Experimental evidence of space charge driven resonances in high intensity linear accelerators

Jeon, D.

doi:10.1103/physrevaccelbeams.19.010101

Cited by 15 publications

(5 citation statements)

References 18 publications

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“…These studies can be extended to higher order structure resonances with phase advance around 60 • (3rd order structure resonance) or 120 • (6th order structure resonance) [23,24]. It is noteworthy that the fact that lower order coherent structure resonances are components of higher order structure resonances is the key to understand the results obtained from simulation and experiment reported in Ref [25,26].…”

Section: Introductionmentioning

confidence: 89%

“…One example is the 3rd/6th mixed structure resonance around 60 • phase advance 3 × 60 • = 180 • , 6 × 60 • = 360 • [16] and 120 • phase advance 3 × 120 • = 360 • , 6 × 120 • = 720 • [19,23]. The understanding of the coherent and incoherent resonance in space charge physics leads us to a better understanding of recent experimental results [25,26,39]. However, despite the progress in interpretation of the nonlinear phenomena, there is still a large gap between analytical prediction, numerical simulation, and the experiment result.…”

Section: Summary and Acknowledgementsmentioning

confidence: 99%

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Structure resonance crossing in space charge dominated beams

Liu

Qin

2019

Physics of Plasmas

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As an extension of previous theoretical study on the coherent structure resonance due to space charge effects [Chao Li and R. A. Jameson, Phys. Rev. Accel. Beams 21, 024204, 2018], this paper aims to demonstrate how the beam, as a whole, is spontaneously affected when the predicted mixed coherent 2nd/4th order structure resonance stop band around 90 • phase advance is crossed. The beam characteristics during the structure resonance crossing, such as the rms emittance growth and the appearance of 2-fold/4-fold structure in phase space, are well explained by the mixture characteristic of different orders of structure resonance. The related "attracting" and "repulsive" effects in the structure resonance stop band from below and above crossing are considered as a natural beam reaction to the coherent structure resonance that the beam spontaneously moves to a structure resonance free region then the space charge takes a weaker importance. In the PIC simulation, it is found that the emittance growth is positively related to the time that the beam spends inside the structure resonance stop band. As a potential candidate mechanism, the incoherent particle-core resonance also has been checked. It is found that this incoherent resonance has basic difficulties in explaining the results obtained from the self-consistent PIC simulation. The incoherent particle-core resonance might lead to phase space distortion, emittance growth, or beam halo formation only on a long-time scale. This clarity of the discrepancies between coherent and incoherent resonance mechanisms will lead to a better understanding of the numerical study and experimental researches obtained recently. In addition, similar understanding can be extended to the study of higher order structure resonance.

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Section: Introductionmentioning

confidence: 89%

Section: Summary and Acknowledgementsmentioning

confidence: 99%

Structure resonance crossing in space charge dominated beams

Liu

Qin

2019

Physics of Plasmas

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“…This experiment left open questions of interpretation, which were addressed in recent theoretical research clarifying the joint appearance of second order parametric (envelope instability) and fourth order single particle resonant space charge effects [9]. Additional studies followed indicating that the subject remains of interest, but also that full agreement between different authors on the interpretation of the phenomena is still pending [10,11].…”

Section: Introductionmentioning

confidence: 99%

Parametric instabilities in 3D periodically focused beams with space charge

Hofmann

2017

Phys. Rev. Accel. Beams

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Parametric resonances of beam eigenmodes with a periodic focusing system under the effect of space charge-also called structural instabilities-are the collective counterparts to parametric resonances of single particles or of mechanical systems. Their common feature is that an exponential instability is driven by a temporal modulation of a system parameter. Thus, they are complementary to the more commonly considered space charge single particle resonances, where space charge pseudo-multipole terms are assumed to exist already at finite level in the initial distribution. This article elaborates on the characteristics of such parametric instabilities in 3D bunched beams-as typical in linear accelerators-for modes of second (envelope), third and fourth order, including the transverse coupled "sum envelope instabilities" recently discovered for 2D beams. Noteworthy results are the finding that parametric resonances can be in competition with single particle resonances of twice the order due to overlapping stopbands; furthermore the surprisingly good applicability of the stopband positions and widths obtained from previously published 2D linearised Vlasov stability theory to the 3D non-Kapchinskij-Vladimirskij particle-in-cell code studies presented here.

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“…11(c)]. The resonance at 90°can be identified as the fourth-order resonance 4σ ¼ 360, where σ is the depressed phase advance of the particle, or equivalently as 4Q ¼ 1 [38][39][40], where Q is the fractional tune of the particle. Similarly, the resonance at 60°can be identified as 6Q ¼ 1 [41].…”

Section: Beam Transport Through the Rfqmentioning

confidence: 99%

Higher order mode beams mitigate halos in high intensity proton linacs

Pathak

Krishnagopal

2017

Phys. Rev. Accel. Beams

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High intensity proton linacs (HIPLs) for applications such as Accelerator Driven Reactor Systems (ADRS) have serious beam dynamics issues related to beam halo formation. This can lead to particle loss and radioactivation of the surroundings which consequently limit the beam current. Beam halos are largely driven by the nonlinear space-charge force of the beam, which depends strongly on the beam distribution and also on the initial beam mismatch. We propose here the use of a higher order mode beam (HOMB), that has a weaker nonlinear force, to mitigate beam halos. We first show how the nonlinear space-charge force can itself be exploited in the presence of nonlinear solenoid fields, to produce a HOMB in the low energy beam transport (LEBT) line. We then study the transport of such a beam through a radio frequency quadrupole (RFQ), and show that the HOMB has a significant advantage in terms of emittance blow-up, halo formation and beam loss, over a Gaussian beam, even with a finite initial mismatch. For example, for the transport of a 30 mA beam through the RFQ, with an initial beam mismatch of 45%, the Gaussian beam sees an emittance blow-up of 125%, while the HOMB sees a blow-up of only 35% (relative to the initial emittance of 0.2π mm-mrad). Similarly, the beam halo parameter and beam loss are 0.95 and 25% respectively for a Gaussian beam, but only 0.35 and 15% for a HOMB. The beam dynamics of the HOMB agrees quite well with the particle-core model, because of the more linear space-charge force, while for the Gaussian beam there are additional particle loss mechanisms arising from nonlinear resonances. Therefore, the HOMB suppresses emittance blow-up and halo formation, and can make high current ADRS systems more viable.

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Experimental evidence of space charge driven resonances in high intensity linear accelerators

Cited by 15 publications

References 18 publications

Structure resonance crossing in space charge dominated beams

Structure resonance crossing in space charge dominated beams

Parametric instabilities in 3D periodically focused beams with space charge

Higher order mode beams mitigate halos in high intensity proton linacs

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