle, L_arc, which is incident perpendicular to the field. The difference between the L_arc and the straight line L_eff is L_arc/L_eff = theta/sin(theta)=1.017 for theta=18.4 deg. So need integral field along a straight path of 11.586 Tm.
    • From map file, shmsD2008.map, B_max=4.7907 and Int(Bdl) = -13.67883 so L_eff=2.855. So need a factor of 0.8478 to scale map to get field for 18.4 deg bend.
  • Quadrupoles
    • From map file, Q1_coldiron.map,Max Bz/r= 10.791 and Int(Bz/r*dl) = 19.9049 for L_eff= 1.844 at r=20cm
    • From map file,Q23nc6.map, Max Bz/r=14.41324 and Int(Bz/r*dl) = 23.04041 for L_eff=1.5985 at r=31cm
    • Determine the scale factors for the quads to given desired 1st order optics.

Determine the magnet setting for 11 GeV/c

  • Fix the map scale factor for the HB and Dipole fields at 0.996 and 0.8478 .
  • Determine the scale factors for the quads, by modifying them so that (xfp|xptar)=0, (yfp|ytar)=1.634 and (yfp|yptar)=0 in 1st order matrix. Found scale factors are -0.792092,0.845324,-0.526535 .
  • 1st order Matrix from target to focal plane has D/M = -1.09:
xtar xptar ytar yptar delta
xfp -1.501 -0.002 -0.024 -0.054 1.634
xpfp -0.049 -0.663 0.001 0.002 0.310
yfp -0.004 -0.002 -1.634 -0.001 -0.025
ypfp 0.000 0.003 -0.277 -0.623 0.020
  • With new scale factors:
    • Q1 Max B = -1.7093 Int(Bdl) = 3.153304 Int(B/rdl) = 15.76652 at r=0.20m L_eff= 1.844
    • Q2 Max B = 3.778 Int(Bdl) = 6.03996 Int(B/rdl) = 19.4736 at r=0.31m L_eff=1.5985
    • Q3 Max B = -2.3536 Int(Bdl) = 3.76275 Int(B/rdl) = 12.1316 at r=0.31m L_eff=1.5985
    • Overall path length = 18.10325m for central track
  • For comparison to COSY, Dave Gaskell optimized for (xfp|xptar)=0, (yfp|yptar)=0 and D/M=-1.09
    • Q1=-2.128585 T at 25cm which at 20cm is q1 = -1.7028 using L_eff = 1.879m.
    • Q2= 4.342608 T at 35cm which at 31cm is q2 = 3.8463 using L_eff=1.64m.
    • Q3=-2.805149 T at 35cm which at 31cm is q3 = -2.484 using L_eff=1.64m.

Study of changing the vertical offset of dipole

  • Ran SNAKE with set of random trajectories for point target with -0.060 < xptar < 0.060, -0.040 < yptar < 0.040 and 8.8 < momentum < 13.42 GeV/c.
  • Input deck to SNAKE has 38 endplanes or apertures. An endplane is a position within SHMS where the the positions and angles are recorded. If the track goes outside the SHMS good volume then a flag is set to indicate a failed track and the positions and angles at the location between the endplanes is recorded.
  • Compared an vertical offset of 20cm, 26cm and 29cm. For each offset the distance between the centerof the dipole and the focal plane center is recalculated.
  • 1D Plot of fraction of total tracks which failed for each endplane number for offset of 20cm (red), 26cm (black) and 29cm (green) offsets.. Apertures (or Endplanes) numbers 3-7 are HB, 8-13 are Q1, 14-18 are Q2, 19-24 are Q3, 25 is dipole entrance, 26-35 are dipole.
  • 2D plot of number tracks which failed for each endplane number versus xptar and yptar for offset of 20cm , 26cm and 29cm. The HB vertical size limits the xptar acceptance to about +/-47-50mr. The Q1 exit limits the horizontal acceptance. For the 20cm offset in the dipole, the dipole entrance (#25) limits the negative xptar acceptance with a delta dependence.
  • 1D Plots of target xp,yp, delta and ytar with for offset of 20cm, 26cm and 29cm. The black line is all tracks. The blue line is failed tracks. The red line is passed tracks.
  • Plot comparing the solid angle has a function of delta for 20 (red), 26cm (black) and 29cm (green) offsets. The solid angle is calculated by the ratio of passed tracks to total tracks multiplied by 0.12*0.08*1000 (the thrown solid angle in msr at each delta).
  • 2D Plots of target xp/delta, yp/delta and xp/yp for offset of 20cm, 26cm and 29cm.
  • 2D Plots of focal plane x/y, xp/yp, yp/y and xp/x for offset of 20cm, 26cm and 29cm.

Study comparing SHMS tuned to D/M = -1.1 to D = -0.8

  • Ran SNAKE with set of random trajectories for point target with -0.060 < xptar < 0.060, -0.040 < yptar < 0.040 and 8.8 < momentum < 13.42 GeV/c.
  • Dave Gaskell fitted tune in COSY for D/M=-0.8 . Scaled the magnets fields in SNAKE.
  • Plot comparing the solid angle has a function of delta for 20 (red) and 26cm (black) offsets at D/M=-1.1 and 26cm offset with D/M=-0.08 (green). The solid angle is calculated by the ratio of passed tracks to total tracks multiplied by 0.12*0.08*1000 (the thrown solid angle in msr at each delta).
  • 1D Plot of fraction of total tracks which failed for each endplane number for offset of 20cm (red) and 26cm (black) at D/M=-1.1 and 26cm offset with D/M=-0.8 (green).
  • 2D Plots of target xp/delta, yp/delta and xp/yp for offset of 26cm with D/M=-1.1 and 26cm with D/M=-0.8.

