Advanced Rare IsotopE Laboratory Research Articles

Design and radiological study of the 225Ac medical target at the TRIUMF-ARIEL proton-target station

At the Advanced Rare Isotope Laboratory (ARIEL) at TRIUMF, two targets will be irradiated in series with up to 100 µA of a 500 MeV proton beam. Whilst the upstream target will be used for radioactive ion beam production via the isotope separation on-line (ISOL) method, the downstream target will make use of the transmitted beam for medical isotope production, especially for targeted radiation therapy.The medical target design was optimized to meet both requirements for in-target 225Ac production as well as to operate within the ARIEL proton station via FLUKA and ANSYS simulations. To host the medical target, a module was specially designed and integrated into the shielding envelope.In addition, three failure scenarios are also considered, featuring maximum credible incidents that highlight the overall shielding performance. An evaluation of the dosimetry impact throughout the final stage of the medical target life cycle was also carried out. The latter entailed the reproduction of residual ambient dose rates when a dismantled target is retrieved from the hotcell and sent for processing in a shielded container. Overall, the simulation work led to the validation of the medical target design and its operation within the scope of ARIEL.

Design optimization of an electron-to-photon conversion target for ultra-high dose rate x-ray (FLASH) experiments at TRIUMF

Objective. To develop a bremsstrahlung target and megavoltage (MV) x-ray irradiation platform for ultrahigh dose-rate (UHDR) irradiation of small-animals on the Advanced Rare Isotope Laboratory (ARIEL) electron linac (e-linac) at TRIUMF. Approach. An electron-to-photon converter design for UHDR radiotherapy (RT) was centered around optimization of a tantalum–aluminum (Ta–Al) explosion-bonded target. Energy deposition within a homogeneous water-phantom and the target itself were evaluated using EGSnrc and FLUKA MC codes, respectively, for various target thicknesses (0.5–1.5 mm), beam energies (E e− = 8, 10 MeV) and electron (Gaussian) beam sizes ( = 2–10 mm). Depth dose-rates in a 3D-printed mouse phantom were also calculated to infer the compatibility of the 10 MV dose distributions for FLASH-RT in small-animal models. Coupled thermo-mechanical FEA simulations in ANSYS were subsequently used to inform the stress–strain conditions and fatigue life of the target assembly. Main results. Dose-rates of up to 128 Gy s−1 at the phantom surface, or 85 Gy s−1 at 1 cm depth, were obtained for a 1 × 1 cm2 field size, 1 mm thick Ta target and 7.5 cm source-to-surface distance using the FLASH-mode beam (E e− = 10 MeV, 2 = 5 mm, P = 1 kW); furthermore, removal of the collimation assembly and using a shorter (3.5 cm) SSD afforded dose-rates >600 Gy s−1, albeit at the expense of field conformality. Target temperatures were maintained below the tantalum, aluminum and cooling-water thresholds of 2000 °C, 300 °C and 100 °C, respectively, while the aluminum strain behavior remained everywhere elastic and helped ensure the converter survives its prescribed 5 yr operational lifetime. Significance. Effective design iteration, target cooling and failure mitigation have culminated in a robust target compatible with intensive transient (FLASH) and steady-state (diagnostic) applications. The ARIEL UHDR photon source will facilitate FLASH-RT experiments concerned with sub-second, pulsed or continuous beam irradiations at dose rates in excess of 40 Gy s−1.

CANREB EBIS commissioning at TRIUMF

The Canadian Rare Isotope facility with Electron Beam ion source (CANREB) is an essential part of the Advanced Rare IsotopE Laboratory (ARIEL) presently under construction at TRIUMF. CANREB was recently commissioned and can accept stable or rare isotope beams from a variety of ion sources, delivering high purity beams of highly charged ions (HCI) to experiments. The injected beams are bunched using a radiofrequency quadrupole cooler-buncher and energy adjusted using a pulsed drift tube for injection into the electron beam ion source (EBIS) charge state breeder. The EBIS is designed for a maximum electron beam current of 500 mA and a maximum magnetic field of 6 T. Ions with energies up to 14 keV can be injected and HCI with mass-to-charge (A/q) ratios 3 ⩽ A/q ⩽ 7 can be charge bred and extracted. The HCI are A/q-selected using a Nier-type spectrometer before being transported to the ISAC linac for post-acceleration. Results from CANREB beam commissioning with focus on the EBIS will be presented.

