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					                                        ESR Operation and Development
                      K. Beckert, P. Beller, W. Bourgeois, B. Franczak, B. Franzke, F. Nolden,
                                  U. Popp, A. Schwinn, M. Steck, GSI Darmstadt

   After a nine months’ shutdown period ESR operation started           Decelerated heavy ion beams have been provided for vari-
in June 2001. During the shutdown the internal target section        ous atomic physics experiments. Bare uranium was decelerated
has been modified and new pressurized air actuators have been         from 300 to 43 MeV/u for the investigation of x-rays emitted
installed which allow fast (within 1 s) positioning of charged       during recombination of the ions with electrons in the cooling
particle detectors. These detector drives have already been suc-     section. The use of a decelerated beam allowed a considerable
cessfully employed in physics experiments. Their motion is           reduction of the background originating from Bremsstrahlung
fully computer controlled and triggered by events from the ac-       of electrons lost in the electron cooler. Up to ¿ ¢ ½¼ ions were
celerator timing system thus avoiding any dead time between          decelerated to the energy of 43 MeV/u and stored for several
beam manipulations and data acquisition for experiments. A           minutes. Later during this beam time the decelerated uranium
new zero degree electron spectrometer has been installed about       beam was also used for tests of the beam line to Cave A.
1 m downstream the interaction point with the gas jet. Mag-             In the final beam time of 2001 uranium ions decelerated to
nets and vacuum system of the electron spectrometer section          20 MeV/u had to be transported to Cave A for channeling ex-
are ready for operation, commissioning with beam is foreseen         periments. Unfortunately the total beam time had to be cut short
for the first beam time period in 2002. All pick up electrodes        due to problems in the Unilac accelerator section. Nevertheless
of the stochastic cooling system have been equipped with indi-       the machine cycle could be successfully established and also
vidual low noise pre-amplifiers in order to improve the signal        the beam line from the ESR to Cave A equipped with new di-
to noise ratio and thus the cooling time. The improved perfor-       agnostics for low energy beams could be commissioned. The
mance has been tested and confirmed with beam and is available        decelerated uranium beam with an energy of 20 MeV/u was ex-
for use in experiments.                                              tracted with extraction times on the order of minutes by charge
   During June and July the ESR was operated together with the       changing of the bare uranium beam. Electron capture in the
SIS in the reinjection mode for five weeks providing bare gold        electron cooler was chosen as the process providing hydrogen-
ions in Cave C at nearly 1.5 GeV/u. A typical beam intensity         like ions at a rate not exceeding ½¼ ions/s. The required ex-
of ¾   ¿ ¢ ½¼ bare gold ions was injected into the ESR at an         traction rate was accomplished by a reduction of the electron
energy of 350 MeV/u. By application of an electron current of        current to 100 mA with a total extraction times of 2 minutes
0.7 A the cooling time was 5 s only. After reinjection into the      per cycle. Figure 1 shows some essential parameters of the ma-
synchrotron SIS the ions were accelerated to 1.499 GeV/u and         chine cycle in this operation mode. After a cooling time of
slowly extracted over 5 s. Compared to previous beam times           about 15 s the beam is decelerated in 8 s to an intermediate en-
the cooling time in the ESR was considerably reduced thus the        ergy of 30 MeV/u and after 6 s of cooling within 2 s to the final
processing time in the ESR contributed less than 30 % to the         energy of 20 MeV/u.
total cycle time. The efficiency of beam transportation from the
ESR to the SIS could be continuously increased in the course
of the beam time. More than 70 % of the ions circulating in the        0.7
ESR were transfered to the SIS resulting in ½   ¾ ¢ ½¼ bare gold                                  magnetic rigidity [10 Tm]
ions supplied to the experiment in one cycle of 20-30 s. Most          0.6                        spill rate [104s-1]
                                                                                                  ion current [mA]
of the losses between ESR and SIS can be attributed to down                                       electron current [A]
charged ions which are produced during the cooling period in
the ESR and which can not be transfered due to their difference        0.4
in magnetic rigidity.
   Bismuth ions in the hydrogen- and lithium-like charge state         0.3
were stored at energies of 415 and 393 MeV/u, respectively, for        0.2
measurements of the hyperfine splitting with a collinear laser.
For efficient production of incompletely stripped ions at this en-      0.1
ergy carbon foils recently installed in the beam line in front of
the ESR were employed. Energies around 415 MeV/u corre-                  0
                                                                             0   25   50     75   100 125         150     175   200
spond to the highest electron energy in the cooler used for an                                     time [s]
experiment. Experience showed that reliable cooler operation
near the current maximum energy requires careful conditioning
of the electron cooling system over several days.                    Figure 1: Typical deceleration cycle for a bare uranium beam
   The transfer of ions through the fragment separator to the        from 300 MeV/u injection energy to an energy of 20 MeV/u
ESR was studied with a nickel beam at 390 MeV/u. Beyond              with slow extraction. The curves show dipole field, ion and
general optimization of the optical setting of the transfer line     electron current and spill rate at the experiment in the units in-
the test revealed an unintentional transposition of a quadrupole     dicated in the plot as a function of time.
dublett which is, at least partially, accountable for beam losses.

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