Indiana University Cyclotron Facility Cooler Research Articles

First spin flipping of a stored spin-1 polarized beam.

We recently studied spin flipping of a 270 MeV vertically polarized deuteron beam stored in the Indiana University Cyclotron Facility Cooler Ring. We adiabatically swept an rf solenoid's frequency through an rf-induced spin resonance and observed its effect on the deuterons' vector and tensor polarizations. After optimizing the resonance crossing rate and maximizing the solenoid's voltage, we measured a vector spin-flip efficiency of 94.2%+/-0.3%. We also found striking behavior of the spin-1 tensor polarization.

99.6% spin-flip efficiency in the presence of a strong Siberian snake.

We recently studied the spin-flipping efficiency of an rf-dipole magnet using a 120-MeV horizontally polarized proton beam stored in the Indiana University Cyclotron Facility Cooler Ring, which contained a nearly full Siberian snake. We flipped the spin by ramping the rf dipole's frequency through an rf-induced depolarizing resonance. By adiabatically turning on the rf dipole, we minimized the beam loss. After optimizing the frequency ramp parameters, we used 100 multiple spin flips to measure a spin-flip efficiency of 99.63+/-0.05%. This result indicates that spin flipping should be possible in very-high-energy polarized storage rings, where Siberian snakes are certainly needed and only dipole rf-flipper magnets are practical.

Spin flipping with an rf dipole and a full Siberian snake

We recently used an rf dipole magnet to study the spin flipping of a 120 MeV horizontally polarized proton beam stored in the presence of a nearly full Siberian snake in the Indiana University Cyclotron Facility Cooler Ring. We flipped the spin by ramping the rf dipole's frequency through an rf-induced depolarizing resonance. After optimizing the frequency ramp parameters, we used multiple spin flips to measure a spin-flip efficiency of $86.5\ifmmode\pm\else\textpm\fi{}0.5%$. The spin-flip efficiency was apparently limited by the field strength in the rf dipole. This result indicates that spin flipping a stored polarized proton beam should be possible in high energy rings such as the Brookhaven Relativistic Heavy Ion Collider and HERA where Siberian snakes are certainly needed and only dipole rf-flipper magnets are practical.

Spin flipping a stored polarized proton beam with an rf dipole

We recently studied the spin flipping of a 202.7 MeV vertically polarized proton beam stored in the Indiana University Cyclotron Facility cooler ring during the first polarized run with its new cooler injector synchrotron and its new cooler injector polarized ion source. We first set the vertical betatron tune to avoid the measured ny value of the Gg 7 2n y intrinsic depolarizing resonance in the cooler ring. We then flipped the spin by ramping the frequency of an rf dipole through an rf-induced depolarizing resonance. After optimizing the rf dipole’s frequency ramp parameters, we used multiple spin flips to measure a maximum spin-flip efficiency of 97.5 6 1%. PACS numbers: 29.27.Bd, 29.27.Hj, 41.75.Ak There is a growing interest in polarized beam experiments in storage rings such as the Indiana University Cyclotron Facility (IUCF) cooler ring [1], the MIT-Bates storage ring [2], the Brookhaven relativistic heavy ion collider (RHIC) [3], and HERA at DESY [4]. Frequent reversals of the beam polarization direction can significantly reduce the systematic errors in an experiment’s spin asymmetry measurements. An rf solenoid was used earlier [5] to spin flip a vertically polarized proton beam stored in the cooler ring with no Siberian snake [6]. Since a solenoid’s spin rotation decreases linearly with energy, a solenoid is impractical for spin flipping in high energy rings. However, a dipole’s spin rotation is energy independent. Therefore, we recently used an rf dipole to spin flip a 202.7 MeV vertically polarized proton beam stored in the IUCF cooler ring with no Siberian snake. In any flat circular accelerator or storage ring with no horizontal magnetic fields, each proton’s spin precesses around the vertical fields of the ring’s dipole magnets. The spin tune ns, which is the number of spin precessions during one turn around the ring, is proportional to the proton’s energy

Production of a tagged medium resolution neutron beam

Dissociation of 260 MeV deuterons in natural C and Cu targets has been studied using an internal deuteron beam in the Indiana University Cyclotron Facility Cooler Ring. Angular distributions and energy correlations are reported for both the (d, pn) and (d, pX) reactions, and implications for using the coincidence reaction for producing a tagged, medium resolution neutron beam are discussed.

A method of detecting coherent synchrotron modes

A method for measuring coherent longitudinal synchrotron modes is developed and tested at the Indiana University Cyclotron Facility Cooler Ring. This method can be used to detect the onset of coherent instability and can provide important diagnosis for the control of beam brightness. Some possible improvement of this technique is discussed.

Measurement of Quasielastic 3He(p

We report measurements of spin correlations and analyzing powers in $^{3}\stackrel{\ensuremath{\rightarrow}}{\mathrm{He}}(\stackrel{\ensuremath{\rightarrow}}{p}, 2p)$ and $^{3}\stackrel{\ensuremath{\rightarrow}}{\mathrm{He}}(\stackrel{\ensuremath{\rightarrow}}{p}, pn)$ quasielastic scattering as a function of momentum transfer and missing momentum at 197 MeV using a polarized internal target at the Indiana University Cyclotron Facility Cooler Ring. At sufficiently high momentum transfer we find $^{3}\stackrel{\ensuremath{\rightarrow}}{\mathrm{He}}(\stackrel{\ensuremath{\rightarrow}}{p}, pn)$ spin observables are in good agreement with free $p\ensuremath{-}n$ scattering observables, and therefore that $^{3}\stackrel{\ensuremath{\rightarrow}}{\mathrm{He}}$ can serve as a good polarized neutron target. The extracted polarizations of nucleons in $^{3}\stackrel{\ensuremath{\rightarrow}}{\mathrm{He}}$ at low missing momentum are consistent with Faddeev calculations.

