Hi,
I have put a file "bgrid3.blast" into the Blast_Params sub-
directory of the blast account. I have not done anything else and
hope someone who knows what they are doing can take the appropriate
action.
This file has the same ranges (ie size) as the previous grid
files so no changes are needed to the code other than whatever is
necessary to have the field calculating code point at this file
rather than bgrid2.blast.
The new file "bgrid3.blast" is based on the field mapping data
from Abby Goodhue "TOT.dat". I used her results but edited to remove
any point which differed by more than 200 G from the Biot-Savard
calculation (this had the effect of removing about 150 bad points).
I then fit the mapped data allowing the coils to move and obtained a
good fit with R = -8.1 mm, Z = 8.09 mm, and some small angle changes.
I then filled the desired grid with the closest mapped result if
one existed and with the offset coil calculated result if no mapped
data was close. If the calculated point is greater than 4000 G
(which can happen close to the coils) I fix its magnitude to 4000 G
to reduce the non-linearities near the coil. Then, since the mapped
values are not exactly on the grid points I loop over the grid points
and determined the field at the grid point by fitting a second order
polynomial in x, y, and z to the 27 points surrounding the desired
grid point. I do this so long as at least one point of the 27 was a
measured value. If all 27 are calculated there is no need to do the
fit.
I am now calculating a new grid following the same procedure as
above but changing the ranges so that the grid extends to the TOF's
in x, y, and z and also extends back to Z = -1.2 m to include the BAT's
The old range was
-200 <= x <= 200
-70 <= y <= 70
-10 <= z <= 290
The new range I am calculating now is:
-250 <= x <= 250, 101 grid steps
-90 <= y <= 90, 37 grid steps
-120 <= z <= 380, 101 grid steps
For comparison the y component of the field at
x = 200, y = 0, z = 0 is -454 G
x = 250, y = 0, z = 0 is -95 G (near face of back angle TOF)
x = 130, y = 0, z = 290 is -269 G
x = 130, y = 0, z = 380 is 10 G (near face of forward angle TOF)
This new grid will be approximately 2.6 times larger. If anyone
thinks this too large please let me know.
Cheers,
Douglas
26-415
M.I.T. Tel:
+1 (617) 258-7199
77 Massachusetts Avenue Fax: +1
(617) 258-5440
Cambridge, MA 02139, USA E-mail:
hasell@mit.edu
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