COMMISSIONING of RHIC with GOLD IONS1
D. Trbojevic, BNL, Upton, New York, USAAbstract
The Relativistic Heavy Ion Collider (RHIC) had beensuccessfully put into operation and provided collisions ofthe fully stripped gold ions at a beam energy of 65
GeV/nucleon during summer 2000. All four experiments"STAR", "PHENIX", "PHOBOS", and "BRAMS"
collected more than 3 inverse micro barn of data. We
present details of the gold beam commissioning as wellas the collision run. We will show measurements ofbetatron and dispersion functions that are, after
corrections, in excellent agreement with prediction.
Diagnostic results from tune-meter, wall current monitor,
chromaticity and decoupling measurements, ionization
beam profile monitor, Schottky monitors, etc. will also beshown. Operational experience for establishing gold ion
beam stores with optimized luminosity will be discussed
as well as plans for future runs and possible futuremachine upgrades.

1 INTRODUCTION
RHIC has two separate, blue and yellow
superconducting rings and it has possibilities to collide
unequal species (between polarized protons and goldions) up to the energies of 100 GeV/nucleon. The
accelerator has six fold symmetry, with two large
detectors, STAR and PHENIX located at 6 and 8 andPHOBOS, and BRAHMS at 10 and 2 o'clock. It should
provide luminosity 2x1026 cm-1 s-1 with 56 bunches inboth rings. This is a fill of 60 of 360 available buckets.
Table 1: Parameters and performance goals forRUN2000
Injection
E=9.57 GeV/nγ=10.27
EnergyStorage
E=65.1 GeV/nγ=70.00
EnergyBunch
0.5 109
intensity
Number of56bunches
Transverse
Normalized
15 π mmEmittance95 %mradLongitudinal
0.3 eVs
Per nucleon per
Emittancebunch
3m @ 2, 4, 8 m @ 6 and 10
β* @ IP8, 12o’clock
Luminosity
2 1025 cm-2
10% of thes-1
designIntegrated
few µb-1
Luminosity

This report describes major steps in RHIC
commissioning during the summer of 2000. In the firstpart, few major commissioning challenges are described.
The most important results, from few RHIC systems, areshown in the next section. Next, bringing beams fromtwo separate “blue” and “yellow” rings, into collisions
and stores of gold ions are described. In the summarypart necessary steps and commissioning of additional
systems during the next RHIC-2001 run are mentioned.
Basic parameters of the previous RHIC RUN2000 are
presented in Table 1.

2 COMMISSIONING CHALLENGES
2.1 Injection
Fully stripped gold ion beams Au79+ were injected into
both blue and yellow rings from the AGS with energy of
9.57 GeV (as presented in Table 1). Orbits in both rings
were successfully corrected with a rms. value of less thanfew millimeters. The betatron tune measurements had
shown unexpected sensitivity to momentum at thebeginning of commissioning. Due to high voltage
problems of the injection kickers, the initial energy ofgold ions was lowered a bit from the design one (currents
in the dipoles were lowered from 545A down to 463A).
The initial measured chromaticities were quite different
from the model predictions, due to a larger sextupole
multipole component in dipoles. A control of the power
supplies and excitations of all magnets in RHIC isperformed by sequencer, ramp, and the wave form
generator manager(they provide a direct
correspondence between the “model” of the accelerator
and actual settings). Additional correction for 60 units ofchromaticity was necessary to compensate for the larger
values of the sextupole multipole within the dipoles.
Very precise and reliable beam position monitors wereavailable early on in the commissioning effort andallowed beam-based diagnostics to detect hardware
problems. They also allowed a demonstration of excellent
agreement between measured and accelerator models
predictions. A discrepancy between the measured andexpected betatron functions was the next challenge. Witha help of on-line model by comparisons with measured
data, a wrong polarity of a shunt quadrupole power
supply was found as illustrated in Fig.1. The global orbitcorrection was able to reduce orbit offsets of the order ofa millimeter. An example of the orbit correction is shownin Fig. 2. The orbit correction program receives
information from the BPM system, calculates corrections
and communicates with the ramp manager. It sets thecorrection magnets to new values. The correction was apart of the preparations for ramping to high energy.
Before any start of the ramp, the sequencer checked andset required values for different systems like RF, tune
meter etc.

of the chromaticity, due to a time dependence of thesextupole multipole in dipoles showed an excellent
agreement (Fig. 3).

Magnetmeasurement

Beam measurements
Figure 1: Comparison between measured dispersion andthe model where the Q89 power supply was reversed.

Figure 3. Persistent current effect: a comparison between
a time dependence of beam measured chromaticity with achange of chromaticity obtained by time dependence inmagnetic field measurements of sextupole component in
dipoles.

2.3 Acceleration

Figure 2. An example of orbit correction in the Blue ringis presented in Figure 4. The red color data are corrected
orbits in horizontal (up) and vertical (down) plane, while
the blue color data are the orbits before corrections.
Injected bunched were captured by digitally controlled
synchronization between the AGS and RHIC RF systems.
The whole RF system performed very reliably and theaccelerating cavities were fully commissioned. Theirhigh voltage status was connected to the permit link.

