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Impedance calculation for ferrite inserts

Description: Passive ferrite inserts were used to compensate the space charge impedance in high intensity space charge dominated accelerators. They study the narrowband longitudinal impedance of these ferrite inserts. they find that the shunt impedance and the quality factor for ferrite inserts are inversely proportional to the imaginary part of the permeability of ferrite materials. They also provide a recipe for attaining a truly passive space charge impedance compensation and avoiding narrowband microwav… more
Date: January 1, 2005
Creator: Breitzmann, S. C.; Lee, S. Y. & Ng, K. Y.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Fast beam stacking using rf barriers

Description: Two barrier RF systems were fabricated, tested and installed in the Fermilab Main Injector. Each can provide 8 kV rectangular pulses (the RF barriers) at 90 kHz. When a stationary barrier is combined with a moving barrier, injected beams from the Booster can be continuously deflected, folded and stacked in the Main Injector, which leads to doubling of the beam intensity. This paper gives a report on the beam experiment using this novel technology.
Date: June 1, 2007
Creator: Chou, W.; Capista, D.; Griffin, J.; Ng, K.-Y.; Wildman, D. & /Fermilab
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Partner: UNT Libraries Government Documents Department
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Correction of unevenness in recycler beam profile

Description: A beam confined between two rf barriers in the Fermilab Recycler Ring exhibits very uneven longitudinal profile. This leads to the consequence that the momentum-mined antiproton bunches will have an intolerable variation in bunch intensity. The observed profile unevenness is the result of a tiny amount of rf imperfection and rf beam-loading. The profile unevenness can be flattened by feeding back the uneven rf fan-back gap voltage to the low-level rf.
Date: May 1, 2006
Creator: Crisp, J.; Hu, M. & Ng, K. Y.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Study of collective effect in ionization cooling

Description: As a charged particle passes through a non-gaseous medium, it polarizes the medium and induces wake fields behind it. Same thing happens in ionization cooling. The interaction with wake fields perturbs the stopping power of beam particles. The perturbation strongly depends on the densities of both the incident beam and the medium. To understand this collective effect, detailed studies have been carried out. Both analytic and simulation results are obtained and compared.
Date: September 1, 2009
Creator: Huang, D.; Ng, K. Y. & Roberts, T. J.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Electron proton two-stream instability at the PSR.

Description: A strong, fast, transverse instability has long been observed at the Los Alamos Proton Storage Ring (PSR) where it is a limiting factor on peak intensity. Most of the available evidence, based on measurements of the unstable proton beam motion, is consistent with an electron-proton two-stream instability. The need for higher beam intensity at PSR [1] and for future high-intensity, proton drivers has motivated a multi-lab collaboration (LANL, ANL, FNAL, LBNL, BNL, ORNL, and PPPL) to coordinate r… more
Date: February 19, 2002
Creator: Macek, R. J.; Browman, A.; Fitzgerald, D.; McCrady, R.; Merrill, F.; Plum, M. et al.
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Partner: UNT Libraries Government Documents Department
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Longitudinal Bunch Dynamics in the Tevatron

Description: The authors present their observations of the longitudinal bunch dynamics in Tevatron for uncoalesced proton bunches at 150 GeV and coalesced proton bunches at 150 GeV and 980 GeV. They have observed long-term (> 15 minutes) coherent oscillations of uncoalesced protons that preserve already existing oscillations from upstream accelerators. A single-bunch instability in large intensity protons bunches at 980 GeV has also been observed.
Date: June 2, 2003
Creator: Moore, R.; Balbekov, V.; Jansson, A.; Lebedev, V.; Ng, K. Y. & Shiltsev, V.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Exploration of ion-antiproton instabilities in the Recycler Ring

Description: Instabilities driven by ions (or electrons) trapped within the space charge potential of a circulating beam are common in accelerators and storage rings. In the recycler, the stored antiproton ({bar p}) beam could trap positive ions (H{sub 2}{sup +}, CO{sup +}, etc.). Conditions for trapping are discussed, and trapping potentials are calculated. Ion trapping can be reduced by clearing electrodes, a beam-free gap (or gaps), and beam shaking. Tune shifts, coherent instabilities and other effects … more
Date: August 4, 2004
Creator: Neuffer, David V.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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The equivalence of inverse Compton scattering and the undulator concept