An overview of the shielding optimization studies for the TRIUMF-ARIEL facility

The Advanced Rare IsotopE Laboratory (ARIEL) facility, dedicated to Radioactive Ion Beam (RIB) production via the Isotope Separation On-Line (ISOL) technique, is currently under construction at TRIUMF. The facility is to host dual target stations that will operate simultaneously, including a 500 MeV proton beam from the main TRIUMF cyclotron and a 50 MeV electron beam from an Electron Linear Accelerator (e-linac). The proton target station will operate a symbiotic medical target in series with the ISOL target.The ARIEL facility features a compact shielding envelope and as a result its optimization relied extensively on simulations generated using the Monte Carlo particle transport and interaction code FLUKA. Dose rate maps were produced of prompt radiation associated with beam losses and expected normal operations. Maps of transient fields were also generated considering radiation sources requiring transport within the facility which include radioactive waste generated in the course of normal operations. Activation studies were also conducted to estimate the amount of residual radioactivity contained in shielding materials at the time of decommissioning. Simulation results are primarily used to inform the ongoing design and construction of ARIEL; at present, the entirety of the proposed facility shielding has been validated by FLUKA simulation data. The specification of shielding geometry and the selection of materials relied extensively on engineering support through verification of CAD models and material sampling to optimize solutions for design simplicity and economy. Normal operation and failure scenarios were both evaluated, with optimized shielding materials and thicknesses selected considering the nature of the radiation fields present and their impact on room occupancy. Finally, a decommissioning plan has been defined based on the anticipated ARIEL lifetime, the characterization of structural activation, and a general disposal strategy.While ARIEL is still under construction and significant progress has been made, the ongoing radiation modelling has enabled validation of the current shielding design for nominal operation. Moreover, the systematic studies performed were paramount in defining the optimal strategies to adopt from target storage to that for decommissioning of the facility.

Remote handling systems for the ISAC and ARIEL high-power fission and spallation ISOL target facilities at TRIUMF

TRIUMF, Canada’s particle accelerator centre, is constructing a new high-power ISOL (Isotope Separation On-Line) facility called ARIEL (Advanced Rare IsotopE Laboratory). Thick porous targets will be bombarded with up to 48 kW of 480 MeV protons from TRIUMF’s cyclotron, or up to 100 kW of 30 MeV electrons from a new e-linac, to produce short-lived radioisotopes for a variety of applications, including nuclear astrophysics, fundamental nuclear structure and nuclear medicine. For efficient release of radioisotopes, the targets are heated to temperatures approaching 2000 °C, and are exposed to GSv/h level radiation fields resulting from intended fissions and spallations. Due to these conditions, the operational life for each target is only about five weeks, calling for frequent remote target exchanges to limit downtime. A few days after irradiation, the targets have a residual radiation field producing a dose rate on the order of 10 Sv/h at 1 m, requiring several years of decay prior to shipment to a national disposal facility. TRIUMF is installing new remote handling infrastructure dedicated to ARIEL, including hot cells and a remote handling crane. The system design applies learnings from multiple existing facilities, including CERN-ISOLDE, GANIL-SPIRAL II as well as TRIUMF’s ISAC (Isotope Separator and ACcelerator).

Development of a continuously tunable titanium-sapphire laser system for the ARIEL laser ion source

A concept for continuously tunable titanium-sapphire (Ti:Sa) lasers using dispersion prisms is under investigation for the ARIEL (Advanced Rare IsotopE Laboratory) laser ion source at TRIUMF (Canada’s particle accelerator center). Wavelength selection for pulsed Ti:Sa lasers used in hot cavity laser resonance ionization spectroscopy is usually done with birefringent filters (BRFs) and etalons or diffraction gratings. For resonance ionization spectroscopy a laser system allowing a continuous wavelength scan is necessary. Tunable lasers based on BRFs and etalons have high output powers however require synchronized optimization for continuous laser wavelength scans and are therefore laborious to use in scanning applications. Diffraction grating tuned lasers can provide continuous wavelength scan over 200 nm range but typically have lower output laser power due to the grating deformation under high pumping power. Aiming to overcome both shortcomings a laser design based on prisms as dispersing element has been revisited. Simulations on the beam path and optical reflectivity are done which show that these losses can be minimized to around 0.04 % for a tuning range from 700 nm up to 920 nm. Further improvement on the tuning range and reduction on the linewidth will be pursued.

