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Magnetic structure near the Co/NiO(001) interface

Description: We investigate the magnetic coupling at the Co/NiO interface using soft x-ray magnetic linear dichroism (XMLD) and circular dichroism taking explicitly into account the recently observed angular dependence of the XMLD with respect to the crystallographic axes. We find that the Co moments are aligned perpendicular to the NiO moments. We discuss the impact of the anisotropic XMLD on the intensity ratio of the two peaks at the Ni L{sub 2} edge, which is commonly employed to determine the spin orientation in antiferromagnets using XMLD.
Date: August 29, 2008
Creator: Arenholz, Elke; van der Laan, Gerrit & Nolting, Frithjof
Partner: UNT Libraries Government Documents Department

Optically pumped polarized ion sources

Description: Polarization transfer collisions between protons, atomic hydrogen, or deuterium and optically pumped alkali-metal vapour are implemented in the high current optically pumped polarized ion source (OPPIS) and the laser driven source (LDS) of nuclear polarized atoms for target applications. The OPPIS technique overcomes the limitations on intensity of the conventional atomic beam source technique and meets the requirements of the new generation of polarization experiments at multi-GeV accelerators and colliders. 17 refs., 3 figs.
Date: December 31, 1995
Creator: Zelenski, A.N.
Partner: UNT Libraries Government Documents Department

Numerical studies of Siberian snakes and spin rotators for RHIC

Description: For the program of polarized protons in RHIC, two Siberian snakes and four spin rotators per ring will be used. The Snakes will produce a complete spin flip. Spin Rotators, in pairs, will rotate the spin from the vertical direction to the horizontal plane at a given insertion, and back to the vertical after the insertion. Snakes, 180{degrees} apart and with their axis of spin precession at 90{degrees} to each other, are an effective means to avoid depolarization of the proton beam in traversing resonances. Classical snakes and rotators are made with magnetic solenoids or with a sequence of magnetic dipoles with fields alternately directed in the radial and vertical direction. Another possibility is to use helical magnets, essentially twisted dipoles, in which the field, transverse the axis of the magnet, continuously rotates as the particles proceed along it. After some comparative studies, the authors decided to adopt for RHIC an elegant solution with four helical magnets both for the snakes and the rotators proposed by Shatunov and Ptitsin. In order to simplify the construction of the magnets and to minimize cost, four identical super conducting helical modules will be used for each device. Snakes will be built with four right-handed helices. Spin rotators with two right-handed and two left-handed helices. The maximum field will be limited to 4 Tesla. While small bore helical undulators have been built for free electron lasers, large super conducting helical magnets have not been built yet. In spite of this difficulty, this choice is dictated by some distinctive advantages of helical over more conventional transverse snakes/rotators: (i) the devices are modular, they can be built with arrangements of identical modules, (ii) the maximum orbit excursion in the magnet is smaller, (iii) orbit excursion is independent from the separation between adjacent magnets, (iv) they allow ...
Date: April 17, 1995
Creator: Luccio, A.
Partner: UNT Libraries Government Documents Department

Overcoming weak intrinsic depolarizing resonances with energy-jump

Description: In the recent polarized proton runs in the AGS, a 5% partial snake was used successfully to overcome the imperfection depolarizing resonances. Polarized proton beam was accelerated up to the required RHIC injection energy of 25 GeV. However, significant amount of polarization was lost at 0+{nu}{sub y}, 12+{nu}{sub y} and 36+{nu}{sub y}, which is believed to be partially due to the coupling resonances. To overcome the coupling resonance, an energy-jump was generated by rapidly changing the beam circumference using the powerful AGS rf system. It clearly demonstrates that the novel energy-jump method can successfully overcome coupling resonances and weak intrinsic resonances.
Date: July 1, 1997
Creator: Huang, H.; Ahrens, L. & Alessi, J.G.
Partner: UNT Libraries Government Documents Department

Spin states separation based on the longitudinal Stern-Gerlach effect

Description: Repetitive longitudinal impulses of the Stern-Gerlach force are proposed for attaining the separation of the opposite spin states of (anti)proton beams, circulating either in existing collider facilities or in a small ring, conceived just for producing polarized antiprotons at very low energy. After a brief presentation of the theoretical background which supports this proposal, the experimental features are discussed emphasizing in particular the bunch separation within the RF bucket and the feasibility of a high magnetic gradient TE cavity.
Date: December 1, 1996
Creator: Akchurin, N.; Conte, M. & MacKay, W.W.
Partner: UNT Libraries Government Documents Department

