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This center was partially funded by the National Cancer Institute. Since then, more than 36 proton radiotherapy centers have gone into operation worldwide, 24 of which are cyclotrons and 12, synchrotrons. Most new facilities that are opening now use cyclotron accelerators Krischel, A significant part of this high cost is due to the very large size, mass, and cost of the conventional cyclotron, the long beam transport system, and the huge rotatable gantry required to direct the proton beam to the patient. The use of superconducting cyclotrons begins to address the size and cost issue by reducing.

This reduction is a consequence of the inverse relationship between the radius of the cyclotron and the magnetic field, as shown below:. Thus cyclotrons can be made very compact by going to high magnetic fields. Currently two superconducting cyclotrons have been built for proton radiotherapy and are treating patients on a regular basis MSU, ; Miyata et al. They are cooled with liquid helium but maintained cold by cryocoolers in a closed cryogenic system, similar to the methods used to cool MRI magnets. These machines are more compact than resistive cyclotrons, reducing the size and weight from 4.

Although this is a factor of 2 reduction in weight, these machines used NbTi superconductor and limited the central gap field to 2. Newer designs by other organizations are capitalizing on the very high current density and high critical field of Nb 3 Sn to develop much more compact synchrocyclotrons. This design takes advantage of a very high current density superconducting wire developed by U.

The device built by Mevion Medical Systems has a diameter of only 1. It is small enough and light enough to be placed on the treatment gantry so that the entire cyclotron rotates around the patient, as shown in Figure 7.

The compact size and light weight of the cyclotron not only reduce cost but also eliminate the stationary beam transport system as well as the heavy gantry-mounted beam transport magnets, thus reducing the gantry weight as well. These systems can be installed as individual treatment machines instead of the contemporary device, which uses a single accelerator with beam line transport of protons to multiple rooms.

Thus the initial capital investment in establishing a center that can scale to multiple treatment rooms is reduced by a factor of Although proton beam radiotherapy is expanding in clinical use, other charged particles such as helium, carbon, and neon have also been used for the treatment of cancers. These charged particles have heavier mass than a single proton and thus require more powerful particle accelerators to achieve effective treatment energies.

The Question

Ongoing activities include efforts in Japan at the Heavy-Ion Medical Accelerator in Chiba HIMAC , which uses a range of charged particles for cancer therapy, and studies at high-energy-physics laboratories in Europe that have used carbon beams. Several organizations in the United States are considering using carbon and other heavy ions for radiotherapy, but there is no existing and mature commercially available accelerator technology ready to satisfy this wish.

It is possible that advances in superconducting technology can be used to develop a medically and economically feasible solution, but this will require a substantial investment in accelerator technology. At present, NIH continues to provide research and development funds for the purpose of developing and installing more powerful MRI magnet systems, and it seems reasonable to extrapolate that support to the development of advanced heavy ion accelerators for radiotherapy applications. Nuclear medicine radionuclide production for research and clinical studies depends for the most part on accelerator and reactor facilities that are remote from clinics and research institutions.

This has severely limited the application of the short-lived nuclides 11 C, 13 N, 15 O to those institutions with a local cyclotron that usually operates with a 1 to 1. The siting costs are dominated by shielding requirements and the size of the installation. Thus for studies that take advantage of positron emission tomography, long half-life radionuclides are used, but even these cannot achieve the needed specificity to enable clinical studies in addiction, aging, heart disease, and some cancers where radionuclides such as 11 C, 14 N, 15 O, and 89 Zr must be produced locally using a particle accelerator.

To overcome this problem, superconducting cyclotron technology is being employed in the production of small cyclotrons at 5 to 9 T with modern cryostats and turnkey operations. A commercial prototype is being developed by Ionetix, Inc. The horizons for increasing field strengths in chemical, biological, and medical research studies are discussed in Chapters 3 and 4 as well as in the recommendations of this report. High fields define a scientific frontier, and the new phases that are discovered as higher fields are made available are the feedstock for new materials and devices that reproduce these new behaviors at low or even zero field.

Increased field strength inevitably leads to enhanced sensitivity and new experimental techniques that in turn increase the tempo of scientific discovery.

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Each breakthrough in magnet technology and experimental capability leads to a new flurry of scientific revelation and discovery, which in turn enables the next round of technological breakthrough. This virtuous cycle is nowhere more evident than in the bootstrap process by which new magnets are themselves developed, where access to higher magnetic fields provides the means for testing and improving the new concepts and components that will make possible the next generation of magnets.

It is imperative that magnet technology be constantly challenged—and also supported! It is in this spirit that the committee recommends here three magnet development goals.

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Each is a novel and first-in-class project, and significant development efforts will be required to reach the stated goals. These magnets also represent significant investments in the national research infrastructure, because. The committee anticipates that it may take as long as a decade until these magnets become available for researchers. As discussed in Chapter 2 of this report, access to higher magnetic fields, both in dc and pulsed modes, will be crucial for progress in many aspects of condensed matter and material physics.

