Internal Target Experiments Research Articles

A Compton Backscattering Polarimeter for Electron Beams below 1 GeV

A recently installed polarized electron source will allow internal target experiments to be performed with polarized electrons at the NIKHEF Internal Target Hall, lb measure the longitudinal component of the polarization vector of the stored electron beam, a Polarimeter based on spin-dependent Compton scattering has been developed and successfully commissioned

Determination of internal-target thickness and experimental luminosity from beam energy loss at HIRFL-CSRe**Supported by National Natural Science Foundation of China (11179017, 11105201, U1532130, and U1332206)

The target thickness for nitrogen was determined from the beam energy loss in HIRFL-CSRe during the experimental study of the K-REC process in 197 MeV/u Xe54+-N2 collisions. Furthermore, the corresponding integrated luminosity of (1.15±0.06) × 1030 cm−2 was obtained. As an independent check on the energy-loss method, we have also determined the integrated luminosity by measuring the produced X-rays from the K-REC process with a known differential cross section. The values of (1.12±0.06) × 1030 and (1.09±0.06) × 1030 cm−2 were obtained by using two high-purity germanium (HPGe) detectors which were oriented at 90° and 120° with respect to the beam path, respectively. The consistent results confirmed the feasibility of the energy-loss method, which may have an important impact on future internal target experiments at HIRFL-CSRe.

Heavy ion storage and acceleration in the HESR with stochastic cooling and internal target

Heavy ion stochastic momentum cooling is investigated under the constraint of the present concept of the high energy storage ring (HESR). A bare uranium beam is injected from the collector ring into the HESR at 740 MeV u−1 and a beam preparation for an internal target experiment is outlined. Further the acceleration of the ion beam to 4.5 GeV u−1 is considered and an internal target experiment is studied. The simulations include the beam-target interaction involved with a hydrogen target. The capability of momentum filter cooling is envisaged and the possibility of time-of-flight momentum cooling is examined at lower energies where the revolution harmonics begin to overlap.

Investigation of the heavy-ion mode in the FAIR High Energy Storage Ring

High energy storage ring (HESR) as a part of the future accelerator facility FAIR (Facility for Antiproton and Ion Research) will serve for a variety of internal target experiments with high-energy stored heavy ions (SPARC collaboration). Bare uranium is planned to be used as a primary beam. Since a storage time in some cases may be significant—up to half an hour—it is important to examine the high-order effects in the long-term beam dynamics.A new ion optics specifically for the heavy ion mode of the HESR is developed and is discussed in this paper. The subjects of an optics design, tune working point and a dynamic aperture are addressed. For that purpose nonlinear beam dynamics simulations are carried out. Also a flexibility of the HESR ion optical lattice is verified with regard to various experimental setups. Specifically, due to charge exchange reactions in the internal target, secondary beams, such as hydrogen-like and helium-like uranium ions, will be produced. Thus the possibility of separation of these secondary ions and the primary beam is presented with different internal target locations.

HIRFL–CSR internal cluster target

Since HIRFL–CSR internal cluster target was built, it has played a key role in in-ring experiments at HIRFL–CSR. So far it have been operated with five gas species as targets for scattering experiments, i.e. hydrogen, nitrogen, argon, neon, and krypton. The obtained highest thickness for hydrogen target amounts up to 1012atoms/cm2, and those of other targets are larger than 1013atoms/cm2 with the background pressure of 10−11mbar in CSR. The target thickness can be varied by regulating the nozzle temperature and pressure of the inlet gas. The first online internal target experiment dedicated to investigate radioactive electron capture (REC) process with Xe54+ ions colliding with the nitrogen target demonstrated the stability and reliability of the internal target system. In addition, hydrogen and krypton were also tested online in recent experiments, which indicate the target system can meet experimental requirements for the thickness of target, pressure in scattering chamber, and long-term stability.

Prospects for searching the η→e+e− rare decay at the CSR

We study the possibility of searching the η→e+e− rare decay on the Cooling Storage Ring (CSR) at Lanzhou. The main features of the proposed Internal Target Experiment (ITE) and External Target Facility (ETF) are included in the Monte Carlo simulation. Both the beam condition at the CSR and the major physics backgrounds are carefully taken into account. We conclude that the ITE is more suitable for such a study due to better detector acceptance and higher beam density. At the maximum designed luminosity (1034 cm−2 s−1), η→e+e− events can be collected every ∼400 seconds at the CSR. With a mass resolution of 1 MeV, the expected signal-to-background (S/B) ratio is around 1.

