# Presentation: 804457

## eRHIC – Future Electron-Ion Collider at BNL

*V.Ptitsyn*
*C-AD, BNL*

## What is eRHIC?

- To probe **fundamental aspects of QCD**

- Relativistic Heavy Ion Collider

- +  Electron accelerator

- A high energy, high intensity polarized electron/positron beam facility could be built at BNL to provide collisions with the existing heavy ion and polarized proton beam.

## eRHIC Scope

- Polarized leptons
- 5-10 Gev

- Polarized light ions (He3)
- 167 Gev/u

- Heavy ions (Au)
- 100 Gev/u

- Polarized protons
- 50-250 Gev

- Electron accelerator

- RHIC

- 70% beam polarization goal

- Center mass energy range: 30-100 Gev

## Advantages of collider

- Goal luminosities:
-   in 1032 - 1034  cm-2s-1 range for e-p collisions
-   in 1030 - 1032  cm-2s-1 range for e-Au collisions

-  Polarized DIS in past only in fixed target mode
-  With collider:
- Higher Center of Mass energies reachable.
- Better angular resolution between beam and target fragments

- eRHIC

## How eRHIC can be realized?

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

## 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.                                   (Parallel mode : Ion-ion collisions in IP6 and IP8 at the same time are possible.)
- Longitudinal polarization produced by local spin rotators in interaction regions.
- Present design luminosities (for high energy setup):
- e-p: 4.4 1032 cm-2s-1
- e-Au: 4.4 1030 cm-2s-1
- e-He3: 3.1 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.
- Technology similar to used at B-factories.

**IP12e-p**

**IP8p-p**

**IP6p-p**

## Linac-ring design

- Electron beam is transported to collision point(s) directly from **superconducting energy recovery linac (ERL).**
- No beam-beam limitation for electron beam (the beam is used once!).
- No prohibited energy areas for the polarization.
-      No spin rotators needed.
- e-p luminosity >1033 cm-2s-1 possible
- But no straightforward way to get polarized positrons

- Design being developed at BNL

## Luminosity for different options

- Linac-Ring:
-    No electron beam-beam limit on ion current.
-       Luminosity is defined by ion beam parameters.
-       IR design allows for round beams at the collision point.
- Ring-ring:
-    Limitation from IR design (septum magnet aperture)  leads to elliptical beam (vertical to horizontal beam size ratio: K=1/2) and the limit on ’xi
-      Electron beam-beam limit (e < 0.08) prevents proton intensity more than
-      1e11 p/bunch

## Luminosity versus proton beam-beam parameter

- Ring-ring with cooling

- Ring-ring, no cooling

- Linac-ring,
- 2e11 p /bunch

- Linac-ring,
- 1e11 p /bunch

- Marks show locations on the luminosity lines where electron current reaches 0.5A,
- which is presently nominal design current for both options.
- In parallel mode (1 e-p + 2 p-p collision points): p~0.0065;
- In dedicated mode (only e-p collision): maximum p~0.018;

- Calculations for 360 bunch mode and 250 Gev(p) x 10 Gev(e) setup

## Major R&D issues 

- Ring-ring:
- The accommodation of synchrotron radiation power load on vacuum chamber. (To go beyond 5.e32 cm-2s-1 luminosity).
- Linac-ring:
- High current polarized electron source
- Energy recovery technology for high energy and high current beams
- Ion ring:
- Beam cooling techniques development (electron, stochastic).
- Increasing total current (ions per bunch and number of bunches)
- Polarized He3 production and acceleration

## Last notes

- Two design options for eRHIC are under development: ring-ring and linac-ring.
- Zero-degree design has been produced ( ZDR, 2004).
- Present development is towards more detailed conceptual design report.
- At similar level of electron beam intensities the linac-ring design provides higher luminosity, but requires significant development for polarized electron source.
- Ring-ring design is at present level of accelerator technology, but   e-p luminosity of 1.e33 cm-2s-1 is very difficult to achieve.
- On present schedule the operation would start at 2016-2017.