The main accelerator SIS100 of the FAIR-complex will provide heavy ion beams of highest intensities. Beam loss due to ionization is the most demanding loss mechanism at operation with high intensity, intermediate charge state heavy ions. A special synchrotron design has been devel- oped for SIS100, aiming for hundred percent control of ion- ization beam loss by means of a dedicated cryogenic ion catcher system. To suppress dynamic vacuum effects, the cryo catcher system shall provide a signiﬁcantly reduced effective desorption yield. The construction and test of a prototype cryocatcher is a task of the EU-FP-7 workpack- age COLMAT. A prototype test setup, including cryostat has been constructed, manufactured and tested under real- istic conditions with beams from the heavy ion synchrotron SIS18. The design and results are presented

Bozyk, Lars

Hoffmann, Dieter

Kollmus, Holger

Spiller, Peter

Wengenroth, Marc

Bozyk, L

Spiller, P

Kollmus, H

Hoffmann, D H H

Wengenroth, M

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Construction and Test of a Cryocatcher Prototype for SIS100

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CONSTRUCTION AND TEST OF ACRYOCATCHER PROTOTYPE FOR SIS100∗L. Bozyk, D.H.H. Hoffmann, TU-Darmstadt, Germany and GSI, Darmstadt, GermanyP. Spiller, H. Kollmus, M.Wengenroth, GSI, Darmstadt, GermanyAbstractThe main accelerator SIS100 of the FAIR-complex willprovide heavy ion beams of highest intensities. Beam lossdue to ionization is the most demanding loss mechanismat operation with high intensity, intermediate charge stateheavy ions. A special synchrotron design has been devel-oped for SIS100, aiming for hundred percent control of ion-ization beam loss by means of a dedicated cryogenic ioncatcher system. To suppress dynamic vacuum effects, thecryocatcher system shall provide a significantly reducedeffective desorption yield. The construction and test of aprototype cryocatcher is a task of the EU-FP-7 workpack-age COLMAT. A prototype test setup, including cryostathas been constructed, manufactured and tested under real-istic conditions with beams from the heavy ion synchrotronSIS18. The design and results are presented.ION CATCHER SYSTEM IN SIS100The ion optical lattice of SIS100 has been optimizedwith respect to the implementation of a dedicated ioncatcher system [1]. Stripped beam ions are lost at well de-fined highly localized positions in the cryogenic arcs. Sucha peaked loss distribution allows the installation of an ef-ficient ion catcher system with perpendicular low desorp-tion surfaces. Thereby, the amount of charge exchange pro-cesses in collisions with residual gas molecules and consec-utive ionization beam loss is stabilized during operation.The basic design considerations of the ion catcher sys-tem have been presented in [2]. In the meantime, the pro-totype has been manufactured, taken into operation, andtested with heavy ion beams from SIS18.DESIGN OF THE PROTOTYPECRYOCATCHER AND ITS TEST SETUPA 3D-model of the cryocatcher and its vacuum chamberis shown in Figure 1. The chamber surrounding the actualcryocatcher acts as a cryopump with high pumping speed.In order to assure a uniform cold temperature distribution,the chamber made of stainless steel is coated with copper.The coating has been explosively plated onto the stainlesssteel before the chamber was manufactured. Several testshave been performed to guarantee the cryo-suitability ofthis coating technique. The chamber is connected to a he-lium supply line via flexible copper straps.∗Work supported by EU (FP7 workpackage COLMAT) and GP-HIR –Graduate Program for Hadron and Ion Research at GSIstripped beam ionscirculating beamcryocatcher for SIS100Figure 1: 3D-modell of the cryocatcher prototype with sur-rounding UHV-chamber (blue) made of stainless steel withan explosively plated copper surface (brown).The cryocatcher will be kept at a higher temperature thanthe chamber to avoid freezing-out of gas molecules on thesurface of beam impact. To minimize the heat load ontothe cooling system, the cryocatcher support acts as a cold-warm-transition. It contains a bellow which provides a highthermal resistance and a separation of the beam vacuumfrom the insulation vacuum. Because of the limited spacein the SIS100 quadrupole cryostat, the mounting with itscold warm transition sticks into the chamber.The actual support of the cryocatcher consists of a cop-per block inside the bellow. The block provides a goodthermal contact to the warmer side