21 research outputs found
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Analysis of HOM Properties of Superconducting Parallel-Bar Deflecting/Crabbing Cavities
The superconducting parallel-bar cavity is currently being considered for a number of deflecting and crabbing applications due to improved properties and compact design geometries. The 499 MHz deflecting cavity proposed for the Jefferson Lab 12 GeV upgrade and the 400 MHz crab cavity for the proposed LHC luminosity upgrade are two of the major applications. For high current applications the higher order modes must be damped to acceptable levels to eliminate any beam instabilities. The frequencies and R/Q of the HOMs and mode separation are evaluated and compared for different parallel-bar cavity designs
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Characteristics and fabrication of a 499 MHz superconducting deflecting cavity for the Jefferson Lab 12 geV Upgrade
A 499 MHz parallel bar superconducting deflecting cavity has been designed and optimized for a possible implementation at the Jefferson Lab. Previously the mechanical analysis, mainly stress, was performed. Since then pressure sensitivity was studied further and the cavity parts were fabricated. The prototype cavity is not completed due to the renovation at Jefferson Lab which resulted in the temporary shutdown of the electron beam welding facility. This paper will present the analysis results and facts encountered during fabrication. The unique geometry of the cavity and its required mechanical strength present interesting manufacturing challenges
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Transverse Effects Due to Random Displacement of Resistive Wall Segments and Focusing Elements
In this paper, we study the single bunch transverse beam dynamics in the presence of random displacements of resistive wall segments and focusing elements. Analytical formulas are obtained for long-range resistive wall wake, together with numerical results for short-range resistive wall wake. The results are applied to the LCLS project and some other proposed accelerators
Magnetized Electron Source for JLEIC Cooler
Magnetized bunched-beam electron cooling is a critical part of the Jefferson Lab Electron Ion Collider (JLEIC). Strong cooling of ion beams will be accomplished inside a cooling solenoid where the ions co-propagate with an electron beam generated from a source immersed in magnetic field. This contribution describes the production and characterization of magnetized electron beam using a compact 300 kV DC high voltage photogun and bialkali-antimonide photocathodes. Beam magnetization was studied using a diagnostic beamline that includes viewer screens for measuring the shearing angle of the electron beamlet passing through a narrow upstream slit. Correlated beam emittance with magnetic field at the photocathode was measured for various laser spot sizes. Measurements of photocathode lifetime were carried out at different magnetized electron beam currents up to 28 mA and high bunch charge up to 0.7 nano-Coulomb was demonstrated
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Development of an upgrade of the CEBAF acceleration system
Long-term plans for CEBAF at Jefferson Lab call for achieving 12 GeV in the middle of the next decade and 24 GeV after 2010. Such energies can be achieved within the existing footprint by fully populating the accelerator with cryomodules capable of providing 3 to 4 times as much voltage as the design value of the existing ones within the same length. In particular, this requires the development of superconducting cavities capable of operating at gradients above 12 MV/m and Q close to 10{sup 10}
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Heavy-ion superconducting linacs
This paper reviews the status of the superconducting heavy-ion accelerators. Most of them are linacs used as boosters for tandem electrostatic accelerators, although the technology is being extended to very low velocity to eliminate the need for an injector. The characteristics and features of the various superconducting heavy-ion accelerators are discussed. 45 refs
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Electronic Damping of Microphonics in Superconducting Cavities
In previous applications of high-velocity superconducting cavities the accelerated beam currents were sufficiently high that the microphonics-induced frequency excursions were significantly less than the loaded bandwidth, and the power absorbed by the beam dominated the total power requirement. In new applications (CEBAF Upgrade, RIA) the beam currents will be sufficiently low that the RF power requirements will be dominated by the control of the cavity fields in the presence of microphonics. Active electronic damping of microphonics by modulation of the cavity field amplitude has been occasionally used in the past in small, low-velocity, low-gradient superconducting structures; its application to much larger, high-velocity, high-gradient structures could result in a substantial reduction of the RF power requirements. This paper presents an analytical study of various schemes for electronic damping and presents formulae that quantify the reduction of microphonics as a function of RF field amplitude modulation
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Light emission phenomena in superconducting niobium cavities
During the investigation of field emission limitations of superconducting niobium cavities, a CCD camera was inserted at the end of the beam pipe on a single-cell 1500 MHz cavity. When operating the cavity in field emission, glowing filaments of light were observed trapped by RF fields in closed-orbit trajectories. These filaments were traveling at frequencies much lower than the oscillating RF fields and formed various patterns of light for up to several seconds. This experiment was then repeated on a production CEBAF five-cell cavity with similar results. Events from both experiments were captured on video tape and are presented in this paper along with a discussion of the possible origin of these types of light patterns and the plans to further investigate the phenomena
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Design and modeling of superconducting RFQ structures
Tests of the first superconducting RFQ structure indicated that high surface electric fields could be sustained in a quadrupole geometry. However, the geometry used in those tests was not appropriate for an accelerating structure and the area sustaining the high electric field was too small to assume that such fields could be achieved in actual RFQ structures. We have initiated a program to analyze and model a variety of geometries suitable for superconducting RFQ structures. We are also designing a niobium RFQ sparker'' to experimentally measure the surface electric fields that can be achieved on large areas in an actual RFQ structure
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Beam breakup with longitudinal halo
We have developed an analytical model of cumulative beam breakup in linear accelerators that predicts the displacement of particles between bunches. Beam breakup is assumed to be caused by a periodic current consisting of an infinite bunch train. The particles in the halo do not contribute to the breakup but experience the deflecting fields and are displaced by them. Under certain circumstances, the displacement of particles in the halo can be considerably larger than that of the bunches. This may have important consequences for the design of high-current cw accelerators where even a small flux of particles striking components of the accelerator cannot be tolerated because of activation. 11 refs., 2 figs