Tritium is a well-known byproduct of particle accelerator operations. To keep levels of tritium below regulatory limits, tritium production is actively monitored and managed at Fermilab. We plan to study tritium production in the targets, beamline components, and shielding elements of the Fermilab facilities such as NuMI, BNB, and MI-65. To facilitate the analysis, we construct a simple model and use three Monte Carlo radiation codes, FLUKA, MARS, and PHITS, to estimate the amount of tritium produced in these facilities. The analysis could also serve as an intercomparison between these code results related to tritium production. To assess the actual amounts of tritium that would be released from various materials, we employ a semi-empirical diffusion model. The results of this analysis are compared to experimental data whenever possible. This approach also helps to optimize proposed target materials with respect to the tritium production and release.

The PIP-II project at Fermilab, which includes an 800-MeV superconducting LINAC, demands rigorous radiation shielding optimization to meet safety requirements. We updated the MARS geometry model to reflect new magnet and collimator designs and introduced high-resolution detector planes to better capture radiation field distributions. To overcome the significant computational demands, we implemented a well-known branching technique that drastically reduced simulation runtimes while maintaining statistical integrity. This was achieved through particle splitting and the application of Russian Roulette techniques. Additionally, new graphical tools were created to streamline data visualization and MARS code usability.

This report describes major features of the most recent version of the MARS code as well as ongoing developments. The list of features includes various options for geometry models, a beam line builder based on MADX code, import of geometry models in GDML format, use of structured and unstructured meshes for scoring purposes, an update to the recent TENDL library for a number of projectiles at low energies (up to 250 MeV), and a recently implemented method to calculate spatial distribution of residual dose in a single computer run without an intermediate source. Examples of the code application to various projects are presented as well.

The Deep Underground Neutrino Experiment and Long-Baseline Neutrino Facility (DUNE-LBNF) are under development at Fermilab since early 2010s [1]. At present, the work is being performed towards a comprehensive review conducted by US Department of Energy (DOE)-the Critical Decision 2 (CD-2)-that is planned to take place in the middle of 2022. The primary scientific objectives of DUNE are to carry out a comprehensive investigation of neutrino oscillations to test CP violation in the lepton sector, determine the ordering of the neutrino masses, and to test the three-neutrino paradigm (electron, muon and tau neutrino). The LBNF will provide a 120-GeV proton beam on a neutrino production target utilizing a new 800-MeV superconducting Linac which is expected to be completed in 2027 [2]. The neutrino beamline, which utilizes a target and horn systems, decay pipe, hadron absorber and other systems, is a core component of the LBNF. At present-as a result of numerous iterations-there exists an optimized design with a 1.5-m graphite target and focusing system consisting of three horns. Further optimization energy deposition and radiological calculations are performed towards CD-2 and beyond. This paper describes results of the most recent MARS15 [3] optimization studies.

The Proton Improvement Plan-II (PIP-II) [1] has been developed at Fermilab to provide powerful proton beams to the laboratorys experiments. An 800-MeV superconducting linear accelerator-a centerpiece of the project-is currently under construction in Batavia, Illinois (USA). After completion, the superconducting linac will be the starting point for the 1.2 MW (Phase 1) and 2.4-MW (Phase 2) proton beam that is needed for the Long-Baseline Neutrino Facility (LBNF) at Fermilab [2]. Due to unavoidable loss of a fraction of the beam in the accelerator components, a certain level of radiation will be generated in the accelerator tunnel both during normal operation and at accidents. This work deals with radiation shielding design for the accelerator facility.

The studies described below have been performed for NuMI Accelerator Improvement Project (NuMI AIP). This work has been done to extend previous studies and address new issues encountered as the project evolves. The calculations have been performed for both normal operation and an accident scenario.

Activation of the soil surrounding the ESS accelerator tunnel calculated by the MARS15 code is presented. A detailed composition of the soil, that comprises about 30 chemical elements, is considered. Spatial distributions of the produced activity are provided in both transverse and longitudinal directions. A realistic irradiation profile for the entire planned lifetime of the facility is used. The nuclear transmutation and decay of the produced radionuclides is calculated with the DeTra code which is a built-in tool for the MARS15 code. Radionuclide production by low-energy neutrons is calculated using the ENDF/B-VII evaluated nuclear data library. In order to estimate quality of this activation assessment, a comparison between calculated and measured activation of various foils in a similar radiation environment is presented.

Measurements and calculations of the air activation at a high-energy proton accelerator are described. The quantity of radionuclides released outdoors depends on operation scenarios including details of the air exchange inside the facility. To improve the prediction of the air activation levels, the MARS15 Monte Carlo code radionuclide production model was modified to be used for these studies. Measurements were done to benchmark the new model and verify its use in optimization studies for the new DUNE experiment at the Long Baseline Neutrino Facility (LBNF) at Fermilab. The measured production rates for the most important radionuclides – 11C, 13N, 15O and 41Ar – are in a good agreement with those calculated with the improved MARS15 code.