Design of a compact shielding envelope and elements of radiological protection at the TRIUMF-ARIEL facility

The Advanced Rare Isotope Laboratory (ARIEL) is currently under construction at TRIUMF. ARIEL's mission is to supply existing experiments with more diverse and more intense radioactive ion beams (RIB) produced via the Isotope Separation On-Line (ISOL) method. The drivers inducing the nuclear reactions at ARIEL include a 500 MeV proton beam from the main cyclotron as well as a 35 MeV electron beam with the intent of simultaneous operation using two separate additional target stations. The generated RIB will be made available to experiments in condensed matter and subatomic physics as well as practical applications such as medical isotopes for life sciences research.This work details the various simulations performed using the Monte Carlo (MC) particle transport and interaction code FLUKA. The code was systematically employed to predict prompt and residual radiation levels to characterize the radiation fields generated via the irradiation of various types of targets. An iterative combined development process between CAD-based engineering of the shielding envelope, nuclear physics optimization of the target system and particle tracing simulations was established.Preliminary simulation studies resulted in the selection of shielding materials and respective thicknesses with the goal of maximizing attenuation while mitigating residual activation. The results provide clear operational constraints and aid in determination of expected dose rates outside of shielding in high occupancy areas. A series of optimization steps followed the preliminary work, testing various parameters including beam power, target material and shielding configurations. These results were evaluated considering technical feasibility, safety, and economic impacts on ARIEL construction and eventual operation.Although the project, in its infancy, is expected to proceed through stages of increasing complexity, the shielding and radiation transport modeling completed to date helps to define and validate nominal operation and failure scenario procedures for all future project stages.

Microphonics Suppression In Ariel Acm1 Cry- Omodule

Now 30 MeV stage of the ARIEL (The Advanced Rare Isotope Laboratory) e-Linac is under commissioning which includes an injector cryomodule (ICM) and the first accelerator cryomodule (ACM1). The two ACM1 cavities are driven by a single klystron with vector-sum control and running in CW mode. During the commissioning, the ACM1 cavities gradient and stability were limited by a ponderomotive effect [1-4]. Acoustic noise from the environment including vibration sources from water- and air-cooling systems, cryogenic system and vacuum system have been identified. In this paper, the progress of the microphonics suppression of ACM1 is presented.

UCx target production at TRIUMF in the ARIEL era

The Advanced Rare IsotopE Laboratory (ARIEL) will increase TRIUMF’s radioactive ion beam capabilities. As part of the ARIEL target material research and development campaign, a new method to produce targets of mixed uranium carbide with excess graphite has been proposed and tested. The resulting material is comparable in composition with the conventional target material and is produced ten times faster. The reduction in production time will liberate the resources and equipment for research and development leading to new target materials with improved radioisotope release properties for ARIEL.

An electron beam ion trap and source for re-acceleration of rare-isotope ion beams at TRIUMF.

Electron beam driven ionization can produce highly charged ions (HCIs) in a few well-defined charge states. Ideal conditions for this are maximally focused electron beams and an extremely clean vacuum environment. A cryogenic electron beam ion trap fulfills these prerequisites and delivers very pure HCI beams. The Canadian rare isotope facility with electron beam ion source-electron beam ion sources developed at the Max-Planck-Institut für Kernphysik (MPIK) reaches already for a 5 keV electron beam and a current of 1 A with a density in excess of 5000 A/cm2 by means of a 6 T axial magnetic field. Within the trap, the beam quickly generates a dense HCI population, tightly confined by a space-charge potential of the order of 1 keV times the ionic charge state. Emitting HCI bunches of ≈107 ions at up to 100 Hz repetition rate, the device will charge-breed rare-isotope beams with the mass-over-charge ratio required for re-acceleration at the Advanced Rare IsotopE Laboratory (ARIEL) facility at TRIUMF. We present here its design and results from commissioning runs at MPIK, including X-ray diagnostics of the electron beam and charge-breeding process, as well as ion injection and HCI-extraction measurements.

