Tagger raytracing results
D. Sober
(Links to results of some earlier studies can be found in the
chronological listing chrono.html)
Path lengths in tagger magnet - 03-Aug-2017
- Not actually a raytracing calcuation --
calculated using circular arcs in uniform-field approximation.
Calculated in 2015, but posted now because requested by Mike Dugger.
- Values are distance from entry edge to focal plane in cm, vs electron energy E for 12 GeV beam. Must add 319.2 cm for goniometer to entry edge.
- (Ray_path_lengths_fine.pdf)
Energy overlap of TAGH counters after 2016/2017 - 08-May-2017
Results of Fall 2016 survey of beam elements - 30-Jan-2017
- Presentation to beam meeting 30-Jan-2017 (TAGH_new_survey.pdf)
- New data file of counter positions and angles (Counter_table2017.txt)
[Note that the energies in Counter_table2017.txt are for reference only and are NOT the most recent values. See the following file (counterbounds2017.out) for accurate energies.]
- New data file of TAGH energy bounds for 0-angle rays (counterbounds2017.out)
Calculations relating to possibility of scattering to counters in same plane - 02-November-2016
First results from tagger Monte Carlo simulation -- 13-Jul-2016
Derivatives files for high-energy rays (no quadrupole) -- added 03-Jun-2016
High-energy rays (6.69 GeV < E_e < 9.00 GeV) -- Calculated 07-Jan-2016
Note: These rays use a different SNAKE setup, with the
EXIT field box instead of the FOCAL field box.
[The derivatives for low-energy rays (0.18 GeV < E_e <6.99 GeV)
were posted on 26-June-2015.]
Tagger beam pipe collimation of low-energy electrons -- rev. 18-May-2016
Beam optics derivatives with quadrupole -- 11-May-2016
[Note: The derivatives for high-energy rays (E_e > 6.99 GeV) with no quadrupole were posted 03-Jun-2016]
Plots of derivatives with quad gradient = 0 and -62.5 G/mm (From
Quad_and_radiator_position.pdf, 26-Feb-2016)
- Derivatives w.r. to x0 and x'0 (derivs1-4qyn.pdf)
- Derivatives w.r. to z0 and z'0 (derivs5-8qyn.pdf)
Comparison of raytracing results at 12 GeV using measured map
and Tosca field -- 07-March-2016
Plot difference in x-intercept, energy, angle (Data-Tosca.pdf)
Quadrupole: Comparison of using Tosca field map and simple
analytic form -- 03 March 2016
Demonstrate that the analytic form employed for the results of my
note of 26-Feb-16 is just as good as using the Tosca quadrupole
field map (Quad_Tosca_and_linear.pdf)
Raytracing with the quadrupole, and effects of radiator
position -- 26 February 2016
A first look at using the quadrupole magnet
(Quad_and_radiator_position.pdf)
Also discusses differences between goniometer and amorphous radiator
positions.
Presented at beam meeting of 29 February 2016
Efficiency of the tagger fixed array -- 02 February 2016
Efficiencies, gaps between counters, and effect of dipole magnet
poles
(Tagger_ratios_and_gaps.pdf)
Presented at beam meeting of 02 February 2016
NOTE: All the material in this note about collimation by the magnet poles
is nonsense. The beampipe apertures between the quadrupole
and the dipole vacuum chamber have a much larger effect -- see
notes of 18 May 2016 and later.
Derivatives of beam optical quantities (no quadrupole) -- 26
July 2015
I have calculated first derivatives of the focal plane quantities
xFP, x-angle, zFP and z-angle, with respect
to x, x', z and z' at the radiator, as a function of electron
energy (assuming E0 = 12 GeV). These derivatives were calculated
by taking positive offsets of 1 mm in x and z and 1 electron
characteristic angle in x' and z', and comparing with the central
ray.
I have checked that the dependence is essentially linear except
for one case: dxFP/dx'0 vanishes at the
point-to-point focal plane, which intersects the nominal focal
plane at Ee ~ 3.3 GeV. In this region, the calculated
first derivative is small and not very meaningful.
