Thomas RoserMIT seminar

November 30, 2004

RHIC - the high luminosity hadron collider

RHIC overview

Luminosity and polarization evolution

Performance limitations

Future upgradesRHIC II luminosity upgradeeRHIC

NSRL

2 superconducting rings3.8 km circumference

A Mini-Bang: Nuclear matter at extreme temperatures and density

Colliding gold at 100 + 100 GeV/nucleon (40 TeV total cm energy)Plus: other species (p-p, Cu-Cu (Run-5), …)

asymmetric collisions (d-Au, p-Au (?))several energies (100+100, 65+65, 32+32, 10+10)

a. Formation phase -parton scattering

b. Hot and dense phase -quark-gluon plasma and hadron gas ? → strongly interacting hot dense material

(sQGP)c. Freeze-out –

emission of hadrons

Produce and explore a new state of matter

Hard Scattering at RHIC

p+p →jet+jet (STAR 200 GeV)

Au+Au →???

(STAR 200 GeV/nucleon pair)

pp data

Central Au+Au collisions

RHIC Spin Physics

Spinning Proton Spinning Proton

Spinning Quarks or Gluons

Quark, Gluon, Photon,Electron or Neutrino fromW or Z Decay

• Spin structure functions of gluon and anti-quarks• Parity violation in parton-parton scattering• Requires high beam polarization and high luminosity

Gold Ion Collisions in RHIC

RHIC

AGSBOOSTER

TANDEMS

9 GeV/uQ = +79

1 MeV/uQ = +32

Beam Energy = 100 GeV/u

RHIC design, achieved and enhanced design parameters

Mode No ofbunches

Ions/bunch [109]

β*[m]

Beampolarization

Lpeak[cm-2s-1]

A1A2Lstore ave[cm-2s-1]

Design values (1999)

8×1026

5×1030

15×1026

5×1030

15×1030

30×1026

80×1030

8×1030

4×1030

16×1030

4×1030

p – p 56 170 1 10×1030 10×1030

31×1030

45%

Achieved values (2004)

Enhance design values (2008)

65×103070%

Lstore ave[cm-2s-1]

Au – Au 56 1.0 2 2×1026

p – p 56 100 2 4×1030

Au – Au 45 1.1 1 4×1026

p↑ – p↑ 56 70 1 4×1030

Au – Au 112 1.1 1 8×1026

p↑ – p↑ 112 200 1 65×1030

*

2

23

εβNN

MEf Brev=L

Other high luminosity hadron colliders:achieved goal scaled to 200 GeV

Tevatron (2 TeV) 100×1030 200×1030 20×1030

LHC (14 TeV) 10000×1030 140×1030

RHIC luminosity evolution

Nucleon-pair luminosity A1A2L allows comparison of different species.

Luminosity increased by 2 orders of magnitude in 4 years.

A day of RHIC operations (Feb. 23, 2004)

Inje

ctor

RH

IC

Performance Limitations

Intra-beam scattering (heavy ions)

Dynamic pressure rises

Instabilities

Beam-beam (light ions and protons)

Polarization (protons)

Luminosity Limit – Intra-Beam Scattering (IBS)

• Debunching requires continuous gap cleaning (tune meter)• Luminosity lifetime requires frequent refills• Ultimately need cooling at full energy

Intensities

Luminosities

τ ≈ 2.5h0.5h 1.5h

Intra-Beam Scattering (IBS) in RHIC

Longitudinal and transverse emittance growth agrees well with model

Some additional source of transverse emittance growth

Deuteron and gold beams are different because of IBS

Bunched Beam Stochastic Cooling

Microwave stochastic cooling (4-8 GHz) should work for longitudinal cooling and limit beam debunching due to IBS during storeLongitudinal bunched-beam Schottky spectra during store (100 GeV):

Test planned for Run-5.

Protons: persistent coherenceinterferes with cooling

Gold: no persistent coherence (IBS)debunched beam visible

Luminosity Limits – Dynamic Pressure Rises86·1011 p+ total, 0.78·1011 p+/bunch, 110 bunches, 108 ns spacing

12 min

electron density and pressure rise

total beam intensity

Ubaldo Iriso

All operational relevant pressure rises can be explained by electron clouds

→ NEG (non-evaporative getter) coated beam pipes installed in warm areas

Luminosity Limits – Fast Instability Near TransitionTomographic reconstructionof 2D bunch density

• Fast transverse instability (~ GHz)• High sensitivity around transition• Effect of broadband impedance, electron cloud (?)

• Cures: beam-beam tune spread, octupoles, cross zero-chromaticity before transition (why?)

