18th International Spin Physics Symposium
Polarized Beams at EIC
V. Ptitsyn
18th International Spin Physics Symposium
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
18th International Spin Physics Symposium
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
18th International Spin Physics Symposium
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)
18th International Spin Physics Symposium
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
18th International Spin Physics Symposium
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
18th International Spin Physics Symposium
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)
18th International Spin Physics Symposium
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
18th International Spin Physics Symposium
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:
18th International Spin Physics Symposium
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
18th International Spin Physics Symposium
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.
18th International Spin Physics Symposium
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
18th International Spin Physics Symposium
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:
18th International Spin Physics Symposium
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.