Ion Polarization Control in the MPD and SPD Detectors of the NICA Collider

Two solenoid Siberian snakes are placed in the oppoutereotion. The change of the polarization direction in the vertical plane of MPD and SPD detectors occurs due to insertion of polarization control (PC) solenoids in the magnetic lattice of the collider. The solenoids rotating spin by small angels practically do not influence on the polarization vector as function of the orbit length for cases of longitudinal and vertical polarization in the MPD and SPD detectors are presented. SPIN TRANSPARANCY MODE IN NICA NICA project at JINR is aimed at the experiments with polarized protons and deuterons at both SPD and MPD detectors over beam momentum range from 2 to 13.5 GeV/c [1, 2]. To control efficiently polarization of protons and deuterons as well it was proposed to use the col, which is realized if two identical solenoid Siberian Snakes are placed in the opposite straight sections of the collider (Fig. 1) [3]. Figure 1: The polarization control scheme of protons and deuterons in the NICA collider. BEAM POLARIZATION MANIPULATION IN SPD AND MPD DETECTORS The unique feature of a spin transparency accelerator is the possibility to obtain any particle polarization using small magnetic field integrals [3]. The proton and deuteron polarization in the NICA collider ring can be efficiently controlled by weak solenoids. Any angle between the polarization and the beam direction lying in the vertical plane of SPD (MPD) detector can be obtained by introducing polarization control (PC) insertions. Each PC indipoles. A symmetric scheme of polarization control with two PC insertions located at the both sides of the SPD (MPD) detector is presented in Fig. 2. Figure 2: Polarization control by means of weak (PC) solenoids in SPD (MPD) detector. The spin tune induced by PC insertions should exceed substantially the strength of = 0 spin resonance. The strength is determined by the beam s emittances and by misalignments and manufacturing imperfections of the es are estimated to p = 0.01 and d = 0.003 for proton and deuteron case respectively. A scheme of the snake solenoids and weak PC solenoids positions is presented in Fig. 3. The eight solenoids of 5.5 m long each are marked with yellow. The ten PC solenoids of 0.4 m long each are marked with orange. The snake solenoid fields are equal to 2.3 T for protons and 7.3 T for deuteron at the maximum momentum. Figure 3: Placement of PC solenoids in NICA collider. Proceedings of IPAC2015, Richmond, VA, USA TUPTY017 1: Circular and Linear Colliders A01 Hadron Colliders ISBN 978-3-95450-168-7 2031 Co py rig ht © 20 15 CC -B Y3. 0 an d by th er es pe ct iv ea ut ho rs Four pairs of PC solenoids with the eld values Bz1 and Bz2 are placed in the straight sections and behind the last structural dipole ( = 4.5 ) respectively for proton or in the middle of the arcs ( = 90 ) for deuteron case. Necessary combination of the PC solenoids switching on in the cases of the spin control in SPD or MPD detectors is shown in Table 1. Table 1: PC Solenoids in NICA Collider Detector Protons Deuterons SPD PC Sol1, PC Sol2 PC Sol1, PC Sol3 MPD PC Sol4, PC Sol5 PC Sol5, PC Sol3 The field integrals required in each insertion to obtain the longitudinal = 00 and vertical = 900 proton and deuteron polarizations are shown in Fig. 4 as functions of the beam momentum. The spin tunes of protons and deuterons in the collider for the given field integrals have values of p = 0.01 and of d = 0.003, which exceed much the zero spin resonance strength caused by imperfections of the collider magnetic structure. The maximum field integral of each PC solenoid at the maximum momentum does not exceed 0.6 , thus practically no disturbance of the particles orbital characteristics in the collider will be occurred. Figure 4: The dependences of the PC solenoid on the particle momentum for the longitudinal (left) and vertical (right) polarizations of the proton and deuteron beams. SPIN-FLIPPING MODE The presented scheme of polarization control allows obtaining not only vertical and longitudinal polarization in each detectors but also any polarization lying in vertical plane of the detector. The dependences of the field integrals on the angle at minimum and maximum beam momentum are shown in Fig. 5. The longitudinal (vertical) polarization can be flipped by reversing the fields of the PC solenoids. To preserve the polarization when changing its direction, the spin tune must remain constant during the solenoid field change. This eliminates the possibility of crossing of spin resonances. To preserve the polarization, one must then only satisfy the condition of adiabatic regime, which means that the characteristic spin reversal time in the indicated examples should not be shorter than 0.3 ms for protons and 1 ms for deuterons. Figure 5: Dependences of the PC solenoid field integrals on the angle between the polarization and the beam direction for proton and deuteron mode of the collider. INFLUENCE OF MPD SOLENOID The MPD setup contains a solenoid ~ 7.5 m long and 0.66 T field [5]. The solenoid does not effect to the longitudinal polarization. The angle of transverse polarization rotation after particle moves throughout the region with longitudinal field Bs and a length L can be calculated as: ] / GeV [ ] m [ ] T [ 48 [deg] , ] / GeV [ ] m [ ] T [ 15 [deg] p d c p L B