2.2 Measurements of the persistent current
effectThe snap back and persistent current effects wereadditional concerns, which were measured [1] andcompared to predicted values (see Fig. 3). The effect ofthe persistent currents was clearly visible at the injection.
The lifetime of bunches injected in a sequence wassteadily improving in time within first few minutes. A
comparison between predicted and measured differences

Unfortunately, RHIC is the first superconducting, slow
ramping accelerator that crosses transition energy during
acceleration. Although some beam loss and longitudinalemittance growth was observed from crossing transitionenergy, the effect was not excessive due to still lower
beam intensity and a favorable lattice functions. The
second order momentum dependence coefficient α1 wasmeasured to be α1=-1.5 due to the lattice functions. It
minimized momentum dependent (chromatic) effects attransition.

Storage energy

Transition

Start of acceleration
Figure 4. Horizontal betatron tunes along the RHIC
acceleration.

To accommodate easier transition crossing a first order γtjump was designed and built. Due to still missing power
supplies, during the RHIC RUN2000, the transition
crossing had to be performed by the RF radial loop jump.
To avoid the beam loss it was important to keep thepartial tunes between 0.2 and 0.25 during acceleration asshown in Fig. 3 by the tune measurements.

Acceleratio

3 ESTABLISHING COLLISIONSAt the end of the acceleration cycle two beams werefirst longitudinally brought by cogging into collisions
with help of a wall current monitor located at theinteraction point at 4 o'clock. This process of bringing
two beams to cross at interaction points is shown inFigure 7.

Correction
Orbit – Tunes Storage

Beam in blue ring
Total Yellow

Beam in yellow ring

Bunched Yellow
Total Blue
Bunched blueBLU
Fill55buncheTransition200 ns (60 m)

YELLO
Fill55bunchesBeams in collision at theinteraction regions

Figure 7. Bringing beams in RHIC longitudinally intocollisions.
Figure 5. Typical ramp during the RHIC RUN2000 isshown in Fig. 5.

The first collisions were recorded on June 12 2000 by
the first STAR event shown in Fig. 8.

Bunch length [ns]The acceleration cycle is shown in Fig. 5. Fifty-six
bunches were filled one ring with a lifetime larger than
30 minutes.

Figure 8. First collisions recorded in RHIC in June2000.

Injection

Transition energy

Storage energy

Figure 6. Wall current monitor along the acceleratingramp in RHIC.
The other ring was filled by a change of polarity of theswitching magnet in the beam line from AGS to RHIC
(ATR). During the acceleration cycle the wall current
monitors in both rings were recording the longitudinal
profiles as presented in Figure 6.

The collision rate was measured using identical Zero
Degree Calorimeters (ZDC) at all four interaction
regions. The ZDC counters detect at least one neutron oneach side from mutual Coulomb and nuclear dissociation
with a total cross section of 10.7 barns at 65 GeV beamenergy. The peak luminosity for the initial rate shown inFig. 9 is then 3.3x 1025 cm-2 s-1 for BRAHMS and theaverage luminosity for the store was 1.7 x 1025 cm-2 s-1.
Independent determination of the luminosity using
Vernier scans gives a cross section for the ZDC counts of
9.1.8 barns, which is consistent with the results givenabove. The overall average luminosity for BRAHMS
during the last 6 days of the run was 0.8 x 1025 cm-2 s-1,
which gives an availability of 47. The integrated

luminosity over the run is shown in Fig. 9 and exceeded
6 µb-1 for BRAHMS and PHENIX.

Collision rate [Hz]BRAHMS:
Lpeak= 3.3× 1025 cm-2 s-1
Lave =1.7×1025 cm-2 s-1

The actual beam positions were measured by beam
position monitors located at the inner side of the DX
magnets. Values are extrapolated to the center of the IR.
The integrated luminosity during the RHIC run 2000 ispresented in Fig. 11.

[σ(Au+Au→≥1n +≥1n) = 10.7 b (theor.)
at least one neutron±1.8= b9.1(meas., prelim.)]Figure 9. Luminosities at all four experiments measuredby the Zero-degree calorimeters.

3.1 Vernier scans:
In addition to monitoring luminosity the Zero Degree
Calorimeters were used for beam studies by performing
Van der Meer scans [2]. A scan performed by setting thecorrector magnets to sweep one beam across the otherwith a step size of 200 µm.

Figure 11. Integrated luminosities during the RHIC run
2000.

4 SUMMARY
RHIC RUN2000 commissioning and first operation
was very successful. Full design luminosity with gold
ions and collisions with polarized protons are plannedfor RUN2001. Other systems to be commissioned in thenext run are:• Phase Lock Tune Feedback• γt jump with all power supplies delivered.
• Storage cavities will make short bunches.
• Beta squeeze with all power supplies installed.
• Bent crystal channeling collimation.

REFERENCES[1] W. Fischer, A. Jain and S. Tepikian, “Beam-based
Measurements of Persistent Current Decay ”, RHIC
notes:C-A/AP/32 (to be published in Phys. Rev. D.)(http://www.rhichome.bnl.gov/AP/ap_notes/cad_ap_index.html) .
[2] S. van der Meer, ISR-PO/68-31, KEK68-64.
Figure 10. Vernier scan at the STAR detector withsuperimposed Gaussian fits.