In the early 1970s, when the electron-positron storage ring DORIS was constructed, Siegfried Wolff moved over to magnet design and measurement. He designed the compensation coils for a DORIS experiment equipped with a superconducting solenoid, and under his leadership the magnetic measurements for the larger storage ring PETRA were carried out. When the proton-electron collider HERA was proposed, Siegfried Wolff joined the task force which was formed by Bjorn Wiik to design and construct the superconducting accelerator magnets of the proton ring. Wolff spent a sabbatical at Fermilab in 1979/1980 where he worked in the superconducting magnet group and acquired a thorough knowledge of the design principles and construction of the superconducting dipoles and quadrupoles for the Tevatron. Back at DESY he contributed heavily to the design of the HERA dipoles and quadrupoles, and in his group of engineers and technicians a number of protype dipoles were built that performed very well and exceeded the design field of 5 Tesla. In 1984 a radical design change was proposed to increase the field capability of the magnets and improve their quench safety. The warm-iron yoke of the Tevatron-like design was to be replaced by a cold-iron yoke directly surrounding the aluminium-collared coil. Within record time Wolff’s group built a short prototype of the new dipole which reached a field of 6 Tesla without training. The new magnet concept proved extremely successful in the industrially produced HERA magnets and had a strong impact on the design of the LHC magnets. During the construction phase of HERA, Wolff and his group performed the electric and cryogenic installation of the HERA proton ring.

 

When the HERA collider was completed, Wolff became head of the cryogenics group at DESY. He and his group contributed strongly to the successful R&D on superconducting cavities with accelerating fields above 25 MV/m, which was carried out by the international TESLA collaboration. Wolff’s group was also involved in the cryostat construction and provided the cryogenics for the TESLA Test Facility linac which was later upgraded to the free-electron laser FLASH.

 

Siegfried Wolff was a superconducting magnet expert of international reputation. He was a member of various advisory committees, among them the LHC Machine Advisory Committee, and he was co-author of a book on superconducting accelerator magnets. Siegfried Wolff will be remembered by his friends and colleagues for his great technical competence, his fairness and reliability, and his willingness to accept responsibility for demanding projects.

(By friends and colleagues at DESY)

Dahl grew up in Bergen, Norway, from the age of 4 until he was 17.  He then came to the U.S. and served three years in the U.S. Army, including two years stationed on Guam in the Pacific.  Taking after his father, Dahl was interested in science and physics from an early age.  He studied science during his Army years, and after leaving the service he entered the University of Wisconsin, obtaining his Ph.D. in Physics in 1960.  His post-doctoral work was done at the Niels Bohr Institute in Copenhagen, Denmark.

 

Per Dahl joined the Brookhaven National Laboratory (BNL) in 1963.  He arrived at a time when superconductors were beginning to move from laboratory development to industrial production. At this time, development of accelerator magnets using NbTi and Nb3Sn began. Per became involved in the design of these magnets early in his BNL career and acquired a good understanding both of the materials and their use in magnets.  He put this knowledge to good use later in his BNL career when he became the principal person writing about magnets and superconductors for technically-oriented audiences.  This work also provided him with an opportunity to display his skills as an artist. His drawing that shows all the critical components of a superconducting cable is still used in talks for visitors to Brookhaven. 

 

Per began working on the larger stage of the Superconducting Super Collider (SSC) in 1987, where he continued work documenting the magnet program.  When the SSC effort moved from the design location, Berkeley, to the laboratory location in Texas, Per expanded his work to include both the documentation of the conventional construction effort and preparation of information in support of the SSC mission (e.g., publisher of the SSC News).

 

Following termination of the SSC project in 1993, Per moved to the Accelerator and Fusion Research Division at Lawrence Berkeley National Lab (LBNL).  During much of that time he was on leave to the Office of High Energy Physics, where he was Program Officer for a number of university grants.  He also consulted with BNL about the nascent RHIC magnet system. He retired from LBNL in 1996 but kept contact with the lab through a visiting scientist appointment and work at the Office for the History of Science and Technology at UC-Berkeley until 2005.

 

Dahl is the author of numerous scientific papers and several books:  From Nuclear Transmutation to Nuclear Fission, 1932-1939 (Institute of Physics Publishing, Co., Bristol, England and Philadelphia, PA, USA, 2002); Heavy Water and the Wartime Race for Nuclear Energy (Institute of Physics Publishing, Co., UK, Bristol England and Philadelphia, PA, USA, 1999), which was featured in the NOVA TV-production, Hitler’s Sunken Secret, DOX Production, London, 2004; Flash of the Cathode Rays: A History of J.J. Thomson’s Electron (Institute of Physics Publishing, Co., UK, Bristol, England and Philadelphia, USA, 1997); Superconductivity: Its Historical Roots and Development from Mercury to the Ceramic Oxides (American Institute of Physics, New York, 1992); Ludvig Colding and the Conservation of Energy Principle: Experimental and Philosophical Contributions, The Sources of Science N. 104 (Johnson Reprint Corp., New York and London, 1972).

 

Throughout his life, Dahl was able to pursue his love for physics, art and his family.  While at Brookhaven, he was a president of the South Bay Art Association (1967-1968), and he was also the president of the Brookhaven National Laboratory Art Society for several years.  He was a fellow of the American Physical Society.

 

He is survived by his devoted wife of 45 years, Eleanor, and two sons: Erik (married to Christa), of Pebble Beach, CA; and Thomas (married to Jo) and two grandchildren, Emily and Alex, of Westford, MA. 
 

Peter Wanderer, Brookhaven National Laboratory, NY
Eleanor Dahl, Emeryville, CA
Erik J. Dahl, Pebble Beach, CA and Thomas F. Dahl, Westford, MA