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| How Darmstadt Became the Center of Heavy Ion Physics |
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How Darmstadt Became the Center of Heavy Ion Physics
GSI owes its existence to two fortunate circumstances: the development of a
new type of accelerator and a "campaign" by physics professors in Hesse
to set up a joint center for university research. The result was a research
center of international standing, which is nowadays used by more than
1000 scientists from both domestic and foreign universities and research
institutes. And the fundamental questions dealt with here today are just as
manifold as at any time during the last 25 years.
The Gesellschaft für Schwerionenforschung (Society for Heavy Ion Research or GSI) in
Darmstadt - Germany's national center for heavy ion physics - owes its existence to two
developments. Although occurring quite independently of each other, both turned out to be of
key importance in making GSI what it is today. One of these developments was the emergence
of a new type of accelerator. The other was a shift in philosophy at the universities, which had
become interested in establishing a central laboratory for advanced physics research.
Back in 1966, Hessian university lecturers set up a nuclear physics study group called the
"Kernphysikalische Arbeitsgemeinschaft Hessen" (KAH) with the aim of establishing a central
accelerator laboratory for the physics institutes at the Hessian universities. Inspired by the old
idea of uniting research and teaching, the intention was that the laboratory should aid both
research at an institute of excellence and the education of students according to a new concept.
Following the then customary practice of "to each institute its own accelerator" some twenty
small to medium-size accelerators - tandems, cyclotrons, Van de Graaffs and electron linacs -
had already been constructed in the Federal Republic since the mid-50s. However, it was now
time to plan extensions involving new accelerator facilities in Marburg and Frankfurt. Rising to
the challenge, Wilhelm Walcher, Erwin Schopper, and Peter Brix decided to put aside their
own local interests and - in both a courageous and farsighted step - strive for a joint center
with a correspondingly more powerful accelerator.
At the start of this project it was necessary to agree on an acceptable and forward-looking
research area. The thorough discussion and investigation that followed crystallized into two
options: heavy ion physics at initially low energies or alternatively, medium energy physics, i.e.
studies of elementary processes at comparatively higher energies. This decision had
consequences regarding the choice of accelerator, which were presented in a memorandum of
1966. Since the early 1960s heavy ion physics had been pursued using the tandem accelerator
at the Max-Planck-Institut für Kernphysik (Max Planck Institute for Nuclear Physics) in
Heidelberg. Moreover, with the appointment of Rudolf Bock to Marburg in 1965, this area of
work also found its way into the KAH, with the result that, together with the Frankfurt Theory
Group based around Walter Greiner, there was a well-staffed research potential in the field of
heavy ion physics.
Accepted as a scientific goal
In addition, the neighboring universities were developing experiments and equipment highly
relevant for heavy ion research. These included mass separators at Giessen and Marburg,
detectors at Frankfurt, Heidelberg, and Marburg, as well as nuclear chemistry techniques at
Darmstadt, Mainz, and Marburg. All these developments helped to give a more varied
structure to the scientific program, thus making heavy ion physics generally accepted as the
scientific goal of the new center from a very early stage.
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The UNILAC, whose principal concept Christoph Schmelzer had already devised in the late
1950s, was an essential precondition for founding GSI at Darmstadt. Later Prof. Schmelzer
became the first Scientific Director of GSI. This photo was taken in 1978.
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The other founding pillar of the GSI—the development of the accelerator—goes back even
further. In the late 50s,
Christoph Schmelzer,
who at the time was working in Geneva on
developing the CERN proton synchrotron, had considered possible ideas for a linear
accelerator for ions up to uranium. Schmelzer was way ahead of his time because in those days
even carbon and oxygen ions were regarded as "heavy." Following his appointment to the
University of Heidelberg, Schmelzer systematically pursued the development of this type of
accelerator. His UNILAC (UNIversal Linear ACcelerator) was to be a high-frequency,
variable-energy accelerator, capable of accelerating ions of all elements to energies above the
Coulomb barrier. Given that the "accelerator world" of the time basically consisted of "off-the-
shelf" tandems and cyclotrons, this was a bold and farsighted venture.
The UNILAC development work was placed on a broader footing by a Heidelberg University
study group. The group, which by 1963 had ensconced itself on the premises of the Max-
Planck-Institut für Kernphysik, was funded by the then Federal Ministry for Scientific
Research. The work involved developing high-frequency structures, ion sources, and other
new technologies. By carrying out experiments using the Institute's tandem accelerator, it was
possible to determine the parameters that were relevant for the construction of the UNILAC.
