18 th international spin physics symposium polarized beams at eic v. ptitsyn

18th International Spin Physics Symposium

Polarized Beams at EIC

V. Ptitsyn


HERA – first lepton-proton collider

Selection of physics results:precise data on details of the proton structurethe discovery of very high density of sea quarks and gluons present in the proton at low-xdetailed data on electro-weak electron-quark interactions precision tests of QCD (s measurements)

Double ring collider (6.3 km)

Completed its operation in 2007

920 GeV (p) X 27.5 GeV (e-, e+)

320 GeV center-of-mass energy

Longitudinal lepton polarization

Superconducting proton ring


Physics scope of electron-ion colliders (EIC) after HERA

Different Center-of-Mass Energy -> Different kinematic regions

Higher Luminosity -> Precision data

Polarized beams -> Spin structure of nucleons (still a puzzle!)

Ions up to large A -> Gluon physics, Saturation.

QCD dynamics in much greater details

R. Milner’s plenary talk yesterday


Future collider designs

Ion ring

Electron linear accelerator Ion ring

Electron storage ring

Ring-ring Linac-ring

CME On the base of

eRHIC ring-ring

30-100 GeV RHIC (BNL)

ELIC 20-90 GeV CEBAF (JLab)

LHeC 0.8-2 TeV LHC (CERN)

CME On the base of

eRHIC ERL-based

30-140 GeV RHIC (BNL)

LHeC

linac based

0.8-2 TeV LHC (CERN)


ERL-based eRHIC at BNL

10 GeV electron design energy. Possible upgrade to 20 GeV by doubling main linac length. 5 recirculation passes ( 4 of them in

the RHIC tunnel) Multiple electron-hadron

interaction points (IPs) and detectors;

Full polarization transparency at all energies for the electron beam;

Ability to take full advantage of transverse cooling of the hadron beams;

Possible options to include polarized positrons:

compact storage ring; compton backscattered.

Though at lower luminosity.

Four recirculation passes

PHENIX

STAR

e-ion detector

eRHIC

Main ERL (1.9 GeV)

Low energy recirculation pass

Beam dump

Electronsource

Possible locationsfor additional e-ion detectors

L=2.6 1033 cm-2 s-1

Polarized p (up to 250 GeV), 3HeHeavy ions (up to Au ions)Electrons: 3-20 GeV


Other design optionsUnder consideration also:Medium Energy EIC at RHIC (MEEIC) Electron energy up to 2-3 GeV. Acceleration done by an ERL linac placed in the RHIC tunnel. It can serve as first stage for following higher electron energy machine.Luminosity ~ 1032 cm-2s-1

High energy (up to 20-30 GeV) ERL-based design with all accelerating linacs and recirculation passes placed in the RHIC tunnel. Considerable cost saving design solution.Luminosity exceeds 1033 cm-2s-1

Ring-ring design option. Backup design solution which uses electron storage ring. See eRHIC ZDR for more details. The average luminosity is at 1032 cm-2s-1 level limited by beam-beam effects.

eSTAR

ePHENIX

ERLs

e

p

e


ELIC: EIC at JLab

12 GeVCEBAF

Polarized p, D, 3HeUnpolarized ions up to A=208

Polarizede-,e+

Ep = 30-225 GeV; Eions = 15-100 GeV/n

Ee = 3-9 GeV

Peak L ~ 5.7 1034 cm-2 s-1 (9 (e) X 225 (p) GeV)

Peak L ~ 7. 1033 cm-2 s-1 (3 (e) X 30 (p) GeV)

“Figure-8” design of ion and lepton storage rings: polarization preservation at all energies.

Very high luminosity approach: moderate bunch intensity, short ion bunches, strong focusing and high bunch repetition rate.

Four interaction regions

The operation compatible with 12 GeV CEBAF operation for fixed target program.

