H. Jürgen Kluge

Prof. H-Jürgen Kluge (born 25 April 1941) is a physicist probably best known for the development of ion-storage devices and methods for accurate measurements of nuclear masses.

Career

University of Mainz

In the early eighties Jürgen Kluge at the University of Mainz considered mass measurements of trapped ions. Gernot Gräff, who worked at the same institute, had developed a time-of-flight technique for the determination of the electron–proton mass ratio from the respective cyclotron-resonance frequencies. During this period the determination of the fundamental properties of the electron was of the highest interest. This included the measurement of the g-factor of the free electron, again with a Penning trap, for which Hans Dehmelt eventually won the Nobel Prize in physics in 1989. Jürgen decided to apply Gräff’s method to the determination of masses of unstable nuclei. A setup was designed and built at Mainz, which comprised two Penning traps in a row. Following the idea of separation of functions, one trap served as the source of well-prepared ions for the actual mass measurement at the second trap. The operation of the setup thus included the ion transfer from one trap to the other. The first successful ion transfer was reported in 1986.

CERN

A proposal to the scientific committee at CERN/Geneva for starting such an experimental program at ISOLDE, the on-line separator for short-lived nuclei at the synchrocyclotron of CERN, was accepted in 1985.

Interestingly, at the same time Gerald Gabrielse proposed using a Penning trap mass spectrometer at CERN for the investigation of antiprotons, which turned out to become another very important and successful endeavor with ion traps.

At that time Jürgen acted as ISOLDE group leader. In the following years the tandem Penning trap setup was transferred from Mainz to ISOLDE and came to be known as ISOLTRAP. It started the measurements of short-lived nuclides in the late eighties and has been at the forefront of the field since then. In its early phase ISOLTRAP used a stopping-reionization procedure in which the 60 keV ions, delivered from ISOLDE in a continuous beam, were implanted in a rhenium foil. This foil was then heated to release and surface-ionize the collected atoms. Thus, only surface-ionizable elements were accessible.

This major limitation was overcome by the introduction of a third ion trap designed to accumulate the ions directly without any implantation, to cool them with buffer gas and to release them as low-energy ion bunches. The first system of this kind was a large Paul trap, developed in collaboration with Bob Moore at Montreal. Short-lived mercury isotopes were the first nuclides of non-surface-ionizable elements studied with ISOLTRAP.

In the early years of ISOLTRAP the ring electrode of the trap was segmented into just two halves. However, it was soon realized that the ring was to be split into four segments for an efficient quadrupolar excitation and conversion of the ion’s magnetron motion into the cyclotron motion. This conversion is the basis of the direct determination of the ion’s “true” cyclotron frequency, $omega\_c\; =\; q\; e\; B\; /\; 2\; pi\; m$(for charge $q$, mass $m$ and magnetic field $B$), i.e. the (angular) cyclotron frequency in the absence of an additional electric field. Today all Penning trap mass spectrometers for radioactive isotopes employ this technique.

At the same time it was also realized, and experimentally confirmed, that the additional application of a buffer gas leads to cooling and mass selective centering of the ion motion. The method was studied in detail and the first Penning trap used in ISOLTRAP was reconstructed and optimized for efficient accumulation, cooling, and ion beam purification via isobar separation. Now implemented in many mass spectrometer systems for the study of exotic nuclei, this technique is also used in the first stage of a post-accelerator system at ISOLDE/CERN. The method was also rapidly adopted in analytical chemistry. Not only the methods were spreading out, but also the instruments: when the use of ion traps for the study of unstable isotopes and antiprotons was originally proposed, Prof. em. Ingmar Bergström, former director of the Manne Siegbahn Institute at Stockholm, was a member of the Scientific Policy Committee at CERN. He became very interested in the new technique and initiated his own trap project named SMILETRAP. The system was built and tested at Mainz and then transferred to Stockholm: The Stockholm-Mainz Ion LEvitation trap (SMILETRAP) has specialized in highly charged ions and thus achieves high resolving powers at the corresponding cyclotron frequencies. Thus, the ToF detection of ion cyclotron resonances joined other methods of highest accuracy as applied to stable species.

Guy Savard, who learnt the ion-trap business during a postdoctoral stay at ISOLTRAP, later went on and built the Canadian Penning Trap Mass Spectrometer (CPT) now hosted at the Argonne National Laboratory. Similarly, Georg Bollen, who had been in charge of ISOLTRAP for more than a decade, has recently built up a new ion-trap system at the National Superconducting Cyclotron Laboratory at Michigan State University.

