| 1. |
- Brunelle, Pascale, et al.
(författare)
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Application of an emittance adapter to increase photon flux density on a synchrotron radiation beam line
- 2019
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Ingår i: Physical Review Accelerators and Beams. - 2469-9888. ; 22:6
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Tidskriftsartikel (refereegranskat)abstract
- The application of the Chao-Raimondi emittance adapter to the SOLEIL storage ring is studied theoretically in terms of linear and nonlinear beam dynamics. This unique scheme recently proposed elsewhere using a pair of emittance adapters and a solenoid in between them allows a local conversion of an electron beam in a third generation light source to an ultralow emittance beam of the fourth generation. The study of potential benefits of the resultant synchrotron radiation is of crucial importance. Electron beam properties and magnetic fields inside the undulator solenoid are treated as inputs of the investigations. Characteristics of photon beams emitted by a round and small electron beam in an undulator are studied in detail on the basis of the near-field wave propagation method. The photon flux density gain, which is a figure of merit along with transverse coherence, is evaluated at the sample of two hard and soft x-ray beam lines existing at SOLEIL.
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| 2. |
- Cullinan, F. J., et al.
(författare)
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The damping of transverse coherent instabilities by harmonic cavities
- 2015
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Ingår i: 6th International Particle Accelerator Conference, IPAC 2015. - 9783954501687 ; , s. 102-105
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Konferensbidrag (refereegranskat)abstract
- At nonzero chromaticity, the threshold current due to transverse coupled bunch instabilities in an electron storage ring is defined by intrabunch head-tail motion of higher than zeroth order. Multibunch tracking simulations predict that this threshold can be increased to several times its original value through the introduction of bunch lengthening harmonic cavities. One previously suggested explanation is the narrower spectra of the elongated bunches but reliable estimates for the threshold currents are not obtainable for anything other than rigid beam motion since the usual Sacherer formalism is not directly applicable to beams in a non-harmonic potential. A new scheme has been developed in which the decay time of a higher than zeroth order transverse head-tail mode may be estimated by taking into account the synchrotron tune spread generated by the harmonic cavity potential. This scheme is presented along with the results of numerical simulations performed in order to confirm the analytical predictions and justify the assumptions made. The extension of the scheme to more complex scenarios is also discussed.
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| 3. |
- Cullinan, F. J., et al.
(författare)
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Transverse coherent instabilities in storage rings with harmonic cavities
- 2016
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Ingår i: IPAC 2016 - Proceedings of the 7th International Particle Accelerator Conference. - 9783954501472 ; , s. 1061-1064
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Konferensbidrag (refereegranskat)abstract
- Many current and future synchrotron light sources employ harmonic cavities to lengthen the electron bunches in order to reduce the emittance dilution caused by intrabeam scattering. In some cases, the harmonic cavities may be tuned to fulfill the flat potential condition. For this condition, a large increase in the threshold currents of transverse coupled-bunch instabilities has been predicted and recently, the physical content behind this stabilisation has been better understood. With this in mind, an investigation is made into the effectiveness of harmonic cavities for different machines. Frequency domain computations employing Laclare's eigenvalue method have been used to investigate the influence of several machine parameters and the results are presented.
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| 4. |
- Cullinan, F. J., et al.
(författare)
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Transverse coupled-bunch instability thresholds in the presence of a harmonic-cavity-flattened rf potential
- 2016
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Ingår i: Physical Review Special Topics - Accelerators and Beams. - 1098-4402. ; 19:12
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Tidskriftsartikel (refereegranskat)abstract
- A small vacuum chamber aperture is a present trend in the design of future synchrotron light sources. This leads to a large resistive-wall impedance that can drive coupled-bunch instabilities. Another trend is the use of passively driven cavities at a harmonic of the main radio frequency to lengthen the electron bunches in order to increase the Touschek lifetime and reduce emittance blowup due to intrabeam scattering. In some cases, the harmonic cavities may be tuned to fulfill the flat potential condition. With this condition met, it has been predicted in simulation that the threshold current for coupled-bunch resistive-wall instabilities is much higher than with no bunch lengthening at all. In this paper, the features of a bunch in the flat potential that would contribute toward this stabilization are identified and discussed. The threshold currents for these instabilities are estimated for the MAX IV 3 GeV storage ring at different values of chromaticity using macroparticle simulations in the time domain and, within the limits of the existing theory, frequency domain calculations. By comparing the results from these two methods and analyzing the spectra of the dominant head-tail modes, the impact of each of the distinguishing features of a bunch in the flat potential can be explained and quantified in terms of the change in threshold current. It is found that, above a certain chromaticity, the threshold current is determined by the radial structure of the zeroth-order head-tail mode. This happens at a lower chromaticity if the bunch length is longer.