Negative resistance instability due to nonlinear damping.

The longitudinal dynamics of a stored proton beam bunch, acted upon by a nonlinear damping force, was studied experimentally at the Indiana University Cyclotron Facility Cooler Ring. The effect of the nonlinear damping force on synchrotron motion was explored by varying the relative velocity between the cooling electron and the stored proton beams. Maintained longitudinal oscillations were observed, whose amplitude grew rapidly once a critical threshold in the relative velocity between the proton and electron beams was exceeded. We attribute this phenomenon to a negative resistance instability occurring after a Hopf bifurcation.

Experimental measurements of a betatron difference resonance.

The betatron difference resonance, ${\mathit{Q}}_{\mathit{x}}$-2${\mathit{Q}}_{\mathit{z}}$=-6, where the ${\mathit{Q}}_{\mathit{x},}$z are the number of betatron oscillations per revolution, was studied at the Indiana University Cyclotron Facility cooler ring. Measurements of both vertical and horizontal coherent betatron oscillations were made, at a nonlinear resonance, after a pulsed dipole kick. We found that the Poincar\'e surface of section for the nonlinear resonance could be described by a simple Hamiltonian. The resonance strength and phase, as well as the tune shift, as a function of betatron amplitude, were deduced from the experimental data. Attempts to deduce the amplitude and phase of the time dependent fluctuations around the time averaged Poincar\'e surface of section will also be discussed.

An internal H 2O vapor jet target for the IUCF Cooler

An internal water vapor jet target is used for the study of the 16O(p, n) 16F reaction in the Indiana University Cyclotron Facility Cooler storage ring. Water in a copper reservoir is heated to a temperature corresponding to the desired vapor pressure (typically 100 Torr), which determines the flow rate through a de Laval-type nozzle and thus the thickness of the target, typically 10 14 atoms/cm 2 7 mm from the nozzle, where the Cooler beam intercepts the jet. The presence of hydrogen in H 2O allows for cross section normalization because pp elastic scattering has a relatively large and well known cross section.

Measurement of spin observables using a storage ring with polarized beam and polarized internal gas target.

We report the first measurement of analyzing powers and spin correlation parameters using a storage ring with both beam and internal target polarized. Spin observables were measured for elastic scattering of 45 and 198 MeV protons from polarized [sup 3]He nuclei in a new laser-pumped internal gas target at the Indiana University Cyclotron Facility Cooler Ring. Scattered protons and recoil [sup 3]He nuclei were detected in coincidence with large acceptance plastic scintillators and silicon detectors. The internal-target technique demonstrated in this experiment has broad applicability to the measurement of spin-dependent scattering in nuclear and particle physics.

Experimental studies of nonlinear beam dynamics.

The nonlinear beam dynamics of transverse betatron oscillations were studied experimentally at the Indiana University Cyclotron Facility cooler ring. Motion in one dimension was measured for betatron tunes near the third, fourth, fifth, and seventh integer resonances. This motion is described by coupling between the transverse modes of motion and nonlinear field errors. The Hamiltonian for nonlinear particle motion near the third- and fourth-integer-resonance conditions has been deduced.

Differential cross section for proton-proton bremsstrahlung at 294 MeV.

The differential cross section for pp\ensuremath{\rightarrow}pp\ensuremath{\gamma} has been measured at an average bombarding energy of 294 MeV and for proton laboratory angles between 5\ifmmode^\circ\else\textdegree\fi{} and 12\ifmmode^\circ\else\textdegree\fi{}. The absolute normalization of the data is based on the concurrent measurement of pp elastic scattering. The experiment has been carried out with the Indiana University Cyclotron Facility Cooler Ring using an internal gas jet target in an electron-cooled beam. The data cover a region of the kinematic space where off-shell contributions of the NN interaction are expected to be enhanced. The shape of the measured cross sections as a function of the photon angle agrees fairly well with the expectation from phase space alone.

Experimental determination of a nonlinear Hamiltonian in a synchrotron.

The nonlinear beam dynamics of transverse betatron oscillators were studied experimentally at the Indiana University Cyclotron Facility Cooler Ring. Particles were kicked onto resonance islands and the properties of these islands were studied. The island tune was determined with high precision by Fourier analyzing the spectrum containing the island oscillations. The island width was estimated based on a single-resonance model. The Hamiltonian of particle motion near a resonance condition was thus deduced.

Energy shift of a depolarizing resonance due to a type-3 Siberian snake.

We recently studied the proton beam polarization in the Indiana University Cyclotron Facility Cooler Ring at five energies. We found that the $G\ensuremath{\gamma}=2$ imperfection depolarizing resonance occurred about 1.9 MeV below the expected resonance energy of 108.4 MeV. This energy shift could be due to a shift of about +0.0036 in the spin tune ${\ensuremath{\nu}}_{s}$, which is the number of spin rotations in each turn around the ring. We then demonstrated that this spin tune shift is consistent with the Cooler Ring containing a partial type-3 Siberian snake, which is apparently caused by the magnets that confine the electron and proton beams in the cooling region.