The current Electron Cyclotron Resonance Ion Sources (ECRISs), constructed with Nb-Ti wires and the conventional racetrack-and-solenoid structure, have achieved operating frequencies up to 28 GHz and utilized about 90% of the critical current of the Nb-Ti wire. A Mixed Axial and Radial field System Demonstrator (MARS-D) is being developed at Lawrence Berkeley National Laboratory (LBNL). This system, which consists of an innovative hexagonal Closed-Loop Coil (CLC) and a set of solenoids, can generate higher magnetic fields (up to 150%) while requiring only about 50% of the superconducting wire, enabling Nb-Ti wires to be used in the next-generation 45 GHz ECRIS. However, the assembly and cooling of such an efficient and compact magnet are particularly challenging due to the small radial gap between the CLC and solenoids, as well as the tight operating temperature margin. To address these challenges, a structure was developed that combines a three-section radially split solenoid mandrel with a series of shrink-fit reinforcement rings and cooling channels. This paper presents the detailed structure, manufacturing method, assembly procedure, impregnation method, mechanical Finite Element Analysis (FEA) comparison, and thermal FEA comparison.

In this work, we consider the optimization of non-invariant systems with both safety and control constraints. We present a new approach based on Bayesian optimization for the dynamic, safe and controlled optimization of such systems. Although there are other possible use cases, we focus on the application to the electron cyclotron resonance ion source VENUS. From experimental data, we have observed that VENUS behaves to first order as a non-invariant dynamic system with moving areas of instability. Our novel approach aims at providing a tool that can maintain system optimization in a safe way. This is accomplished by making sure the objective function, the beam current in the case of VENUS, does not fall under an operational minimum, while simultaneously requiring the optimization to avoid areas where VENUS is unstable. We compare the result of our approach on synthetic data modeled to mimic the behavior of VENUS with two methods from the literature, a standard Bayesian optimizer and a safe Bayesian optimizer, both adapted to deal with dynamic systems. A cross Student T-test is conducted to show the significance of the improvement given by the new method we introduce here, regarding the two preexisting methods we compared to. The results of the tests conducted on synthetic data show that the proposed method succeeds at maintaining the system optimized and obeys the predefined constraints better than the literature methods explored.

Electron Cyclotron Resonance Ion Sources (ECRISs) that utilize Nb-Ti superconducting coils for 28 GHz frequencies have been operating effectively for over twenty years. However, transitioning to higher frequencies demands stronger magnetic fields, and the conventional racetrack-and-solenoid ECRIS structures have reached their maximum capability with Nb-Ti. To address this, a Mixed Axial and Radial field System Demonstrator (MARS-D) is being developed at Lawrence Berkeley National Laboratory (LBNL). This system features an innovative Closed-Loop Coil (CLC) design that optimizes the use of the conductor fields, enabling the application of Nb-Ti in the next-generation 45 GHz ECRISs. The fabrication of the hexagonal CLC is particularly challenging due to its complex winding path and shape, the stiffness of the Nb-Ti superconducting wire, and the small bending radius. To address these challenges, a series of unique fixtures and tools, as well as a pre-over-bending method, were developed for winding the CLC. To validate the winding fixtures, tools, procedures, and materials used in the coil assembly, a 4-layer practice CLC was wound, epoxy-impregnated, and then cold-tested using liquid nitrogen. The full-size MARS-D CLC is in the process of winding. This paper presents the structure of the MARS-D CLC, the winding fixtures and tools, the winding procedures, the quality control, the impregnation, the test results, and the potential future improvements.

The proposed search for element 120 at LBNL’s 88-Inch Cyclotron will require the continual delivery of over a particle microamp of 50Ti12+ for weeks-long campaigns spanning many months. The VENUS electron cyclotron resonance ion source is the primary injector source for the 88-Inch Cyclotron, and the oven presented here can survive the source’s high magnetic fields while injecting metallic gas into the plasma with high efficiency. The oven design is vertical to permit use with metals that melt before outgassing sufficiently, while also allowing a rotation of the oven’s material exit toward the plasma center for better conversion efficiency to the produced beam. The overall oven design is presented, along with performance results from both the source and the accelerated beams through the cyclotron.