Top Quark Physics at a Polarized Muon Collider

Description: Top quark pair production is presented at a polarized Muon Collider above the threshold region. The off-diagonal spin basis is the natural basis for this discussion as the top quark pairs are produced in an essentially unique spin configuration for 100% polarization. Modest polarization, say 30%, can lead to 90% of all top quark pair events being in one spin configuration. This will lead to sensitive tests on anomalous top quark couplings.
Date: February 1, 1998
Creator: Parke, S.
Partner: UNT Libraries Government Documents Department

Spin polarization and magnetic dichroism in core-level photoemission from ferromagnets

Description: In this thesis we present a theoretical investigation of angle- and spin-resolved core-level photoemission from ferromagnetic Fe and Ni. We also consider magneto-dichroic effects due to reversal of the photon helicity or reversal of the sample magnetization direction. In chapter 1, we provide a brief outline of the history of photoemission, and show how it has played an important role in the development of modern physics. We then review the basic elements of the theory of core-level photoemission, and discuss the validity of the some of the commonly-used approximations. In chapter 2, we present a one-electron theory to calculate spin- and angle-resolved photoemission spectra for an arbitrary photon polarization. The Hamiltonian includes both spin-orbit and exchange interactions. As test cases for the theory, we calculate the spin polarization and magnetic dichroism for the Fe 2p core level, and find that agreement with experiment is very good.
Date: May 1, 1997
Creator: Menchero, J.G.
Partner: UNT Libraries Government Documents Department

Measurement of a Weak Polarization Sensitivity to the Beam Orbit of the CEBAF Accelerator

Description: An accelerator-based experiment was performed using the CEBAF accelerator of the Thomas Jefferson National Accelerator Facility to investigate a predicted sensitivity of the beam polarization to the vertical betatron orbit in the recirculation arcs. This is the first measurement of any such effect at CEBAF, and provides information about the polarized beam delivery performance of the accelerator. A brief description of the accelerator is given, followed by the experimental methods used and the relevant issues involved in measuring a small ({approximately} 10{sup {minus}2}) change in the beam polarization. Results of measurements of the polarization sensitivity parameters and the machine energy by polarization transport techniques are presented. The parameters were obtained by measurement of the strength of the effect as a function of orbit amplitude and spin orientation, to confirm the predicted coupling between the spin orientation and the quadrupole fields in the beam transport system. This experiment included characterizing the injector spin manipulation system and 5 MeV Mott polarimeter, modeling of the polarization transport of the accelerator, installation of magnets to create a modulated orbit perturbation in a single recirculation arc, and detailed studies of the Hall C Moeller polarimeter.
Date: April 1, 2000
Creator: Grames, Joseph
Partner: UNT Libraries Government Documents Department

Electron beam polarimetry

Description: Along with its well known charge and mass, the electron also carries an intrinsic angular momentum, or ''spin.'' The rules of quantum mechanics allow one to measure only the probability that the electron spin is in one of two allowed spin states. When a beam carries a net excess of electrons in one of these two allowed spin states, the beam is said to be ''polarized.'' The beam polarization may be measured by observing a sufficient number of electrons scattered by a spin-dependent interaction. For electrons, the useful scattering processes involve coulomb scattering by heavy nuclei, or scattering from either polarized photons or other polarized electrons (known as Mott, Compton, or Moller scattering, respectively). In this tutorial, the authors briefly review how beam polarization is measured through a general scattering process, followed by a discussion of how the three scattering processes above are used to measure electron beam polarization. Descriptions of electron polarimeters based on the three scattering processes will be given.
Date: January 1, 1998
Creator: Sinclair, Charles K.
Partner: UNT Libraries Government Documents Department

Experiment to measure total cross sections, differential cross sections and polarization effects in pp elastic scattering at RHIC