An additional recommendation calling for a design and feasibility study for a 20 T magnet for use in MRI studies of humans was discussed earlier, at the end of Chapter 4 , and recommendations for the development and installation of new types of magnets for use at X-ray and neutron scattering facilities is presented in Chapter 6. Finding: Recent advances in high-temperature superconductor HTS magnet technology are an important step forward, with the potential for making possible a new generation of all-superconducting high-field magnets that would be transformational in many research areas.

Such magnets will enable steady-state physics measurements at very high magnetic fields without the constraints and attendant costs of huge power supplies and a large-scale cooling facility. This means that significant reductions in both the construction and operation costs of a T class magnet can be envisioned, making it possible to locate these magnets in regional centers, built around teams of users with specific measurement needs.

The improved accessibility to the T class magnet will greatly facilitate the advancement of sciences that require steady-state measurements in magnetic fields significantly higher than the ordinary laboratory fields; furthermore, all-superconducting magnets can be used in the persistent-current mode, which provides a noise-free environment and makes it possible to perform ultrahigh-sensitivity measurements that have not been possible in hybrid-type magnets. It seems likely that the availability of these magnets would significantly change the mix of users at NHMFL-Tallahassee and would free that facility to develop new and complementary capabilities that cannot be reproduced elsewhere.

As the committee has discussed elsewhere in this report, the United States has largely ceded leadership in constructing high-field superconducting magnets for NMR to Europe, where there is a closer relationship between the national labs that provide the required technology and the companies that will build these magnets.

In part, this reflects a long-term underfunding of both magnet technology research in this country and the research in high-strength materials that underlies this important area. Surmounting the technological challenges associated with realizing a 40 T all-superconducting magnet will be a big step toward making U. Recommendation: A 40 T all-superconducting magnet should be designed and constructed, building on recent advances in high-temperature superconducting magnet technology. Finding: The veritable explosion of new materials with new functionalities that we have witnessed in the past decade is a potent driving force for the need to push experimentation to higher fields, where new phases and new behaviors are invariably found.

Although pulsed fields will always provide the highest peak fields, many of the most revealing measurement techniques have inherent timescales or sensitivity requirements that make them practical only in constant magnetic fields.

Techniques requiring dc magnetic fields include ultrasensitive voltage measurements that allow high-precision parametric studies of electrical resistance, heat capacity, susceptibility, and thermopower; scanned probe microscopies that provide both atomic-scale imaging and spectroscopic information; and optical spectroscopies performed over a wide range of frequencies. The ability to carry out these measurements, already proven in zero field to provide crucial information, has the potential to open up whole new fields of research and technology.

Some examples include the exploration of the normal state that precedes the unconventional superconductivity in the cuprates and iron pnictides and chalcogenides, the manipulation of symmetry-broken phases and unconventional quantum Hall effects in single-layer and few-layer graphene, and the investigation of the interplay between topological insulators and superconductivity. The ability to bring these measurements to new generations of materials and devices in increasingly high magnetic fields would define a world-leading capability and confer a distinct advantage to the researchers who can exploit them.

Finding: Many crucial measurements requiring the highest attainable fields can be performed in pulsed magnetic fields with durations on the order of 10 ms. Similar measurements at higher fields than are currently available would allow investigation of phenomena that are now beyond reach. The ability to routinely access T fields will enable unprecedented research in topological insulators, quantum matter, and electronic structure determination.

Fields much higher than T have been achieved in very short pulsed field magnets microseconds duration , which destroy the magnet coil and in many cases also the sample. However, the types of measurements that can be performed on microsecond timescales are much too limited to provide the type of information needed for elucidating the most pressing research problems. From a scientific point of view, a desirable long-term goal would be the ability to extend the suite of measurements now available at T to fields on the order of T or beyond.

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Fields of this magnitude would allow direct investigations of unusual phases and phase transitions in quantum spin systems with strong exchange couplings. They would also enable investigations of some of the most important high-temperature superconductors by allowing field-induced suppression of superconductivity in the ground state of these materials.

Unfortunately, no clear route currently exists for producing nondestructive fields as high as T. Among other limitations, magnets of this strength would have to sustain forces well beyond the yield strengths of any known material. Nevertheless, important advantages could be obtained already by extending the availability of nondestructive pulsed fields in a series of smaller steps, perhaps achieving T by the year Higher-field magnet technology might be developed hand-in-hand with the ability to make required measurements on smaller samples and in shorter times.


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Recommendation: Higher-field pulsed magnets should be developed, together with the necessary instrumentation, in a series of steps, to provide facilities available to users that might eventually extend the current suite of thermal, transport, and optical measurements to fields of T and beyond. Hahn, D. Keun Park, and Y. Chong, S.

Mochiji, S. Sato, and K.