Beam Dynamics and Electromagnetic Fields




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ABSTRACTS SUBMITTED IN SESSION 4

Beam Dynamics and Electromagnetic Fields



915 - RHIC Vertical AC Dipole Commissioning*
M. Bai, J. Delong, P. Oddo, C.-I. Pai, S. Peggs, T. Roser, T. Satogata, D. Trbojevic, A. Zaltsman, BNL, Upton, Long Island, New York

The vertical RHIC ac dipole was installed in the summer of 2001. The magnet is located in the interaction region between sector 3 and sector 4 and common to both beams. The resonant frequency of the ac dipole was first configured to be around half of the beam revolution frequency to act as a spin flipper. At the end of the RHIC 2002 run, the RHIC vertical ac dipole frequency was reconfigured for beam dynamics studies.A 3~$\sigma$ vertical betatron oscillation was

excited with the vertical ac dipole, where $\sigma$ is the rms vertical beam size. RHIC IPM (Ionization Profile Monitor) measurements also confirm that the beam transverse emittance is preserved after the vertical excitation. The betatron functions and phase advances at each BPM~(Beam Position Monitor) around the ring were measured using the coherence excited by the vertical ac dipole. We also used the excited coherence to measure the 2x2 coupling transfer matrix at each BPM location. Both measurements for are presented in the paper along with the analysis algorisms for each of these measurements.

The work was performed under the auspices of the US Department of Energy

Type of presentation requested : Poster

Classification : [D01] Beam Optics - Lattices, Correction Schemes, Transport


1496 - Adiabatic Matching in Periodic Accelerating Lattices for Superconducting Proton Linacs
G. Bellomo, P. Pierini, INFN LASA, Segrate (MI)

Superconducting proton Linacs with multicell cavities are split in sections (using cavities with different geometrical length) with a spatially periodic lattice (typically a focusing doublet and 2-4 cavities in a lattice period) and slowly varying focusing and acceleration parameters. The usual matching procedure for a constant parameter lattice, namely periodic conditions on the transverse and longitudinal Twiss parameters gives poor results, especially in the presence of strong space charge forces. A novel matching procedure has been devised, valid for adiabatic variations of the beamline and beam parameters. This procedure gives smooth beam envelope variations along the machine, as well as a smooth phase advance per period. Examples will be given for the case of the superconducting TRASCO Linac.

Type of presentation requested : Poster

Classification : [D01] Beam Optics - Lattices, Correction Schemes, Transport


1849 - Recent Progress in Six-Dimensional Ionization Cooling Techniques for Muon-Based Machines*
J.S. Berg, R. Palmer, BNL, Upton, Long Island, New York

Ionization cooling is an essential component of a neutrino factory or a muon collider. Ionization cooling in the transverse dimensions is reasonably straightforward, and has been incorporated in published neutrino factory studies. Achieving cooling in the longitudinal dimensions is more difficult, but has the potential to greatly improve the performance of neutrino factories, and is essential to muon colliders. Much progress has recently been made in describing ring cooling lattices which achieve cooling in all three phase space planes, and in the design of the required, but difficult, injection systems. Ring cooling lattices also have the potential of significantly reduced cost compared to single-pass cooling systems with comparable performance. We will present some recent lattice designs, describing their theory, features, and performance, including injection and extraction systems.

*Work supported by the Department of Energy, contract DE--AC02--98CH10886.

Type of presentation requested : Poster

Classification : [D01] Beam Optics - Lattices, Correction Schemes, Transport


1850 - Longitudinal Beam Dynamics in Imperfectly-Ioschronous FFAG Accelerators*
J.S. Berg, BNL, Upton, Long Island, New York

Using FFAGs for the arcs of recirculating accelerators has the potential to achieve significant cost savings over a multiple-arc design. The problem with such a design is that no FFAG arc will have the same path length over its entire energy range. This leads to problems with synchronizing high-frequency RF with the beam on each pass. It has been demonstrated [1] that in fact a reference particle can be accelerated in such a system for an arbitrary number of turns, although the amount of linac required for a given energy gain never falls below a certain nonzero value for a larger number of turns. Here we examine the longitudinal phase space acceptance of such a system as a function of the number of turns in the accelerator.

*Work supported by the Department of Energy, contract DE--AC02--98CH10886.

[1] J. Scott Berg. Longitudinal Reference Particle Motion in Nearly Isochronous FFAG Recirculating Accelerators. To appear in the proceedings of Snowmass 2001, 30 Jun-21 Jul 2001, Snowmass Village, CO.