Description: The author is describing an experiment to study proton-proton (pp) elastic scattering experiment at the Relativistic Heavy Ion Collider (RHIC). Using both polarized and unpolarized beams, the experiment will study pp elastic scattering from {radical}s = 60 GeV to {radical}s = 500 GeV in two kinematical regions .In the Coulomb Nuclear Interference (CNI) region, 0.0005 < {vert_bar}t{vert_bar} < 0.12 (GeV/c){sup 2}, we will measure and study the s dependence of the total and elastic cross sections, {sigma}{sub tot} and {sigma}{sub el}; the ratio of the real to the imaginary part of the forward elastic scattering amplitude, {rho}; and the nuclear slope parameter of the pp elastic scattering, b. In the medium {vert_bar}t{vert_bar}, {vert_bar}t{vert_bar} {le} 1.5 (GeV/c){sup 2}, we plan to study the evolution of the dip structure with s, as observed at ISR in the differential elastic cross section, d{sigma}{sub el}/dt, and the s and {vert_bar}t{vert_bar} dependence of b. With the polarized beams the following can be measured: the difference in the total cross sections as function of initial transverse spin stated {Delta}{sigma}{sub T}, the analyzing power, A{sub N}, and the transverse spin correlation parameter A{sub NN}. The behavior of the analyzing power A{sub N} at RHIC energies in the dip region of d{sigma}{sub el}/dt, where a pronounced structure was found at fixed-target experiments will be studied.
Date: December 31, 1995
Creator: Guryn, W.
Partner: UNT Libraries Government Documents Department


Description: Insight into the anisotropy behavior of Nd{sub 2}Fe{sub 14}B may be obtained by measurements of the spin reorientation temperature T{sub S} where the overall magnetocrystalline anisotropy changes to allow the magnetic moment to relax from an easy axis to an easy cone configuration. DC magnetization measurements made at various applied fields on sintered and nanocrystalline forms of Nd{sub 2}Fe{sub 14}B indicate a T{sub S} that remains constant for the sintered sample but is strongly field-dependent for the nanocrystalline forms of the material. Specifically, T{sub S} decreases with decreasing applied fields of strengths 5 T, 1 T and 0.01 T. A simple model that minimizes the total energy of the system leads to the conclusion that the spin reorientation temperature is insensitive to applied field. Therefore it is concluded that the apparent decrease in the system's spin reorientation temperatures with decrease in measuring field can be attributed to the nanoscale structure of the system and a difference in the anisotropy constants compared to their bulk values.
Date: August 18, 2002
Creator: LEWIS,L.H. & HARLAND,C.L.
Partner: UNT Libraries Government Documents Department

Effect of NiO spin orientation on the magnetic anisotropy of the Fe film in epitaxially grown Fe/NiO/Ag(001) and Fe/NiO/MgO(001)

Description: Single crystalline Fe/NiO bilayers were epitaxially grown on Ag(001) and on MgO(001), and investigated by Low Energy Electron Diffraction (LEED), Magneto-Optic Kerr Effect (MOKE), and X-ray Magnetic Linear Dichroism (XMLD). We find that while the Fe film has an in-plane magnetization in both Fe/NiO/Ag(001) and Fe/NiO/MgO(001) systems, the NiO spin orientation changes from in-plane direction in Fe/NiO/Ag(001) to out-of-plane direction in Fe/NiO/MgO(001). These two different NiO spin orientations generate remarkable different effects that the NiO induced magnetic anisotropy in the Fe film is much greater in Fe/NiO/Ag(001) than in Fe/NiO/MgO(001). XMLD measurement shows that the much greater magnetic anisotropy in Fe/NiO/Ag(001) is due to a 90{sup o}-coupling between the in-plane NiO spins and the in-plane Fe spins.
Date: February 10, 2010
Creator: Kim, W.; Jin, E.; Wu, J.; Park, J.; Arenholz, E.; Scholl, A. et al.
Partner: UNT Libraries Government Documents Department

Continuous spin reorientation transition in epitaxially grown antiferromagnetic NiO thin films

Description: Fe/NiO/MgO/Ag(001) films were grown epitaxially, and the Fe and NiO spin orientations were determined using x-ray magnetic dichroism. We find that the NiO spins are aligned perpendicularly to the in-plane Fe spins. Analyzing both the in-plane and out-of-plane spin components of the NiO layer, we demonstrate unambiguously that the antiferromagnetic NiO spins undergo a continuous spin reorientation transition from the in-plane to out-of-plane directions with increasing of the MgO thickness.
Date: March 1, 2011
Creator: Li, J.; Arenholz, E.; Meng, Y.; Tan, A.; Park, J.; Jin, E. et al.
Partner: UNT Libraries Government Documents Department

