Mechanisms of halo formation

Fedotov, A. V.

doi:10.1063/1.1638311

Cited by 17 publications

(21 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Several mechanisms can lead to the formation of a beam halo including machine mismatch, beam dispersion and scattering effects [1]. Measurements done in proton machines [2,3] confirm, to a large extent, the validity of the particle core model [4,5,6].…”

Section: Introductionmentioning

confidence: 85%

Alternative techniques for beam halo measurements

Welsch¹,

Bravin²,

Burel³

et al. 2006

Meas. Sci. Technol.

View full text Add to dashboard Cite

In future high intensity, high energy accelerators it must be ensured that particle losses are minimized, as activation of the vacuum chambers or other components makes maintenance and upgrade work time consuming and costly. It is imperative to have a clear understanding of the mechanisms that can lead to halo formation and to have the possibility to test available theoretical models with an adequate experimental setup.Measurements based on optical transition radiation (OTR) are a well-established technique for measurements of the transverse beam profile. However, in order to be suitable for halo measurements as well, the dynamic range of the final image acquisition system needs to be high, being able to cover at least five orders of magnitude in intensity changes.Here, the performance of a standard acquisition system as it is used in the CLIC test facility (CTF3) is compared to a step-by-step measurement with a small movable photo multiplier tube and an innovative camera system based on charge injection device (CID) technology. Special emphasis is given on a description of the characteristics of the latter system. In future high intensity, high energy accelerators it must be ensured that particle losses are minimized, as activation of the vacuum chambers or other components makes maintenance and upgrade work time consuming and costly. It is imperative to have a clear understanding of the mechanisms that can lead to halo formation and to have the possibility to test available theoretical models with an adequate experimental setup. Published in MEASUREMENT SCIENCEMeasurements based on optical transition radiation (OTR) are a well-established technique for measurements of the transverse beam profile. However, in order to be suitable for halo measurements as well, the dynamic range of the final image acquisition system needs to be high, being able to cover at least five orders of magnitude in intensity changes.Here, the performance of a standard acquisition system as it is used in the CLIC test facility (CTF3) is compared to a step-by-step measurement with a small movable photo multiplier tube and an innovative camera system based on charge injection device (CID) technology. Special emphasis is given on a description of the characteristics of the latter system. INTRODUCTIONFor a future linear collider, it will be of central importance to have a detailed understanding of beam halo formation, since beam losses in high intensity machines will cause severe activation of the surrounding vacuum chambers and thus complicate maintenance and increase costs. Several mechanisms can lead to the formation of a beam halo including machine mismatch, beam dispersion and scattering effects [1]. Measurements done in proton machines [2,3] confirm, to a large extent, the validity of the particle core model [4,5,6].On the other hand, limited experience on halo formation in intense electron beams is available on the international scene, and besides the clear need for corresponding models, beam diagnostic techniques need to be de...

show abstract

Section: Introductionmentioning

confidence: 85%

Alternative techniques for beam halo measurements

Welsch¹,

Bravin²,

Burel³

et al. 2006

Meas. Sci. Technol.

View full text Add to dashboard Cite

show abstract

“…(6.23,6.20). This is also confirmed by space-charge simulations [2]. A question may arise regarding the effect of the coupling Montague resonance 2Q x ; 2Q y = 0 : indeed, for certain type of beam distributions (as the square shaped beam produced by anti-correlated painting [14]), this resonance can be a problem.…”

Section: Resultsmentioning

confidence: 66%

“…The second question with respect to the choice of (6.23,6.20) as the SNS ring w.p., comes from the possibility of crossing the integer resonances (Q x Q y = 6 ). Taking into account that beam loss is enhanced when crossing the resonance in the coherent sense (see [2] for details), the succesfull 2MW beam operation with this w.p. seams feasible.…”

Section: Resultsmentioning

confidence: 99%

“…the excitation of the structural coupling resonance (1 1), due to quadrupole fringe fields and/or skew quadrupole errors. This resonance in combination with the space-charge can enhance particle loss to a level as high as 10% [2]. In order to compare the performance of each w.p., we use the tune diffusion indicator, which is computed by the average of the tune differences used for the construction of the diffusion maps and normalized by the initial emittances, for all the integrated orbits [6].…”

Section: Working Point Comparisonmentioning

confidence: 99%

“…The ring lattice has a 4-fold symmetry and consists of FODO arcs and quadrupole doublet straight sections [1]. The beam dynamics is mostly dominated by multi-particle effects such as space-charge [2] and other collective instabilities (e.g. electron-proton [3]), which are mostly intensity dependent.…”

Section: The Sns Accumulator Ringmentioning

confidence: 99%

See 2 more Smart Citations

Frequency and diffusion maps for the SNS ring

Papaphilippou

PACS2001. Proceedings of the 2001 Particle Accelerator Conference (Cat. No.01CH37268)

View full text Add to dashboard Cite

Using a single particle dynamics approach, the major magnetic non-linearities of the SNS accumulator ring are studied. Frequency maps are employed in order to display the global dynamics of the beam, for several working points. By means of diffusion maps the major resonances are explored and their bandwidth is estimated. The global tune diffusion coefficient is finally used to compare and choose the best working point. THE SNS ACCUMULATOR RINGThe SNS ring is designed to accumulate a high-intensity beam with a beam power of up to 2MW. The ring lattice has a 4-fold symmetry and consists of FODO arcs and quadrupole doublet straight sections [1]. The beam dynamics is mostly dominated by multi-particle effects such as space-charge [2] and other collective instabilities (e.g. electron-proton [3]), which are mostly intensity dependent. On the other hand, the strict fractional beam loss, dictated by the permissible radiation level for hands-on maintenance [4], imposes a very good control and correction of all non-linear effects. This includes the ones coming from magnet imperfections, the impact of which is amplified due to the large beam emittance. Indeed, in the early commissioning stages where the beam intensity will be low, the dominant effects will be of a single-particle nature. One of them is the chromaticity: in order to reduce the effect of collective instabilities the longitudinal phase space is painted to a large momentum spread of p = p= 0 :7%, with the bucket size set at p = p= 1 % and the momentum aperture at p = p = 2%. Taken the bucket size as the reference, the chromatic tune-shift is around 0.08, which is close to the space charge tune-shift of 0:15 ; 0:20. Another key issue for the performance of the SNS ring is the proper working point (w.p.) choice. After an extensive tuning campaign [5], we have concentrated on 4 potential w.p. candidates, due to optical matching and aperture considerations. Two of them have a tune-split of more than half a unit, in order to avoid strong coupling from spacecharge and/or magnet errors: (Q x Q y ) = (6:3 5:8), the old "nominal" w.p. for which most of the past studies have order resonances and (Q x Q y ) = (6:4 6:3). In order to choose the best w.p., with respect to the non-linear particle Work performed under the auspices of the US Department of Energy y papap@bnl.gov behavior, we use Laskar's frequency map analysis [6]. In brief, the frequency map is a detailed tune footprint. Due to the very high precision of the tune determination through a refined Fourier analysis using the NAFF algorithm, all the excited resonances appear as line distortions of the footprint. The tune variation along the particle trajectory can give a good estimation of the diffusion rate, which can then be mapped to the real space, for each particle initial condition. Finally, the average tune diffusion coefficient can be used as a global quality factor for comparison between the dynamics of the different designs. WORKING POINT COMPARISONWe choose a standard SNS ring lattice matched for...

show abstract