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Fast Correction Optics to Reduce Chromatic Aberrations in Longitudinally Compressed Ion Beams

Description: Longitudinally compressed ion beam pulses are currently employed in ion-beam based warm dense matter studies [1]. Compression arises from an imposed time-dependent longitudinal velocity ramp followed by drift in a neutralized channel. Chromatic aberrations in the final focusing system arising from this chirp increase the attainable beam spot and reduce the effective fluence on target. We report recent work on fast correction optics that remove the time-dependent beam envelope divergence and minimizes the beam spot on target. We present models of the optical element design and predicted ion beam fluence.
Date: April 30, 2009
Creator: Lidia, S.M.; Lee, E.P.; Ogata, D.; Seidl, P.A.; Waldron, W.L. & Lund, S.M.
Partner: UNT Libraries Government Documents Department

Momentum errors in an RF separated beam

Description: The purity of an RF separated beam is affected by the difference in mass of the particle types and the momentum bite of the beam. The resulting time-of-flight difference between different types allows separation to occur; the finite momentum bite results in chromatic aberration. Both these features also give rise to a particle type dependent velocity bite, which must also be taken into account. This memo demonstrates a generalizable method for calculating the effect.
Date: September 19, 2002
Creator: Kobilarcik, T.
Partner: UNT Libraries Government Documents Department

Chromaticity control in the Fermilab Main Injector

Description: Chromaticity control in the Fermilab Main Injector will be important both in accelerating protons and antiprotons from 8 GeV to 150 GeV (or 120 GeV) and in decelerating recycled 150 GeV antiprotons to 8 GeV for storage in the Recycler Ring. The Main Injector has two families of sextupoles to control the chromaticity. In addition to the natural chromaticity, they must correct for sextupole fields from ramp-rate-dependent eddy currents in the dipole beampipes and current-dependent sextupole fields in the dipole magnets. The horizontal sextupole family is required to operate in a bipolar mode below the transition energy of 20 GeV. We describe methods used to control chromaticities in the Fermilab Main Injector. Emphasis is given to the software implementation of the operator interface to the front-end ramp controllers. Results of chromaticity measurements and their comparison with the design model will be presented.
Date: April 16, 1999
Creator: al., G. Wu et
Partner: UNT Libraries Government Documents Department

Chromatic Correction in the CEBAF Beam Transport System

Description: The CEBAF accelerator beam transport system contains 104 sextupoles to correct chromatic aberrations. We describe the layout of these elements and discuss schemes for suppressing chromatic errors. Analytic results for the required sextupole strengths are given and computations of chromatic aberrations are documented. Numerical results using two correction methods are provided.
Date: May 1, 1991
Creator: Douglas, David
Partner: UNT Libraries Government Documents Department

Notes on lie algebraic analysis of achromats

Description: Normal form technique is a powerful method to analyze the achromat problem. Assume the one cell map M{sub cell} = ARe{sup :h{sub 3}}:{sub e}{sup :h{sub 4}}: A{sup {minus}1}, where h{sub 3},h{sub 4} are the normal forms of the generators of the unit cell map, and A is the nonlinear transformation that brings M{sub cell} into its normal form; then the map of the whole system is M{sub N} = M{sub cell}{sup N} = AR{sup N} A{sup {minus}1} = I, provided that we can set e{sup :h{sub 3}}:, e{sup :h{sub 4}}, and R{sup N} to the identity (or only {delta} dependent) maps. Therefore, the conditions to form an achromat are h{sub 3} and h{sub 4} equal to zero (or {delta} dependent only) and the total linear map is identity. In this report, we will apply these conditions to a FODO array (a simple model system) to make it an achromat. We will start from Hamiltonians and work all the way up to obtain the analytical expressions of the required sextupole and octupole strengths.
Date: January 1, 1995
Creator: Wang, Chunxi & Chao, A.
Partner: UNT Libraries Government Documents Department


