The radioactive beam experiment REX-ISOLDE, a pilot experiment testing a new concept of post acceleration of radioactive ions at ISOLDE/CERN is in progress. Singly charged radioactive ions delivered by the online mass separator ISOLDE are accumulated in a Penning trap (REX trap), charge bred in an electron beam ion source (EBIS), separated from the residual gas in a mass separator and then accelerated in a linac with output energies between 0.8 and 2.2 MeV /u. The REX trap is in operation, a first test beam was already injected. The design phase of the EBIS is finished and the construction has been started. The superconducting magnet is delivered. The linac consists of a radiofrequency quadrupole (RFQ) accelerator, an interdigital IH-structure and 3 seven gap resonators to vary the final energy. (12 refs)

Bollen, G

Bongers, H

Deloose, I

Grieser, M

Habs, D

Kester, O

Liljeby, L

MacKay, W W

Ostrowski, A N

Podlech, H

Ratzinger, U

Rensfelt, K G

Repnow, R

Richter, A

Rudolph, K

Schempp, A

Schotter, A

Schwalm, D

Sieber, T

Smes, F

Thirolf, P G

Van Duppen, P

Von Hahn, R

Walter, G

Wenander, F

CERN Document Server

STATUS OF THE REX-ISOLDE PROJECTR. von Hahny , M. Grieser, H. Podlech, R. Repnow, D. SchwalmMax-Planck-Institut fu¨r Kernphysik, Heidelberg, GermanyH. Bongers, D. Habs, O. Kester, T. Sieber, K. Rudolph, P. ThirolfLMU Mu¨nchen, Garching, GermanyA. Schempp, Universita¨t Frankfurt, Frankfurt, GermanyF. Ames, G. Bollen, I. Deloose, CERN, Geneva, SwitzerlandU. Ratzinger, GSI, Darmstadt, GermanyL. Liljeby, K.G. Rensfelt, F. Wenander, Manne Siegbahn Institute of Physics, Stockholm, SwedenP. van Duppen, Instituut voor Kern- en Stralingsfysica, Leuven, BelgiumG. Walter, Unversite Louis Pasteur, Strasbourg, FranceA. Richter, TU Darmstadt, GermanyA. Ostrowski, A. Schotter, University of Edinburgh, Great Britainand the REX-ISOLDE collaborationAbstractThe Radioactive beam Experiment REX-ISOLDE, a pilotexperiment testing a new concept of post acceleration ofradioactive ions at ISOLDE/CERN is in progress. Singlycharged radioactive ions delivered by the online mass sep-arator ISOLDE are accumulated in a Penning trap (REXtrap), charge bred in an electron beam ion source (EBIS),separated from the residual gas in a mass separator and thenaccelerated in a Linac with output energies between 0.8 and2.2 MeV/u.The REX trap is in operation, a first test beam was al-ready injected. The design phase of the EBIS is finishedand the construction has been started. The superconductingmagnet is delivered.The Linac consists of a radio frequency quadrupole(RFQ) accelerator, an interdigital IH-structure and 3 sevengap resonators to vary the final energy. The RFQ is assem-bled and vacuum tested, a beam test for the RFQ is in prepa-ration. The vacuum tank of the IH-structure is machined,the assembly of the resonator has started. The first 2 sevengap resonators of the high energy section are finished andready for power tests, the last one is ready for assembly.1 INTRODUCTIONThe Radioactive beam Experiment (REX-ISOLDE) atISOLDE/CERN [1, 2, 3] is under progress, first hardwarecomponents are completed and some tests of the com-ponents were performed. In the experiment the radioac-tive ions of charge 1+ from the on-line mass separatorISOLDE will be cooled and bunched in a Penning trap(REX trap), charge bred in an electron beam ion source(EBIS), separated from the residual gas ions and finally ac-celerated in a short LINAC to a target energy between 0.8Work supported in part by the German Federal Ministery for Edu-cation, Science, Research and Technology (BMBF) under contract No.06HD802I and No. 06LM868I(2).y Email: robert.von.hahn@mpi-hd.mpg.deand 2.2 MeV/u. The LINAC consists of a radio frequencyquadrupole (RFQ) accelerator, which accelerates the ionsup to 0.3 MeV/u, an interdigital H-type (IH) structure witha final energy between 1.1 and 1.2 MeV/u and three sevengap resonators, which allow the variation of the final en-ergy. All components of the experiment are either in pro-duction or undergo first test measurements. The lay-out ofREX-ISOLDE is shown in fig. 1.2 REX TRAPThe Penning trap is fed from the ISOLDE main