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| 5. |
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| 6. |
- Skripka, G., et al.
(författare)
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Commissioning of the harmonic cavities in the MAX IV 3 GeV ring
- 2016
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Ingår i: IPAC 2016 - Proceedings of the 7th International Particle Accelerator Conference. - 9783954501472 ; , s. 2911-2913
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Konferensbidrag (refereegranskat)abstract
- The MAX IV 3 GeV storage ring operates with beam of high current and ultralow emittance. These beam parameters in combination with the small effective aperture enhance possible collective beam instabilities. Three passive harmonic cavities are installed to introduce bunch lengthening and tune spread, leading to decoupling of the bunch spectrum from the machine effective impedance and mitigating instabilities by Landau damping respectively. In this paper we present the first results of the commissioning of the passive third harmonic cavities in the MAX IV 3 GeV ring. The additional harmonic cavity potential significantly improved the beam lifetime. First observations of the harmonic cavity effect on the damping of collective beam instabilities are discussed.
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| 7. |
- Skripka, Galina, et al.
(författare)
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Simultaneous computation of intrabunch and interbunch collective beam motions in storage rings
- 2016
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 806, s. 221-230
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Tidskriftsartikel (refereegranskat)abstract
- We present the multibunch tracking code mbtrack developed to simulate, in 6-dimensional phase space, single- and multibunch collective instabilities driven by short- and long-range wakefields in storage rings. Multiple bunches, each composed of a large number of macroparticles, are tracked, allowing simulation of both intra- and interbunch motions. Besides analytical impedance models, the code allows employment of numerical wake potentials computed with electromagnetic (EM) field solvers. The corresponding impedances are fitted to a number of known analytical functions and the coefficients obtained in the fit are used as an input to the code. mbtrack performs a dynamic treatment of long-range resistive-wall and harmonic cavity fields, which are likely to be the two major factors impacting multibunch collective motions in many present and future ring-based light sources. Furthermore, it is capable of simulating beam-ion interactions as well as transverse bunch-by-bunch feedback. We describe the physical effects considered in the code and their implementation, which makes use of parallel processing to significantly shorten the computation time. mbtrack is benchmarked against other codes and applied to the MAX IV 3 GeV ring as an example, where the importance of the interplay of various physical effects as well as coupling among different degrees of freedom is demonstrated.
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| 8. |
- Skripka, Galina, et al.
(författare)
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Transverse Instabilities in the MAX IV 3 GeV Ring
- 2014
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Ingår i: Proceedings of IPAC2014, Dresden, Germany. - 9783954501328 ; , s. 1689-1691
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Collective effects in MAX IV 3 GeV storage ring are strongly enhanced by the combination of low emittance, high current and small effective aperture. Three passive harmonic cavities (HC) are introduced to lengthen the bunches, by which beam stabilization is anticipated via decoupling to high frequency wakes, along with Landau damping. The role of the transverse impedance budget of the MAX IV 3 GeV storage ring as a source of collective beam instabilities was determined. With the help of the macroparticle multibunch tracking code mbtrack that directly uses the former as input, we studied the influence of geometric and resistive wall impedance in both transverse planes, as well as that of chromaticity shifting. A fully dynamic treatment of the passive harmonic cavities developed for this study allowed us to evaluate their effectiveness under varying beam conditions.
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