Barth, W.

Groening, L.

Kim, V.

Lomonosov, I. V.

Piriz, A. R.

Schlitt, B.

Stöhlker, T.

Tahir, N. A.

Vormann, H.

GSI Repository

Thermal Simulations of Thin Solid Carbon Foils for Charge Stripping of HighCurrent Uranium Ion Beams at New GSI Heavy-Ion Linac∗N.A. Tahir1, V. Kim2, W. Barth1, L. Groening1, I.V. Lomonosov2, A.R. Piriz3, B. Schlitt1,Th. Sto¨hlker1,4, and H. Vormann11GSI, Darmstadt, Germany; 2IPCP, Chernogolovka, Russia; 3UCLM, Ciudad Real, Spain; 4IOQ Friedrich-SchillerUniversita¨t and Helmholtz Institute, Jena, GermanyThis paper presents an extensive numerical study of heat-ing of thin solid carbon foils by 1.4 MeV/u uranium ionbeams to explore the possibility of using such a target asa charge stripper at the proposed new GSI high energyheavy–ion linac. These simulations have been carried outusing a sophisticated 3D computer code that accounts forphysical phenomena that are important in this problem.The stripper is assumed to be a thin circular foil of solidgraphite with density 2.28 g/cm3 and radius, Rf = 1.5 cmwhile the uranium beam is incident perpendicular to its sur-face. Three different foil thicknesses including 20, 30 and40 μg/cm2, have been considered.Figure 1: T vs time (during pulse length) at differentpoints along foil radius, foil thickness = 20 μg/cm2, cur-rent 6 emA and pulse length = 100 μs.Two different current values, namely, 6 emA and 18 emAhave been used where the latter is the FAIR design value.A pulse length of 100 μs is considered that leads to pulseintensities, N = 9.375 × 1011 and 2.8125 × 1012 for thebeam current values of 6 emA and 18 emA, respectively.The transverse particle distribution in the focal spot is as-sumed to be Gaussian with σ = 3.67 mm, whereas the rep-etition rate of the ion beam pulses is 2 Hz.The initial charge state is U4+ while the ion is strippedto a charge state of U39+ after passing through either 20 or30 μg/cm2 thick stripper foils. A slightly higher chargedstate of U40+ is achieved with a 40 μg/cm2 thick foil. Forsimplicity, we assume in the calculations a uniform ioncharge state along the foil thickness (39+ in case of 20 and30 μg/cm2 and 40+ in case of 40 μg/cm2 thickness). Inpractice, however, there will be an exponential type chargedistribution along the ion trajectory.∗Work supported by the BMBFFigure 2: Same as in Fig. 1, but using beam current 18 emAIn Fig. 1 we plot the temperature for 6 emA currentat three different points along the foil radius, namely,r = 0 (center), 5 mm and 15 mm (outer boundary), re-spectively. It is seen that a maximum temperature ofaround 2200 K is achieved at the target center at the endof the pulse (100 μs), whereas the maximum temperatureat r = 5 mm is about 1250 K. The temperature at the foilboundary, on the other hand, does not change. It is to benoted that although the sublimation temperature of carbonin air is much higher (3925 K), the target could be dam-aged due to the induced thermal stresses [1,2]. The corre-sponding temeprature at the foil center in case of 30 and40 μg/cm2 is 2300 K and 2400 K, respectively. This is be-cause diffusion of heat from the target center to the surfacetakes longer time that reduces the cooling rate.In Fig. 2 we plote the same variables as in Fig. 1, butusing 18 emA current. It is seen that the temperature at thefoil center approaches the carbon sublimations temperaturewhich means that it will not survive a single irradiation inthis case. For 30 and 40 μg/cm2 foil thickness, the maxi-mum temperature is even higher. It is therefore concludedthat use of a solid stripper foil is not feasible at the newhigh energy drift tube linac at GSI. Further details can befound in [3]References[1] N.A. Tahir et al., NIMB 276 (2012) 66.[2] N.A. Tahir et al., NIMB 290 (2012) 43.[3] N.A. Tahir et al., PRSTAB (2014) Submitted.GSI SCIENTIFIC REPORT 2013 FG-UNILAC-09doi:10.15120/GR-2014-1-FG-UNILAC-09 FAIR@GSI 305

Thermal Simulations of Thin Solid Carbon Foils for Charge Stripping of High Current Uranium Ion Beams at New GSI Heavy-Ion Linac

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Thermal Simulations of Thin Solid Carbon Foils for Charge Stripping of High Current Uranium Ion Beams at New GSI Heavy-Ion Linac

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