Third-generation electron cyclotron resonance ion sources (ECRISs) have relied on a combination of sextupole and solenoid fields from Nb-Ti superconductors to produce the magnetic fields required for 28 GHz operation. The VENUS ion source at Lawrence Berkeley National Laboratory (LBNL) was the first third-generation ion source optimized for 28 GHz operation, and since that time a similar design has been adopted at other heavy-ion facilities such as RIKEN, GANIL and FRIB. These sources utilize a sextupole-in-solenoid design and represent the high-field limit of this design using Nb-Ti superconductor. To get past this limit without moving to a more difficult-to-use superconductor material, LBNL is developing a fourth-generation, 45 GHz ECRIS, called MARS-D, with a closed-loop coil structure. Since both the sextupole and solenoid fields are efficiently produced by the closed-looped coil, the 45 GHz ECRIS can be realized using the Nb-Ti conductor. In the MARS-D design, the maximum field on the conductor is 8.3 T at 4.2 K, and the operation point is about 90% of the short sample limit. As this tight load line margin may leave the source susceptible to quench, we investigate and compare the design parameters with the most recent VENUS-type superconducting ECRIS which is already under operation at FRIB in this paper. Additionally, we investigate the advantages of the MARS-D-type structure by keeping the coil design constant and only replacing the conductor with the one used in FRIB and VENUS.

The ^{244}Pu(^{50}Ti,xn)^{294-x}Lv reaction was investigated at Lawrence Berkeley National Laboratory's 88-Inch Cyclotron. The experiment was aimed at the production of a superheavy element with Z≥114 by irradiating an actinide target with a beam heavier than ^{48}Ca. Produced Lv ions were separated from the unwanted beam and nuclear reaction products using the Berkeley Gas-filled Separator and implanted into a newly commissioned focal-plane detector system. Two decay chains were observed and assigned to the decay of ^{290}Lv. The production cross section was measured to be σ_{prod}=0.44(_{-0.28}^{+0.58})  pb at a center-of-target center-of-mass energy of 220(3) MeV. This represents the first published measurement of the production of a superheavy element near the "island of stability," with a beam of ^{50}Ti and is an essential precursor in the pursuit of searching for new elements beyond Z=118.

A custom waveguide dc break, developed for the versatile ECR for nuclear science (VENUS) ion source at Lawrence Berkeley National Laboratory, features an innovative impedance matching network. This network consists of two inductive irises located adjacent to a capacitive gap, which not only provides dc isolation but also facilitates the coupling of a new 2.4 kW Klystron, effectively doubling the power available for plasma production at the secondary frequency of 18 GHz. The design allows the ion source to operate at elevated potentials while keeping the RF system grounded, thereby ensuring efficient ion beam extraction and transportation to the cyclotron for acceleration, and maintaining easy access to the RF system. Simulations conducted with the ANSYS High-Frequency Structure Simulator, a finite element analysis tool, have demonstrated exceptional impedance matching at the Klystron frequency. These results have been corroborated by microwave measurements, showing excellent agreement.

The first deflector circuitry at the extraction of the 88-in Cyclotron at the Lawrence Berkeley National Laboratory has been modified to enable switching within a few hundreds of nanoseconds. This modification, along with the pre-chopper, allows the cyclotron to achieve single-bunch extraction. The novel procedure involves adjusting the pre-chopper to control the number of ion bunches injected into the cyclotron, thus managing ion energy deposition. These bunches are then accelerated until they reach the electrostatic deflectors, which control their extraction. After the deflectors are adjusted to transport the beam, the first deflector voltage is decreased until no beam current is extracted. Finally, through switching and selective phase adjustment of the first deflector to match the transit time of a bunch, the cyclotron is capable of extracting a single bunch. This capability is crucial for time-sensitive experiments and allows control over dose distribution in previously inaccessible regimes. The straightforward and cost-efficient implementation of this technique makes it an attractive option for many cyclotron facilities and medical cyclotron manufacturers.

A single radio frequency bucket of the 88-Inch Cyclotron is filled using a fast chopper located in the axial line. The bucket then accelerates until it reaches the deflector, at which point, it is extracted as a train of bunches. This phenomenon can be attributed to the characteristic multi-turn extraction of the cyclotron and, by simplifying the complex dynamics of a cyclotron, corresponds to the conceptual transfer function of the cyclotron. The confirmation of the single radio frequency bucket injection was achieved by operating the cyclotron in the third harmonic mode and observing the absence of intermediate bunches during the multiple-bunch extraction.