LEBIT, the Low-Energy Beam and Ion Trap Facility, is the first system of its kind allowing high-precision mass measurements to be performed on short-lived isotopes produced by fast-beam fragmentation and delivered at half the speed of light. Jürgen Kluge has always been open for any kind of collaboration. As coordinator of European networks he promoted the idea of trap-based nuclear-physics research. Further projects that took advantage of the know-how exchange are JYFLTRAP at Jyväskylä, WITCH at CERN, and TITAN at TRIUMF/Vancouver. Jürgen also included the theoretical aspects of the various nuclear and atomic physics research into the networks, bilateral collaborations, and close contacts.

Move to GSI at Darmstadt

Not being content with ISOLTRAP and its on-going success, Jürgen himself started two new trap projects, SHIPTRAP and HITRAP after his change from the University of Mainz to GSI at Darmstadt (Gesellschaft für Schwerionenforschung) as the atomic physics group leader. He also realized the great possibilities of storage-ring based mass spectrometry and supported the very successful efforts at GSI. As described, Jürgen is probably best known for the development of ion-storage devices and methods for accurate measurements of nuclear masses. However, in more general terms he has been a key player in pioneering the application of methods of atomic physics at accelerators. Starting with the work on his doctoral thesis at Heidelberg.

CV of Prof. H.-Jürgen Kluge

25 April 1941 Born in Sorau, Germany

1960–1963 Study at the University of Bonn

1963 Pre-diploma examination at the University of Bonn

1963–1967 Study at the University of Heidelberg

1967 Diploma examination at the University of Heidelberg

1970 Dissertation at the University of Heidelberg on “Hyperfine structure of the lowest P-states of alkaline earthsisotopes” (Ph.D.)

1970–1972 Research stay at CERN, Geneva, Switzerland

1972 Assistant Professor for Experimental Physics at the University of Mainz1974–1975 Paid Scientific Associate at CERN

1975 Habilitation for Experimental Physics at the University of Mainz

1978 Professor for Experimental Physics at the University of Mainz

1980–1981 Temporary replacement of Prof. G. zu Putlitz at the University of Heidelberg

1983–1984 Chairman of the ISOLDE Collaboration at CERN

1984–1987 Member of the PSCC-Committee at CERN (program advisory committee)

1985–1987 Research Scientist Staff Member and Leader of the ISOLDE Group at CERNsince 1985 Associate Editor of “Hyperfine Interactions”

1988 Fellowship of the Japan Society for Promotion of Science

1989–1992 Member and Vice Chairman of the Program Advisory Committee of GSI, Darmstadt

1990 Helmholtz-Prize for Physical Measuring Techniques in Medicine and Environmental Monitoring

1990–1996 Officer of the International Union of Pure and Applied Physics (IUPAP), SUNAMCO (C2)

1991–1994 Member of the Executive Committee of the German Physical Society (DPG)

1991–1994 Member of the Executive Board of the Deutsche Gesellschaft für Massenspektrometrie(DGMS)

1992 Call for a chair in physics at the University of Heidelberg and as a Leading Scientist at GSIsince 1994 Professor of Physics at the University of Heidelberg and Head of Atomic Physics Division/GSI

1995–1998 Associate Member of the International Union of Pure and Applied Chemistry (IUPAC)

1996–2003 Member of the Evaluation Committee “Hadrons and Nuclei” of the German Ministry for Research and Technology

1999–2005 Member of the Editorial Board of the European Physical Journal D

1999–2005 Research Director of GSI

2000–2004 Member of the evaluation committee (Fachgutachter) for atomic physics proposals of the Deutsche Forschungsgemeinschaft (DFG, Germanscience foundation)

2000–2004 Member of the ISOLDE Neutron Time of Flight Committee (INTC) at CERN

2001–2004 Member of the Emmy-Noether Selection Board of the DFG (German science foundation)

2002–2004 Member of the PALS User Selection Board (kJ laser at Prague)

since 2000 Member of the Committee of the PTB Braunschweig for the Helmholtz Prize

since 2000 Member of the Advisory Board for Danish CERN Physics

since 2004 Member of the International Program Committee of the LMJ/LIL Facility (Laser MegaJoule and Ligned'Intégration Laser) of CEA-CESTA Center, Bordeauxsince 2004 Member of the JYFL Program Advisory Committee (cyclotron at Jyväskylä, Finland)

2005 Fellow of the American Physical Society

since 2005 Editor of Hyperfine Interactions