Description: Beam stability up the ramp requires the appropriate sign and magnitude of the chromaticity. We developed a way to measure the chromaticity using the PLL (Phase Locked Loop) tune-meter. Since, the accuracy of the PLL tune-meter with properly adjusted loop gain is better than {approx} 0.0001 in tune units, the radial loop needs only be changed by a small amount of 0.2mm at a 1Hz rate. Thus, we can achieve fast chromaticity measurements in 1 sec. Except during the very beginning of the ramp where there are snapback effects and the gamma changes very rapidly, we can have good chromaticcity measurements along the ramp. This leads to the possibility of correcting the chromaticity during the ramp using a feedback system.
Date: June 2, 2002
Partner: UNT Libraries Government Documents Department

Compendation of SSC lattice optics in the presence of dipole field errors: Report of the Correction Element Working Group

Description: The assignment of the Correction Element Working Group (CEWG) is to advance the designs of various candidate correction schemes to a point where they can be compared and distilled down to a single plan. Choosing among, the options often involves consideration of incommensurate factors such as cost, practicality, and theoretical performance. Except for minor issues, the CEWG purpose is to gather and array the facts in a form from which these decisions can be rationally made, but not to make the decisions. The present report analyses various schemes for compensating nonlinear multipole errors in the main arc dipoles of the Superconducting Super Collider. Emphasis is on comparing lumped and distributed compensation, on minimizing the total number of correction elements, and on reducing the sensitivity to closed-orbit errors.
Date: February 1, 1989
Creator: Bintinger, D.; Chao, A. & Forest, E.
Partner: UNT Libraries Government Documents Department

Skew chromaticity in large accelerators

Description: The 2-D ``skew chromaticity`` vector k is introduced when the standard on-momentum description of linear coupling is extended to include off-momentum particles. A lattice that is well decoupled on-momentum may be badly decoupled off-momentum, inside the natural momentum spread of the beam. There are two general areas of concern: (1) the free space in the tune plane is decreased; (2) collective phenomena may be destabilized. Two strong new criteria for head-tail stability in the presence of off-momentum coupling are derived, which are consistent with experimental and operational observations at the Tevatron, and with tracking data from RHIC.
Date: May 1, 1995
Creator: Peggs, S. & Dell, G.F.
Partner: UNT Libraries Government Documents Department

Correct chromaticities of circular accelerators without sextupoles

Description: A new method of correcting chromaticities of circular accelerators is introduced. Instead of using two families of sextupoles, as the standard way to correct chromaticities, two pairs of TM(210) mode RF cavities are used. The betatron phase advances (both horizontal and vertical) between the two cavities are set to be a multiple of it, and a proper momentum compaction is required. With this method, sextupole nonlinear terms are eliminated. There are octupole terms left by this method. However, they are explicit and should be easy to compensate. An example lattice demonstrates the method. The power required for the RF cavities is estimated.
Date: June 1, 1996
Creator: Chen, Tong
Partner: UNT Libraries Government Documents Department

Tune modulation due to synchrotron oscillations and chromaticity, and the dynamic aperture

Description: A tracking study was done of the effects of a tune modulations, due to synchrotron oscillations and the tune dependence on momentum (chromaticity), on the dynamic aperture. The studies were done using several RHIC lattices and tracking runs of about 1 {times} 10{sup 6} turns. The dynamic aperture was found to decrease roughly linearly with the amplitude of the tune modulation. Lower order non-linear resonances, like the 1/3 and 1/4 resonance are not crossed because of the tune modulation. Three different cases were studied, corresponding to RHIC lattices with different {beta}*, and with different synchrotron oscillation amplitudes. In each case, the tune modulation amplitude was varied by changing the chromaticity. In each case, roughly the same result, was found. The result found here for the effect of a tune modulation due to chromaticity may be compared with the result found for the effect of a tune modulation due to a gradient ripple in the quadrupoles. The effect of a tune modulation due to a gradient ripple appears to be about 4 times stronger than the effect of a tune modulation due to chromaticity and synchrotron oscillations.
Date: May 1, 1995
Creator: Parzen, G.
Partner: UNT Libraries Government Documents Department

Efficient broadband second-harmonic generation by dispersive achromatic nonlinear conversion using only prisms

