Franchetti, G.

Sorge, S.

GSI Repository

Effect of beam loss on long-term beam survival in SIS100G. Franchetti, S. SorgeGSI, Darmstadt, GermanyWe present here results of beam loss during the injec-tion of U+28 for an improved modeling of the nonlin-ear lattice of SIS100 as previous simulations reported inRef. [1] where lacking of the effect of gradient errors.In Fig. 1a is shown for a possible model of the SIS100the resonance web, which is formed by integer, half inte-ger, third and fourth order normal and skew resonances.These resonances are found via tune scans of the short-term dynamic aperture (1000 turns). Beam survival (firstbunch) for several intensities during one second storageare shown in Fig. 1b. The maximum intensity injected isof 0.625 × 1011 ions/bunch, which creates a large tune-shift represented schematically in the picture. The spacecharge tune-spread overlaps with 4 resonances hence sev-eral macro-particles will cross one or more lattice reso-nances, therefore periodic resonance crossing will affectthe particle dynamics. The resulting first bunch survivalis distinctively intensity dependent as shown by the blackcurve (0.125 × 1011 ion/bunch) in which beam survival ismuch better with almost no beam loss (Fig. 1b). Note thatfor the maximum intensity bunches, beam loss is more than90% conflicting with the requirement of “low beam loss”needed for applying frozen model algorithms. Regardlessthe issue of self-consistency, the reduction of beam losswill certainly make the prediction with frozen algorithmsmore reliable. In Fig. 1c is shown again the working dia-gram with now the effect of an “ad hoc” activated compen-sation system, using also skew sextupoles located in the ac-tual position of those foreseen in SIS100. The correspond-ing beam survival is comforting (Fig. 1d) as the beam lossappears significantly mitigated, validating also the compu-tational algorithm for space charge. We also estimate theeffect of the self-consistency on large beam loss scenariowhere the main complexity arises from the multiple res-onance crossing. To assess the effect of large beam loss,as first approach we re-update in the algorithm only theintensity leaving the bunch sizes unchanged (hence noiseis avoided). The results are shown in Fig. 2. The twoblack curves show the beam survival for 0.250× 1011, and0.625 × 1011 ions/bunch, correspondent to the green andred curves in Fig. 1b. This improved procedure causes theblack curves of beam survival to shift upward to the corre-sponding red curves as indicated by the blue arrows. Thereason of this improved beam survival cannot be explainedeasier, but it appears that for SIS100 there is a beneficialeffect. The green curves in Fig. 2 show results from anattempt of modeling the algorithm (Markovian mappingRef. [2]) via a semi-analytic approach. These results are,however, conflicting with experimental findings in whichbeam loss (naturally self-consistent) are found larger thanthose predicted by simulations [3]. Further studies will bededicated to this topic.18.218.418.618.81918 18.2 18.4 18.6 18.8 19 01234QxQ yDA/σ0204060801000 25 50 75 100 125 150Nb = 0.125 × 1011Nb = 0.25 × 1011Nb = 0.375 × 1011Nb = 0.5 × 1011Nb = 0.625 × 1011×10 3 turns% of particles18.218.418.618.81918 18.2 18.4 18.6 18.8 19 01234QxQ yDA/σ0204060801000 25 50 75 100 125 150Nb = 0.125 × 1011Nb = 0.25 × 1011Nb = 0.375 × 1011Nb = 0.5 × 1011Nb = 0.625 × 1011×10 3 turns% of particlesc) d)a) b)Figure 1: Resonance diagram and beam survival for uncor-rected system (top). The same simulation when resonanceoverlapping the space charge tune-spread are compensated.0204060801000 25 50 75 100 125 150turns x 10 3I / I 0I / I 0Figure 2: Comparison of the frozen space charge improvedsimulations (red curves) with a Markovian mapping ap-proach (green curves). In black are shown the frozen spacecharge simulation results.References[1] G. Franchetti and S. Sorge, IPAC 2011, MOPS002. p. 589.[2] G. Franchetti, Proc. HB2012, to be published on JACoW.[3] G. Franchetti et al., Phys. Rev. ST Accel. Beams 13, 114203(2010); G. Franchetti et el., Phys. Rev. ST Accel. Beams 6,124201 (2003).GSI SCIENTIFIC REPORT 2012 PHN-FAIR-09FAIR@GSI 233

Effect of Beam Loss on Long-Term Beam Survival in SIS100

http://repository.gsi.de/record/52132/files/PHN-FAIR-09.pdf

Effect of Beam Loss on Long-Term Beam Survival in SIS100

Abstract

Similar works

Full text

Available Versions

GSI Repository