IV.1 Manpower and Training

The crucial element of any science, more important than facilities, instrumentation, or funding, are the people who pursue it. Reflecting a combination of circumstances, historical, economic, and sociological, there has been a substantial decline in the rate at which scientists, physicists and nuclear physicists, in particular, are being trained in the United States. Yet the continued need for nuclear scientists is considerable, with people trained in this discipline carrying out a variety of tasks in nuclear medicine, energy research, in many industrial research tasks and government service, in addition to providing the basic resource for continued research in the discipline.

It is becoming apparent that the rate at which nuclear scientists are being trained will not be adequate to meet the country's needs within the decade. Every year a large number of fresh Ph.D.'s trained in nuclear physics, and particularly in experimental nuclear physics, are hired by industrial laboratories with extraordinary alacrity. Their training in many aspects of advanced technology, the hands-on experience with relatively small-scale experiments where the student gains a measure of self reliance, seem to be factors in this phenomenon. And the forces of the marketplace are such that salaries in basic research positions cannot compete with those offered by industrial laboratories. The training in experimental nuclear science seems to be valued and this skilled manpower represents a major contribution of the field to the nation and to our society.

A healthy program of training nuclear theorists is also vital to the science. With the new construction plans, further upgrades, and fuller use of existing facilities, the theoretical efforts, presently severely limited by manpower, must also be strengthened. We recommend that the trend of the recent past, of increased funding for the buildup of strong theoretical programs be continued.

One reason that the shortage of nuclear scientists is not

more acute now is that the condition in a number of countries is the inverse of that in the United States-more scientists are being trained than there are open positions. Some of the best young scientists from abroad come to the United States shortly after getting their doctorates, and either return to their home countries after having spent their most productive years in American laboratories, or sometimes stay on permanently. This influx of young scientists is mutually beneficial, and even healthyleading to long term international ties-but it is not a viable long term solution to our manpower problems, since the training patterns and needs of other countries are also subject to change.

The reasons for the decline in U.S. graduate student enrollments in physics are complex. The fact that declining college enrollments have led to static and in some cases decreased faculty size at universities has had an especially strong impact on physics departments. For example, the ratio of junior to senior faculty positions in universities is lowest for physics among all the natural sciences. The fact that this has been widely discussed has caused many young people to decide not to take up physics as a profession. It is probably also true that the well-documented deterioration of the secondary school system in the United States is having an especially serious effect on basic training for the physical sciences. Students who have never been exposed to the excitement of science are unlikely to choose physics as a career path. Another effect is more peculiar to nuclear science. Unlike high-energy physics, which has been mostly a "user field" since its inception, university nuclear physics groups usually started with the operation of small in-house accelerators. With much research shifting to the larger facilities, the shutting down of many small university accelerators was inevitable. The psychological impact of having a facility at one's own institution closed down can be devastating and has slowed the momentum of Ph.D. training at the universities thus affected.

While it is important to upgrade science education at

all levels, the following recommendations, if acted on, would make physics in general and nuclear physics in particular more attractive to young people.

1. Programs which involve undergraduates in nuclear science research are extremely important in attracting students to the field. Many outstanding scientists were first attracted to a career in science through participation in such programs. A number of laboratories and universities have programs of this type; efforts should be made to strengthen and expand these, or to start them where they do not exist, if necessary with specific funding from the agencies. Similar programs to involve secondary school students in nuclear science research can also lead to long term benefits, and the involvement of secondary school science teachers in physics research will benefit the field and the nation.

2. Competitive predoctoral fellowships can contribute significantly in encouraging the best young people to study nuclear science. Any increase in the number of NSF Fellowships will naturally help all disciplines and is strongly supported. In addition, we suggest to the Department of Energy that it consider committing funds specifically for fellowships in nuclear science.

3. A competitive program of temporary direct support of new research initiatives by young nuclear scientists should be funded. This would encourage scientists starting in the field to develop new initiatives and an increased measure of independence.