Of the 16 possible derivatives, four (the derivatives of z and z'
with respect to x and x') are exactly zero. The "crossed"
derivatives of x and x' with respect to z and z' are small and,
for much of their range, randomly distributed due to precision
uncertainties of order 0.5 ppm.
- Low-energy rays (0.18 GeV < E_e < 6.99 GeV)
- ascii file of 8 derivatives
d{x,x'}/d{x,x'} and d{z,z'}/d{z,z'}
- ascii file of the 4
non-zero "crossed" derivatives d{x,x'}/d{z,z'}
- plots of derivatives
d{x,x'}/d{x,x'}
plots of derivatives d{z,z'}/d{z,z'}
- plots of derivatives
d{x,x'}/d{z,z'}
- High-energy rays (6.69 GeV < E_e < 9.00 GeV)
Note: These rays use a different SNAKE setup, with the EXIT
field box instead of the FOCAL field box.
[Calculated 07-Jan-2016; links added 03-Jun-2016]
Using the new fixed-array counter positions from the mounting
plates -- 02-July-2014
The fixed-array counters were installed in the tagger hall on June
30. Only then did it come to my attention that the counter positions
on the mounting plates are not the same as those in the
table in the GlueX Wiki (based on our May 2013
calculations). Many of the counters were shifted along their nominal
electron trajectories either (a) to increase the spacing between
phototube assemblies or (b) to avoid other conflicts with mounting
hardware. The net effect of these changes on the energy calibration
is small but not negligible, as described below.
- Table of new counter positions CounterPlates.txt CounterPlates.xlsx
- Table of fixed-array counters with nominal and new energy
boundaries and angles countertest-new.txt
- Plot of difference between actual (mounting-plate) and
nominal (Wiki table) fixed-array counter positions counterpos_old+new.pdf
The X and Y values are in Focal Plane coordinates. The blue +
symbols show the nominal positions, and the red circles show the
actual positions. The diagonal dashed lines show the normal
Microscope region, in which the fixed-array counters are not
installed.
The principal differences are
- Counters 1-131, which originally alternated between y=-8
and -13 cm, now alternate between -8 and -18 cm (counters
1-80) and then cycle between the 3 planes -8/-13/-18 cm for
counters 81-131.
- Counters 194-274, in the "sampling" region below the
Microscope, now (mostly) alternate between -8 and -18 cm
instead of all being at -8 cm.
- Plot of revised energy boundaries of counters counter_bounds1.pdf
This is a revised version of the plot of 26-June-2014 posted
previously. It shows the upper and lower energies relative to
the nominal central energy, for both nominal and the revised
calculations. The new calculations include both the new raytracing
results and the corrected counter positions.
The largest change is seen in part of the sampling region (E_gamma
between 5.6 and 7.3 GeV), where the alternation of the counters
between the -8 and -18 cm planes now gives a substantial
alternation in the energy limits. This is seen more clearly in the
following plot.
- Plot of energy width and energy spacing of counters
counter_width+spacing-all.pdf
The energy width (E_high - E_low) is plotted with blue squares,
and the energy spacing (E_high_[n] - E_high_[n+1]) with red
triangles. We see that the large variation in energy limits
between 5.6 and 7.3 GeV is due to a variation in the energy spacing,
which alternates between 57 and 63 MeV, rather than the nominal 60
MeV. Note that the alternation between the y=-8 and y=-18 cm
planes has little effect on the energy width.
A more disturbing effect is seen between 8 and 10 GeV, where for
some counters the energy spacing is smaller than the energy width,
i.e. there is a partial overlap between adjacent counters even for
central rays. For the full-coverage region above the Microscope
(9-10 GeV) this overlap never exceeds 0.3 MeV out of a total width
of 15 to 21 MeV, i.e. less than 2%. In the 8-9 GeV region, which
will be installed only if the microscope is moved to lower energy,
the overlap rises to 5%, plus one channel at 10%. We may wish to
consider re-making the mounting plate for that region.
(Links to results of some earlier studies can be found in the
chronological listing chrono.html>