Barth, W.

Bevcic, M.

Düllmann, Christoph Emanuel

Groening, L.

Horn, K. P.

Jäger, E.

Khuyagbaatar, J.

Krier, J.

Scharrer, P.

Yakushev, A.

GSI Repository

Upgrade preparation for the 1.4 MeV/u gas stripper system for FAIRE. Ja¨ger1, P. Scharrer2, A. Yakushev1, Ch. E. Du¨llmann1,2,3, J. Khuyagbaatar2, J. Krier1, K.P. Horn1,L. Groening1, M. Bevcic1, and W. Barth1,21GSI, Darmstadt, Germany; 2HIM, Mainz, Germany; 3Johannes Gutenberg-Universita¨t Mainz, GermanyA key projectile for the FAIR facility will be 238U. Inroutine operation of the GSI UNILAC, 238U is generatedby a MEVVA ion source that delivers ions with comparablylow charge states (4+), which are accelerated to 1.4 MeV/uin the high current injector (HSI). The 1.4 MeV/u beampasses a region of high gas density, in which the charge isincreased to 28+ by stripping of electrons. [1] Generally,higher intensities at charge states, preferably above 28+,are desirable. This would allow to operate the acceleratormore reliable and efficiently.To optimize the stripping efficiency and potentially in-crease the achieved ion charge states a program to upgradethe gas stripper has started. The modified stripper setup isdepicted in Fig. 1. As a first modification, switching fromthe continuously fed supersonic N2-jet to a pulsed gas in-jection, synchronized with the beam timing structure, hasbeen implemented. This allows to increase the gas pressureinside the stripper chamber during a beam pulse, while stillreducing the total gas flow. The gas injection was posi-tioned inside a T-fitting, which was installed in the mainstripper chamber to match the beamline. In a first test thepressure in the main stripping section as function of theopening time of the valve and the pressure along the beam-line adjacent to the gas stripper section were measured.F12312Main stripper chamberPulsed gas valveBeamline3P1P3 P2P4 P5 P6Figure 1: Schematic view of the modified 1.4 MeV/u gasstripper as to be used for first measurements with a pulsedgas valve in beam experiments in 2014.The gas pressure on the valve was 3 MPa. The dependencyof the pressure inside the stripper chamber and the pump-ing performance on the valve opening time was evaluated01234560 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30Pressure[hPa]Opening time [ms]HeArN2Figure 2: Pressure measurements at the gas stripper for dif-ferent stripper gases as function of the opening time of thepulsed gas valve.for three different gases (N2, Ar and He). These gases areplanned to be investigated as potential stripper gases in thefuture, together with Xe.The results of the pressure measurements near the gas out-let in the main stripper chamber (diaphragm vacuum gaugeat P1, Fig. 1) are shown in Fig. 2. As the pressure varriedaccording to the pulsed gas flow regime, only the maxi-mum pressure values during one pulse are shown. Notethat the vacuum gauge was placed at an entry point on topof the main stripper chamber, so the shown pressures donot represent the real pressure in the beamline. The pres-sure increases with increasing opening time and starts tolevel off at longer opening times. N2 and Ar are pumped atabout the same rate whereas He is pumped less efficiently.Therefore, the pressure at the vacuum gauge is higher forHe at the same opening times. The measured pressure in-creases to values above 5 hPa, independent of which gaswas used. The pressure in the adjacent beamline was alsomeasured (vacuum gauges P2-P6, Fig. 1).The optimum conditions with respect to the pressure in themain stripping region and the adjacent beamline as well asthe experimental charge state distribution will be evaluatedin beam experiements in 2014.References[1] W. Barth, et. al., The new gas stripper and charge state sepa-rator of the GSI high current injector, Proccedings of LINAC,2000.FG-UNILAC-08 GSI SCIENTIFIC REPORT 2013304 doi:10.15120/GR-2014-1-FG-UNILAC-08

Upgrade preparation for the 1.4 MeV/u gas stripper system for FAIR

http://repository.gsi.de/record/68005/files/FG-UNILAC-08.pdf

Upgrade preparation for the 1.4 MeV/u gas stripper system for FAIR

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