# Presentation: 118587

## The Strong Snake for the AGSHaixin Huang

- Why strong snake?
- How strong it needs to be?
- Design Status

- 2/22/02

## Why Strong snake?

- AC dipole operation need precise control of betatron tunes to the level of 0.0005 and need to be constantly monitored for polarized proton operation.
- Due to the linear coupling from the solenoidal field of 5%  partial snake, there are  polarization loss at the so-called coupling resonances, which is due to the the vertical betatron motion with  horizontal betatron tune. So we would like to have a new snake with less coupling.
- The polarization loss at those weak intrinsic resonances can not be overcome by AC dipole.
- A strong snake can eliminate the use of AC dipole can correct all intrinsic resonances when betatron tunes are set properly.

- 2/22/02

## How a strong snake works

- The stronger the snake, the larger the spin tune gap when G=N. When the snake is strong enough so we can put betatron tune in the gap, then the resonance condition will never be met.
- In a different view, The snake acts as a resonance at G=N. If the intrinsic resonance is overpowered by the snake, then full spin flip can be achieved.
- Note: With a strong snake, the stable spin detection will be deviate from vertical significantly(18 degree for 20% snake).

- 2/22/02

## Simulation results

- (done by M. Bai)

- A simple model simulation shows that 20% snake is needed to overcome the  strongest resonance 36+. More simulation is going on especially for 9-y between 0.05 and 0.1.
- Snake resonances occur when factional betatron tune equals 1/2, 1/3 of spin tune.

- 2/22/02

## Test results with 10% snake at 0+

- Experiment done in January. It follows the simulation trend nicely.
- The blue line is the injected beam polarization. The difference between the red dots and blue line is due to the coupling resonance and tilted stable spin direction.

- 2/22/02

## Spin matching at injection and extraction

- Stable Spin Direction (SSD)in AGS is tilted away from vertical due to a strong snake. We have to match  the injected and extracted beam stable spin direction to avoid polarization loss.
- Injection:
-      1. one possibility is to raise the injection energy to get G from 4.7 to 5 (2.27GeV/c to 2.44GeV/c) and run the Booster vertical tune at 5.1 (in the past it was set at 4.9). Then the SSD is in horizontal plane in both Booster and AGS. A proper choice of 5th harmonic corrector setting  of the Booster can match the SSD in the Booster  to the SSD in AGS.
-      2. Use the current solenoid snake in the BtA lline  as a spin rotator. But it needs a lot space.
-  Extraction:
-        There are many ways to manipulate SSD in RHIC (snakes, spin rotators). It is less a problem.

- 2/22/02

## Operation Scenario

- 20% partial snake at top energy (24.3GeV/c), which means ~30% at injection (2.27GeV/c). More simulation is still going on (M. Bai).
- Radiation environment needs to be evaluated:
-       From high intensity protons: power off but cold;                                	               From polarized protons: power on and maybe the limiting 		               aperture.                                                                                  		               2”2” collimator in the upstream will be needed for      	              polarized proton operation as a protection device.
- Suppose 15 beam  at injection(Pol. Proton), =3.6mm. Orbit excursion 4cm in horizontal, 4cm in vertical. So the available room is >9 .
- High intensity proton beam: 100  at injection, =1.1cm. There is no aperture problem for high intensity operation.
- Betatron tune settings: y~8.95, x~8.55.

- 2/22/02

## Design of the snake

- The snake is going to be a super-conducting full helical dipole magnet.
- The available space in the AGS is 2.6 meter long. Two bending dipole magnets on both sides of the helical snake.
- 2-layer design with 400A to reach 4T.
- Beam pipe is 6” by 6” (15cm by 15cm).
- 1.36 meter long and operation field is 3.28T(30% at injection).
- Cryogenic design: try to reach 1w heat load. But as long as the heat load is below 5w, then the cryo dewar can be filled once/day (without ring access).
- Coupling at injection is still significant due to sextupole field feed down. The design goal is to have no sextupole field along the beam trajectory by adding compensation coils.

- 2/22/02