Spectrometer Description

The Møller polarimeter spectrometer consists of three quadrupole magnets and one dipole magnet:

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quadrupole MQM1H02 (on the yoke labeled $PATSY$);

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quadrupole MQO1H03 (on the yoke labeled $TESSA$);

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quadrupole MQO1H03A (on the yoke labeled $FELICIA$)

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dipole MMA1H01 (on the yoke marked as $University \, of \, Kentucky$).

These magnetic elements are controlled by MCC operators.

The spectrometer accepts electrons scattered close to the horizontal plane. The electrons have to pass through the beam pipe in the region of the quads, through a collimator in front of the dipole magnet, with a slit of 2-4 cm high, through two vertical slits in the dipole, about 2 cm wide, positioned at $\pm$4 cm from the beam. These slits are ended with vacuum tight windows at the end of the dipole. The dipole deflects the scattered electrons down, towards the detector. The detector, consisting of 2 arms - 2 vertical columns - is positioned such that electrons, scattered at $\theta_{CM}=90^o$ pass close to its center. The vertical size of the detector and the magnetic field in the dipole magnet limit the acceptance of the polarimeter in $\theta_{CM}$. This acceptance is about $76-104^o$. At beam energies below 1 GeV the vertical slits in the dipole limit the acceptance to about $83-97^o$.

For a given beam energy there is an optimal setting of the currents in these 4 magnets. In order to get the optimal settings for, say 3.2 GeV one should:

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login to adaqs3 as moller;

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$adaqs3>~cd~paw/analysis$, start PAW, select Workstation type 3;

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$paw>~exec~sett\_{}magp~e0=3.2$, the required values of $GL$ or $BdL$ are printed.

At energies higher than 2.5 GeV it is possible to optimize the beam line for both regular running and for Møller measurements. Typically, the dipole magnet should be turned on only for the Møller measurements.