Superconducting electron cyclotron resonance ion sources (ECRISs) using NbTi coils and optimized for 28 GHz resonant heating have been successfully operated for almost two decades. Moving to higher heating frequencies requires increased magnetic fields, but traditional racetrack-and-solenoid ECRIS structures are at their limit using NbTi. Rather than moving to a superconductor untested in this field, the Mixed Axial and Radial field System (MARS) being developed at Lawrence Berkeley National Laboratory employs a novel closed-loop-coil design that more efficiently utilizes conductor fields and will allow the use of NbTi in a next-generation, 45 GHz ECRIS. This article presents the design of the shell-based support structure central to the MARS-D magnet design, as well as structural analysis of its components and optimization of pre-load parameters that will guarantee its successful operation.

In addition to the ongoing investigation of bremsstrahlung radiation produced by energetic electrons in the superconducting Electron Cyclotron Resonance (ECR) ion source VENUS, the LBNL ion source group has pursued several other research topics since 2015 to explore potential advancements of ECR ion sources. Three of these activities are investigations into the benefits of non-cylindrical plasma chambers, the development of new high-temperature ovens that will efficiently produce the intense, metallic ion beams necessary for super heavy element production at the 88-Inch Cyclotron facility, and the finalization of the conceptual and engineering design of the superconducting NbTi magnet structure for the 4th generation, 45 GHz ECR ion source MARS-D. This article summarizes and briefly discusses the highlights of these ECRIS developments.

Intense Highly Charged Ion Beams (HCIB) from injector and charge-breeder ion sources at heavy ion accelerator facilities are in demand to expand research in particle and nuclear physics as well as for radiation effects testing. With current accelerator upgrades and advances in accelerator technologies, not all HCIB demands can be met with existing ion sources. Continued Research and Development (R&D) in this field are therefore essential to continually improve their performance and match the unprecedented and increasingly higher HCIB requirements from the accelerator community. This White Paper discusses the present production capabilities of ion sources of HCIB, and the potentials of future Highly Charged Ion (HCI) sources. It discusses the strengths and weaknesses of such sources along with paths forward for improving their performance to meet the requirements of present and future heavy ion accelerator facilities. This document is meant to be utilized as a basis to guide the conceptual design of future accelerators.

Though known for their production of high currents of highly-charged ion beams, advanced electron cyclotron resonance (ECR) ion sources like VENUS at Lawrence Berkeley National Laboratory (LBNL) also generate significant numbers of x-rays. The LBNL ECR ion source group has spent many years studying the x-rays emitted from VENUS in order to gain a better understanding of the ECR plasma. Based on the emitted bremsstrahlung continuum, a spectral temperature T s can be calculated which is a relative indication of the temperature of the plasma electrons. We will present correlations between Ts with respect to parameters such as magnetic fields. In addition to the bremsstrahlung continuum, the plasma ions emit characteristic x-rays. We will show that additional information can be gained by investigating spectral line shifts. A summary of this recent research using VENUS will be presented and discussed.

In outer space down to the altitudes routinely flown by larger aircrafts, radiation can pose serious issues for microelectronics circuits. The 88-Inch Cyclotron at Lawrence Berkeley National Laboratory is a sector-focused cyclotron and home of the Berkeley Accelerator Space Effects Facility, where the effects of energetic particles on sensitive microelectronics are studied with the goal of designing electronic systems for the space community. This paper describes the flexibility of the facility and its capabilities for testing the bombardment of electronics by heavy ions, light ions, and neutrons. Experimental capabilities for the generation of neutron beams from deuteron breakups and radiation testing of carbon nanotube field effect transistor will be discussed.

MARS (Mixed Axial and Radial field System) is a new superconducting magnet under development with a novel coil layout for more efficiently generating high strength minimum-B fields for the next generation of Electron Cyclotron Resonance (ECR) ion source. It consists of a hexagonal closed-loop-coil and a set of auxiliary solenoids. A new quench protection system is needed for a MARS magnet to be built with NbTi conductor cooled through thermal conductions. Using the Vector Fields' 3-D QUENCH program, different scenarios were computed to investigate the key parameters in the cases with and without energy-extraction during quenches. The analyses have resulted in the design of a quench protection system for a MARS NbTi magnet with maximum quench voltage of similar to 400 V and hot-spot temperature of similar to 80 K.