These included the ion charge-exchange cross-sections and the charge distribution after passing
through foils or gases.
Once Christoph Schmelzer had been won over to the KAH project in 1967, it was quickly
agreed that the accelerator to be built should be a UNILAC - a fact documented in a second
memorandum of July 1968. Yet as the scale of the enterprise grew, so too did insight into what
it involved. The KAH, which had originally concentrated on the state of Hesse, had since
spilled over into Heidelberg and Mainz, while the project itself had rapidly outgrown the role
of a single establishment funded only by the state of Hesse. Now the aim was to acquire the
federal government as a sponsor of this laboratory alongside the state. In other words the
project was to become a major research center - similar to Deutsche Elektronen Synchrotron
(German Electron Synchrotron or DESY), which had been founded in Hamburg in 1959.
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An undeveloped area of damp woodland situated to the north of Darmstadt was chosen as the
site for the new center. So that building could commence, workers set about clearing trees
from the new site in March 1971.
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With regard to the level of staffing, the project originally envisaged some 330 members of
staff. They would be needed to operate the accelerator and to provide technical support for the
scientific equipment, while simultaneously undertaking research of their own to a certain
extent. The larger part of research, some two thirds, was to be carried out by university staff,
whereby the main impetus was expected to come from Ph.D. students. As for the location, the
present site to the north of Darmstadt, at that time an undeveloped area of damp woodland,
was chosen from a number of proposals.
A certain amount of turbulence arose towards the end of 1968 when the Kernforschungsanlage
Karlsruhe (Nuclear Research Center or KFA at Karlsruhe) made a surprise bid to acquire the
UNILAC. While those interested in the accelerator aspects of the project viewed this
application with an open mind, those representing the universities were adamant in their
opposition. The large nuclear research centers were not exactly user-friendly places. What the
Hessian users were aiming for was closeness to the university - also with regard to the
organization of the laboratory - free access for students and autonomy from encrusted
structures. What they did not want to see were barbed-wire fences, pass controls, and
incorporation into a "typical project" administration. In the end the Hessians more or less got
their way - it was their "shopping list" of requirements which essentially shaped the GSI in
Darmstadt.
This poaching attempt also had another important consequence. Both camps became embroiled
in arguments about a new, completely novel accelerator concept, involving helical resonators,
developed at the University of Frankfurt. Though nothing came of it, the debate "helical versus
conventional accelerator structures" was to keep the GSI occupied for some time after its
formation.
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Following the example previously set by DESY in Hamburg, the GSI formed a five- man
management committee known as the Scientific Directorate. This photograph, which was taken
in February 1971, shows four members of the Directorate - from left to right: Prof. Rudolf
Bock, Prof. Peter Brix, Prof. Christoph Schmelzer and the administrative director Hans Otto
Schuff - in conversation with Mr. Flöter, an official from the Regional Finance Office at
Wiesbaden.
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Without the active involvement of the state of Hesse, the new center would not have
materialized in the form originally conceived. Hesse was prepared, for instance, to provide the
extra funds needed to cover the difference in cost between the new site and the cheaper
Karlsruhe option. Whereas, the home state usually only provided 10% of the funding required
to finance a major research center, the state of Hesse was prepared to cover 20% of costs
during the period of construction. In other words, the government contribution would be
temporarily reduced from the normal 90% to 80%.
The GSI was officially constituted as the "Gesellschaft für Schwerionenforschung mbH" on
December 17, 1969. It had the legal form of a private limited company and the status of a
"Großforschungseinrichtung" - a major research center - of the federal government and the
state of Hesse. The research center was headed by a five-strong management committee - the
Scientific Directorate.
This created a satisfactory framework for realizing both the
scientific and the higher educational objectives. Finally, in 1971, following numerous
committee and advisory meetings, UNILAC was chosen as the accelerator. The accelerator
question had at last been put to rest. The entire construction work and project coordination
were now in the hands of GSI. Moreover, thanks to preliminary work carried out in
Heidelberg, the ordering of components could begin.
Generous funding for the university groups
In keeping with the founding fathers' idea of "proximity" to university interests, the university
groups were involved in the preparation of experiments from the planning stage onwards. A
new type of funding model - later known as the GSI model - was also established. It
incorporated a budget allowance for the university groups so that they could develop methods
and equipment, and finance staff. This budget item initially amounted to over 70% of GSI
internal research funds and still accounts for around 30% of these funds today. Thanks to such
generous funding, the university groups were able to quickly get moving on putting the broad
research program into effect.