Description: Inverse Compton scattering is a method to produce very high frequency photon beam. However, the production mechanism can also be viewed as a undulator emission. This is because the electron sees electric and magnetic fields of the incident laser beam and is driven into transverse oscillatory motion in exactly the same way when the electron passes through a undulator consisting of alternating magnetic field. This note gives a detailed examination of the similarity about the two views. Equivalent… more
Date: August 1, 2009
Creator: Ng, K. Y,
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Betatron tune shifts and Laslett image coefficients

Description: The complicated expressions of betatron tune shifts in terms of Laslett image coefficients are explained. The expressions of image coefficients for a centered or off-centered beam inside an elliptical or rectangular vacuum chamber are gathered. Typos in earlier literature are corrected.
Date: July 20, 2001
Creator: Ng, K. Y.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Comments on Landau damping due to synchrotron frequency spread

Description: An inductive/space-charge impedance shifts the synchrotron frequency downwards above/below transition, but it is often said that the coherent synchrotron frequency of the bunch is not shifted in the rigid-dipole mode. On the other hand, the incoherent synchrotron frequency due to the sinusoidal rf always spreads in the downward direction. This spread will therefore not be able to cover the coherent synchrotron frequency, implying that there will not be any Landau damping no matter how large the… more
Date: January 1, 2005
Creator: Ng, K. Y.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Coupled-bunch instabilities of the Tevatron at Run II

Description: The longitudinal and transverse coupled-bunch instabilities of the Tevatron at Run II are addressed in two scenarios. The first scenario corresponds to the present Run II condition: 36 proton bunches on 36 antiprotons. Each proton bunch contains 1.7 x 10{sup 11} particles with a rms bunch length 60 cm. The second scenario is for the future upgrade when there are 108 proton bunches colliding with 108 antiproton bunches. Each proton bunch contains 2.7 x 10{sup 11} particles with a rms bunch lengt… more
Date: March 6, 2003
Creator: Ng, K. Y.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Distribution of incoherent space - Charge tune shift of a bi-Gaussian beam

Description: The incoherent space-charge self-force tune shift of a bi-Gaussian coasting beam is revisited. The distribution density of the incoherent horizontal or vertical space-charge tune shift is computed numerically using a statistical method. Analytic approach has also been made with approximation. The results show a broad peak centered about 0.633 with a rms spread 0.168 of the linear space-charge tune shift.
Date: April 1, 2004
Creator: Ng, K. Y.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Distribution of incoherent space-charge tune shift of a bigaussian beam

Description: The incoherent space-charge self-force tune shift of a bi-Gaussian coasting beam is revisited. The distribution density of the incoherent horizontal or vertical space-charge tune shift is computed numerically using a statistical method. Analytic approach has also been made with approximation. The results show a broad peak centered about 0.633 with a rms spread 0.168 of the linear space-charge tune shift.
Date: April 1, 2004
Creator: Ng, K. Y.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Electron cloud and space charge effects in the Fermilab Booster

Description: The stable region of the Fermilab Booster beam in the complex coherent-tune-shift plane appears to have been shifted far away from the origin by its intense space charge making Landau damping appear impossible. Simulations reveal a substantial buildup of electron cloud in the whole Booster ramping cycle, both inside the unshielded combined-function magnets and the beam pipes joining the magnets, whenever the secondary-emission yield (SEY) is larger than {approx}1.6. The implication of the elect… more
Date: June 1, 2007
Creator: Ng, K. Y.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Electron cloud in the Fermilab Booster

Description: Simulations of the Fermilab Booster reveal a substantial electron-cloud buildup both inside the unshielded combined-function magnets and the beam pipes joining the magnets, when the second-emission yield (SEY) is larger than {approx}1.6. The implication of the electron-cloud effects on space charge and collective instabilities of the beam is discussed.
Date: June 1, 2007
Creator: Ng, K. Y.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Impedances of Tevatron separators