Description: Using a lossless dispersive apparatus consisting of six prisms, optimized to match a second-harmonic crystal phase-matching angle vs. wavelength to second order, we efficiently doubled tunable fundamental light near 660 nm over a range of 80 nm using a 4-mm-long type-I {beta}-Barium Borate (BBO) crystal. Another lossless set of six prisms after the crystal realigned the propagation directions of the various second-harmonic frequencies to be collinear to within 1/4 spot diameter in position and 200 {mu}rad in angle. The measured conversion efficiency of a 40-mJ, 5-ns fundamental pulse was 10%.
Date: December 1, 1997
Creator: Richman, B.A.; Bisson, S.E. & Trebino, R.
Partner: UNT Libraries Government Documents Department


Description: The two RHIC rings are equipped with superconducting dipole magnets. At injection, induced persistent currents in these magnets lead to a sextupole component. As the persistent currents decay with time, the horizontal and vertical chromaticities change. From magnet measurements of persistent current decays, chromaticity changes in the machine are estimated and compared with chromaticity measurements.
Date: June 18, 2001
Partner: UNT Libraries Government Documents Department

Limitations of interaction-point spot-size tuning at the SLC

Description: At the Stanford Linear Collider (SLC), the interaction-point spot size is minimized by repeatedly correcting, for both beams, various low-order optical aberrations, such as dispersion, waist position or coupling. These corrections are performed about every 8 hours, by minimizing the IP spot size while exciting different orthogonal combinations of final-focus magnets. The spot size itself is determined by measuring the beam deflection angle as a function of the beam-beam separation. Additional information is derived from the energy loss due to beamstrahlung and from luminosity-related signals. In the 1996 SLC run, the typical corrections were so large as to imply a 20-40% average luminosity loss due to residual uncompensated or fluctuating tunable aberrations. In this paper, the authors explore the origin of these large tuning corrections and study possible mitigations for the next SLC run.
Date: May 1, 1997
Creator: Emma, P.; Hendrickson, L.J.; Zimmermann, F. & Raimondi, P.
Partner: UNT Libraries Government Documents Department

Emittance growth due to decoherence and wakefields

Description: Suddenly induced coherent centroid oscillations about the closed orbit will decohere due to nonlinearities in the magnetic optics - at the expense of a stored beam`s emittance. Collective effects mediated by the vacuum chamber wakefield and dependent on the beam current, can however damp the coherent oscillations-ameliorating the emittance growth. Closed form expressions for both the beam centroid and the beam size are obtained in the absence of collective effects. Simultaneous turn-by-turn measurements of beam centroid and size in the SLC damping ring are presented, and the importance and intricacy of collective effects is discussed.
Date: May 1, 1995
Creator: Minty, M.G.; Chao, A.W. & Spence, W.L.
Partner: UNT Libraries Government Documents Department

Skew chromaticity

Description: The on-momentum description of linear coupling between horizontal and vertical betatron motion is extended to include off-momentum particles, introducing a vector quantity called the ``skew chromaticity``. This vector tends to be long in large superconducting storage rings, where it restricts the available working space in the tune plane, and modifies collective effect stability criteria. Skew chromaticity measurements at the Cornell Electron Storage Ring (CESR) and at the Fermilab Tevatron are reported, as well as tracking results from the Relativistic Heavy Ion Collider (RHIC). The observation of anomalous head-tail beam Iowa new the tune diagonal in the Tevatron are explained in terms of the extended theory, including modified criteria for headtail stability. These results are confirmed in head-tail simulations. Sources of skew chromaticity are investigated.
Date: December 31, 1994
Creator: Peggs, S. & Dell, G.F.
Partner: UNT Libraries Government Documents Department

Retuning the APS storage ring for better chromaticity correction.

