Measurements of a Three- Dimensional Field Distribution of Spectrometric Magnet of "Delta-Sigma" Set-up for Spin Physics Experiments I.P. Yudin, S.A. Dolgii, A.A. Morozov, G.P. Nikolaevsky, V.I. Sharov, R.A. Shindin, V.L. Smirnov, A.Yu. Starikov, L.N. Strunov Joint Institute for Nuclear Research, Dubna , Moscow region, Russia DSPIN-2009, September 2, 2009, JINR, Dubna

Abstract. One of the main goals of the "Delta-Sigma-experiment" project is measurement of the energy behaviour of spin-dependent NN observables A00kk(np), A00nn(np) and Rdp in the GeV region of the neutron beam. These observables are determined by measurement of proton yields from the np > pn charge-exchange reaction at 0. using a magnetic spectrometer. Measurements of the magnetic field map of the spectrometer magnet providing high accuracy in determining the proton momentum were carried out. The "Delta-Sigma" set-up is placed at building 205 of the LHEP, JINR. The spectrometer magnet 2-SP-94-1V has the external sizes 2.95 x 2.12 x 1.62 m and aperture 0.30 x 0.13 m. A three-component Hall probe was used. The measurement volume is 0.34 x 0.07 x 2.18 m. A description of the measuring equipment, method and results is presented. The results are used for analysis of the physical data.

Graph_1. Schematic diagram of the Delta-Sigma setup: H2/D2 is the polarized liquid hydrogen (deuterium) target; SP-94 is the spectrometric magnet; SH is the pulsed hodoscope; A,S1,S2,S3 are the scintillation detectors; and Gx, Gy, 1x, 2x, 3x,y, 4x, y is the system of proportional chambers.

Cut of 1-SP-94-1В magnet in XOY plane The general view of 1-SP-94-1B magnet

The Hall probe construction The Hall probe construction

Graphics of Hall probe calibration (mV->Gs) ПХ 22 ПХ 27 ПХ 43

Graph_4. Measuring system (frame) and coordinate system in which measurements with respect to the magnet pole were performed.

An error for y=1.0 T An error for y=0.75 T An error for y=1.5 T An error for y=1.3 T

Graph

Graph_7 Dependence of main component of magnetic induction By(0, 0, z) on longitudinal coordinate z at fixed x = 0 and y = 0 for different magnet winding current values.

The median plane, y=0. The y=0.05 m plane

Graph

The z=0 planeThe z=0.6 m plane

Fig_14а Graphics of By=By(x=-0.15m, y=0.05m), Bx=Bx(x=-0.15m, y=0.05m), Bz=Bz(x=-0.15m, y=0.05m) as functions of longitudinal coordinate z.

CONCLUSIONS Measurements of the magnetic field of the analyzing magnet 2-SP- 94-1V of the Delta-Sigma setup in the spatial volume with dimensions 0.34 × 0.07 × 2.18 m were performed. A three- dimensional map of the distribution of all components of the magnetic field vector in this volume was obtained. The plots of characteristic distributions of field components on a level of 0.75, 1.00, 1.3, and 1.5 T were constructed. The measuring equipment and measurement procedure were described. The measurements were performed with an error of ΔB/B ≤ 0.5% (≤70 Gs on a level of 1.5 T at the center of the magnet) for the field region near the edges of the poles and ΔB/B ≤ 0.1% (10 Gs on a level of 1.5 T at the center of the magnet) for the remaining measurement region. These results will be used to process the physical data obtained in the seanses of experiment. ACKNOWLEDGMENTS This work was supported by the Russian Foundation for Basic Research, project no a.

References References 1. V. I. Sharov et al., “Measurements of the Total Cross- Section Difference ΔσL(np) at 1.39; 1.69; 1.89 and 1.99 GeV,” JINR Preprint E (Dubna, 2004); Yad. Fiz. 68, 1858 (2005) [Phys. At. Nucl. 68, 1796 (2005)]. 2. V. I. Sharov et al., Czech. J. Phys. B 54, 173–178 (2004). 3. V. I. Sharov et al., “Measurements of Energy Behaviours of Spin-Dependent np-Observables over a GeV Region, Dubna 'Delta–Sigma’ Experiment,” Eur. Phys. J. C 37, 79–90 (2004). 4. V. I. Sharov et al., “Measurements of Energy Behaviours of Spin-Dependent np-Observables over GeV Energy Region, Dubna 'Delta-Sigma’ Exreriment,” in Relativistic Nuclear Physics: from Hundreds MeV to TeV (Dubna, 2006), pp. 118–129 [in Russian].