Complete Baseline Scheme for Ion Polarization Preservation and Control in the MEIC Ion Complex Yu.N. Filatov, A.M. Kondratenko, M.A. Kondratenko Science and Technique Laboratory Zaryad, Novosibirsk, Russia translated and presented by V.S. Morozov JLab MEIC R&D meeting, February 19, 2015 F. Lin
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Contents of the Report Introduction Colliders with “preferred spin axis” and “transparent to the spin” Strength of the zero-integer spin resonance in a figure-8 collider Ion polarization in the MEIC accelerator complex Preservation of the ion polarization in the prebooster and large booster Ion polarization control in the collider ring Calculation of the ion polarization in the collider’s experimental straight Spin flipping in the ion collider ring Conclusions
Introduction Polarization design requirements High polarization (over 70%) for protons or light ions (d, 3He++, and possibly 6Li+++) Both longitudinal and transverse polarization at all interaction points Sufficiently long polarization lifetime Spin flipping at a high frequency Figure 8 features advantageous for satisfying the design requirements The spin tune is energy independent but is equal to zero The figure-8 topology eliminates the effect of arcs on the spin motion Control the polarization of any particle species including deuterons, using longitudinal fields of small integrated strength (weak solenoids) Control the polarization at the interaction points without essentially any effect on the beam’s orbital characteristics Elegant solution to the problem of ion acceleration completely eliminating resonant beam depolarization Allows one to easily adjust the polarization in any direction at any orbital location necessary when transferring the beam from one ring into another or when measuring the polarization by polarimeters Allows for an easy manipulation of the spin direction at an interaction point during an experiment Spin-flipping system with a spin reversal time of less than a second Polarized beam studies in MEIC at an unprecedented precision level
Collider Types Colliders (accelerators) with preferred spin direction Conventional accelerator Collider with a single Siberian snake Collider with two Siberian snakes with their axes at 90 Colliders (accelerators) transparent to the spin Conventional accelerator (resonant case) Collider with two identical Siberian snakes Collider in the shape of a figure 8 The most natural representative of a collider “transparent to the spin” Unique opportunities with colliders (accelerators) transparent to the spin Efficient control of the ion polarization using small magnetic field integrals 10 Tm vs ~100 and 2500 Tm for protons and deuterons, respectively, at 100 GeV/c Polarization control at the interaction points during experiments Efficiently control using “weak” fields, which have essentially no effect on the beam’s orbital characteristics Spin reversal in less than a second
Zero-Integer Spin Resonance The frequency spectrum of the spin motion in a figure 8 consists of integer-multiple harmonics of the particle revolution frequency Zero-integer resonance strength determines polarization stability Resonance strength components Coherent part Due to additional dipole and longitudinal fields along the closed orbit Linear effect Can be compensated, compensation technique is well known and has been successfully used, for instance, at the AGS Incoherent part Nonlinear effect Much weaker than the coherent part
Ion Polarization in MEIC Polarization preservation during acceleration Ion source Ion linac Prebooster Large booster Ion collider ring Polarization control in the ion collider ring
Polarization in Prebooster and Large Booster Figure 8 eliminates spin resonance crossing during acceleration Polarization stabilized by a single weak solenoid Polarization is longitudinal in the solenoid straight, which can be used for polarization matching Spin tune shift by the solenoid must greatly exceed the zero-integer spin resonance strength Required solenoid field integral does not exceed 2 Tm, compare to a full Siberian snake of 75 and 250 Tm for protons and deuterons, respectively, at 20 GeV
Optical Effect of Solenoid Linear optics without solenoid Linear optics with solenoid Betatron tune shift
Ion Polarization Control in Collider Ring 3D spin rotator consisting of weak dipoles and solenoids Any polarization orientation No effect on the optics Three modules for control of the three polarization components Fixed orbit bumps of ~12 mm Spin rotations for a certain polarization direction
Ion Polarization Control in Collider Ring Field integrals as functions of energy for deuterons assuming 0.58 bends and a spin tune of 2.510-4 Field integrals as functions of energy for protons assuming 0.58 bends and a spin tune of 0.01 Lattice integration Each module is ~6 m long
Calculation of Deuteron Polarization Schematic of the experimental straight with bend locations Deuteron polarization along the collider ring
Calculation of Proton Polarization Proton polarization in the experimental straight
Spin Flipping The universal 3D spin rotator can be used to flip the polarization Consider e.g. longitudinal polarization at the IP at 100 GeV/c Polarization is flipped by reversing the fields of the solenoids in the radial and longitudinal spin control modules Polarization is preserved if The spin tune is kept constant No resonant depolarization The rate of change of the polarization direction is slow compared to the spin precession rate >0.1 ms for protons and >3 ms for deuterons
Conclusions Figure 8 design allows for use of weak solenoids for polarization control at high energies of any particle type including deuterons; seamless integration of the spin control elements into the collider lattice with fixed closed orbit and no optics distortion; elimination of the resonant depolarization at all stages of the beam acceleration from the linac to the collider ring; adjustment of any polarization orientation at any orbital location (spin matching at injection into the different accelerator complex components, polarimetry, spin flipping); manipulation of the particle spin during an experiment without affecting the beam orbital properties, which provides a capability of carrying out polarized beam experiments at a new precision level; compensation of the manufacturing and alignment errors of the lattice magnetic elements, which additionally substantially enhances the precision of polarized beam experiments; ease of adjusting the spin dynamics to meet any experimental requirements, which may arise in the future.