experience with asymmetric hadron collisions at rhic todd satogata (and a cast of thousands) cern...

Experience with AsymmetricHadron Collisions at RHIC

Experience with AsymmetricHadron Collisions at RHIC

Todd Satogata(and a cast of thousands)

CERN p-A Workshop May 25, 2005

Brief RHIC machine description, program goals Challenges and limiting factors Injection at same rigidity Ramp design and performance Conclusions

May 25, 2005 T. Satogata - RHIC Deuteron-Gold Experience 2/21

The RHIC LayoutThe RHIC Layout

RHIC rings are independent except for DX magnets 4.3T, 180mm aperture “combiner” magnet between two rings Design bend angle is 18.86 mrad Deuteron Z/A=0.5, not far from Au Z/A=0.4 no need to move DX magnets

Blue RingYellow Ring

AGS

MP6

MP7

Tandems

Booster

Linac

RHIC

STAR

PHENIX

PHOBOS BRAHMS

d Au

DX

DXD

0D0


Program Goals and AchievementsProgram Goals and Achievements

16 weeks of setup and operations in FY03 schedule Short time: only one energy, only one ring configuration Decision made with experiments, motivated by early d

setup Deuterons in blue ring only, Gold in yellow ring only

All major program goals met within this running periodPerformance Goal Achieved

Setup/Ramp-up time [days] 14/21 18/20 days

Storage energy [GeV/u] 100 100

Number of bunches 55 110/55

* [m] 2 2/3/4

Diamond length [cm] 20 15

Peak luminosity [x1028 cm-2 s-1] 4.0 6.2

Average luminosity (store) [x1028 cm-2 s-1]

1.6 2.8

Integrated luminosity (week) [nb-1/week]

4.0 4.6


Program Goals, Achievements, ChallengesProgram Goals, Achievements, Challenges

Many challenges for a short run Injector performance and mode switching Ramp design issues

Inject at constant B, then constant frequencyCommon DX magnets, crossing angles, optimal *Separate transition jumps in both rings

110 bunch operations, vacuum and radiation issues Luminosity monitoring (ZDC acceptance) Secondary beams, experiment backgrounds, ion beam IBS Instability monitoring and amelioration

Storage Parameter Au Goal Au Achieved d Goal d Achieved

Intensity/bunch 1.0x109 0.7x109 0.8x1011

1.2x1011

Total intensity (55/110 bunches) 55x109 38/60x109 45x101

1

57/69x1011

Transverse emittance (95%, rad)

10-40 10-30 15 12

Bunch length [ns] 5 5 5 5


Injector ChallengesInjector Challenges

Both Tandems required Foil changes scheduled

routinely No redundancy against failure

Deuteron Z/A=1/2 is very low Longitudinal emittance and

intensity were major challenges Mode switching

All transfer lines (big magnets) Stripping foils moved in/out Kicker PFNs adjusted

(dominated mode switch time) Met 5 minute goal after 4 weeks

Inject d then Au to limit effects of IBS at injection


Deuteron Booster ChallengesDeuteron Booster Challenges

d beam only about 1/3 rigidity of Au in Booster, extraction septum didn’t regulate so low.

Transferred 2/3 Booster bunches to AGS in 6 cycles; 124 bunch merge in AGS Booster extraction septum AGS injection kicker magnet

pulse length

Increased d KE from Tandem to 8.7 MeV/u, allowing h=2 capture. Proton RF cavities allow merge at 830 kHz to h=1 and eliminated septum pulse length issues. 84 bunch merge in AGS

doubled total intensity

Deuteron Booster bunch merge

RF harmonic h=2 to h=1

Deuteron intensity: 5-6x1010 to 1-1.1x1011


Single-Bunch Run PerformanceSingle-Bunch Run Performance

d merge

Majority of run was single-bunch intensity limited Multiple demands on injectors made optimization difficult Very little lead time for injector preparation before run

startNew species (d) always contain surprises

Au was almost always single-bunch limitedLater resolved to be heavy ion injector septum apertureTandem/source inconsistency apparent late in run

Deuteron bunch merge worked well in last month of run


Total Intensity Run PerformanceTotal Intensity Run Performance

56110

Pushed bunch # since single-bunch intensity was limited Maximum total intensity 60-65x109 Au, near ecloud limit Deuteron max total intensity around 70x1011 d Upgraded injection kickers worked well for 110 bunches Long-range beam-beam present but not disasterous