Description: When the APS storage ring was retuned to provide smaller {beta}{sub y} values in the insertion straight sections, it was necessary to increase the vertical tune by at least two units. Since the design values for the horizontal and vertical tunes are 35.22 and 16.30, respectively, this put the tunes dangerously close to the sextupole 2v{sub y}-v{sub x} coupling resonance. The large injection horizontal oscillations could couple to the vertical plane and exceed the 5-mm vertical apertures that exist in some of the insertion straight sections. To avoid this resonance, the vertical tune was raised beyond the resonance to 19.30. The result was a reduction in the ability of the chromaticity sextuples to correct the chromaticity. Recent investigation has shown that the chromaticity correction capability of the sextuples can be greatly increased by a modest increase in the horizontal tune. Increasing the horizontal tune by one unit and reducing the vertical tune by three units produces a lattice with better chromaticity control while maintaining an acceptable dynamic aperture.
Date: September 11, 1999
Creator: Chae, Y.-C. & Crosbie, E.A.
Partner: UNT Libraries Government Documents Department


Description: The accumulator ring of the Spallation Neutron Source (SNS) will accumulate a high-intensity beam of 2.1 x 10{sup 14} protons in a single bunch with large transverse emittance of 160{pi} mm mrad at 95% beam intensity and energies of 1 to 1.3 GeV. In order to keep low beam losses ({approx} 10{sup {minus}4}) in the ring, it is necessary to control the chromaticity and to minimize the dependence of the optical properties on the momentum spread. In this paper, we describe the procedure to accomplish this by using chromaticity sextupoles. We finally discuss the impact of these sextupoles in non-linear dynamics.
Date: June 30, 2000
Partner: UNT Libraries Government Documents Department

The main injector chromaticity correction sextupole magnets: Measurements and operating schemes

Description: The Fermilab Main Injector (FMI) is a high intensity proton synchrotron which will be used to accelerate protons and antiprotons from 8.9 GeV/c to 150 GeV/c. The natural chromaticities of the machine for the horizontal and the vertical Planes are {minus}33.6 and {minus}33.9 respectively. The {Delta}p/p of the beam at injection is about 0.002. The chromaticity requirements of the FMI, are primarily decided by the {Delta}p/p = 0.002 of the beam at injection. This limits the final chromaticity of the FMI to be {plus_minus}5 units. To correct the chromaticity in the FMI two families of sextupole magnets will be installed in the lattice, one for each plane. A sextupole magnet suitable for the FMI needs has been designed and a number of them are being built. New chromaticity compensation schemes have been worked out in the light of recently proposed faster acceleration ramps. On an R/D sextupole magnet the low current measurements have been carried out to determine the electrical properties. Also, using a Morgan coil, measurements have been performed to determine the higher ordered multipole components up to 18-poles. An overview of these result are presented here.
Date: May 1, 1995
Creator: Bhat, C.M.; Bogacz, A.; Brown, B.C.; Harding, D.J.; Fang, S.J.; Martin, P.S. et al.
Partner: UNT Libraries Government Documents Department

Recent Progress on Design Studies of High-Luminosity Ring-Ring Electron-Ion Collider at CEBAF

Description: The conceptual design of a ring-ring electron-ion collider based on CEBAF has been continuously optimized to cover a wide center-of-mass energy region and to achieve high luminosity and polarization to support next generation nuclear science programs. Here, we summarize the recent design improvements and R&D progress on interaction region optics with chromatic aberration compensation, matching and tracking of electron polarization in the Figure-8 ring, beam-beam simulations and ion beam cooling studies.
Date: May 1, 2009
Creator: Zhang, Y.; Bruell, A.; Chevtsov, P.; Derbenev, Y. S.; Ent, R.; Krafft, G. A. et al.
Partner: UNT Libraries Government Documents Department

Three-Dimensional Aberration-Corrected Scanning Transmission Electron Microscopy for Biology

Description: Recent instrumental developments have enabled greatly improved resolution of scanning transmission electron microscopes (STEM) through aberration correction. An additional and previously unanticipated advantage of aberration correction is the greatly improved depth sensitivity that has led to the reconstruction of a three-dimensional (3D) image from a focal series. In this chapter the potential of aberration-corrected 3D STEM to provide major improvements in the imaging capabilities for biological samples will be discussed. This chapter contains a brief overview ofthe various high-resolution 3D imaging techniques, a historical perspective of the development of STEM, first estimates of the dose-limited axial and lateral resolution on biological samples and initial experiments on stained thin sections.
Date: January 1, 2007
Creator: De Jonge, Niels; Sougrat, Rachid; Pennycook, Stephen J; Peckys, Diana B & Lupini, Andrew R
Partner: UNT Libraries Government Documents Department