beam linewhere the beam axis is 1.27 m above the floor. The Penningtrap is fully assembled on a 60 kV high voltage platform in-cluding the differential pumping stages which ensure goodvacuum conditions in the beam line. High tension tests withthe equipment and first tests of ion injection into the traphave been carried out in order to investigate the injectionoptic [4]. The electrode structure consisting of gold platedcopper rings isolated by ceramic spacers is assembled andinstalled in the solenoid bore. The central field strength is 3T and the gas pressure inside the trap 10 3 mbar for rest gascooling. A plasma ion source has been installed to test theion capture with a stable 60 keV 40Ar+ beam. These cap-ture tests were done in the beginning of 1999 and the firstions were trapped. A new shielding due to charging of theinsulators are installed and will be tested in the near future.The singly charged ions will be extracted from the trap witha typical bunch length of 10 s every 20 ms and acceleratedto 60 keV.3 EBISIn the EBIS the ions are bombarded by a 0.5 A, 5 keV elec-tron beam with a current density of about 200 A/cm2 [5].In the EBIS the ions will be charge bred in about 15 ms toa charge to mass ratio between 0.22 and 0.34, which is wellsuited for the mass separator and the LINAC. After several0-7803-5573-3/99/$10.00@1999 IEEE. 1955Proceedings of the 1999 Particle Accelerator Conference, New York, 1999MQT4MQD210 2 3 4 5 6 7 8 9 10 mEBIS22.5-60 kVPenning-Trap 60 kVEinzellensEQD1EQD2EQS1 EQS2ED1EQT1SED1diag diagD2SMq/A-selectionEQD3 EQT2IH-structureRFQMQT1MQT2diagBuncher7-gap-5.4% 6.0% 6.6%resonatorsD3diagMINIBALLTargetMQT6MQT5side viewFigure 1: Lay-out of the REX-ISOLDE experimentrepairs of the REX-EBIS solenoid by the manufacturer dueto damages occurring during quench tests, the EBIS mag-net is now back at CERN and ready for operation. The vac-uum system is completed and being assembled at Stock-holm. The electron gun, the collector and the electrode sys-tem are completed and will be shipped to CERN. As shownin fig. 1 the EBIS rests on a platform above the trap. Thisplatform has been completed and the high voltage platformfor the EBIS has been mounted on top of that support.4 MASS SEPARATORThe S-shaped beam line between the EBIS and the LINACconsists of a mass separator [6] to separate the few highly-charged radioactive ions from ions originating from theresidual gas. The deflecting magnet has been ordered andthe construction of the electrostatic elements has been com-pleted. The electrostatic lenses are now in production. Themassive ridge which carries the electrostatic deflector andthe vertical beam line of the separator (fig. 1) will bemounted to the same concrete tower which carries the trap-EBIS transfer beam line.5 LINACThe RFQ is the first structure of the LINAC [7]. It isnow fully assembled, which means the water cooled groundplates, the stems and the mini-vane like quadrupole elec-trodes are mounted in the tank and the capacitive plungersare installed, cabled and tested. The vacuum system hasbeen installed and first vacuum tests have been performed.Low level frequency tuning and flatness measurementshave been done. Alignment of the electrodes, final adjust-ment of the voltage flatness and the installation of the in-coupling loop are presently being performed.The IH-structure of REX-ISOLDE [8] is a short versionof the IH-tank1 of the CERN LINAC III [9] and consistsof a center frame which carries the drift tubes and two halfshells carrying cooling jackets. The first acceleration sec-tion is followed by an inner tank quadrupole triplet lens,which has been delivered and will be installed after sometest measurements and the delivery of the IH-vacuum tank.The drift tubes and the stems are completed and are nowbeeing copper plated together with the IH-vacuum tank.The piston tuners are in production. The change of the fi-nal energy of the IH-structure via the piston tuners has beenexamined once more by a detailed MAFIA model of thepower resonator. The calculations are in very good agree-ment with measurements taken from the vacuum tank of thepower resonator and show the required tuning by