determination_of_angles_and_momentum

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determination_of_angles_and_momentum [2013/12/24 09:18] pereira [Reconstruction method] |
determination_of_angles_and_momentum [2020/02/14 10:51] pereira [Calculation of the inverse map] |
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===== Calculation of the inverse map ===== | ===== Calculation of the inverse map ===== | ||

- | Since the energy coordinate //d// is one of the quantities deduced from the inverse map, the beam position x<sub>t</sub> cannot be calculated and is assumed to be zero. This assumption implies that the final resolution is obtained by folding the finite size of the beam spot in that direction with the size obtained from the reconstruction, itself depending on the detector resolution and the order to which the calculation is performed. Note that this is still the case when the S800 is operated in [[Modes of Operation#Dispersion-matched Mode|dispersion-matched mode]], where the incoming beam is momentum dispersed—and therefore rather large—on the target. In that case it is the size at the object location that matters since the entire S800 ([[Introduction#Analysis Line|analysis line]] + [[Introduction#Spectrograph|spectrograph]]) is achromatic. Because the shapes of the fringe fields vary significantly with the absolute strength of the magnets, inverse maps need to be calculated for each magnetic-rigidity setting of the spectrograph. The inverse transfer maps can be calculated [[http://maps.nscl.msu.edu/~s800maps/|online]] from the currents of the S800 [[Magnets#Spectrograph Dipoles|dipoles]] and [[Magnets#Spectrograph Quadrupole Doublet|quadrupole doublet]], magnetic rigidity, and the particle (A,Z) are necessary. The process takes about 20 seconds. | + | Since the energy coordinate //d// is one of the quantities deduced from the inverse map, the beam position //x<sub>t</sub>// cannot be calculated and is assumed to be zero. This assumption implies that the final resolution is obtained by folding the finite size of the beam spot in that direction with the size obtained from the reconstruction, itself depending on the detector resolution and the order to which the calculation is performed. Note that this is still the case when the S800 is operated in [[Modes of Operation#Dispersion-matching Mode|dispersion-matching mode]], where the incoming beam is momentum dispersed—and therefore rather large—on the target. In that case it is the size at the object location that matters since the entire S800 ([[Introduction#Analysis Line|analysis line]] + [[Introduction#Spectrograph|spectrograph]]) is achromatic. Because the shapes of the fringe fields vary significantly with the absolute strength of the magnets, inverse maps need to be calculated for each magnetic-rigidity setting of the spectrograph. |

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+ | **Instructions on how to calculate the inverse transfer maps can be found [[mapserver|here]]**. | ||

determination_of_angles_and_momentum.txt · Last modified: 2020/02/14 10:51 by pereira