4. Many existing small user groups in nuclear science are so constrained that they put all available funds for manpower into hiring research associates. With no direct technical or engineering staff working with these groups, they either become too dependent for instrumentation development and technical planning on the facility where they are users or an undue burden falls on in-house students and research associates. While clearly some such work should properly be part of a training in nuclear physics, it would considerably strengthen small university user groups to be able to hire their own technical staff, either engineers or scientists specializing in technical problems. The impact on developments of instrumentation, on the style and quality of research and on the attractiveness of doing research as a graduate student in the user mode could be considerable. We recommend that the agencies seriously consider funding supplementary requests for such manpower.

5. Educational aspects, the importance of attracting high caliber graduate students to nuclear physics and giving

them the best possible training, should be given consideration in decisions on new facilities.

With the variety of challenging and important research opportunities outlined in Chapter II, both qualitative and quantitative aspects of our manpower and training ultimately determine the viability of the field. The steps outlined here will help the United States to continue to play a leading role in this area of basic research and to continue to train young scientists in skills and techniques which society puts to excellent use in numerous applications.

IV.2 Accelerator Facilities

The particle accelerator is the basic tool of the nuclear physicist and the development of accelerators is tied intimately to the development of nuclear science. Accelerators have also found powerful applications in almost every science ranging from nuclear medicine, through condensed matter and materials research to archeology and geophysics, where use of accelerators as ultra sensitive mass spectrometers has recently had dramatic consequences. The development of accelerators is an essential part of our science that has suffered all too often in times of budget stringencies and manpower shortages. There are major opportunities in the field of accelerator physics, many of them outside the immediate concerns of basic nuclear physics research, and our field must train specialists in this area of applied physics in numbers sufficient to meet the challenges in the future.

During the last decade a number of important advances have been achieved in accelerator physics: the uses of superconducting magnets, of superconducting resonators capable of producing high radiofrequency fields for the acceleration of particles, of beam cooling in storage rings, to mention just a few.

The accelerator facilities of nuclear physics are here separated into two groups. There are nine major national facilities whose operation and research programs account for about 80% of the budgets for experimental nuclear physics. These facilities are used for an important share of the research effort by the national and international community of scientists, with experimental time allocated with the help of Program Advisory Committees. The remaining support is largely for dedicated smaller university research accelerators that play an important role in the education and training of graduate students (along with the major facilities), and in the pursuit of many important research goals.

A. MAJOR NATIONAL FACILITIES

The nine facilities listed here are all "user facilities" in the sense that, because of their unique characteristics, they are generally available to scientists throughout the U.S. and the world, and their experimental priorities are set on the basis of recommendations of Program Advisory Committees. These facilities vary in size from the large U.S. meson factory LAMPF and the one relativistic heavyion accelerator in the world the BEVALAC (which between them account for about two-thirds of the above mentioned 80%), to some much smaller and less costly-though still very important accelerators.

For each of these facilities we list present capabilities and future aspirations, without making specific priority recommendations on the implementation of the latter.

1. INTERMEDIATE ENERGY ACCELERATORS

The Los Alamos Meson Physics Facility (LAMPF) is a national facility providing both primary and secondary particle beams for an extensive program of research including nuclear, elementary particle, and condensed state physics. The heart of the facility is a linear accelerator providing a beam of protons of variable energy up to 800 MeV, intensity of 1 mA and a duty factor of 9%. A separate H ion source provides the capability of accelerating simultaneously a low current H beam with a high current of H+. The 800 MeV proton beam is used primarily for the production of secondary beams of pions, muons, and neutrinos. Several magnetic channels allow experimentalists to select independently the desired beams of secondary particles. Part of the proton beam is also used for neutron production, and with the completion of the proton storage ring (PSR), will provide an intense pulsed neutron source. H beams, polarized or unpolarized, can be obtained at different energies (down to 218 MeV) and used for studies of proton induced reactions. The H beam is split between the high-resolution proton spectrometer facility where nuclear structure studies predominate and the nucleon physics laboratory where a comprehensive program of measurements of the two nucleon system is carried out. An extensive program of nuclear structure studies with pions is carried out using the high-resolution pion spectrometer, EPICS. Other major hardware facilities include a n° spectrometer capable of measurements with energy resolution of ~1-2 MeV, a time projection chamber, and a large Nal(TI) "crystal box" facility. A new low-energy pion spectrometer, currently under construction, will be installed in the Low Energy Pion Channel to extend the capabilities for high resolution pion spectroscopy to 10-100 MeV.