After instability with ~ 10 ms growth rate

Before instability

Luminosity Limits – Beam-Beam Interaction

Beam lifetime with different number of collisions, ξ=0.003/IP(due to abort gaps some bunches see only 2 or 3 collisions per turn)

Luminosity Limits – Beam-Beam Interaction

Experiment:- single p bunch/ring- ξ = 0.003- |Qx,B–Qx,Y| < 0.001

Observation:- πx-mode shift: 0.004- expectation:

1.21·ξ = 0.0036[Yokoya, Meller, Siemann]

No operational problem so far.

4096 turn spectraRHIC is the first hadron collider to see coherent beam-beam effects

Luminosity Limits – Betatron Tune Working Point

Loss

rat

e

working point during ramp

working point during store• Tried several working points:

[.18,.19] (RHIC design)[.22,.23] (RHIC init. ops.)[.31,.32] (LHC design)[.68,.69] (SppbarS ops.)[.73,.74] (?)

• [.68,.69] is best. It improves collision lifetime and polarization transmission/lifetime

• Beam-beam tune spread 0.016 with 2 collisions

R. Tomas, M. Bai Qx

Qy

snake resonanceorbit resonance

RHIC polarized proton accelerator complex

BRAHMS & PP2PP

STAR

PHENIX

AGS

LINACBOOSTER

Pol. H- Source

Spin Rotators(longitudinal polarization)

Solenoid Partial Siberian Snake

Siberian Snakes

200 MeV Polarimeter AGS Internal Polarimeter

Rf Dipole

RHIC pC PolarimetersAbsolute Polarimeter (H↑ jet)

AGS pC PolarimetersStrong AGS Snake

Helical Partial Siberian Snake

PHOBOS

Spin Rotators(longitudinal polarization)

Spin flipper

Siberian Snakes

Installed and commissioned during FY04 runPlan to be commissioned during FY05 runPlan to be installed and commissioned during FY05 run

Proton polarization at the AGS

• Full spin flip at all imperfection and strong intrinsic resonances using partial Siberian snake and rf dipole

• Ramp measurement with new AGS pC CNI polarimeter:

• Remaining polarization loss from coupling and weak intrinsic resonances

• New helical partial snake (RIKEN funded) eliminated coupling resonances

• To avoid all depolarization in AGS build strong AGS helical Siberian snake!

raw

asy

mm

etry

= A

N·P

B

Simulation (2003)

G γ5 10 15 20 25 30 35 40 45 50

| Ver

tical

Pol

ariz

atio

n |

0

10

20

30

40

50

60

70

80

0

10

20

30

40

50

60

70

80

Experiment data (2000)

Simulation (2000)Experiment data (2002)

Simulation (2002)Experiment data (2003)

Simulation (2003)

19972000200220032004

24−νy 12+νy0+νy 36−νy 24+νy 48−νy 36+νy

Simulation and measurement at 25 GeV

Strong Partial Siberian Snake in AGS

partial snake resonance

Pola

riza

tion

Intrinsic resonance

Imperfection resonance

desired vertical betatron tune to avoid depolarization

Challenges:1. SC element in warm machine2. Lattice disturbances

New AGS helical snakes

2.6 m

5 % helical snake build at Tokana Industries funded by RIKEN.

• Cold strong snake eliminates all depolarizing resonances in AGS.

• Warm snake avoids polarization mismatch at AGS injection and extraction.

2.6 m

30% s.c. helical snake build at SMD (AIP)Installation: Jan. 2005

Siberian Snake in RHIC Tunnel

Siberian Snake: 4 superconducting helical dipoles, 4Tesla, 2.4 m long with full 360° twist

Funded by RIKEN, JapanDesigned and constructed at BNL

Polarization survival in RHIC

06:00 07:00 08:00 09:00 10:00 11:00

20

40

60

0

20

40

60

0

0

2

4

6

8

% P

olar

izat

ion

Lum

inos

ity 1

030cm

-2s-1

Prot

ons x

1011

Spin rotator rampAcceleration and squeeze ramp

RHIC II luminosity upgrade

Eliminate beam blow-up from intra-beam scattering with electron beam cooling at full energy!What will remain the same:

120 bunch pattern100 ns collision spacing ( ~ same data acquisition system)Only one beam collision between DX magnets

20 m magnet-free space for detectorsNo “mini-beta” quadrupoles

Approx. the same bunch intensityNo new vacuum or instability issuesBackground similar as before upgrade

What changes:Smaller transverse and longitudinal emittance

Smaller vertex regionBeta squeeze during store to level luminosityStore length is limited to ~ 5 hours by “burn-off” due to Au-Au interactions (~ 200 b)

Electron cooling and IBSIntra-Beam Scattering:The ions collide with each other, leadingto accumulation of random energy(heat) derived from the guide fields and the beam’s energy.