Type of presentation requested : Poster

Classification : [D01] Beam Optics - Lattices, Correction Schemes, Transport


1216 - Extraction by Stripping at JINR
O. Borisov, JINR, Dubna, Moscow Region

Numerical simulation results of the heavy ions extraction by stripping for various magnetic structures, chage-exchange ratio and other parameters are considered. The possibilities and advantage of this extraction method are discussed. Experimental results for U-400 and U-400M cyclotrons are present.

Type of presentation requested : Poster

Classification : [D01] Beam Optics - Lattices, Correction Schemes, Transport


250 - Field Quality vs Beam Based Corrections in Large Hadron Colliders
O.S. Bruning, CERN, Geneva

The paper discusses limits for correcting the magnet field quality via dedicated correction circuits in a collider storage ring and the possibility of adjusting the powering of such correction circuits via beam based measurements.

Type of presentation requested : Invited Paper

Classification : [D01] Beam Optics - Lattices, Correction Schemes, Transport


1632 - Measurement and Correction of Imperfections in the SLS Storage Ring
M. Böge, V. Schlott, A. Streun, PSI, Villigen

Based on precise average beta function measurements with errors of ~1 % for the locations of the 174 quadrupoles an SVD based beta beat correction has been applied using the individually powered quadrupoles as correctors. Residual horizontal and vertical beta beats of 4 and 2 % have been measured after correction. Beam based alignment techniques have been applied to determine BPM centers with respect to adjacent quadrupoles. Furthermore the analysis of Corrector/BPM response matrices within a parameterized model gives a detailed understanding of the underlying imperfections. The foreseen SVD based beam based girder alignment adjusts the 48 magnet girders in order to minimize the closed orbit distortions. Linear encoders allow to monitor the movement of BPMs and girders once the imperfections have been corrected.

Type of presentation requested : Poster

Classification : [D01] Beam Optics - Lattices, Correction Schemes, Transport


520 - Creation of Hollow Bunches by Redistribution of Phase Space Surfaces
C. Carli, M. Chanel, CERN, Geneva

The creation of hollow bunches in the longitudinal phase space, in order to decrease the peak current and in turn the transverse direct space charge forces, is an old idea. A new method to create such hollow a distribution at high energy has been simulated and tested experimentally at the PS Booster synchrotron. It is based on a redistribution of surfaces in the longitudinal phase space by using a double harmonic RF system. During the process, the beam is transferred from one second harmonic sub-bucket to the other. Low density phase space surfaces from the periphery and high density regions from the centre are exchanged, leading to flat profiles, even after switching off the second harmonic RF system. During the process, the peak current is temporarily increased, which makes it suitable only to improve the situation in a receiving machine (in our case the PS) after transfer. In practice, the set-up of this new scheme turned out to be fast and simple and to yield reliable and reproducible results.

Type of presentation requested : Poster

Classification : [D01] Beam Optics - Lattices, Correction Schemes, Transport


1378 - Coupling Correction for the SNS Accumulator Ring
N. Catalan-Lasheras, CERN, Geneva; C. Gardner, I. Papaphilippou, G. Parzen, BNL, Upton, Long Island, New York

In high intensity machines as the SNS accumulator ring, coupling resonances combined with the space-charge effect may produce excessive emittance growth leading to intolerable beam losses. Several correction schemes have been investigated to achieve local and global decoupling and the correction of vertical dispersion. A minimal set of skew quadrupole correctors and their maximum strength have been defined. The final configuration robustness and sensitivity for all the potential working points has been tested and the results are discussed.

Type of presentation requested : Poster

Classification : [D01] Beam Optics - Lattices, Correction Schemes, Transport


270 - Downstream Beamline for the 2-us, 2-kA and 20-MeV DARHT-II*
Y.-J. Chen, L. Bertolini, G.J. Caporaso, A. Paul, B. Poole, L.-F. Wang, G.A. Westenskow, LLNL, Livermore

