Machine Learning in Nuclear Physics

Advances in machine learning methods provide tools that have broad applicability in scientific research. These techniques are being applied across the diversity of nuclear physics research topics, leading to advances that will facilitate scientific discoveries and societal applications. This Review gives a snapshot of nuclear physics research which has been transformed by machine learning techniques.Comment: Comments are welcom

Superconducting Hadron Linacs

This article discusses the main building blocks of a superconducting (SC) linac, the choice of SC resonators, their frequencies, accelerating gradients and apertures, focusing structures, practical aspects of cryomodule design, and concepts to minimize the heat load into the cryogenic system. It starts with an overview of design concepts for all types of hadron linacs differentiated by duty cycle (pulsed or continuous wave) or by the type of ion species (protons, H-, and ions) being accelerated. Design concepts are detailed for SC linacs in application to both light ion (proton, deuteron) and heavy ion linacs. The physics design of SC linacs, including transverse and longitudinal lattice designs, matching between different accelerating–focusing lattices, and transition from NC to SC sections, is detailed. Design of high-intensity SC linacs for light ions, methods for the reduction of beam losses, preventing beam halo formation, and the effect of HOMs and errors on beam quality are discussed. Examples are taken from existing designs of continuous wave (CW) heavy ion linacs and high-intensity pulsed or CW proton linacs. Finally, we review ongoing R&D work toward high-power SC linacs for various applications

Simultaneous Acceleration of Radioactive and Stable Beams in the ATLAS Linac

ATLAS is now the only US DOE National User Facility for low-energy heavy-ion stable beams. With the recent commissioning of the Californium Rare Isotope Breeder Upgrade (CARIBU), ATLAS is now also used to accelerate radioactive beams. The demand for both stable and radioactive beam time is already exceeding two to three times the 5500 hours delivered by ATLAS every year. The time structure of the EBIS charge breeder to be installed next year for CARIBU beams is such that only 3% of the ATLAS duty cycle will be used for radioactive beams. Being a CW machine, 97% of the ATLAS cycle will be available for the injection and acceleration of stable beams without retuning. This simultaneous acceleration is possible for stable and radioactive beams with charge-to-mass ratios within 3%. We have developed a strategic plan to upgrade ATLAS for this purpose over the next few years, where two to three beams could be delivered simultaneously to different experimental areas. The upgrade concept will be presented and discussed along with the recent studies and developments done in this direction

Simulation and design of an electron beam ion source charge breeder for the californium rare isotope breeder upgrade

An electron beam ion source (EBIS) will be constructed and used to charge breed ions from the californium rare isotope breeder upgrade (CARIBU) for postacceleration into the Argonne tandem linear accelerator system (ATLAS). Simulations of the EBIS charge breeder performance and the related ion transport systems are reported. Propagation of the electron beam through the EBIS was verified, and the anticipated incident power density within the electron collector was identified. The full normalized acceptance of the charge breeder with a 2 A electron beam, 0.024π  mm mrad for nominal operating parameters, was determined by simulating ion injection into the EBIS. The optics of the ion transport lines were carefully optimized to achieve well-matched ion injection, to minimize emittance growth of the injected and extracted ion beams, and to enable adequate testing of the charge bred ions prior to installation in ATLAS

Pushing the intensity envelope at the ATLAS linac

The ATLAS linac at Argonne National Laboratory has recently been upgraded for higher beam intensity and transport efficiency. Following the installation of the new RFQ, we have performed a high-intensity run using a 40Ar⁸⁺ beam. A beam current of 7 pμA was successfully injected and accelerated in the RFQ and the first superconducting section of the linac to an energy of 1.5 MeV/u. Since then, a new superconducting module was installed in the Booster section of the linac replacing three old cryomodules of split-ring resonators. The split-rings are known to cause excessive beam steering leading to beam loss which limits the maximum current in ATLAS. We are planning a second run to try to push the beam current higher and farther into the linac. The ultimate goal is to accelerate 10 pμA to the Booster exit at 5 MeV/u. Among the limitations encountered in the first run are the large beam emittance at the ECR source and the beam loss in the LEBT. The results of these attempts will be presented and discussed

High-gradient low-β accelerating structure using the first negative spatial harmonic of the fundamental mode

The development of high-gradient accelerating structures for low-β particles is the key for compact hadron linear accelerators. A particular example of such a machine is a hadron therapy linac, which is a promising alternative to cyclic machines, traditionally used for cancer treatment. Currently, the practical utilization of linear accelerators in radiation therapy is limited by the requirement to be under 50 m in length. A usable device for cancer therapy should produce 200–250 MeV protons and/or 400–450  MeV/u carbon ions, which sets the requirement of having 35  MV/m average “real-estate gradient” or gradient per unit of actual accelerator length, including different accelerating sections, focusing elements and beam transport lines, and at least 50  MV/m accelerating gradients in the high-energy section of the linac. Such high accelerating gradients for ion linacs have recently become feasible for operations at S-band frequencies. However, the reasonable application of traditional S-band structures is practically limited to β=v/c>0.4. However, the simulations show that for lower phase velocities, these structures have either high surface fields (>200  MV/m) or low shunt impedances (<35  MΩ/m). At the same time, a significant (∼10%) reduction in the linac length can be achieved by using the 50  MV/m structures starting from β∼0.3. To address this issue, we have designed a novel radio frequency structure where the beam is synchronous with the higher spatial harmonic of the electromagnetic field. In this paper, we discuss the principles of this approach, the related beam dynamics and especially the electromagnetic and thermomechanical designs of this novel structure. Besides the application to ion therapy, the technology described in this paper can be applied to future high gradient normal conducting ion linacs and high energy physics machines, such as a compact hadron collider. This approach preserves linac compactness in settings with limited space availability

The ATLAS Intensity upgrade: Project overview and online operating experience

ATLAS, the world's first accelerator to use RF superconductivity for ion acceleration, has undergone a major facility upgrade with the goals of significantly increased stable-beam current for experiments and improved transmission for all beams. The dominant components of the upgrade are a) new CW-RFQ to replace the first three low β resonators, b) a new cryostat of seven β=0.077 quarter-wave resonators demonstrating world-record accelerating fields, c) an improved cryogenics system, and d) the retirement of the original tandem injector. This latest upgrade followed closely on the earlier development of a cryostat of β=0.144 quarter-wave resonators. This reconfigured ATLAS system has been in operation for over one year. This paper will discuss the on-line performance achieved for the redesigned system, plans for further improvement, and long term facility plans for new performance capabilities. This work was supported by the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357. This research used resources of ANL's ATLAS facility, which is a DOE Office of Science User Facility