The LAMPF user group currently has a membership of more than 900 scientists. Approximately 300-400 scientists

from ~90 universities are participating in research at LAMPF in any given year.

Future facility plans include an upgrade of the PSR area to provide a pulsed muon facility and a high intensity neutrino source. In addition to numerous planned developments and improvements in the present LAMPF accelerator, a design effort is under way for a major new future accelerator (LAMPF II) that would be based upon a 16-32 GeV synchrotron and stretcher ring injected by LAMPF. This accelerator would provide K-meson beams 100 times as intense as present facilities, as well as improved pion, muon, neutrino and antiproton beams.

The Bates Electron Accelerator Center of the Massachusetts Institute of Technology centers on a highintensity pulsed S-Band electron linac covering the energy range 50-750 MeV. The typical average current and duty cycle at present are 40 μamp and 0.5%, respectively. This laboratory is recognized worldwide for its leading contributions to high-resolution electron scattering. In the past five years, there has been substantial progress toward expansion of the facilities which includes: (1) increase of the energy to 750 MeV by a single recirculation of the beam through the linac, (2) construction of a second experimental hall (120′ x 80′), (3) construction of two large solid-angle spectrometers capable of measurement of momenta up to 400 MeV/c and 1300 MeV/c, respectively, (4) construction of a large opening angle n° spectrometer. In addition, a polarized injector will be installed in the immediate future for use in nuclear polarization studies and parity violation experiments.

The further stages of improvement under way are: (1) beam-sharing capability, allowing simultaneous 50 μamp beams in each experimental hall, and (2) the addition of a sixth two-klystron modulator and some increase in the peak-power capability of the existing modulators to achieve both greater reliability and energy capability of at least 900 MeV. In addition, a pulsed stretcher ring to provide~100% duty factor beams for South Hall experiments is being planned. Provision will be included in the ring design for internal target experiments and for delivery of polarized beams. Bates serves a large community of outside users; about 180 scientists coming from approximately 40 universities and national laboratories. About 50% of the beam time goes to outside users.

The Indiana University Cyclotron Facility provides a variety of light-ion beams over a range of bombarding energies and momentum transfers. The ion beams are generated by a coupled pair of separated sector cyclotrons. Proton currents typically are ~1 μamp and proton energies are in the range 12-210 MeV. Light ions including polarized protons and deuterons are available with

energies up to 220 q2/A MeV and with pulse widths of 0.35 nsec. Present major experimental facilities include a beam swinger for time-of-flight measurements with path lengths up to 160 m, a QDDM spectrograph, a QQSD spectrograph for low rigidity particles such as pions, two scattering chambers, and a polarized neutron beam. Presently, a dual spectrometer facility, one spectrometer to be high resolution (p/Ap≈ 35,000) is under construction. Accelerator improvements underway include the construction of a storage ring, with electron cooling to reduce dramatically the phase space of the beam and internal targeting, which is to be completed by 1986-1987. Upon completion, three internal target experiments may be carried out simultaneously. Future plans include the possibility of an additional cyclotron to triple the energy. or ramping the energy in the storage ring to 500 MeV and/or addition of a two-ring collider.

IUCF has been in operation since late 1975 as a national user facility. More than 250 scientists from 47 U. S. institutions have been actively involved in the research program.