Disentangling the Mn moments on different sublattices in the half-metallic ferrimagnet Mn3?xCoxGa

Description: Ferrimagnetic Mn{sub 3-x}Co{sub x}Ga compounds have been investigated by magnetic circular dichroism in x-ray absorption (XMCD). Compounds with x &gt; 0.5 crystallize in the CuHg{sub 2}Ti structure. A tetragonal distortion of the cubic structure occurs for x {le} 0.5. For the cubic phase, magnetometry reveals a linearly increasing magnetization of 2x Bohr magnetons per formula unit obeying the generalized Slater-Pauling rule. XMCD confirms the ferrimagnetic character with Mn atoms occupying two different sublattices with antiparallel spin orientation and different degrees of spin localization and identifies the region 0.6 &lt; x {le} 0.8 as most promising for a high spin polarization at the Fermi level. Individual Mn moments on inequivalent sites are compared to theoretical predictions.
Date: May 3, 2011
Creator: Klaer, P.; Jenkins, C.A.; Alijani, V.; Winterlik, J.; Balke, B.; Felser, C. et al.
Partner: UNT Libraries Government Documents Department

RHIC polarized proton performance in run-8.

Description: During Run-8, the Relativistic Heavy Ion Collider (RHIC) provided collisions of spin-polarized proton beams at two interaction regions. Helical spin rotators at these two interaction regions were used to control the spin orientation of both beams at the collision points. Physics data were taken with different orientations of the beam polarization. We present recent developments and improvements as well as the luminosity and polarization performance achieved during Run-8.
Date: June 23, 2008
Creator: Montag,C.; Abreu, N.; Ahrens, L.; Bai, M.; Barton, D. & al., et
Partner: UNT Libraries Government Documents Department

Relativistic Stern-Gerlach Interaction in an RF Cavity

Description: The general expression of the Stern-Gerlach (SG) force is deduced for a relativistic charged spin-1/2 particle which travels inside a time varying magnetic field. This result was obtained either by means of two Lorentz boosts or starting from Dirac's equation. Then, the utilization of this interaction for attaining the spin states separation is reconsidered in a new example using a new radio-frequency arrangement. On the basis of the previous estimates, we feel ready to propose the time varying SG interaction as a method for attaining a spin state separation of an unpolarized beam of, say (anti)protons, since the energy of particles with opposite spin orientations will differ and beams in the two states can be separated. In a first stage of the study of a sensible practical design, we intend to proceed with numerical simulations. As a first step, we intend to verify the correctness of Eqs.(42) and (43) setting once {beta}{sub ph} = 2 and then {beta}{sub ph} = 3, in a cavity where the field line pattern can be realistically controlled. Beyond the verification of the present theory, there is also the aim of studying the effects generated by the spin precession inside the cavity, that we did not yet address in this note. Next, we shall consider a spin splitter scheme based on the lattice of an existing or planned (anti)proton ring endowed with an array of splitting cavities. The principal aim of the latter implementations is to check the mixing effect of the longitudinal phase-plane filamentation, i.e. the actual foe which could frustrate the entire spin splitting process.
Date: May 1, 2009
Creator: Conte,M.; Luccio, A. U. & Pusterla, M.
Partner: UNT Libraries Government Documents Department

On effective temperatures and electron spin polarization in storage rings

Description: This note is a summary of the author`s views on the subject of effective temperatures (and the Unruh temperature in particular) in accelerators. Unruh analyzes the response to vacuum fluctuations of a linearly accelerated two-level atom serving as a detector and shows that the relative populations of the two states are given by a boltzmann factor with kT = {h_bar}a/2{pi}c, where a is the acceleration. The inference is that the detector is immersed in a black-body spectrum of Unruh radiation at the Unruh temperature. He refers to these ideas as the Unruh effect.
Date: May 1, 1998
Creator: Jackson, J.D.
Partner: UNT Libraries Government Documents Department