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By June 1973 things had progressed so far that future users were in a position to
participate in the topping-out ceremony.
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As far as research was concerned, the symbolic objective had always been the search for
superheavy elements. However, this by no means excluded a wide range of other fascinating
topics from the research program. Questions from the areas of nuclear reaction physics,
nuclear structure, atomic physics, and nuclear chemistry were attracting interest, as were
potentially pioneering new applications. Moreover, the surrounding universities were showing
keen interest in developments, and played an important role in helping design and develop the
first fifteen experimental areas.
In November 1975, after just four years construction, the center's UNILAC produced its first
heavy ion beam. Part of the experiential setup had also already been completed. The challenges
still faced included the conditioning of the accelerator, improving the quality of the beam, and
developing sources capable of producing the broad spectrum of ions required. Mastering these
challenges was to occupy the accelerator team completely over the next few years. That having
been said, there were also achievements to celebrate along the way. For instance, in April
1976, just a short time after UNILAC began operation, uranium was accelerated for the first
time anywhere in the world - a milestone in the history of the GSI.
The 330 staff originally planned had meanwhile grown to become around 450. However, this
was still too few for the considerably enhanced work of the new laboratory. Unfortunately, the
federal government's research funding had also reached the limits of its growth - long before
the GSI's infrastructure had been adequately developed. This turned out to be a very serious
problem, particularly later when it came to financing the extension of the accelerator facility.
Despite these deficiencies, the prospects looked bright. The ever-growing number of users, the
positive response of the universities, and the growing interest in the center, even outside the
Federal Republic, were irrefutable evidence that GSI had become the undisputed center of
heavy ion research.
In 1974 the GSI entered a new phase in its history - and at the same time a new era of nuclear
physics - even before the UNILAC had supplied its first beam. This departure was motivated
by the desire to investigate nuclear matter at a high density and temperature, and thus evaluate
the astrophysical significance of this type of matter in connection with supernova explosions
and neutron stars. High-energy, heavy ion collisions produce a whole range of interesting
phenomena associated with such cosmic occurrences. These include cooperative effects, so-
called delta matter, and exotic nuclides. Possible applications in the areas of medicine and
materials research were also discussed.
However, the topic dominating all these discussions was the nuclear equation of state, in
particular theoreticians' predictions of a phase transition to a new state of nuclear matter - the
so-called quark matter. According to the state of knowledge at that time, a compression of
nuclear matter could only be achieved - if at all - by colliding heavy nuclei at relativistic
energies. The aim was therefore to move into the "relativistic" energy range. In this region,
which was 100 times higher than that provided by the UNILAC, the ions would be accelerated
to speeds approaching that of light.
At the same time, the BEVALAC accelerator for heavy ions was nearing completion at the
Lawrence Berkeley Laboratory (LBL) in California. The BEVALAC was actually a hybrid
accelerator produced by combining the Super HILAC and the old Bevatron. With an eye on its
own extension plans, GSI decided it would be a good move to participate in the pilot studies of
this project. Thus it was, in fall 1974, that a joint GSI/LBL group began conducting
experiments on the BEVALAC.
The way to higher energies
In 1976, GSI presented its new project plans for moving into this new territory. At the heart of
its recommendations was the construction of a heavy ion synchrotron (SIS), which would be
capable of producing an acceleration energy of 1 GeV per nucleon and would utilize the
UNILAC as an injector. In the meantime, GSI's enthusiastic and successful participation in the
experiments on the BEVALAC had proved its worth: it was now clear that the investigation of
nuclear matter at maximum densities and the transition to quark matter would require
significantly higher energies. The GSI accelerator group immediately set about developing
alternative scenarios as a response to the new situation. In particular, the feasibility and cost of
a two-ring machine for accelerating uranium to a final energy of 10 GeV per nucleon were
closely scrutinized.
From 1978 to 1983 the extension plans underwent substantial modifications. One of the main
dilemmas of these years focused on the different beam requirements of the two communities of
users: the initiators of nuclear matter physics wanted the highest possible energies, whereas the
other users were interested in high beam intensity at moderate energy. The solution to the
dilemma was ultimately arrived at via a different route altogether.
