RHIC Polarized Proton Operation for 2013 (original) (raw)

RHIC Polarized Proton-Proton Operation at 100 GeV in Run 15

The first part of RHIC Run 15 consisted of ten weeks of polarized proton on proton collisions at a beam energy of 100 GeV at two interaction points. In this paper we discuss several of the upgrades to the collider complex that allowed for improved performance. The largest effort consisted in commissioning of the electron lenses, one in each ring, which are designed to compensate one of the two beambeam interactions experienced by the proton bunches. The e-lenses raise the per bunch intensity at which luminosity becomes beam-beam limited. A new lattice was designed to create the phase advances necessary for a beam-beam compensation with the e-lens, which also has an improved off-momentum dynamic aperture relative to previous runs. In order to take advantage of the new, higher intensity limit without suffering intensity driven emittance deterioration, other features were commissioned including a continuous transverse bunch-by-bunch damper in RHIC and a double harmonic RF cature scheme in the Booster. Other high intensity protections include improvements to the abort system and the installation of masks to intercept beam lost due to abort kicker pre-fires.

RHIC upgrades for heavy ions and polarized protons

AIP Conference Proceedings, 2006

The Relativistic Heavy Ion Collider (RHIC), in operation since 2000, has exceeded its design parameters. The Enhanced Design parameters, expected to be reached in 2009, call for a 4-fold increase over the heavy ion design luminosity, and a 15-fold increase over the proton design luminosity, the latter with an average polarization of 70%. Also in 2009, it is planned to commission a new Electron Beam Ion Source, offering increased reliability and ion species that cannot be supplied currently. The upgrade to RHIC 11, based on electron cooling of the beams, aims to increase the average heavy ion luminosity by an order of magnitude, and the polarized proton luminosity by a factor 2-5. Plans for an electron-ion collider eRHIC is covered in another article in these proceedings.

Polarized proton collider at RHIC

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2003

In addition to heavy ion collisions (RHIC Design Manual, Brookhaven National Laboratory), RHIC will also collide intense beams of polarized protons (I. Alekseev, et al., Design Manual Polarized Proton Collider at RHIC, Brookhaven National Laboratory, 1998 [2]), reaching transverse energies where the protons scatter as beams of polarized quarks and gluons. The study of high energy polarized protons beams has been a long term part of the program at BNL with the development of polarized beams in the Booster and AGS rings for fixed target experiments.

Status and Plans for the Polarized Hadron Collider at RHIC

As the world's only high energy polarized proton collider, the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) has been providing collisions of polarized proton beams at beam energy from 100 GeV to 255 GeV for the past decade to explore the proton spin structure as well as other spin dependent measurements. With the help of two Siberian Snakes per accelerator plus outstanding beam control, beam polarization is preserved up to 100 GeV. About 10% polarization loss has been observed during the acceleration between 100 GeV and 255 GeV due to several strong depolarizing resonances. Moderate polarization loss was also observed during a typical 8 hour physics store.

RHIC polarized proton operation in Run 12

Successful RHIC operation with polarized protons requires meeting demanding and sometimes competing goals for maximizing both luminosity and beam polarization. Run 12 consisted of four weeks of collisions with 100 GeV beams and five weeks colliding 255 GeV beams. We sought to fully integrate into operation the many systems that were newly commissioned in Run 11 as well as to enhance collider performance with incremental improvements throughout the acceleration cycle. Improvements to the luminosity were provided largely by increased intensity delivered by the polarized proton source. Increases in beam polarization came from improvements in both the injectors and in RHIC.

RHIC Performance as a 100 GeV Polarized Proton Collider in Run-9

2010

During the second half of Run-9, the Relativistic Heavy Ion Collider (RHIC) provided polarized proton collisions at two interaction points with both longitudinal and vertical spin direction. Despite an increase in the peak luminosity by up to 40%, the average store luminosity did not increase compared to previous runs. We discuss the luminosity limitations and polarization performance during Run-9.

RHIC polarized proton operation

2011

The Relativistic Heavy Ion Collider (RHIC) operation as the polarized proton collider presents unique challenges since both luminosity(L) and spin polarization(P) are important. With longitudinally polarized beams at the experiments, the figure of merit is LP 4 . A lot of upgrades and modifications have been made since last polarized proton operation. A 9 MHz rf system is installed to improve longitudinal match at injection and to increase luminosity. The beam dump was upgraded to increase bunch intensity. A vertical survey of RHIC was performed before the run to get better magnet alignment. The orbit control is also improved this year. Additional efforts are put in to improve source polarization and AGS polarization transfer efficiency. To preserve polarization on the ramp, a new working point is chosen such that the vertical tune is near a third order resonance. The overview of the changes and the operation results are presented in this paper.

RHIC polarized proton operation and highlights

RHIC operation as a polarized proton collider presents unique challenges since both luminosity and spin polarization are important. Many improvements and modifications have been made since the last polarized proton operation in 2009. A 9 MHz rf system was completed that improved the longitudinal match at injection. To preserve polarization on the ramp, a new working point was chosen with the vertical tune near a third order resonance. The newly realized orbit and tune feedback systems are essential for polarization preservation. To calibrate the polarization measurement at 250 GeV, polarized protons were accelerated up to 250GeV and decelerated back to 100GeV. A vertical realignment of RHIC was conducted before the run to reduce magnet misalignment. A record peak luminosity was achieved with higher polarization at 250 GeV in this run.

Commissioning and future plans for polarized protons in RHIC

2001

Polarized protons were injected and accelerated in the clockwise ring of RHIC to commission the first full helical Siberian snake ever used in an accelerator. With the snake turned on, the stable spin direction is in the horizontal plane. Vertically polarized protons were injected with the snake off. The snake was adiabatically ramped to give a spin rotation of 180 • around a horizontal rotation axis about 13 • from the longitudinal. When the beam was accelerated from injection Gγ = 46.5 to Gγ = 48 the spin flipped sign as expected and polarization was preserved. At Gγ = 48 without the snake, no polarization was observed since several spin resonances were crossed. Eventually polarized beam was accelerated to Gγ = 55.7 (29.1 GeV). In the next proton running period we plan to run with two full helical snakes in each ring and collide both transversely and longitudinally polarized protons at an energy around 100 GeV per beam.

COMMISSIONING RHIC'S ELECTRON LENS *

In the 2013 RHIC polarized-proton run, it was found that the intensity of the RHIC bunch had reached a limit due to the head-on beam-beam interaction at intensity of 2x10 11 , as we expected from our simulations [1]. To overcome this limitation, we have planned to implement two electron lenses for beam-beam compensation. During and after the 2013 RHIC run, some e-lens systems were commissioned. The effect of the e-lens warm solenoids on the protons orbit was observed and corrected by orbit feedback. The blue electron-lens system was fully tested, except for the superconducting magnet; the electron beam was propagated from the gun to the collector, and most of the instrumentation for the blue e-lens was commissioned. The straightness of the superconducting solenoid #2 field was measured for the first time. The installation of the yellow e-lens system and two superconducting magnets are underway.