ELIC ZDR (Draft)


Polarized source development

• eRHIC: ~ 250 mA average I, 20 nC/bunch• MEEIC at RHIC: 50 mA average I, 5 nC/bunch

R&D development for a source with large cathode area and, probably, ring like cathode shape is underway (MIT-Bates, E.Tsentalovich)Major issues:Cathode deterioration by ion back bombardmentCathode heating -> cooling will be required

ELIC: moderate polarized source current demands (1mA in 5s pulses during the fill)

0

0.2

0.4

0.6

0.8

1

-6 -4 -2 0 2 4 6

R,mm

axicon, 17.4 C axicon, 17.4 C, anode 1 kV small spot, 12.3 C large spot, 17.5 C laser(small) laser (axicon)

Cathode deterioration measured withvarious shape of laser spot on the cathodeconfirms possible advantages of ring-likecathode shape. (E.Tsentalovich)

Laser beam forms:small central spotring-like (+anode bias)ring-likelarge central spot


Electron polarization in ERL eRHIC

• No problem with depolarizing resonances• Spin orientation control at the collision point:

– Spin rotators after the electron source (Wien filter, solenoid)

– Slight adjustment of energy gain in main and pre-accelerator linacs (keeping the final energy constant) (V.N.Litvinenko)

fiiiicp DCaBAak 22

i,,i

Gun

eSTAR

ePHENIX

a is anomalous magnetic momentA,B,C,D are constants depending on general configuration: location of linacs and collision point, number of recirculation passes (n).

f,,cp

E i max 37 MeV n 5

Variation of pre-accelerator linac energy:


Electron polarization in ELIC• The spin control scheme is based on solenoidal snakes and spin rotators

(combination of solenoidal magnets and dipoles).• Vertical orientation of the spin in the arcs with opposite direction in two halves:

– Prevents the depolarization of the electrons ( Peq ~ 90%)– Provides self-polarization of the positrons ( tpol ~ 2h at 7 GeV)

• Longitudinal spin orientation at all interaction points• Challenge: develop spin matched optics to prevent (or minimize) depolarizing

effects coming from snakes and rotators. (Next talk by P. Chevtsov)• Detector solenoid compensation (?).• Spin tune control.

spin rotatorspin rotator

spin rotatorspin rotator

collision point

spin rotator with 90º solenoid snake

collision point

collision point

collision point

spin rotator with 90º solenoid snake


eRHIC, polarized protons RHIC :- only polarized proton collider in the world. 100 GeV operation so far. Up to 65% polarization achieved.- successful first test with acceleration to 250 GeV in 2006. ~45% polarization- several week operation with 250 GeV protons planned in coming run (February)

PHENIX (p)

AGS

LINACBOOSTER

Pol. H- Source

Solenoid Partial Siberian Snake

200 MeV Polarimeter

Helical Partial Siberian Snake

Spin Rotators(longitudinal polarization)

Siberian Snakes

Spin Rotators(longitudinal polarization)

Strong AGS Snake

RHIC pC PolarimetersAbsolute Polarimeter (H jet)

STAR (p)

AGS Polarimeters

Spin flipper

eRHIC will take favor of existing hardware in RHIC and in the injector chain to accelerate polarized protons up to 250 GeV.


Polarized 3He+2 for eRHIC• Larger G factor than for protons• RHIC Siberian snakes and spin rotators can be used for the spin control,

with less orbit excursions than with protons.• More spin resonances. Larger resonance strength.• Spin dynamics at the acceleration in the injector chain and in RHIC has to

be studied.

3He+2 p

m, GeV 2.808 0.938

G -4.18 1.79

E/n, GeV 16.2-166.7 24.3-250

17.3-177 25.9-266

|G 72.5-744.9 46.5-477.7

Max strength for protons

W.MacKay and M.Bai


Proton/ion polarization in ELIC

Figure-8 shape of the storage rings:-eliminates spin sensitivity to energy for all species. No resonance crossing at the acceleration.

-the control of spin direction by small spin rotation force:

stabilizing solenoidcontrolled vertical orbit distortion (for transverse spin)

-For longitudinal spin in all 4 IPs:

two longitudinal axis Siberian Snakes

Accelerates of polarized beams of proton, deutrons and 3He ions.From ELIC ZDR:


Summary• Polarized beams of electrons, protons and light ions are essential

component of the future electron-ion colliders.

• Polarized electron beam challenges:– High average current polarized source for linac-ring scheme (eRHIC)– Spin matching of complex rotator scheme for ring-ring scheme (ELIC)

• Polarized proton and light ions beams:– RHIC: state-of-art technology in place and working well; 250 GeV polarized

proton run is coming.– ELIC: novel technology (Figure-8). Theoretically well based.

Acknowledgments to M.Bai, D.Barber, P.Chevtsov, Ya.Derbenev, V.N.Litvinenko, W.Mackay, T.Roser, E.Tsentalovich.

18 th international spin physics symposium polarized beams at eic v. ptitsyn

Documents

gev center

gev eions

gev p x

gev rhic bnlelic20

gev erlbased design

gev cebaf operation

electron storage ring

design of ion