Development of a new RFQ beam cooler and buncher for the CANREB project at TRIUMF

A new radiofrequency quadrupole (RFQ) based ion beam cooler and buncher is under development for the CANadian Rare-isotope facility with Electron Beam ion source (CANREB) project at TRIUMF. The CANREB project requires an RFQ buncher that will efficiently accept continuous beams of rare isotopes from either the Advanced Rare IsotopE Laboratory (ARIEL) or Isotope Separator and ACcelerator (ISAC) target by way of a high resolution magnetic spectrometer, with energies up to 60keV and deliver bunched beams to an electron beam ion source (EBIS) for charge breeding. The energy of the bunched beam delivered to the EBIS will be adjustable to match the requirements of the existing post acceleration infrastructure. The CANREB RFQ incorporates design considerations to facilitate ease of use over a wide range of ion masses, and is intended to accommodate incident beam rates as high as 108pps, delivering beam bunches at 100Hz. An overview of the CANREB RFQ design concept will be presented, informed by results from both ion optical simulations as well as commissioning efforts with other beam cooler and buncher devices. Simulation results indicate that the design is well suited to deliver high quality bunched beams with high efficiency with as many as 106 ions per bunch.

Delivering multiple independent RIB simultaneously: Technical and operational challenges

ISAC is an ISOL-type facility at which RIB are produced by direct reactions of 480MeV protons from TRIUMFs main cyclotron on thick targets. Like other ISOL-type facilities, ISAC is limited to the production and delivery of a single RIB at any given time. ARIEL, the Advanced Rare-IsotopE Laboratory, will provide for the production and delivery of, ultimately, two additional RIB, the first produced by photofission on actinide targets using electrons from a new superconducting electron linac and the second by direct and indirect reactions with protons from TRIUMFs main cyclotron. This will allow for the simultaneous delivery of three independent RIB to experimental areas at ARIEL and ISAC.The shift from single-user to multi-user operation will introduce significant technical and operational challenges that RIB facilities have not yet had to address. Almost all aspects of facility operation will become more complex as the first RIB from ARIEL targets become available.

New design studies for TRIUMF’s ARIEL High Resolution Separator

As part of its new Advanced Rare IsotopE Laboratory (ARIEL), TRIUMF is designing a novel High Resolution Separator (HRS) (Maloney et al., 2015) to separate rare isotopes. The HRS has a 180° bend, separated into two 90° magnetic dipoles, bend radius 1.2m, with an electrostatic multipole corrector between them. Second order correction comes mainly from the dipole edge curvatures, but is intended to be fine-tuned with a sextupole component and a small octupole component in the multipole. This combination is designed to achieve 1:20,000 resolution for a 3μm (horizontal) and 6μm (vertical) emittance. A design for the HRS dipole magnets achieves both radial and integral flatness goals of <10−5. A review of the optical design for the HRS is presented, including the study of limiting factors affecting separation, matching and aberration correction. Field simulations from the OPERA-3D (OPERA) [2] models of the dipole magnets are used in COSY Infinity (COSY) (Berz and Makino, 2005) [3] to find and optimize the transfer maps to 3rd order and study residual nonlinearities to 8th order.

