# Presentation: 683496

## Collider aspects of the polarized beams at RHIC,RHICII and eRHIC

- V.Ptitsyn, C-AD, BNL

## RHIC Luminosity History

## Luminosity and polarization projections to 2008for 100 GeV energy beam

- AGS polarization gain (65%->70% (75%)):
-  both betatron tunes placed in the spin tune gap that dual snakes provide

##  Luminosity improvement factors for next 100 GeV runs

- Goal: doubling, then tripling the luminosity, by bunch intensity increase and increased time in store
- Nonlinear chromaticity correction
- 10Hz IR orbit feedback
- 2/3 resonance compensation
- New working point test  ~(0.92;0.93)
- Additional NEG pipes (100m)
- 9.3Mhz RF cavity system for the injection ( should allow for smaller longitudinal emittance)
- Possible problem to watch: slow emittance growth due to electron cloud

- Beam lifetime in the store

## Polarization preservation

- Polarization transmission in RHIC close to 100% (i.e. no polarization loss during the acceleration).
-  Main factors for the polarization preservation:
**Optimal Snake current setting.** To avoid the deviation of spin tune from 1⁄2 and corresponding shift in the position of high order spin resonances)
**Betatron tune control.** To avoid the depolarization caused by 3⁄4 and 7/10 high order spin resonances.
- Tune+decoupling feedback system was applied succesfully on the machine setup stage of Run-6.
**Vertical orbit control.** To minimize the strength of 3⁄4 spin resonance
- Whole machine vertical realignment was done before the run 6.
- Reliability of BPM system.
-  orbit rms <0.5mm

## Golden Store #7909 (including polarization)

- slow depolarization in store

## 250 Gev polarized protons

- Luminosity: increased by factor 2.5 due to transverse emittance reduction,       L ~ 2.2 1032 cm-2 s-1
- Polarization:
-     stronger depolarizing resonances, tighter requirements for vertical beam orbit control:
- Orbit rms < 0.3mm
- Beam-based alignment (BPM relative to quad center)
- Vertical ring realignment (how often?)

## 250 GeV polarization ramp measurement

- M.Bai

## RHIC II polarized proton parameters

**500**

**RHICII**

**RHIC**

-  Main luminosity gain (x2) is from reducing * by factor 2.
-      Modified Interaction Regions (added doublets?)
-  Pre-cooling at the low energy (injection).
-     Minimum emittance value is defined by beam-beam limit.
-     Moderate luminosity gain ~20%
-  Cooling at store can be done for protons up to 100 GeV
-     Increased average luminosity.

**Total beam-beam parameter                                                                         0.017             0.02**

## Other possible luminosity improvements

- Beam-beam compensation by electron beam lens
- Increase of number of bunches (upgrade of the injection system):  111 -> 166 ( -> 330?)
-     Planned for eRHIC

## How eRHIC can be realized?

- Two design options:
- Ring-ring:
- Linac-ring:

## The design based on Energy Recovery Linac (ERL)

- Electron energy range: 3-10 GeV (possible upgrade option to 20 GeV)
- Proton energy range: 50-250 GeV
- Au ion energy range: 50-100 Gev/n

- Peak luminosity:
- 2.6 1033 cm-2s-1

- Energy recovery:
*decelerate bunches in the same linac; the energy taken from decelerated bunches can be reused for  acceleration of new bunches*

- Lower energy pass

## eRHIC beam parameter for e-p collisions

|  | High energy setup |  | Low energy setup |  |
| --- | --- | --- | --- | --- |
|  | p | e | p | e |
| Energy, GeV | 250 | 10 | 50 | 3 |
| Number of bunches | 166 |  | 166 |  |
| Bunch spacing, ns | 71 | 71 | 71 | 71 |
| Bunch intensity, 1011 | 2 | 1.2 | 2.0 | 1.2 |
| Beam current, mA | 420 | 260 | 420 | 260 |
| Normalized 95% emittance,  m | 6 | 115 | 6 | 115 |
| Rms emittance, nm | 3.8 | 1.0 | 19 | 3.3 |
| beta*,  x/y, cm | 26 | 100 | 26 | 150 |
| Beam-beam parameters, x/y | 0.015 | 2.3 | 0.015 | 2.3 |
| Rms bunch length, cm | 20 | 1 | 20 | 1 |
| Polarization, % | 70 | 80 | 70 | 80 |
| Peak Luminosity, 1.e33 cm-2s-1
Aver.Luminosity, 1.e33 cm-2s-1 | 2.6 |  | 0.53 |  |
|  | 0.87 |  | 0.18 |  |
| Luminosity integral /week, pb-1 | 530 |  | 105 |  |

## Interaction region design

- Yellow ion ring makes 3m vertical excursion.
- Design incorporates both normal and superconducting magnets.
- Fast beam separation. Besides the interaction point no electron-ion collisions allowed.
- Synchrotron radiation emitted by electrons does not hit surfaces of cold magnets

- C.Montag, B.Parker, S.Tepikian

## IR design schemes

|  | Distance to nearest magnet
from IP | Beam separation | Magnets used | Hor/Ver beam size ratio |
| --- | --- | --- | --- | --- |
| Ring-ring,
l*=1m | 1m | Combined field quadrupoles | Warm and cold | 0.5 |
| Ring-ring, l*=3m | 3m | Detector integrated dipole | Warm and cold | 0.5 |
| Linac-ring | >3m | Detector integrated dipole | Warm | 1 |

- No crossing angle at the IP
- Linac-ring: larger electron beta*; relaxed aperture limits ; allows round beam collision geometry (the luminosity gain by the factor 2.5).
- Detector integrated dipole: dipole field superimposed on detector solenoid.

## R&D issues 

- Linac-ring:
- High current polarized electron source (for polarized beams!)
- Energy recovery technology for high energy and high current beams
- Beam-beam effects
- Ion ring:
- Beam cooling techniques development (electron, stochastic).
- Increasing total current (ions per bunch and number of bunches).
- Polarized He3 production (EBIS) and acceleration

## Ring-ring design option 

- The electron ring of 1/3 of the RHIC ion ring circumference
- Full energy injection using polarized electron source and 10 GeV energy linac.
- e-ion collisions in one interaction point.
- Longitudinal polarization produced by local spin rotators in interaction regions.
- Aver Luminosity, 1-2 1032 cm-2s-1

**AGS**

**BOOSTER**

**RHIC**

**e-cooling**

**LINAC**

**EBIS**

**recirculating linac injector**

**5-10 GeV static electron ring**

- The e-ring design development led by MIT-Bates

**IP12e-p**

**IP8p-p**

**IP6p-p**

## Electron polarization 

- Beam polarization can not be achieved in certain energy areas.                           (Spin resonance zones)
- Requirements for good vertical alignment and precise vertical orbit control:
-            yco rms < 150 m
- Positrons: self-polarized in the ring :
- pol = 20min at 10 GeV

- D.Barber