of the bellow. In thisway, a thermal contact to the ion catcher from the insula-tion vacuum is established. The thermal contact is usedfor connecting the cryocatcher to the thermal shield. Thusthe deposited energy of lost ions is dissipated via the shieldcooling instead of the chamber cooling.The cryocatcher itself is a 25 cm long copper block. Thelength was optimized by FLUKA-simulations [2, 3, 4]. Thefront part is electrically insulated from the rear part, suchthat the electrical current of ions hitting the cryocatcher canbe measured. The copper catcher has a Nickel-Gold coat-ing, which provides low desorption yields at room temper-ature [5]. Two different geometries are tested: A blockcatcher, as indicated in Figure 1, similar to the establishedcatchers in SIS18, and a stair-like catcher, which providesperpendicular incidence and a shielding of the desorbedmolecules from the circulating beam.The cryocatcher is surrounded by a shielding. ThisProceedings of IPAC2011, San Sebastián, Spain TUPS00707 Accelerator TechnologyT14 Vacuum Technology 1527 Copyrightc ○2011byIPAC’11/EPS-AG—ccCreativeCommonsAttribution3.0(CCBY3.0)Figure 2: Picture of the assembled cryocatcher prototypefrom the backside: The actual cryocatcher (gold) is sur-rounded by the explosively plated UHV-chamber, which isaligned inside the thermal shield of the test-cryostat.shielding prevents the desorbed gases from reaching thebeam axis and provides additional cold surfaces for pump-ing. The position of the cryocatcher inside this secondarychamber minimizes the pressure rise on the beam axis.The cryocatcher chamber is cooled via flexible copperstraps which are connected to a LHe pipe. Both are sur-rounded by a LN2 cooled thermal shield inside the cryostatchamber. A cold-warm-transition connects the cryocatcherchamber to a warm beam line of the GSI accelerator com-plex. Different than in SIS100, the prototype is irradiateddirectly by the primary beam from SIS18.Figure 2 shows a photography of the assembled proto-type cryocatcher inside the thermal shield.DIAGNOSTICS OF THE PROTOTYPETEST SETUPA 3D-modell of the test-setup is shown in Figure 3. Dur-ing the tests the pressure rise induced by heavy ion bom-bardment has been investigated. The pressure was mea-sured by a cold penning gauge which is mounted on thebackside of the chamber and a thermally shielded hot ex-tractor gauge, which is mounted on a long pipe sticking intothe chamber. This pressure gauge allows pressure measure-ments close to the cryocatcher head surface. In front of thecold-warm-transition, in a warm beam pipe, a further ex-tractor gauge and a residual gas analyzer are situated.A beam screen situated in the same chamber is used toadjust the beam position. For further control of the beamposition during the tests, several plates around the cryo-catcher have been mounted electrically insulated. The cur-vacuumconductancebeam transformerpumpingpostswarm UHVdiagnosticscintillatorscintillatorLHe + LN2 supplycryocatchergate valvescreened pressure gaugecold warm transitionFigure 3: 3D-scetch of the prototype cryocatcher test setup.rents onto these plates have to be minimized, whereas thecurrent on the cryocatcher has to be maximal.Since a residual gas pressure of p < 10−11 mbar has tobe reached inside the cold chamber, a differential pump-ing system with a small vacuum conductance is installedin front of the setup. Upstream the pumping line a furtherbeam screen is located to assure a parallel incoming beam.To control the cooling, verify temperature models, andto get reference temperatures for pressure measurements,temperature sensors were mounted onto different compo-nents like the LHe-pipe, cold chamber, vacuum gauges, thecroycatcher, and its mounting.TESTING OF THE PROTOTYPECRYOCATCHERDuring the experiments several parameters were inves-tigated, e.g. cooling power, end-pressure, and heavy ionbombardment induced pressure rise as a function of thebeam energy and cryocatcher temperature. On the innerchamber temperatures down to 10 K were reached. A tran-sition temperature of ∼18 K, underneath a serious pump-ing speed for hydrogen emerges, could be verified severaltimes. Each time a lower temperature has been reached,the pressure dropped by two orders of magnitude down to10−12 mbar within several minutes.The cryocatcher and its mounting showed a quite ho-mogeneous temperature. Fast beam-induced tempera-ture changes on the cryocatcher-head were distributedquickly. The temperature of the support, measured fromthe