Study of changing the vertical opening of the HB

  • Drawing of the proposed change by Mike Fowler on Sept 28th.
  • Plot comparing the solid angle has a function of delta for HB vertical opening of 20.75cm(red) and 23cm (black) with dipole offset = 26cm. The solid angle is calculated by the ratio of passed tracks to total tracks multiplied by 0.12*0.08*1000 (the thrown solid angle in msr at each delta). With the increased HB acceptance, the xptar acceptance grows about 10% in negative delta region. Makes no difference in positive delta region.

SNAKE versus COSY comparison

  • Ran SNAKE for xptar = +/- 80mr , yptar = +/- 80mr , -22 < delta < 33 and 20cm target at 20deg. Ran mc_shms_single for xptar = +/- 80mr , yptar = +/- 80mr , -22 < delta < 22 and 20cm target at 20deg.
  • Plot comparing solid angle acceptance versus delta for SNAKE (blue) and COSY (red).
  • Plots comparing x (vertical) and y (horizontal) positions at various locations from dipole optical entrance to the focal plane for SNAKE (blue) and COSY (red).

Collimator study

  • Run SNAKE with target of length +/-10cm at 20deg. Use a 26cm offset in the dipole with 23cm opening in HB.
  • Plot of the vertical position versus the horizontal position at Q1 entrance. The red boxes are events which are accepted up through aperture #11 ( as defined in plot of apertures in SIMC). The green boxs are events which fail at aperture #12. The blue boxes are those events which fail in aperture #13 and after.
  • Study putting a cut at the vertical position at the Q1 entrance. Table of solid angle and fractional loss is percentage of events which have made it through Q1 but fail either in aperture #12 and after, or in aperture #13 and after:
Cut Solid angle Frac loss after #13 Frac loss after #12
none 3.75mr 3.6% 4.7%
<+7cm 3.10 0.0% 1.4%
<+9cm 3.38 0.2% 1.5%
<+11cm 3.60 1.5% 2.6%
<+13cm 3.75 3.6% 4.7%
  • Plot of solid acceptance versus delta for cuts in the vertical acceptance at the entrance of Q1 for events with vertical position at Q1 less than 7 (red) , 9 (green), 11 (purple) and 13cm (cyan).
  • Phase space of beam through SHMS. 2d histograms of the relative vertical ( y-axis) vs horizontal ( x-axis) positions at different locations in the Horizontal Bender,Q1, Q2, Q3, Dipole entrance,Dipole exit. The coordinates are in the coordinate system relative to the center of that magnet element. The vertical axis has positive direction is physical down. The horizontal axis has positive direction is away from beam line. The blue squares are events which make it to the focal plane. The colored squares are events which are rejected at the aperture. The critical aperatures are the HB entrance (horizontal), HB optical and physical exit (vertical), Q1 optical and physical exit (vertical and horizontal), dipole entrance (negative vertical), dipole middle and before (positive vertical), dipole exit (negative vertical).

COSY

[Dave G. notes on 2009 shms studies]

[Comparison of 1st order matrix elements from Dave G. COSY fits and John LeRose tech note]

Aperture study

  • Aperture 1, compared 20cm target at 20 deg with: (top panel), the blue points show the distribution when all apertures are included, while the red points are with no dipole apertures and no HB mechanical apertures. (Bottom panel), blue is same as above and the red show distributions with no dipole apertures, no HB apertures and no Q1,Q2,and Q3 Mech apertures, ie only apertures included are the Q1, Q2, Q3 magnetic centers.


  • Apertures 3, Here in the bottom panel, only the HB apertures and Q1,Q2, Q3 mechanical apertures are removed. This is the minimal set of apertures which have to be turned off to get the distributions similar to the pre 2009 distributions. It should also be noted that this is the set of apertures is what existed in the pre 2006 mc_shms.f


  • Acceptance for the no aperture (other than Q1,2, and 3 magnetic center apertures) is 4.6 msr

Collimator study

  • Run COSY based MC with target of length +/-10cm at 20deg. Use a 26cm offset in the dipole with 23cm opening in HB.
  • Plot1, Plot2of the vertical position versus the horizontal position at Q1 entrance. In the bottom right plot the red are events which are accepted up to the dipole entrance. The blue are those events which fail in the dipole. Plot1 is for D/M=0.08, Plot2 is for D/M=0.12, cut on delta -10<delta<22
  • Plot1, Plot2 of solid acceptance versus delta for cuts in the vertical acceptance at the entrance of Q1 for events with vertical position at Q1 less than 7 (magenta) , 9 (blue), 11 (green), 13cm (red) and no cut (black). The no cut acceptance was assumed to be 4 msr. Plot1 for D/M=0.08 and Plot2 for D/M=0.12, no delta cut is applied
  • Plot1, Plot2 of vertical position vs horizontal position at Q1 entrance for events with vertical position at Q1 less than 7 (green) , 11 (magenta), 13cm (blue) and no cut (red). Plot1 is for D/M=0.08 and Plot2 is for D/M=0.12, cut on delta -10<delta<22

SLITS & COLLIMATORS

Detector Positions

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