Internal-target polarized Drell-Yan Experiment at RHIC

We present physics motivations and experimental considerations for an internal-target polarized Drell-Yan dimuon experiment at RHIC. Dimuons from the Drell-Yan process are detected using a spectrometer based on the existing Fermilab-E906/SeaQuest spectrometer. The primary goal of the proposed experiment is to extract the Sivers parton distribution function in the valence-quark region from the measurement of the single transverse-spin asymmetry. The sensitivity of the proposed internal-target experiment will provide a stringent test of the QCD prediction that the Sivers function in the Drell-Yan process has an opposite sign with respect to that in deep-inelastic scattering. Results of some initial studies of the expected sensitivity are shown.

Excitation functions of the analyzing power in elastic proton-proton scattering from 0.45 to 2.5 GeV

Excitation functions A_N(p_{lab},Theta_{c.m.}) of the analyzing power in elastic proton-proton scattering have been measured in an internal target experiment at the Cooler Synchrotron COSY with an unpolarized proton beam and a polarized atomic hydrogen target. Data were taken continuously during the acceleration and deceleration for proton kinetic energies T_{lab} (momenta p_{lab}) between 0.45 and 2.5 GeV (1.0 and 3.3 GeV/c) and scattering angles 30 deg < Theta_{c.m.} < 90 deg. The results provide excitation functions and angular distributions of high precision and internal consistency. The data can be used as calibration standard between 0.45 and 2.5 GeV. They have significant impact on phase shift solutions, in particular on the spin triplet phase shifts between 1.0 and 1.8 GeV.

Electron-RI collider and internal target operation of RIKEN storage ring project

A versatile heavy-ion accelerator system is under construction at RIKEN which is composed of a cascade of cyclotrons. The ions, from proton to Uranium, are planned to be accelerated up to around 400MeV/u. As a second phase of the project, MUSES was planned which is composed of an accumulator/cooler ring for RI beam and an electron–RI collider. The available luminosity of collider is dependent upon the production cross-section of RI beam through the projectile fragmentation process, cooling time of RI beams and the intensity limit of electron beam in the electron ring. We investigated the feasibility of experiments to determine the charge distribution in the unstable nuclei. On the other hand, internal target experiments at the accumulator ring will open new and precise physics with use of inverse kinematics. A new scheme of internal target experiments is conceived where a quite thick target is installed and high repetition of beam injection is used from the injector cyclotron. In the present paper, essence of design works of electron–RI collision experiments and accumulator/cooler ring are described emphasizing the role of stochastic and electron cooling, as well as new scheme of internal target operation.

Nuclear structure studies with RI beams and cooler rings

Selected topics in present days nuclear structure physics studied by reactions of RI beams are presented. They are change in nuclear radii, single particle orbitals, and shapes. Dynamical changes are shown for nuclei far from the stability line in particular in p-sd shell. Among the future reaction study, a thick target method for a storage ring is presented. A possibility to obtain the highest luminosity for an internal target experiment is proposed.

Study of the reaction pp $ \to$ pp $\pi^0$ within 10 MeV above the threshold

Kinematically complete measurements of the $pp\to pp\pi^{0}$ reaction were performed for beam energies in the range $292 - 298 $MeV. By detecting both protons in coincidence with the large acceptance COSY-TOF spectrometer set up at an external beam line of the proton synchrotron COSY-J\"ulich, total and differential cross sections and energy distributions were obtained. A strong enhancement is observed in the Dalitz plots resulting from the final state interaction between the outgoing proton pair; the data are well reproduced by Monte Carlo simulations with standard parameters for scattering length $a_0$=-7.83 fm and effective range $r_0$=2.8 fm. The total cross sections exceed the ones measured recently in internal target experiments at IUCF and CELSIUS by roughly 50%. Arguments are presented which link this discrepancy with the effect of the final state interaction pushing yield into the very small-angle region and the near-impossibility of an internal target experiment to cover just this range.

The heavy ion cooler-storage-ring project (HIRFL-CSR) at Lanzhou

HIRFL-CSR, a new ion Cooler-Storage-Ring (CSR) project, is the post-acceleration system of the Heavy Ion Research Facility in Lanzhou (HIRFL). It consists of a main ring (CSRm) and an experimental ring (CSRe). From the HIRFL cyclotron system the heavy ions will be accumulated, cooled and accelerated in the CSRm, then extracted fast to produce radioactive ion beams (RIB) or highly charged heavy ions. Those secondary beams will be accepted and stored by the CSRe for many internal-target experiments with electron cooling.

A polarized hydrogen/deuterium atomic beam source for internal target experiments

A high-brightness hydrogen/deuterium atomic beam source is presented. The apparatus, previously used in electron scattering experiments with tensor-polarized deuterium (Ferro-Luzzi et al., Phys. Rev. Lett. 77 (1996) 2630; van den Brand et al., Phys. Rev. Lett. 78 (1997) 1235; Zhou et al., Phys. Rev. Lett. 82 (1998) 687; Bouwhuis et al., Phys. Rev. Lett. 82 (1999) 3755), was configured as a source for internal target experiments to measure single- and double-polarization observables, with either polarized hydrogen or vector/tensor polarized deuterium. The atomic beam intensity was enhanced by a factor of ∼2.5 by optimizing the Stern–Gerlach focusing system using high tip-field (∼1.5 T) rare-earth permanent magnets, and by increasing the pumping speed in the beam-formation chamber. Fluxes of (5.9±0.2)×10 16 1 H/s were measured in a ∅12 mm×122 mm compression tube with its entrance at a distance of 27 cm from the last focusing element. The total output flux amounted to (7.6±0.2)×10 16 1 H/s .