Electron cooling:The high-current high-brightness electron beam from an ERL will cool the RHIC ions in a high-precision, 26 m long superconducting solenoid.

RHIC electron cooling

Au ions in RHIC are 100 times more energetic than in a typical cooler ring. Relativistic factors slow the cooling by a factor of γ2. Cooling power needs to be a factor of γ2 higher than typical.

Bunched electron beam requirements for 100 GeV/u gold beams: E = 54 MeV, <I> ~ 100 mA, electron beam power: ~ 5 MW!

Requires high brightness, high power, energy recovering superconducting linac, as demonstrated by JLab for IR FEL. (50 MeV, 5 mA)

First linac based, bunched electron beam cooling system used at a collider

Future RHIC upgrades – electron cooling R&D

Superconducting ERL

Buncher Cavity

Cooling Solenoids (2 x 13m, 2-5 T)

Debuncher Cavity

Gold beam

Benchmarking of IBS and cooling simulation codes

Demonstrate high precision (<10 ppm) solenoid (2-5 T)Demonstrate 20 nC, 100-200 mA 703.8 MHz CW SCRF electron gun

Develop 703.8 MHz CW superconducting cavity for high intensity beams

Build R&D Energy Recovering Linac (ERL)

RHIC Luminosity with and without CoolingFuture RHIC upgrades – electron cooling

0

20

40

60

80

100

0 1 2 3 4 5

Time, hours

Lum

inos

ity, 1

026 c

m-2

s-1

With e-coolingWithout e-cooling

Luminosity leveling through continuously adjusted cooling

Store length limited to 4 hours by “burn-off”

Four IRs with two at high luminosity

2 mm

5 hours

Transverse beam profile during store

Also may be able to pre-cool polarized protons at injection energy

RHIC II Luminosities with Electron Cooling

Gold collisions (100 GeV/n x 100 GeV/n): w/o e-cooling with e-coolingEmittance (95%) πµm 15 → 40 15 → 3Beta function at IR [m] 1.0 1.0 → 0.5Number of bunches 112 112Bunch population [109] 1 1 → 0.3Beam-beam parameter per IR 0.0016 0.004Ave. store luminosity [1026 cm-2 s-1] 8 70

Pol. Proton Collision (250 GeV x 250 GeV):Emittance (95%) πµm 20 12Beta function at IR [m] 1.0 0.5Number of bunches 112 112Bunch population [1011] 2 2Beam-beam parameter per IR 0.007 0.012 ?Ave. store luminosity [1032 cm-2 s-1] 1.5 5.0

CW Photo-cathode and Superconducting rf Gun R&D

Emission enhancement (x 30-80) using a diamond window

Initial design for a superconducting gun with diamond amplified photo-cathode.

Cavity

Tuner Cathode insert on choke jointLiquid helium

Ilan Ben-Zvi et al.

703.8 MHz CW Superconducting Cavity for High Intensity Beams

2K main line

Inner magnetic shield

Large bore cavity

4” RF shieldedgate valve

2K fill line

He vessel

Vacuum vessel

Fundamental PowerCoupler assembly

HOM ferritedampers

Outer magnetic shield

Thermal shield

Tuner location Space framesupport structure

Vacuum vessel

Cold model tested successfully

Solenoid R&D: <10 ppm Directional Uniformity

Copper Solenoid18 mT; 1.83 m longDipole Corrector

LASER

BEAMSPLITTER

MAGNETICNEEDLE

MIRROR

OPTICALFILTER

POSITION SENSITIVE DETECTOR

5 T design started

Electron-Ion Collider at RHIC: eRHIC• 10 GeV, 0.5 A e-ring with ¼ of RHIC circumference (similar to PEP II HER)• 10 GeV electron beam → s1/2 for e-A : 63 GeV/u; s1/2 for e↑-p↑: 100 GeV• Existing RHIC interaction region allows for typical asymmetric detector• Luminosity: up to 1 × 1033 cm−2s−1 per nucleon

BNL, MIT Batescollaboration

Alternative Design: Linac - Ring(V. Litvinenko, I. Ben-Zvi, et al)Electron ring replaced by energy-recovering linac, electrons in RHIC arcs+ no hadron beam effect on electrons (single pass), simpler IR design, multiple IRs possible, 20

GeV upgrade- no positrons possible, cost

Summary

Since 2000 RHIC has collided, for the first time,Heavy ionsLight on heavy ionsPolarized protons (45% beam polarization)

Heavy ion luminosity increased by factor 100For next 4 years planned:

Factor 2 increase in heavy ion luminosityFactor 2 increase in proton beam polarizationFactor 40 increase in proton luminosity

Future upgrades:RHIC luminosity upgrade using electron cooling at storeElectron-ion collider eRHIC