changingthe half shell height [10].The production of the three seven gap spiral resonatorsforming the back part of the LINAC [11] is almost finished.The design velocities of the resonators were fixed to 5.4%,6.0% and 6.6% of the velocity of light and the field opti-mization at the operation frequency of the power amplifiers(f=101.28 MHz) of the three down scaled models resultedin an achievable resonator voltage of 1.75 MV at 90 kW in-coupled rf power.The 5.4% und 6.0% power resonators arefinished and ready for high power rf and beam tests. Fig. 2presents a view inside the resonator. The resonance struc-ture is connected to the tank via three stems, in which thecopper hollow profiles for the cooling of the arms and thedrift tubes are brazed together. Fine tuning is done with atuning plate. With segments connected on the half shell theso called rough tuning to 101.28 MHz is done. The res-onator is seen here on a test bench where the low level rfmeasurements were done.The 6.6% resonator is assembled, the tuning to the am-plifier frequency of 101.28 MHz is presently done.So far low level RF measurements have been performedwith the 5.4% and 6.0% resonator yielding parametersshown in table 1. In particular, these measurements showthat a resonator voltage of 1.9 MV can be expected with arf power of 90 kW, which is safely above the design volt-age of 1.75 MV. As the first out of three rf power amplifiers1956Proceedings of the 1999 Particle Accelerator Conference, New York, 1999Figure 2: The 5.4% power type resonatorproviding 100 kW with a duty factor of 10% has been de-livered in December 1998, high power and beam tests havenow been started. The second rf amplifier is in productionand will be delivered directly to Munich. The residual threerf power amplifiers will be completed until end of 1999 anddelivered directly to CERN.The set up of the fully tested 7-gap-resonators at CERNis planned to take place in autumn 1999.parameter 5.4% resonator 6.0% resonatorf [MHz] 101.28 101.28Q–value 5620 50 5420 50Z [M/m] 71 6 68 5U0[MV] 1:9 0:1 1:9 0:1Table 1: Measured parameters of the 5.4% and 6.0% powertype resonators, f = frequency, Z = shunt impedance,U0isthe expected resonator voltage reached with an rf power of90 kW.6 TARGETThe MINIBALL -detector array [12] consists of a newgeneration of Ge-detectors with large full-energy peak effi-ciency to make an optimum use of the expensive radioactivebeams. With its compact arrangement it is mainly suited fordetecting events with small -ray multiplicities. In the finalsystem the array will consist of 14 clusters with 3 individu-ally encapsulated 6-fold segmented Ge-detectors. A proto-type has been tested and have shown resolutions around 2.1keV at 1.33 MeV -energy. 6 Clusters are expected to beoperational when REX-ISOLDE starts operation. The elec-tronics for MINIBALL will be purchased from the com-pany XIA; in contrast to former Ge-detector electronics,all analog circuits are replaced by digital electronics usingflash ADC’s and DSP’s. The target chamber is completedand has been vacuum tested. Prototypes of the particle de-tectors (double sided silicon strip detector DSSSD) havebeen produced and tested with an alpha-source.7 REFERENCES[1] D. Habs et al., Nucl. Phys.A616199729c[2] D. Habs et al., Nucl. Instrum. and Meth.B1261997218[3] D. Habs et al., Nucl. Instrum. and Meth.B1391998128[4] F.Ames, G. Bollen, G. Huber and P. Schmidt, ”REXTRAP, anIon Buncher for REX-ISOLDE”, presented at the ENAM98,Michigan, USA, June 1998[5] F. Wenander, Ph.D. thesis, Chalmers University of Go¨theborg1998[6] R. Rao et al., ”Beam optics Design of the REX-ISOLDE q/m-Separator”, to be published in NIM A[7] T. Sieber et al., this report p.xxx[8] S. Emhofer et al., contribution to LINAC98[9] D. Warner et al., ”CERN Heavy-Ion Facility Design Re-port”CERN 93-011993[10] H. Bongers et al., contribution to LINAC98[11] H. Podlech et al., Nucl. Instrum. and Meth.B1391998447[12] P. Reiter et al., contribution to LINAC981957Proceedings of the 1999 Particle Accelerator Conference, New York, 1999

Status of the REX-ISOLDE project

Status of the REX-ISOLDE project

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