Recoil detection with a polarized [formula omitted]He target

The ultra-thin gas targets used in storage ring internal target experiments allow low energy, heavy nuclei to emerge from the target region. A detector capable of analyzing these nuclei provides unique access to many nuclear reactions. We report here the first use of such a detector in conjunction with a polarized 3 He internal target and a polarized electron beam. The results of using the detector as a luminosity monitor and as a polarimeter to measure the product of beam and target polarizations are presented. The ability to study coherent pion production via the reactions 3 He → ( e → , e′ 3 He)π 0 and 3 He → ( e → , e′ 3 H)π + is shown along with the ability of the detector to unambiguously separate the two- and three-body breakup channels of the reaction 3 He → ( e → , e′p) .

A Compton polarimeter for the MIT/Bates South Hall Ring

A Compton polarimeter is being developed for the MIT/Bates South Hall Storage Ring. This polarimeter will be used to make measurements of the polarization of stored electron beams with energies below 1 GeV during internal target experiments.

A helical scintillating fiber hodoscope

A novel scintillating fiber hodoscope in helically cylindric geometry has been developed for detection of low multiplicity events of fast protons and other light charged particles in the internal target experiment EDDA at the Cooler Synchrotron COSY. The hodoscope consists of 640 scintillating fibers (2.5 mm diameter), arranged in four layers surrounding the COSY beam pipe. The fibers are helically wound in opposing directions and read out individually using 16-channel photomultipliers connected to a modified commercial encoding system. The detector covers an angular range of 9°⩽ Θ ⩽72° and 0°⩽ ϕ ⩽360° in the lab frame. The detector length is 590 mm, the inner diameter 161 mm. Geometry and granularity of the hodoscope afford a position resolution of about 1.3 mm. The detector design took into consideration a maximum of reliability and a minimum of maintenance. An LED array may be used for monitoring purposes.

A Compton backscattering polarimeter for measuring longitudinal electron polarization

Compton backscattering polarimetry provides a fast and accurate method to measure the polarization of an electron beam in a storage ring. Since the method is non-destructive, the polarization of the electron beam can be monitored during internal target experiments. For this reason, a Compton polarimeter has been constructed at NIKHEF to measure the polarization of the longitudinally polarized electrons which can be stored in the AmPS ring. The design and results of the polarimeter, the first Compton polarimeter to measure the polarization of a stored longitudinally polarized electron beam directly, are presented in this paper.

A recoil detector for the internal target facility of AmPS (NIKHEF)

A recoil detector has been built for internal target experiments with the Amsterdam Pulse Stretcher and storage ring, AmPS, of NIKHEF. The detector was designed to detect low-energy (1–20MeV/nucleon) and low-mass (A≤4) recoiling nuclei emerging from electron-induced reactions. The detector consists of a low-pressure, two-step avalanche chamber, two layers of silicon strip detectors of 100 and 475μm thickness and a scintillator. The signals from the separate detector elements are processed by custom-made analog electronics and dedicated VME-based digitizer modules. The detector was operated successfully at the AmPS electron scattering facility with a gaseous He target of 1015atoms/cm2 internal to the storage ring and beam currents up to 200mA of 660MeV electrons. Unambiguous particle separation was achieved.

Ion-extraction polarimetry for tensor polarized deuterium internal targets

An ion-extraction polarimeter has been developed for internal target experiments in storage rings. Here, we report on the application of such a device for a tensor polarized deuterium gas target internal to a medium-energy electron storage ring. Ions, produced by the stored electron beam, were extracted from a storage cell using electrostatic lenses and a spherical deflector, transported to a mass-analyzer, and subsequently to a 3H( d ,n)α tensor polarization analyzer. The method allows determining the density-averaged nuclear polarization of the target gas, independent of spatial and temporal variations. We discuss in detail the systematic uncertainties (< 5%) associated with this technique.

PLANS FOR ATOMIC PHYSICS WITH HIGHLY-CHARGED IONS AT LANZHOU

The upgraded radioactive ion beam line of Lanzhou and the project of the cooler storage ring of Lanzhou are presented in this paper. The plans for atomic physics with highly charged ions at the cooler storage ring are discussed briefly, including precision spectroscopy of highly charged ions, free- and laser-induced electron–ion recombination, test of special relativity, hyperfine structure of radioactive ions, lifetime measurements, and internal target experiments.