CERN's accelerator scenario was - at least in principle - ideally suited to the acceleration of
heavy ions at high energies. All that was missing was the appropriate injector and, for the
moment, the acceptance of such experiments by the particle physicists. After almost two years
of discussions and some tough negotiating with CERN, an agreement paving the way for
CERN's entry into the field of heavy ion physics was finally reached in August 1983. GSI and
LBL took on the joint task of developing an injector for relatively light ions such as oxygen
and sulfur. Although this step may sound like a modest start, it was to have far-reaching
consequences: at GSI the way was now clear for the small machine.
Following on the heels of these developments came the idea of cooling the heavy ion beam.
Since 1982, GSI had been planning the introduction of a modest cooler ring, known as SITAR.
The idea was to conduct machine experiments in conjunction with the "Inertial Fusion Using
Heavy Ion Beams" research program, which was running at the center. Although the cooling of
heavy ions was new at that time, nuclear and atomic physicists were quick to recognize the
potential of beam cooling.
A second high point to rank with the UNILAC decision
Under the new Scientific Director of GSI, Prof. Paul Kienle, it was possible to integrate this
aspect into a new extension proposal, which was subsequently realized, alongside a
correspondingly expanded research program. Thus it was that the SIS/ESR project came into
being - much to the relief of the committees and the users. After the UNILAC
decision, this was the second high point in the history of GSI.
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In the second half of the 1980's a huge building site sprang up immediately next to the
existing GSI buildings: the extension resulting from the SIS/ESR project. In the background
of the picture it is possible to make out the first signs of the ring tunnel of the future
heavy ion synchrotron.
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On April 23, 1990, the SIS/ESR extension was officially handed over in the new experiment
hall. Numerous guests from Germany and abroad attended the ceremony.
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Once the high-energy aspect became irrelevant, the original concept for a normal synchrotron
with a higher repetition rate and a final energy of 1.3 GeV per nucleon for uranium was quickly
agreed upon. The cooling and storage of heavy ions were the key new features. Moreover,
high beam intensities would also be possible. For these reasons, the new concept was of
particular interest for heavy ion plasma physics and research aimed at generating exotic nuclei.
The new project proposal was presented to the committees in 1984 and approved by the
shareholders of GSI - the federal government and the state of Hesse - one year later. The
project was realized according to schedule and inaugurated in 1990.
The research landscape at GSI was considerably enriched in this period by new research topics
and a new generation of experimental facilities. The number of users increased to over 1,000
thanks to the participation of more than 25 German universities and numerous international
research laboratories. This, in turn, generated new international contacts. In terms of scale, the
GSI accelerator facility was expanded to more than twice its previous size, although the
growth in staffing, unfortunately, remained minimal.
Crystallization seed for two large CERN collaborations
At the end of this project, the GSI high-energy group at LBL became the seed of
crystallization for two large-scale experiment collaborations at CERN. Thanks to tremendous
initiative on the part of GSI and the active support of many colleagues, new opportunities have
been opened up here for research - a development which has attracted a lot of other groups in
its wake. The search for the quark-gluon plasma has, however, remained the dominant goal. In
addition, GSI was also heavily involved in the construction of a larger injector at CERN. The
"lead injector," as it is commonly known was officially commissioned in 1994. Since November
1994, it has been used intensively for an experimental program involving lead beams at the
SPS. It will also provide the basis for accelerating lead ions in CERN's "Large Hadron
Collider" (LHC) once this starts to supply the highest particle energies ever produced during
the coming decade.
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The occasion of the 85th birthday of Christoph Schmelzer brought together the four
Scientific Directors of GSI at an event organized by the University of Heidelberg, the
Max-Planck-Institut für Kernphysik and GSI (from left to right: Prof. Schmelzer, Prof.
Gisbert zu Putlitz, Prof. Paul Kienle and the present Director Prof. Hans Joachim Specht).
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After a period spanning 25 years of heavy ion research at GSI and four Scientific Directors,
the fundamental questions of nuclear and atomic physics have not become any
fewer. In contrast, there are now many more such questions requiring answers. Relativistic
heavy ion physics increasingly combines the interests of particle and nuclear physicists.
Moreover, there is a whole series of significant developments taking place within applied
research. Heavy ion research is nowadays an interdisciplinary field. And, whether it be for the
universities or international collaborations, GSI has a vital integrating role to play at the heart
of this research field.
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