The second-axis of the Dual-Axis Radiographic Hydrodynamic Test facility (DARHT-II) is to perform multiple-pulses x-ray flash radiography. The DARHT-II accelerator will provide a 2-kA, 20-MeV and 2-microsecond electron beam with a ± 0.5% energy variation. We have designed a beamline to select several short current pulses from the 2-microsecond beam and to deliver those pulses to a x-ray converter target. The remained beam will be delivered to a beam dump. With the diagnostic beam stop inline, the transport system provides emittance diagnose capability for the beam exiting the accelerator. The beamline consists of several long drift sections. The transverse resistive wall instability and the background gas focusing effects in the long drift sections could be potential problems for maintaining the quality of the long pulse, high current beam. The beam exiting the accelerator has a rise time of 50 - 150 ns with the beam head energy varying from 16 - 20 MeV. Gas desorption caused by beam spill of the long off-energy beam head is also a concern. We will present the beamline configuration and its beam parameter acceptance, the transverse resistive wall instability modeling, the final spot size variation caused by the background vacuum, and the simulations of beam spill. The beam spot size on the target will be discussed.

*This work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.

Type of presentation requested : Poster

Classification : [D01] Beam Optics - Lattices, Correction Schemes, Transport


1231 - Measurement of Optical Functions in HERA
W. Decking, B. Holzer, J. Keil, T. Limberg, DESY, Hamburg

The linear optics of both HERA electron and proton ring have been measured with several methods, including gradient changes in individual powered quadrupoles, local orbit changes in the arc sextupoles and response matrix fitting. Only a combination of all methods allows a complete understanding of the linear optics. Automated data taking and analysis has proven to be an important tool in the re-commissioning of HERA and revealed several optics errors. A review of the methods and results of the measurements will be presented.

Type of presentation requested : Poster

Classification : [D01] Beam Optics - Lattices, Correction Schemes, Transport


1227 - Studies for Beam Lifetime Optimization in DAFNE
S. Guiducci, INFN-LNF, Frascati (Roma)

Since the DAFNE beam lifetime is strongly dominated by the Touschek effect, an analysis of its dependence on the ring dynamic aperture and on machine parameters has been done in order to improve the machine performances. Measurements taken in different conditions are here presented and compared with simulations. The agreement is quite satisfactory when taking into account the measured bunch length and machine coupling, and the actual dynamic aperture.

Type of presentation requested : Poster

Classification : [D01] Beam Optics - Lattices, Correction Schemes, Transport


311 - The Influence of Time-Dependent Magnetic Field Errors on the Specifications of Feedback and Collimation Systems
M. Hayes, R.W. Assmann, J. Wenninger, CERN, Geneva

The LHC requires an excellent beam stability during all phases of the LHC cycle. This stability must be ensured inspite of the time-dependent field errors in the superconducting main dipoles. The field errors will change significantly during injection and ramp, inducing perturbations of the circulating beam. The known time-dependent field errors of the LHC magnets and their effects on the LHC beam were simulated using latest tracking codes, allowing the prediction of the beam stability during injection and ramp. Using these results the constraints and specifications for beam collimation and the LHC orbit feedback are studied.


Type of presentation requested : Poster

Classification : [D01] Beam Optics - Lattices, Correction Schemes, Transport


1148 - A Generalized Orbit Correction Scheme
E. Karantzoulis, F. Iazzourene, L. Tosi, ELETTRA, Trieste

The special operating conditions of ELETTRA have strongly influenced the orbit correction philosophy. A hybrid orbit correction scheme is presented whereby local orbit corrections at arbitrary positions and angles at three light source points of each of the eleven user dedicated sections are performed that also maintain the global orbit stable. The method, the stability and the implications are presented and discussed.

Type of presentation requested : Poster

Classification : [D01] Beam Optics - Lattices, Correction Schemes, Transport


1035 - Ionization Cooling of Muon Beams
E.-S. Kim, PAL, Pohang

We present an ionization cooling lattice design which use solenoidal focusing channels and liquid hydrogen absorber wedge for the transverse and longitudinal cooling of muon beams. The cooling performances in the cooling system are investigated.

Type of presentation requested : Poster

Speaker :
Eun-San Kim

Classification : [D01] Beam Optics - Lattices, Correction Schemes, Transport


420 - Vertical Beam Size Control at SRRC
C.-C. Kuo, H.P. Chang, H.J. Tsai, SRRC, Hsinchu

Vertical beam size control in the 1.5 GeV synchrotron radiation storage ring at SRRC was investigated. Linear coupling model with measured orbit response was attempted. Manipulation of transverse beam betatron coupling as well as the vertical dispersion correction using a set of skew quadrupoles around the ring has been conducted. The correlation of the coupling strength, vertical beam size, beam brightness, as well as beam lifetime was measured and optimal operation conditions have been searched for the routine users operations.
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