Localized Chromaticity Correction of Low-Beta Insertions in Storage Rings

Description: The correction of the chromaticity of low-beta insertions in the storage rings is usually made with sextupole lenses in the ring's arcs. When decreasing the beta functions at the insertion point (IP), this technique becomes fairly ineffective, since it fails to properly correct the higher order chromatic aberrations. Here we consider the approach where the chromatic effects of the quadrupole lenses generating low beta functions at the IP are corrected locally with two families of sextupoles, one family for each plane. Each family has two pairs of sextupoles which are located symmetrically on both sides of the IP. The sextupole-like aberrations of individual sextupoles are eliminated by utilizing optics forming a -I transformation between sextupoles in the pair. The optics also includes bending magnets which preserve equal dispersion functions at the two sextupoles in each pair. At sextupoles in one family, the vertical beta function is made large and the horizontal is made small. The situation is reversed in the sextupoles of the other family. The betatron phase advances from the IP to the sextupoles are chosen to eliminate a second order chromatic aberration. The application of the localized chromatic correction is demonstrated using as an example the lattice design for the Low Energy Ring of the SLAC/LBL/LLNL PEP-II B Factory.
Date: May 1, 1993
Creator: Donald, M.; Helm, R.; Moshammer, I.H.; Forest, E.; Robin, David; Zholents, A.A. et al.
Partner: UNT Libraries Government Documents Department

Estimates of energy fluence at the focal plane in beams undergoing neutralized drift compression

Description: The authors estimate the energy fluence (energy per unit area) at the focal plane of a beam undergoing neutralized drift compression and neutralized solenoidal final focus, as is being carried out in the Neutralized Drift Compression Experiment (NDCX) at LBNL. In these experiments, in order to reach high beam intensity, the beam is compressed longitudinally by ramping the beam velocity (i.e. introducing a velocity tilt) over the course of the pulse, and the beam is transversely focused in a high field solenoid just before the target. To remove the effects of space charge, the beam drifts in a plasma. The tilt introduces chromatic aberrations, with different slices of the original beam having different radii at the focal plane. The fluence can be calculated by summing the contribution from the various slices. They develop analytic formulae for the energy fluence for beams that have current profiles that are initially constant in time. They compare with envelope and particle-in-cell calculations. The expressions derived are useful for predicting how the fluence scales with accelerator and beam parameters.
Date: September 2, 2008
Creator: Barnard, J.J.; Seidl, P.A.; Coleman, J.E.; Ogata, D. & Welch, D.R.
Partner: UNT Libraries Government Documents Department

Simulation results of corkscrew motion in DARHT-II

Description: DARHT-II, the second axis of the Dual-Axis Radiographic Hydrodynamics Test Facility, is being commissioned. DARHT-II is a linear induction accelerator producing 2-microsecond electron beam pulses at 20 MeV and 2 kA. These 2-microsecond pulses will be chopped into four short pulses to produce time resolved x-ray images. Radiographic application requires the DARHT-II beam to have excellent beam quality, and it is important to study various beam effects that may cause quality degradation of a DARHT-II beam. One of the beam dynamic effects under study is 'corkscrew' motion. For corkscrew motion, the beam centroid is deflected off axis due to misalignments of the solenoid magnets. The deflection depends on the beam energy variation, which is expected to vary by {+-}0.5% during the 'flat-top' part of a beam pulse. Such chromatic aberration will result in broadening of beam spot size. In this paper, we will report simulation results of our study of corkscrew motion in DARHT-II. Sensitivities of beam spot size to various accelerator parameters and the strategy for minimizing corkscrew motion will be described. Measured magnet misalignment is used in the simulation.
Date: January 1, 2003
Creator: Chan, K. D. (Kwok-Chi D.); Ekdahl, C. A. (Carl A.); Chen, Y. J. (Yu-Jiuan) & Hughes, T. P. (Thomas P.)
Partner: UNT Libraries Government Documents Department