Adonin, A.

Barth, W.

Berezov, R.

Dahl, L.

Gerhard, P.

Groening, L.

Hollinger, R.

Maier, M.

Mickat, S.

Orzhekhovskaya, A.

Vormann, H.

Xiao, C.

Yaramyshev, S.

GSI Repository

Investigation of the Compact LEBT Design PrerequisitesS. Yaramyshev, H. Vormann, A. Adonin, W. Barth, R. Berezov, L. Dahl, P. Gerhard, L. Groening, R.Hollinger, M. Maier, S. Mickat, A. Orzhekhovskaya, C. XiaoGSI, Darmstadt, GermanyA new injection line [1,2,3] is proposed as a part of theupgrade and further development of the high current heavyion linac UNILAC for the FAIR requirements. The finaldesign of this straight line should be based on precise andcomplete information about beam current and emittancecoming from ion source. An intense experimental cam-paign was carried out in June-November 2013 at the NorthTerminal of the UNILAC. Full and self-consistent data foruranium beam including detailed knoweledge about thebeam current phase density in the transverse phase spacehas been obtained [4].As the new LEBT (Low Energy Beam Transport) hasno separation by bending magnets, the full spectra of dif-ferent uranium charge states (2+, 3+, 4+, 5+, ...) will betransported through the line. Then the beam emittanceof only design ions U4+ should be matched to the HSI-RFQ acceptance. Although the neighboring charge statescould be partly separated at the LEBT, a significant por-tion of mainly U3+ ions will be also injected into the RFQ.This leads to an increased space charge effects and makesa strong influence on particle motion. Therefore an infor-mation about ratio U4+ / U3+ is important for proper beamtransport and matching. Measurements of beam parame-ters have been performed at existing UNILAC beam line,directly behind North ion source terminal. Obviously abeam current and beam emittance could be measured onlyfor all charge states together. The standard diagnostics isnot able to distinguish ions with different charge states. Tosolve this problem, a set of measurements behind the firstquadrupole triplet (UL4QT1) of the North LEBT was insis-tently proposed. As it is shown on Fig.1 (left), a differentfocusing efficiency for the different charge states leads to acomplicate shape of a composite beam emittance.To distinguish between different charge states a dedi-cated algorithm was proposed, developed and realized. Amacroparticle distribution was generated from the raw dataof measured (with slit-grid device) emittance. The den-sity of macroparticles is proportional to the measured in-tensity in each bin. Beam dynamics simulations with DY-NAMION code have been firstly done backward (upstreambeam direction) through the measured magnetic field ofthe triplet. Two identical distributions, but with differentcharge state of macroparticles (U3+ and U4+) have beentransported separately. In assumption that the beam pa-rameters behind an ion source terminal are the same forevery charge state, only a phase space overlapping of re-sulted particle distributions has been treated as an emit-tance formed by the complete beam. The obtained ”realis-tic” particle ensemble has been simulated forward (down-Figure 1: Measured beam emittance (left) and macropar-ticle distributions (right): generated from measurements(black), reconstructed U4+ fraction (green), reconstructedU3+ fraction (red)stream a beam), again separately as U3+ and as U4+.The transported particles at the position of measurementsform separately beam emittances for different charge stateswhich perfectly cover the originally measured phase spacedistribution (Fig. 1, right).Additionally a dedicated algorithm, based on leastsquares calculations, provides for an estimated U4+ inten-sity inside the measured one for all charge states together.With use of this algorithm one can extract from the recentmeasurements for the mixed beam (U3+ and U4+ mainly)the beam parameters for the design ion U4+ only. Thebeam current and emittance obtained with different settingsof the ion source terminal are in the range of 20-35 mA in-side 300-450 mm*mrad respectively. For comparison, theHSI-RFQ high current acceptance with these beam param-eters is in the frame of 250-300 mm*mrad.Generally the proposed coupling of detailed measure-ments and precise simulations acts as a virtual charge stateseparator. Being implemented simultaneously for bothtransverse phase planes, it provides for a better beam trans-port, refined matching with an RFQ acceptance, as well asfor an improved UNILAC performance.References[1] L. Dahl et al, Proceedings LINAC 2002[2] S. Yaramyshev et al, GSI internal Report 2009[3] H. Vormann et al, these Proceedings[4] S. Yaramyshev et al, GSI internal Report 2013GSI SCIENTIFIC REPORT 2013 FG-UNILAC-03doi:10.15120/GR-2014-1-FG-UNILAC-03 FAIR@GSI 299

Investigation of the Compact LEBT Design Prerequisites

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Investigation of the Compact LEBT Design Prerequisites

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