Bonaventura, D.

Grieser, S.

Hergemöller, A.-K.

Khoukaz, A.

Köhler, E.

Ortjohann, H.-W.

Täschner, A.

GSI Repository

Laval Nozzle Production for Internal Targets∗E. Ko¨hler†1, D. Bonaventura1, S. Grieser1, A.-K. Hergemo¨ller1, H.-W. Ortjohann1, A. Ta¨schner1,and A. Khoukaz11Institut fu¨r Kernphysik, Westfa¨lische Wilhelms-Universita¨t Mu¨nster, GermanyA powerful type of target for internal fixed target ex-periments at storage rings is given by the cluster-jet tar-get which allows for typical target thicknesses of 1012 to1015 atoms/cm2. Furthermore, this type of target providesa stream of particles which is homogeneous and constantin space and time. At the University of Mu¨nster severalcluster-jet targets were already designed and constructed,e.g., for COSY-11, ANKE, and PANDA, where the latterone is currently under construction. The target density canbe easily adjusted by changing the temperature or pressureof the gaseous target material (e.g., hydrogen, deuterium)before the so-called Laval nozzle, the heart of a clustersource. The specific convergent-divergent shape of theLaval nozzle generates a supersonic flow of the target ma-terial. Supported by the adiabatic cooling the, e.g., hydro-gen, molecules condensate to clusters (see Figure 1). Themean velocity and the velocity distribution of the extractedand shaped cluster-jet beams are strongly dependent on theoperational parameters. In recent measurements mean ve-locities of 200 to 1000 m/s were observed when a 28µmLaval nozzle was operated with hydrogen at 17 bar and atemperature between 20 and 50 K [1, 2]. This velocitiescould be described by numerical calculations [3]. EssentialskimmerLaval nozzleH2 gascollimatorclustergasFigure 1: Cluster production process with a Laval nozzle.Skimmer and collimator are responsible for extracting andbeam shaping [4].for the performance of a cluster-jet target are the propertiesof the Laval nozzle which itself can be divided into an in-let and an outlet zone (see Figure 1). The short inlet zoneconverges to the narrowest point of the nozzle and mergesinto the divergent, long outlet zone. The production of asmall inner diameter (e.g., 30µm) in combination with thelong trumpet part with an opening angle of, e.g., 7 ◦, rep-resents a major technical challenge. In the past these fineLaval nozzles were produced at CERN but the manufacturewas discontinued [5]. To ensure the production of thesefine Laval nozzles for future internal targets and for furthertarget optimisation studies an improved production process∗Work supported by EU (FP7), BMBF, and GSI.† e koeh02@uni-muenster.deFigure 2: Left: Finished Laval nozzle of the first success-fully produced set, Right: First cluster-jet beam of a newLaval nozzle (beam direction from left to right) installed atthe PANDA cluster-jet target prototype.based on the initial CERN production was recently devel-oped at the University of Mu¨nster. Due to several optimisedproduction steps a minimal failure rate of the particularlyfine Laval nozzles is ensured.A first set of Laval nozzles was successfully produced andinitial measurements with these new nozzles (see Figure 2left) are running at the PANDA cluster-jet target prototype.Figure 2 (right) presents the first cluster-jet beam of a newnozzle with the characteristic high intense core beam struc-tures [6]. The part of the cluster beam directly after theLaval nozzle (left, not visible) is illuminated with a laserdiode. The possibility to produce new micrometer nozzlesopens the way for future investigations on the cluster pro-duction process with the modification of, e.g., length andaperture angle of the trumpet, with the objective to furtheroptimise cluster-jet targets for storage rings.References[1] E. Ko¨hler, Das Mu¨nsteraner Cluster-Jet Target MCT2, einPrototyp fu¨r das PANDA-Experiment, & die Analyse derEigenschaften des Clusterstrahls, Diploma Thesis, Universityof Mu¨nster, 2010[2] A. Ta¨schner et al., Nucl. Instr. and Meth. A 660 (2011) 22-30,doi:10.1016/j.nima.2011.09.024[3] A. Ta¨schner, Entwicklung und Untersuchung von Cluster-Jet-Targets ho¨chster Dichte, PhD Thesis, University of Mu¨nster,2013[4] A.-K. Hergemo¨ller, Preparation of cluster beams and the con-struction of the final cluster source for the PANDA experi-ment, Master Thesis, University of Mu¨nster, (in preparation)2013[5] R. Kopp, N. Me´zin, Technical Note EST-MF 96-05, CERN,1996[6] E. Ko¨hler, High Intense Hydrogen Cluster-Jet Beams forPANDA, Annual Report GSI, 2011GSI SCIENTIFIC REPORT 2012 PHN-HSD-EXP-1117

Laval Nozzle Production of Internal Targets

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Laval Nozzle Production of Internal Targets

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