Description: The relativistic Stem-Gerlach interaction is here considered as a tool for obtaining the spin state separation of an unpolarized (anti)proton beam circulating in a ring. Drawbacks, such as spin precessions within the TE rf cavity, spurious kicks due to the transverse electric field and, worst of all, filamentation in the longitudinal phase plane are analyzed. Possible remedies are proposed and their feasibility is discussed.
Date: September 9, 2002
Partner: UNT Libraries Government Documents Department

Measurement of spin motions in a storage ring outside the stable polarization direction

Description: Polarized, stored beams are becoming a more and more important tool in nuclear and high energy physics. In order to measure the beam polarization in a storage ring the polarization vector of the stored beams has to aim, revolution for revolution, over a period of seconds to minutes, into the same, so-called ``stable`` direction. In this paper measurements at the Indiana University cooler ring (IUCF) are described in which for the first time in a storage ring oscillations of the polarization vector around this stable direction have been measured. The existence and the dynamics of such oscillations are, for instance, important for a new proposed technique for polarizing stored hadron beams.
Date: June 1, 1993
Creator: Akchurin, N.; Badano, L. & Bravar, A.
Partner: UNT Libraries Government Documents Department

Overcoming intrinsic spin resonance by using an AC dipole

Description: Depolarization from an intrinsic spin resonance can be avoided by adiabatically exciting a coherent betatron oscillation. Sustained coherent transverse beam oscillations have been achieved in the AGS using a high frequency AC driven dipole magnet. The amplitude of the oscillations using the present system has been as large as 2.6 times the rms beam size, and the oscillations were held at this level for over 1,000 revolutions. By adiabatically increasing and decreasing the dipole field amplitude during this procedure, the transverse emittance of the beam was left unaffected. To set the scale, had an oscillation of that amplitude been left to oscillate freely, the beam emittance would have increased by a factor of 7 after filamentation. This result provides encouragement that this technique can be used to induce spin flip of polarized proton beams in synchrotrons when crossing strong intrinsic depolarizing resonances during acceleration. Another application of this device in a polarized beams storage ring would be the reversal of the polarized beams storage ring would be the reversal of the polarization direction of the beam. By slowly sweeping the frequency of the modulated dipole field through the spin precession frequency of the storage ring, an adiabatic spin flip can be induced, thus reversing the polarization direction of each individual particle in the storage ring without increasing the beam emittance. This can be useful for reducing systematic errors in polarized beam experiments.
Date: July 1, 1997
Creator: Bai, M.; Ahrens, L. & Glenn, J.W.
Partner: UNT Libraries Government Documents Department

Spin tracking in RHIC (Code Spink)

Description: The evolution of the spin during acceleration in the Relativistic Heavy Ion Collider (RHIC) has been studied with a new numerical code, Spink. Results of spin tracking through resonances are shown.
Date: December 31, 1995
Creator: Luccio, A.U.
Partner: UNT Libraries Government Documents Department

Expected polarization in the present PEP-2 design

Description: In the present design of PEP-2, operation with polarized beams is not anticipated. The amount of polarization that the existing design does support is however of interest. Calculations are presented for the expected polarization for both the High Energy (HER) and the Low Energy (LER) Rings of PEP-2 arising from the Sokolov-Ternov build-up. In both rings, the authors find that with the detector solenoid turned on, the equilibrium polarization is less than 1% at the design operating energies. Furthermore, if a polarized beam were injected, it would depolarize in a short time. To improve the polarization, they consider spin matching; i.e., implementing a set of spin transparency conditions on the lattice design. While to demand complete spin transparency around the entire machine is impractical, six conditions are derived to make the lattice partially spin transparent. Among these six conditions, perhaps only two are dominant for PEP-2. It remains to be seen whether these six (or two) conditions can be implemented into the lattice design in practice, and if implemented, whether they are sufficient to increase the polarization to useful levels. The authors have not studied spin rotator schemes to provide longitudinal polarization at the interaction point or their effect on the beam polarization. Similar calculations are presented for the Beijing Tau-Charm Factory (BTCF) design, including a possible spin rotator scheme. It is found that when this spin rotator is turned on without spin matching, the polarization level is low.
Date: October 1, 1996
Creator: Nosochkov, Y.; Minty, M. & Chao, A.
Partner: UNT Libraries Government Documents Department