Constructing a minimum-B structure with higher magnetic fields is the prerequisite for the next generation of Electron Cyclotron Resonance Ion Sources (ECRIS): ion sources that will operate at substantially higher heating frequencies than those currently in use. There are three leading candidates of Nb3Sn coil structures for use in future ECRISs: a Mixed Axial and Radial field System (MARS) that merges the sextupole racetrack coils and partial end-solenoids into an exotic closed-loop-coil; a classical Sextupole-In-Solenoids design; and a Solenoids-In-Sextupole configuration. Focusing on efficient magnetic field generation, this article briefly reviews the advantages and disadvantages of each of these magnet structures. Though Sextupole-In-Solenoids and Solenoids-In-Sextupole magnetic structures using NbTi conductor have been validated by current ECRISs, improvements of these magnet structures remain possible. Possible optimizations to the two existing magnet structures, such as using a non-conventional sextupole magnet consisting of either V-bend or skew racetrack coils, are discussed. The development status of a MARS NbTi magnet at LBNL for a new ECRIS will be also presented.

The spectral temperature T-s obtained from bremsstrahlung spectra emitted from electron cyclotron resonance (ECR) ion sources (ECRISs), in which the plasma is confined in a minimum-B magnetic field, is used as a relative indication of the temperature of the plasma hot electrons. Past bremsstrahlung measurements taken on ECRISs indicate that Ts is strongly dependent on the magnetic field gradient at the resonance zone or (B-min/B-ECR). However, this dependence was never fully proven or explained. To further our understanding a more detailed study of the bremsstrahlung radiation for X-rays above 10 keV is underway using VENUS, a third-generation ECRIS at Lawrence Berkeley National Laboratory. Initial analysis of previous and new data has revealed that Ts appears to be dependent solely on the minimum magnetic field B-min rather than (B-min/B-ECR) and the microwave frequency omega. Decoupling T-s from (B-min/B-ECR), mainly B-ECR, implies that T-s does not depend on the magnitude of the heating frequency omega. While it certainly appears to be true that plasma density n(e)(alpha omega(2) alpha B-2) increases with heating frequency, as was postulated by Geller in 1987, a more careful consideration into the heating mechanism of the plasma electrons is warranted. The disassociation of T-s from the heating frequency omega, while an interesting discovery, implies that we must change the way we understand how ECRISs operate. This paper presents new bremsstrahlung measurements, analyses, and discussions of the results.

Electron Cyclotron Resonance (ECR) Ion Sources at Lawrence Berkeley National Laboratory's (LBNL) 88-Inch Cyclotron produce heavy ion cocktails to test the radiation hardness of spacecraft electronics. A 20 MeV/u cocktail is underway and the 10 MeV/u cocktail has been expanded to include gold.

Axial bremsstrahlung from the superconducting Electron Cyclotron Resonance ion source VENUS have been systematically measured as a function of RF heating frequency, and the axial and radial field strengths. The work focuses on bremsstrahlung with energies greater than 10 keV to extract the spectral temperature Ts. The three axial coils and the radial coils in the superconducting VENUS can all be set independently and have a large dynamic range, which makes it possible to decouple Bmin and and study their effects on the bremsstrahlung independently. With typical pressure and RF power levels, the measurements show that Ts depends approximately linearly on Bmin and is not correlated with the , the magnetic field mirror ratios, or the RF frequency. These results are important for the next generation of ECR ion sources, which are designed to operate at frequencies above 40 GHz and significantly higher magnetic fields where bremsstrahlung is expected to cause a significant cryogenic heat load and increase the radiation shielding requirements.

A novel Mixed Axial and Radial field System (MARS) seeks to enhance the B fields inside the plasma chamber within the limits of a given conductor, thereby making it possible to raise the operating fields for Electron Cyclotron Resonance Ion Sources (ECRISs). The MARS concept consists of a hexagonally shaped closed-loop coil and a set of auxiliary solenoids. The application of MARS will be combined with a hexagonal plasma chamber to maximize the use of the radial fields at the chamber inner surfaces. Calculations using Opera's TOSCA-3D solver have shown that MARS can potentially generate up to 50% higher fields and use of only about one half of the same superconducting wire, as compared with existing magnet designs in ECRISs. A MARS magnet system built with Nb 3 Sn coils could generate a high strength minimum-B field of maxima of ≥ 10 T on axis and ~6 T radially in an ECRIS plasma chamber. Following successful development, the MARS magnet system will be the best magnet scheme for the next generation of ECRISs. This paper will present the MARS concept, magnet design, prototyping a copper closed-loop coil, and discussions.