eRHIC with Self-Polarizing Electron Ring

V.Ptitsyn, J.Kewisch, B.Parker, S.Peggs, D.Trbojevic, BNL, USAD.E.Berkaev, I.A.Koop, A.V.Otboev, Yu.M.Shatunov, BINP, Russia

C.Tschalaer, J.B. van der Laan, F.Wang, MIT-Bates, USA D.P.Barber, DESY, Hamburg, Germany

The EIC w.r.t. Other Experimental Facilities

Large luminosity and high CM Energy makes EIC unique!

Variable CM energy enhancesits versatility!

TESLA-N

EIC Objectives

e-p and e-ions collisions 5-10 GeV electrons; 25-250 Gev protons; 100 Gev/u Au Luminosity:

L = (0.3-1)x1033 for e-p collisions

L = (0.3-1)x1031 for e-Au collisions

Polarized electron and proton beams Longitudinal polarization at collision point; 70% 35 nsec minimum separation between bunches

BRAHMS & PP2PP (p)

STAR (p)

PHENIX (p)

AGS

LINACBOOSTER

Polarized Proton in RHIC

Pol. Proton Source500 A, 300 s

GeVs

cmsL

50050

onPolarizati%70

102 2132max

Spin Rotators

Partial Siberian Snake

Siberian Snakes

200 MeV Polarimeter AGS Internal Polarimeter

Rf Dipoles

RHIC pC PolarimetersAbsolute Polarimeter (H jet)

2 1011 Pol. Protons / Bunch = 20 mm mrad

AGS pC Polarimeters

Strong AGS Snake

eRHIC collider layout

• e-ring is 5/16 of RHIC ring

• Collisions at one IP

• 28 MHz collision rate

• Unpolarized electron source

• Electron beam polarization by the synchrotron radiation

• e-ring lattice based on

”superbend” magnets

p

e2GeV (5GeV)

2-10 GeV

IP12

RHICp 50-250 GeVAu 100 Gev/u

Superbend magnet

Issues:• Accomodation of radiated power

(7MW radiated at 10 GeV)

• Orbit lengthening versus beam energy

B,T

0.15m

3m

321 Bpol 2

0.2

10GeV

5GeV

0.57

10GeV

5GeV

22BESRL

The desired balance:short polarization time at theacceptable level of synchrotron radiation losses

Flexible control of the beam emittance

Polarization time with superbend

• Magnet bending field scaled proportionally with energy

• The superbend control of polarization time.

8-15min polarization time is achievable.

3

51

pol

0

50

100

150

200

250

300

4 5 6 7 8 9 10 11

Electron energy, GeV

Po

lari

zati

on

tim

e, m

in

0

2

4

6

8

10

12

14

16

18

4 5 6 7 8 9 10 11

Electron energy, GeV

Po

lari

zati

on

tim

e, m

in

Luminosity and beam-beam limits

Round beams:

x=y , x=y for electrons

Matching of the e and p beam sizes is crucial.

Reasonably achievable values:

0.05

0.005

Electron emittance versus electron energyfor different superbend settings

Ee=10GeV

Ee=5GeV

e-co

ol z

one

• Required normalized emittances for Au: 5-8 Pi mm*mrad at 5-10 GeV electron energies;

The cooling is required.

• Cooling of the proton beam is required for proton energies below 200 GeV

• Electron cooling system for RHIC is being developed.

0

10

20

30

40

50

60

70

4 6 8 10

Energy, GeV

Em

itta

nc

e, m

m m

ura

dBeam emittance control

Main beam parameters 2

Parameters e-ring

ion ring

p Au

C, m 1022 3833

E, GeV 5–10 250 100/u

nb 96 360

Nb 11011 11011 1109

I, Arms,mmrad

*, cm*, mm

0.4545–25100.07–0.050.05

0.4517–9

270.07–0.05

0.005

L, cm-2 s-1   (0.5-0.9)1033 (0.5-0.9)1031

Polarization issues

• 0.5mm rms closed orbit error assumed.

• The correction scheme similar to the one used at HERA should solve the problem.

• Fast polarimeter for the on-line spin resonance corrections.

The possibility to accelerate polarized light ions: deutrons, tritium, 3He, 19F (E.Courant).The polarized sources development is required.

Depolarization from ring imperfections in the e-ring

Horizontal separation scheme Vertical separation scheme

IR Design

• IR development proceeds in close link with the detector design• Detector background and protection from synchrotron radiation issues

Spin rotator

e-ring: solenoidal spin rotator -> simplest solution• Perfect longitudinal polarization at 7.5GeV

~15% reduction at 5 or 10 GeV.

• Spin transparency conditions on optics

n

12

solenoid solenoid

quadsn

1

2

Rotator design

p-ring: Helical spin rotator like being used already at two RHIC experiments

Summary:

The design is based on the construction of a self-polarizing electron ring.

Polarized e-p and unpolarized e-ion beam collisions in the center of mass energy range of 30-100 Gev and at luminosities up to 0.9x1033 cm-2s-1 for e-p and 0.9x1031 cm-2s-1 for e-Au collisions.

The electron polarization time of 8-15min is achieved with superbend magnets.

The collider design could be realized using the present level of the accelerator technology.