The Facility for Rare Isotope Beams (FRIB) being constructed at Michigan State University [J. Wei et al., The FRIB superconducting linac-status and plans, LINAC'16, Lansing, MI, p. 1, http://accelconf .web.cern.ch/AccelConf/linac2016/papers/mo1a01.pdf] is based on a cw superconducting linear accelerator which is designed to deliver unprecedented 400 kW heavy ion beam power to the fragmentation target. The installation of the accelerator equipment is approaching completion and multistage beam commissioning activities started in the summer of 2017 with expected completion in 2021. A roomtemperature test electron cyclotron resonance ion source, ARTEMIS, provided argon and krypton beams for the commissioning of the low energy beam transport, a radio frequency quadrupole (RFQ), the medium energy beam transport (MEBT) and the first three accelerating cryomodules. The commissioning of the first linac segment (LS1), composed of 15 cryomodules, is planned in the spring of 2019. This paper describes the first results of experimental beam dynamics studies in the LEBT, RFQ, MEBT and the first three cryomodules with comparison to the numerical simulations.

We show through numerical simulations that dispersion oscillating fibers can be used for the fusion of fundamental solitons into high-intensity pulse. Three particular cases are considered: fusion of two co-propagating fundamental solitons, fusion of three co-propagating fundamental solitons and merge of two colliding solitons into breather bound state. Generation of high-intensity pulse is associated with the formation of distinct high-amplitude soliton.

Trapezoidal modulation of quadrupole electrodes offers additional benefits to the concept of a radiofrequency quadrupole (RFQ). Because of the significant increase of the effective shunt impedance, RFQs with trapezoidal modulation have a reduced interelectrode voltage or resonator length as compared to conventional RFQs with sinusoidal modulation. This feature is especially valuable for RFQs operating in cw mode, since it reduces the required rf power. We develop a detailed procedure for the design of RFQ electrodes with trapezoidal modulation. With our design procedure and by properly choosing the trapezoidal cell parameters, we can easily control the peak surface fields in the RFQ to the same level as for sinusoidal cell modulation. The procedure is applied to the design of the electrodes for the ReA3 RFQ at Michigan State University.

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 ¼ 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 new design for a spatially periodical rf quadrupole focusing linac is proposed. It consists of accelerating gaps formed between conventional cylindrical drift tubes, between drift tubes and rf quadrupoles with nonzero axial potential, and inside these rf quadrupoles, formed in the same way as in a conventional radio-frequency quadrupole (RFQ) linac with modulated electrodes. Such a combination provides both higher energy gain rate than conventional RFQ and stability of transverse motion for ion beams. The structure can be designed using various combinations of quadrupoles and drift tubes. Some options are considered in the paper using the smooth approximation method and computer simulation of beam dynamics. Transverse stability of particles has been studied. The proposed structure can provide suppression of rf defocusing effects on transverse beam dynamics. Some limitations of the spatially periodic rf quadrupole structure are mentioned.