Description: The impedances of the Tevatron separators are revisited and are found to be negligibly small in the few hundred MHz region, except for resonances at 22.5 MHz. The later are contributions from the power cables which may drive head-tail instabilities if the bunch is long enough.
Date: May 28, 2003
Creator: Ng, K. Y.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Space charge and beam stability issues of the Fermilab proton driver in Phase I

Description: Issues concerning beam stability of the proposed Fermilab Proton Driver are studied in its Phase I. Although the betatron tune shifts are dominated by space charge, these shifts are less than 0.25 and will therefore not drive the symmetric and antisymmetric modes of the beam envelope into instability. The longitudinal space charge force is large and inductive inserts may be needed to compensate for the distortion of the rf potential. Although the longitudinal impedance is space charge dominated… more
Date: August 24, 2001
Creator: Ng, K. Y.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Stability of barrier buckets with short barrier separations

Description: A barrier bucket with very short or zero rf-barrier separation (relative to the barrier widths) has its synchrotron tune decreasing from a very large value towards the bucket boundary. As a result, chaotic region may form near the bucket center and extends outward under increasing modulation of rf voltage and/or rf phase. Application is made to those barrier buckets used in momentum mining at the Fermilab Recycler Ring.
Date: April 1, 2005
Creator: Ng, K. Y.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Stability of barrier buckets with zero RF-barrier separations

Description: A barrier bucket with very small separation between the rf barriers (relative to the barrier widths) or even zero separation has its synchrotron tune decreasing rather slowly from a large value towards the boundary of the bucket. As a result, large area at the bucket edges can become unstable under the modulation of rf voltage and/or rf phase. In addition, chaotic regions may form near the bucket center and extend outward under increasing modulation. Application is made to those barrier buckets… more
Date: March 1, 2005
Creator: Ng, K. Y.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Transverse instability at the recycler ring

Description: Sporadic transverse instabilities have been observed at the Fermilab Recycler Ring leading to increase in transverse emittances and beam loss. The driving source of these instabilities has been attributed to the resistive-wall impedance with space-charge playing an important role in suppressing Landau damping. Growth rates of the instabilities are computed. Remaining problems are discussed.
Date: October 1, 2004
Creator: Ng, K. Y.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Analysis of emittance growth in the Fermilab Booster

Description: Multi-particle simulations are performed to study emittance growth in the Fermilab Booster. Analysis shows that the source of vertical emittance growth comes mostly from random errors in skew quadrupoles in the presence of a strong transverse space-charge force. [1] Random errors in dipole rolls and the Montague resonance do contribute but to lesser extent. The effect of random errors in the quadrupoles is small because the betatron envelope tunes are reasonably far away from the half-integer s… more
Date: May 1, 2006
Creator: Ng, K. Y.; Huang, X. & Lee, S. Y.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Comments on optical stochastic cooling

Description: An important necessary condition for transverse phase space damping in the optical stochastic cooling with transit-time method is derived. The longitudinal and transverse damping dynamics for the optical stochastic cooling is studied. The authors also obtain an optimal laser focusing condition for laser-beam interaction in the correction undulator. The amplification factor and the output peak power of the laser amplifier are found to differ substantially from earlier publications. The required … more
Date: October 8, 2002
Creator: Ng, K. Y.; Lee, S. Y. & Zhang, Y. K.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Emittance growths in resonance crossing at FFAGs

Description: Scaling laws of the emittance growth for a beam crossing the 6th-order systematic space-charge resonances and the random-octupole driven 4th-order resonance are obtained by numerical multi-particle simulations. These laws can be important in setting the minimum acceleration rate and maximum tolerable resonance strength for the design of non-scaling fixed-field alternating gradient accelerators.
Date: October 1, 2007
Creator: Ng, K. Y.; Pang, X.; Wang, F.; Wang, X. & Lee, S. Y.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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