ARIEL E-linac Cryogenic System: Commissioning and First Operational Experience

The Advanced Rare IsotopE Laboratory (ARIEL) is a major expansion of the Isotope Separator and Accelerator (ISAC) facility at TRIUMF. A key part of the ARIEL project is a 10 mA 50 MeV continuous-wave superconducting radiofrequency (SRF) electron linear accelerator (e-linac). The 1.3 GHz SRF cavities are operated at 2 K. HELIAL LL helium liquefier by Air Liquide Advanced Technologies (ALAT) with a tuneable liquid helium (LHe) production was installed and commissioned in Q4’2013 [1]. It provides 4 K liquid helium to one injector and one accelerator cryomodules that were installed and tested in 2014. The 4 K to 2 K liquid helium transition is achieved on-board of each cryomodule. The cryoplant, LHe and LN2 distributions, sub-atmospheric (S/A) system and cryomodules were successfully commissioned and integrated into the e-linac cryogenic system. Required pressure regulation for both 4 K cryoplant in the Dewar and 2 K with the S/A system was achieved under simulated load. Final integration tests confirmed overall stable performance of the cryogenic system with two cryomodules installed. The paper presents details of the cryogenic system commissioning tests as well as highlights of the initial operational experience.

Charge state breeding experiences and plans at TRIUMF.

At the Isotope Separation and ACceleration (ISAC) facility at TRIUMF, an electron cyclotron resonance ion source (ECRIS) has been set up for the charge state breeding of radioactive ions. In order to reduce background from stable ions generated in the ECRIS, several measures, including changing materials for the plasma chamber and the surrounding components, have been implemented. Further reduction has been achieved by using the post-accelerator chain as a mass filter. Since the implementation of those measures in 2013, physics experiments with accelerated radioactive isotopes of Rb, Sr, K, and Mg have been performed. In most cases, a charge breeding efficiency of several percent has been achieved. With the planned expansion of the isotope production capabilities at TRIUMF within the Advanced Rare IsotopE Laboratory project, two new target stations, one using photo-fission induced by a high-power electron beam at 50 MeV and the other one using 480 MeV protons as at ISAC, will be put into operation within the next 5 yr. Additionally, a new electron beam ion source (EBIS) based charge state breeding system will be installed. Background from such a source is expected to be much lower. The drawback is that for the efficient operation of such a system, pulsed beam operation is required, which makes the installation of an additional ion buncher in front of the EBIS necessary.

Integration and Commissioning of the ARIEL e-linac Cryogenic System at TRIUMF

The Advanced Rare IsotopE Laboratory (ARIEL) is a major expansion of the Isotope Separation and Acceleration (ISAC) facility at TRIUMF. The key part of the ARIEL project is a superconducting radiofrequency (SRF) linear electron accelerator (e-linac). The e-linac helium cryogenic system was designed to meet the ARIEL specifications. The HELIAL LL helium liquefier byAir Liquide Advanced Technologiessupplies 4 K liquid helium (LHe) to cryomodules via aLHe distribution system. The cryomodules have a top-loaded-coldmass design. The 4 K–2 K temperature conversion is achieved by a counter flow heat exchanger and a JT-valve installed onboard each cryomodule[1]. The temperature in the 2 K volume of the cryomodules is controlled by pressure control in the sub-atmospheric line. Sub-atmospheric helium is warmed up in a custom-designed heat exchanger and after passing sub-atmospheric pumps goes to the helium compressor suction line. The LN2 system supplies liquid nitrogen to the liquefier, 80 K shielding of the cryomodules and LHe distribution system, as well as to the freeze-out helium purifier. The installation of the e-linac cryogenic system components started in February 2013 while the corresponding subsystems tests started in November 2013.This paper describes the e-linac cryogenic system components integration and presents the results of the acceptance tests and commissioning activities performed at TRIUMF since November 2013.

ARIEL e-linac

The design and implementation of a 1/2 MW beam power electron linear accelerator (e-linac) for the production of rare isotope beams (RIB) via photo-fission in the context of the Advanced Rare IsotopE Laboratory, ARIEL (Koscielniak et al. 2008; Merminga et al. 2011; Dilling et al., Hyperfine Interact, 2013), is described. The 100 % duty factor e-linac is based on super-conducting radiofrequency (SRF) technology at 1.3 GHz and has a nominal energy of 50 MeV. This paper provides an overview of the accelerator major components including the gun, cryomodules and cryoplant, high power RF sources, and machine layout including beam lines. Design features to facilitate operation of the linac as a Recirculating Linear Accelerator (RLA) for various applications, including Free Electron Lasers, are also noted.