1. RHIC Spin Flipper M. Bai, T. Roser Collider Accelerator Department
Brookhaven National Laboratory, Upton, NY 11973

2. Outline Goal: achieve full spin flip in RHIC
without detuning the snake
setting
How to obtain full spin flip of polarized protons with spin precession tune of 1/2
RHIC spin flipper parameters

3. Traditional spin flipping technique
Adiabatically crossing an artificial spin resonance induced by an ac dipole.
This technique has been demonstrated in the Brookhaven AGS, IUCF Cooler Ring as well as the Cozy 3 GeV storage ring
How to spin flip?
Qsf
Qspin
0.5

4. Traditional spin flipping technique
However, this technique excites not only an resonance at Qsf but Also an resonance at –Qsf. Hence, the condition of adiabatic resonance crossing is broken when the beam spin precession tune is at or close to ½, and one can not achieve full spin flipping.
It is critical for this technique to have spin precession tune stay away from 1/2 requires to detune the snake settings. This requirement it can not be an operational tool to realize routine spin flipping at high energy colliders like RHIC.

5. Spin flipper for operational high energy pp accelerators
Has to provide full spin flip in the presence of the nominal snake configuration, i.e. the beam spin precession tune is at or close to ½
Use a rotating spin kick field instead of an oscillating spin kick field by a single ac dipole to eliminate the resonance at –Qsf.

6. Implementation of spin flipper
Schematic layout
Ac dipole 1:
Ac dipole 2:
Spin rotator 1:
Axis: vertical
Angle 0: 90o
Spin rotator 2:
Axis: vertical
Angle 0: -90o
For small , the equation then becomes:
Let  =90o, we then get:

7. Simulation results Single particle with spin tune = 0.5 Spin flipper:
Amplitude: 20 Gauss-m
Tune: > 0.51
Sweep in half million turns

8. Spin tune meter
Instead of sweeping the spin flipper tune across the beam spin precession tune, one can also keep the spin flipper tune fixed nearby the beam spin tune. In this case, the stable spin direction is given by
The beam spin tune can be calculated by measuring the turn by turn horizontal and vertical asymmetry

9. Using rotating field
Using a single ac dipole

10. Spin vector in the rotating frame
Using a single ac dipole
Using rotating field

11. How to construct a rotating field with ac dipoles
90o Spin rotator
-45o Spin rotator
Specs:
Ac dipole:
field amplitude: 20 Gauss-m
frequency:
90o Spin rotator:
magnet: a DC dipole with vertical field
integrated field strength: 2.7 Tesla-m
dipole deflection:
100 GeV: 8.2 mrad
250 GeV: 3.2mrad