A new 4-GeV Electron Accelerator Laboratory operating at a beam current of 240 μA and a duty cycle of about 90%, to be built by the Southeastern Universities Research Association (SURA), was recommended for construction by NSAC earlier this year. The main components are a 2-GeV pulsed linac with a single-pass recirculator and a beam-stretcher ring system. With double-pass, head-to-tail recirculation, the linac will produce a 4-GeV beam having a pulse length and intensity that allow singleturn injection into the stretcher ring. The accelerator could be upgraded in the future to achieve energies of 6 GeV or higher, should the physics in this region make such an upgrade desirable.

SURA plans to build a tagged-photon facility and two end stations for coincidence experiments and spectroscopy. The designs and specifications for the spectrometers available at each experimental area will be set in close consultation with the user community. As presently envisioned one end station may receive beam from either the linac or the pulse stretcher ring; it will be the location for a moderate-resolution spectrometer with a high-resolution spectrometer to be added later. The second end station will receive beam only from the stretcher ring and will house a moderate-resolution and a low-resolution (large acceptance) pair of spectrometers suitable for coincidence experiments. A tagged-photon facility will include a moderate-resolution spectrometer.

2. HEAVY ION ACCELERATORS

Six of the national user facilities are classified as heavyion facilities. In most respects, the characteristics of these

accelerators are complementary rather than competitive, since none of the technologies are the same and the beam energies and other capabilities of the several machines are quite different, as required by the wide range of research objectives. At all of these facilities, outside users participate actively in much of the research, are involved in the development of new experimental apparatus and, in a variety of ways, influence the accelerator-operating policies. Typically, outsider users are allocated at least 50% of the running time. The total numbers of outside users during a given year varies from about 50 for the smaller facilities to several hundred for the largest.

The Double MP Tandem Accelerator at Brookhaven, which came into operation in 1970, covers the low-energy end of the range of heavy-ion projectiles of interest to nuclear physics, providing precise high-resolution beams with energies above the Coulomb barrier for ions in the lower third of the periodic table. Two upgraded model MP tandem electrostatic accelerators can be operated separately or jointly, in several different configurations. The highest energies are obtained with the 3-stage mode in which a negative-ion source is mounted in the highvoltage terminal of the first machine, operated at a negative potential. The heavy-ion performance of this 3-stage system is roughly equivalent to that of a single tandem with 18 or 19 MV on the terminal. The system is also used to accelerate light ions and provides energies as high as 42 MeV for protons

Brookhaven National Laboratory has proposed major expansion of its present facility by combining it with the AGS (the 30-GeV Alternating Gradient Synchrotron) to accelerate heavy ions to relativistic energies up to ~15 GeV per nucleon. Using direct injection of the AGS, ions up to A = 32 and currents >109 pps would be available. Construction of a modest intermediate booster accelerator would permit injection of heavier ions, up to about A = 130, into the AGS. This system would provide significantly higher-energy relativistic heavy-ion beams than are now available at the Bevalac. Present studies indicate that beams accelerated in the AGS are suitable for injection into a relativistic collider system which BNL is designing for possible future construction.

The 88-Inch Cyclotron at the Lawrence Berkeley Laboratory emphasizes nuclear-structure physics with heavy-ion beams in the lower fifth of the periodic table. The accelerator is a variable-energy isochronous cyclotron with spiral sector focusing. Light ions are produced by an internal filament source, polarized protons (up to 55 MeV) and deuterons by an external polarized ion source, and heavy ions by an internal heavy-ion PIG source. One third of the beam time is used for light ions. The high intensity polarized ion source produces a microampere of

beam on target. A pair of 110° analyzing magnets are dispersion matched for the QSD spectrometer.

The energy range of the 88-Inch Cyclotron will be enhanced considerably and the mass range will be extended to 100 amu by the installation of an electroncyclotron resonance (ECR) ion source, now under construction. This accelerator improvement is being accompanied by the construction of a major new experimental tool, a compact assembly of 21 Compton-shielded germanium detectors and 44 bismuth-germanate detectors designed to study high-spin nuclear states.