Locked RF frequencies between rings, no modulation Final performance limited by Au injector, d total intensity


Injection at Same RigidityInjection at Same Rigidity

Blue and Yellow rings independent (except DX) Inject at same rigidity in both rings, different frf

Minimize transfer line changes, maximize flexibility RF frequencies were not initially synchronized between

rings when injecting at same rigidity 28 MHz acceleration system, h = 360 197 MHz storage system, h = 2520 (= 7360)

DX

IP

DX

Beam-beam ON Beam-beam OFFBeam-beam OFF

v=5m·frf

Moving crossing points if frf0

W. Fischer

20 m


Tune Modulation From Moving Crossing PointTune Modulation From Moving Crossing Point

W. Fischer

T revolution time h harmonic number frf radio frequency frf difference between two rings

Example 1: RHIC Au-Au frf = 28 MHz, frf = 5 Hz vCP = 27 m/s modulated interaction

Example 2: RHIC d-Au, same rigidity at injection frf = 28 MHz, frf = 44 kHz vCP = 3 m/turn pseudo-random interaction

Distance between DX magnets is 16 m

Longitudinal velocityof crossing point


Beam Loss from Unequal RF Frequencies at InjectionBeam Loss from Unequal RF Frequencies at Injection

Beam-beam effect during injection, d and Au with same rigidity

frf = 44kHz, vertical separation was 10 mm ( 10) in all IRs

Pseudo-random dipole kicks lead to emittance increase

Very

mod

est

inte

nsit

ies!


DX Magnet Geometries for Ramp DesignDX Magnet Geometries for Ramp Design

DX magnets had unipolar shunts reversed for lower field Injection with equal rigidity 1 mrad crossing angle Injection/store with equal frequency 1 mrad common angle

Zero-degree calorimeter lumi monitors moved by 1 cm

ZDC moved by 1 cm


Acceleration Ramp and OpticsAcceleration Ramp and Optics

Final production acceleration ramp and optics Different B at injection/store, same RF frequency through ramp Modest * due to concerns about DX outer edge aperture

800

0 50 100 150 200 250Time [seconds]

0

2

4

6

8

10

0

200

400

600

* [

m]

B[

T-m

, B

lue a

nd Y

ello

w r

ings]

Tra

nsi

tion

Sto

rage

Inje

ctio

n


120 Bunches and Beam-Beam Background120 Bunches and Beam-Beam Background

Transition losses seed pressure bumps in PHOBOS/BRAHMS Small pressure bumps in STAR/PHENIX, not transition seeded RHIC dAu: removed transverse separation then cogged

SY. Zhang


120 Bunches and PHOBOS Pressure Burst120 Bunches and PHOBOS Pressure Burst

Pressure rise in interaction areas varied quasi-exponentially with total beam current electron cloud pressure rise

No pressure rise seen in solenoidal field detectors PHOBOS background/radiation very sensitive to IR pressure burst

Total Normalized Beam Intensity90 140

Vacu

um

Pre

ssure

[Torr

]1

e-

10

1e-

6

0

Pressure rise [10-9 Torr]1.2

PH

OB

OS B

ack

gro

und [

Hz]

0

450

SY. Zhang


Transverse microwave instabilities while rampingTransverse microwave instabilities while ramping

01:53:43

01:53:44

Wit

h I

nsta

bilit

y

Wit

hou

t In

sta

bilit

y

Single-bunch transverse instability monitor later in run No multibunch instability monitoring/coupled bunch

damping Correlated with emittance growth; retuned chroms to

fix


Typical RHIC dAu StoresTypical RHIC dAu Stores

dAu luminosity lifetime about 1.5h, dominated by Au IBS Higher intensity d beam likely suffered less from beam-beam Au debunching resolved with RF noise fix, additional RF voltage


RHIC dAu Integrated LuminosityRHIC dAu Integrated Luminosity

PHENIX last two weeks:

4.58 nb-1/weekBest 2-3 day periods:7-9 nb-1/week @ PHENIX/STAR

Fixed instabilityPHOBOS to

b*=4m


RHIC dAu Performance LimitationsRHIC dAu Performance Limitations

Vacuum pressure rise Total intensity apparently limited to 100-110 109 Au equivalent Limits deuteron-gold operations to 56 bunches/ring NEG

coatings Transition instabilities

Coherent bunch oscillations drive beam growth/reduce luminosity Corrected with machine tuning Feb 23 in deuteron beam

Longitudinal instabilities Leads to factors 2–3 in diamond size, Landau cavities 200 MHz RF driver noise fixed during run

Au beam intensity/lifetime IBS, Transverse/longitudinal emittance growth Electron cooling

Startup time, finding “best conditions” for operation Balance between stability/development, experiments/operations Flexibly determine, switch to “good” conditions for production 2 days to change ramp from same rigidity to same frequency


RHIC dAu ConclusionsRHIC dAu Conclusions

Nearly all significant program challenges were overcome Injector mode switching between d/Au worked well Tandem redundancy problems were not an issue Deuteron intensities well beyond goal with bunch merging

Injectors contained surprises with low Z/A Constant Bp injection did not work due to modulated

beam-beam interaction issuesRequired development of cross-ring RF frequency

locking, new ramps developed in a few days Ramp design of common dipole orbits can hold surprises

1 mrad common angle, limited * to maintain aperture Transverse instability diagnosis/fix improved luminosity by

factor of two

Already talk of a possible second RHIC dAu run


AcknowledgementsAcknowledgements

Many thanks to…

Thomas Roser, Johannes van Zeijts, Wolfram Fischer

L. Ahrens, M. Bai, M. Blaskiewicz, J.M. Brennan, P. Cameron, A. Drees, H. Huang, H.C. Hseuh, P. Ingrassia, U. Iriso, Y. Luo, Y. Makdisi, G. Marr, W.W.MacKay, R. Michnoff, C. Montag, F. Pilat, V. Ptitsyn, R. Tomas, D. Trbojevic

…and of course all RHIC Operations teams


================================================

Spare slides


RHIC Achieved and Planned ParametersRHIC Achieved and Planned Parameters

[best store or week]

[incl. beam studiesand maintenance]

Mode No ofbunche

s

Ions/bunch

[9]

*[m]

Emittance

[ m]

Lpeak

[cm-2s-1] Lstore ave

[cm-2s-1] Lweek Time

inStore

Au-Au design 56 1 2 15-40 91026 21026 50 b-1 --

p-p design 56 100 2 20 51030 41030 1.2 pb-1 --

Au-Au [Run-2]

55 0.7 1 15-40 61026 11026 15 b-1 26%

d-Au [Run-3]

55 (110)

110d/0.7Au

1 15 121028 31028 4.5 nb-1 31%

Au-Au [Run-4]

45 1.1 1 15-40 151026 51026 160 b-1 53%

p-p [Run-4] *

28 170 1 20 151030 101030 0.9 pb- 1 n/a

Au-Au upgrade

112 1.1 1 15-40 361026 91026 350 b-1 60%

p-p upgrade*

112 200 1 20 801030 651030 25 pb-1 60%* Achieved polarization performance in p-p Run-4 was 40-45% in store* Planned polarization performance by p-p enhanced is 70% in store


Machine Challenges at RHICMachine Challenges at RHIC

More flexibility than at other hadron colliders Variation in particle species, including asymmetric operations

So far Au+Au, d+Au, p+p, p+p, Cu+Cu Variation in energy, energy scans

d+Au at 100 GeV/u Au+Au, Cu+Cu at 10, 31, 65, 100 GeV/u p+p at 100 GeV (250 GeV planned in 2006)

Variation in lattice Low * in most cases (0.8-3 m) Polarity change in experimental magnets ~ every 2 weeks

Short runs (~30 weeks/year), with multiple modes Very short amount of set-up time (2-3 weeks) required

Four experiments (2 large, 1-2 small) Work to avoid single-experiment bottlenecks

Short luminosity lifetime with heavy ions (IBS, ~ few hours) Fast refills essential


Booster Injection/Extraction, AGS Injection ParametersBooster Injection/Extraction, AGS Injection Parameters

C. Gardner


AGS Extraction, RHIC Ramp ParametersAGS Extraction, RHIC Ramp Parameters

C. Gardner

experience with asymmetric hadron collisions at rhic todd satogata (and a cast of thousands) cern...

Documents