insulation-vacuum side, differs only slightly from thecryocatcher’s head, i.e. the deposited energy can be dissi-pated.During three beam tests the ion beam induced pressurerise was investigated. The two different catcher geometrieswere tested with Gold and Tantalum beams at energies be-tween 50 MeV and 800 MeV. During the Ta-beamtime, atest at room temperature has been performed. The stair-like catcher was tested with Bismuth ions at beam energiesbetween 100 MeV and 600 MeV. Each time fast extractionwas used, with intensities of up to 2 · 109 ions/spill.TUPS007 Proceedings of IPAC2011, San Sebastián, Spain1528Copyrightc ○2011byIPAC’11/EPS-AG—ccCreativeCommonsAttribution3.0(CCBY3.0)07 Accelerator TechnologyT14 Vacuum TechnologyTime in s0 2 4 6 8 10Pressure in mbar00.050.10.150.20.250.3-910×600 MeV500 MeV400 MeV300 MeV100 MeVFigure 4: Some exemplarily pressure developments afterbeam impact onto the cryocatcher for different Bi-beams.For selected energies, the cryocatcher’s temperature wasvaried between 35 K and 90 K.The ion current of the extractor gauge situated next tothe cryocatcher head was measured with an external am-pere meter. Thereby, a fast pressure measurement, trig-gered by the incoming beam, could be realized. Figure 4shows some exemplarily pressure developments for differ-ent impact energies.The base pressure after relaxation and the peak pressurewere determined for each measurement. The difference,normalized to the number of incident particles, determinesthe effective pressure rise.RESULTSAll pressure measurements were corrected by the tem-perature of the vacuum gauge. After cooling the cham-ber below 18 K, a base pressure in the lower 10−12 mbarregime was reached. The normalized effective pressure risewas measured for different beam energies and temperaturesof the cryocatcher. From room-temperature experiments, adE/dx-scaling of the pressure rise, i.e. a decrease with ris-ing energy is known [6, 7]. During the cold tests, a contrarybehavior could be observed: The pressure rise increaseswith rising energy, see Figure 5. Using the same setup butat room temperature, the pressure rise drops with increas-ing energy, as expected.In the investigated temperature range no real dependenceof the effective pressure rise from the cryocatcher’s tem-perature could be observed (see Figure 6). Although va-por pressure curves were crossed during the cooldown pro-cesses, no pressure drop could be observed in this tempera-ture interval. This means only cryoadsorption and no cryo-condensation plays a role.Comparing the results carefully, the stair-like cryo-catcher data in Figure 5 seem to rise slightly less thanthe block data, although Bismuth is heavier than Gold andTantalum. Beam impacts were seen in the slow pressuremeasurement of the cold cathode ion gauge only using theEnergy in MeV/u0 100 200 300 400 500 600 700 800p / Ion in mbarΔ-2110-2010-1910-1810Au, T < 35 KTa, T < 50 KTa, 290 KBi, T < 45 KBi, T > 70 K3(dE/dx)Figure 5: Effective pressure rises as a function of the beamenergy for all measurements and different cryocatcher tem-peratures.Cryocatcher Temperature in K30 40 50 60 70 80 90p / Ion in mbarΔ00.010.020.030.040.050.060.070.080.090.1-1810×300 MeV 400 MeV 550 MeVFigure 6: Effective pressure rise as a function of the cryo-catcher’s temperature for different Bi-beam energies.block cryocatcher. This indicates that the pressure rise us-ing the stair-like cryocatcher is less pronounced.The StrahlSim code was used to verify the stability of thedynamic vacuum in SIS100 [8]. Considering the describedenergy scaling of the desorption yields, the results show astable operation of SIS100 even at highest heavy ion beamintensities.REFERENCES[1] P. Spiller et al., Proc. of ICFA04 (2005)[2] L. Bozyk et al., Proceedings of IPAC’10 (2010)[3] G. Battistoni, et al., Proc. of Hadronic Shower SimulationWorkshop 2006[4] A. Fasso et al., CERN-2005-10 (2005), INFN/TC 05/11,SLAC-R-773[5] M. Bender, Dissertation, Goethe-Uni Frankfurt (2008)[6] H. Kollmus et al., J. Vac. Sci. Technol. A 27, 245 (2009)[7] A. W. Molvik et al., Phys. Rev. Lett. 98, 064801 (2007)[8] P. Puppel et al., Proceedings of IPAC’11 (2011).Proceedings of IPAC2011, San Sebastián, Spain TUPS00707 Accelerator TechnologyT14 Vacuum Technology 1529 Copyrightc ○2011byIPAC’11/EPS-AG—ccCreativeCommonsAttribution3.0(CCBY3.0)

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Construction and Test of a Cryocatcher Prototype for SIS100

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