The Holifield Heavy-lon Research Facility at Oak Ridge National Laboratory, completed in 1982, consists of a new 25-MV tandem, the K = 100 Oak Ridge Isochronous Cyclotron (ORIC) which has been modified to serve as an energy booster for tandem beams, and experimental apparatus to utilize beams provided by these accelerators operating both in stand-alone and coupled modes. The beam energy is easily varied in both modes. For ions in the intermediate region of the periodic table (say 40 < A < 110), the coupled system provides beams in an energy range that is not available at this time elsewhere in the United States for nuclear-structure research. This advantage and an extensive complement of experimental apparatus (4-m, 70-detector gamma-ray spectrometer, online isotope separator, two high-resolution magnetic spectrometers, time-of-flight spectrometers, etc.) provide an opportunity for the facility to be especially productive during the next few years.

Two approaches to an extension of the energy and mass range of the Holifield facility have been studied, both involving an improved cyclotron injected by the 25-MV tandem. One approach would increase the beam energy by about 40% and reduce power consumption by using superconducting coils for ORIC. The second option would extend the energy into an entirely new range (200 MeV/nucleon for light ions and 40 MeV/nucleon for uranium) by adding a K = 1200 superconducting cyclotron of the kind under construction at Michigan State University.

A heavy-ion accelerator-collider is being studied as a possibility for a major new facility at ORNL. As now conceived the system would consist of a linac injector, a conventional synchrotron booster, a stacker-stretcher ring. and a pair of superconducting intersecting accelerationstorage rings. For uranium ions the system would provide ~10 GeV/nucleon with a luminosity of ~1029/cm2-sec and intensities of 1010-10 particles/sec for fixed target experiments. Straightforward modifications to this design to extend the energies to 30 GeV per nucleon and above are also being explored.

The Argonne Tandem-Linac Accelerator System (ATLAS) at Argonne National Laboratory is the world's first successful accelerator to use r.f. superconductivity for the acceleration of projectiles heavier than the electron. It is being built in two phases. The first phase, completed in 1982, consists of a small (9-MV) tandem injecting into a 20-MV superconducting linac which was originally constructed as a prototype machine designed to develop a new technology, but is now used routinely as a research tool. The performance characteristics of the tandem-linac system are similar to those of a very large stand-alone tandem, and consequently the system is most useful for precision nuclear-structure research. Noteworthy features of the performance are the ease with which the energy may be changed and the availability of ultra-short beam pulses.

In the second stage of construction, the present facility is being expanded to form ATLAS. This project will double the size and accelerating power of the linac and add a large, well-equipped experimental area. At the interface between the present prototype linac and the ATLAS addition the beam will be separated into two components, one of which is accelerated to the full energy and the other is directed simultaneously, without further acceleration, into the present experimental area.

Because of the modular character of the tandem-linac system, it can rather easily be modified or expanded. Future options for ATLAS include (a) improving the overall performance of the system by replacing the present FNmodel injector by a better machine for the purpose and (b) extending effective acceleration to the heaviest nuclei by modifying and enlarging the linac.

All of the heavy-ion accelerators described above have beam energies that are within an order of magnitude of the Coulomb barrier. The remaining two facilities are designed to provide much higher energies with which to investigate quite different physics.

The accelerators at the National Superconducting Cyclotron Laboratory at Michigan State University are two superconducting cyclotrons, which are designed to be operated either as independent machines or in 2-stage acceleration. The phase I machine, the world's first operating superconducting cyclotron, was used to develop a new technology and is now being turned to research. It has a bending-limit parameter of K = 500 and a focusing limit of 80 MeV/nucleon for q = A/2. The first beam was extracted from this prototype machine in 1982. and since then a variety of ion species in the lower part of the periodic table have been developed and used for research. Beams have been extracted at the full K = 500 design limit of the superconducting magnet.