Status of the TASCA Commissioning Program * M. Schädel 1,# , D. Ackermann 1 , W. Brüchle 1 , Ch.E. Düllmann 1 , J. Dvorak 2 , K. Eberhardt 3 , J. Even 3 , A. Gorshkov 2 , R. Gräger 2 , K.E. Gregorich 4 , F.P. Heßberger 1 , A. Hübner 1 , E. Jäger 1 , J. Khuyag- baatar 1 , B. Kindler 1 , J.V. Kratz 3 , D. Liebe 3 , B. Lommel 1 , J.P. Omtvedt 5 , K. Opel 5 , A. Sabelnikov 5 , F. Samadani 5 , B. Schausten 1 , R. Schuber 2 , E. Schimpf 1 , A. Semchenkov 1,2,5 , J. Steiner 1 , J. Szerypo 6 , A. Türler 2 , and A. Yakushev 2 for the TASCA Collaboration 1 GSI, Darmstadt, Germany; 2 Technical University München, Garching, Germany; 3 University of Mainz, Mainz, Ger- many; 4 LBNL, Berkeley, CA, U.S.A.; 5 University of Oslo, Oslo, Norway; 6 LMU München, Garching, Germany The TransActinide Separator and Chemistry Apparatus, TASCA, project [1] is focusing on the separation and investigation of neutron-rich transactinide nuclides pro- duced in actinide target based reactions. The envisioned research program includes both chemical investigations of transactinide or superheavy elements after preseparation with the gas-filled separator and physics motivated nu- clear structure and nuclear reaction studies. The central device of TASCA is a gas-filled separator in a DQQ configuration. It can be operated in the "High Transmission Mode" (HTM, DQ h Q v ) and in the "Small Image Mode" (SIM, DQ v Q h ); see Refs. [1-4] for more details. The separator was installed at the UNILAC beam line X8 and, after having all crucial parts of the control system [5] running, an extensive commissioning program was carried out in 2007. This report briefly summarizes the nuclear reactions applied and the most important pa- rameters studied. A few examples are discussed in a very exemplary way. In addition, recent target developments and the progress in the coupling of chemistry set-ups will be outlined. The first chemical study behind TASCA is described in a separate contribution [6]. All nuclear reactions applied are listed in Table 1 to- gether with the mode of TASCA operation (HTM=H, SIM=S) and the separator gas. Also indicated are experi- ments aimed to test or apply a recoil transfer chamber (RTC) in addition to measurements performed with a fo- cal plane detector (FPD). As the standard FPD we used a (8x3.6) cm 2 large position-sensitive 16-strip silicon detec- tor. Some experiments were devoted to test prototype double-sided silicon strip detectors (DSSSD) which are planned to be used in future experiments with superheavy elements (SHE). To understand TASCA as a separator and to build up a solid data base providing good predictive power concern- ing separator operation for future SHE experiments, we investigated the following most important parameters: (i) the magnetic rigidity of reaction products between Z=76, Os, and Z=102, No, produced at different recoil velocities, and the corresponding best settings of the dipole magnet, (ii) the quadrupole focusing, which is especially relevant for the SIM, (iii) the target thickness dependence of the separator transmission - strongly depending on the asym- metry of the nuclear reaction -, and (iv) the optimum gas pressure with respect to focusing and to transmission - being quite different in the HTM and in the SIM. The analysis of a huge amount of data from these experiments is in progress, and it is important to realize that most of the above mentioned parameters influence each other. Table 1: Nuclear reactions applied in TASCA commis- sioning experiments; see text for details. Beam Target Product Mode Gas RTC 22 Ne nat Ta 198m-199 Bi H + S He 179 Au 215 Ac H + S He 238 U 255 No H + S He 30 Si no 30 Si H + S Vac 181 Ta 205-206 Fr H He 40 Ar nat Ce 173,175 Os H He yes 144 Sm 180-182 Hg H + S He yes nat Gd, 152 Gd 194-196 Pb, 188 Pb H + S He yes nat Lu 210 Ac H + S He, N 2 208 Pb 245 Fm H + S He yes 232 Th, 238 U targettest, background H He 48 Ca 144 Sm 188 Pb H + S He 206 Pb 252 No H + S He 208 Pb 254 No H He, H 2 54 Cr nat Gd 209-210 Ra H + S Always as a first step, the best dipole setting was found in HTM by centring the product distribution with a typical width of 6 cm on the FPD. A magnetic rigidity range from 1.5 to 2.2 Tm was covered in those experiments. The quadrupole focusing was found to be insensitive to small quadrupole current changes in the HTM while it reacts very sensitively in the SIM. Optimized SIM settings were determined to obtain maximum rates and narrow distribu- tions of 1.5 cm FWHM. The target thickness dependence of the transmission was extensively studied in the reactions 22 Ne + 197 Au (55, 130, 255, 580 μg/cm 2 ) and 40 Ar + 144 Sm (75, 190, 380, 930 μg/cm 2 ) in both modes. A comparison of these data with model calculations [7] will allow selecting an opti- mum target thickness with the highest product rate for all the envisioned nuclear reactions. Many experiments were devoted to find the optimum He pressure and to determine the response to pressure changes. For this we checked the spatial distribution and the total rate of the products in the FPD. While a pressure of about 1 mbar is generally best in the HTM, a signifi- _________________________________________ * Work supported by BMBF (06MT247I, 06MT248, 06MZ223I) and GSI-F&E (MT/TÜR, MZJVKR) # m.schaedel@gsi.de NUSTAR-SHE-11 152