The Integrable Optics Test Accelerator (IOTA) at Fermilab’s Accelerator Science and Technology (FAST) facility [1] is a storage ring for advanced high intensity beam physics research. Layout of the ring is shown in Fig. 1. A plan view of the ring with enclosure walls are shown in Fig. 2. The entire beam, stored in the IOTA ring, is assumed to be completely lost at either of the three locations shown in Fig. 2. Therefore, we will consider three separate corresponding accident scenarios. The maximal amount of electrons stored in the IOTA ring is estimated to be 2×1010 electrons with energy of 150 MeV. At locations 1 and 2 the beam is lost on 60-deg dipole walls, while at location 3 the beam is lost on Lambertson magnet wall.

PIP-II is the Fermilab's flagship project for providing powerful, high-intensity proton beams to the laboratory's experiments. The heart of PIP-II is an 800-MeV superconducting linac accelerator. It will be located in a new tunnel with new service buildings and connected to the present Booster through a new transfer line. To support the design of civil engineering and mechanical integration, this paper provides preliminary estimation of radiation level in the gallery at an operational beam loss limit of 0.1 W/m, by means of Monte Carlo calculations with FLUKA and MARS15 codes.

Chapter 10 in High-Luminosity Large Hadron Collider (HL-LHC) : Preliminary Design Report. The Large Hadron Collider (LHC) is one of the largest scientific instruments ever built. Since opening up a new energy frontier for exploration in 2010, it has gathered a global user community of about 7,000 scientists working in fundamental particle physics and the physics of hadronic matter at extreme temperature and density. To sustain and extend its discovery potential, the LHC will need a major upgrade in the 2020s. This will increase its luminosity (rate of collisions) by a factor of five beyond the original design value and the integrated luminosity (total collisions created) by a factor ten. The LHC is already a highly complex and exquisitely optimised machine so this upgrade must be carefully conceived and will require about ten years to implement. The new configuration, known as High Luminosity LHC (HL-LHC), will rely on a number of key innovations that push accelerator technology beyond its present limits. Among these are cutting-edge 11-12 tesla superconducting magnets, compact superconducting cavities for beam rotation with ultra-precise phase control, new technology and physical processes for beam collimation and 300 metre-long high-power superconducting links with negligible energy dissipation. The present document describes the technologies and components that will be used to realise the project and is intended to serve as the basis for the detailed engineering design of HL-LHC.

Studies and optimization of design of the International Linear Collider (ILC) based on the TESLA-type 9-cell 1.3 GHz superconducting RF (SRF) cavities are currently underway. Dark current electron generated by field emission (FE) in SRF cavities can be captured and accelerated in the main ILC linac up to very high energy before they are removed by focusing and steering magnets. Dark current electrons, interacting with the materials surrounding SRF cavities, produce electromagnetic showers and contribute to the radiation in the main ILC tunnel. In this paper present preliminary results of the simulation study of dark current in the ILC linac.

Electromagnetic and hadron showers generated by electrons of dark current (DC) can represent a significant radiation threat to the ILC linac equipment and personnel. In this study, a commissioning scenario is analysed which is considered as the worst-case scenario for the main linac regarding the DC contribution to the radiation environment in the tunnel. A normal operation scenario is analysed as well. An emphasis is made on radiation load to sensitive electronic equipment—cryogenic thermometers inside the cryomodules. Prompt and residual dose rates in the ILC main linac tunnels were also calculated in these new high-statistics runs. A novel approach was developed—as a part of general purpose Monte Carlo code MARS15—to model generation, acceleration and transport of DC electrons in electromagnetic fields inside SRF cavities. Comparisons were made with a standard approach when a set of pre-calculated DC electron trajectories is used, with a proper normalization, as a source for Monte Carlo modelling. Results of MARS15 Monte Carlo calculations, performed for the current main linac tunnel design, reveal that the peak absorbed dose in the cryogenic thermometers in the main tunnel for 20 years of operation is about 0.8 MGy. The calculated contact residual dose on cryomodules and tunnel walls in the main tunnel for typical irradiation and cooling conditions is 0.1 and 0.01 mSv/hr, respectively.

Chapter 10 in High-Luminosity Large Hadron Collider (HL-LHC) : Preliminary Design Report. The Large Hadron Collider (LHC) is one of the largest scientific instruments ever built. Since opening up a new energy frontier for exploration in 2010, it has gathered a global user community of about 7,000 scientists working in fundamental particle physics and the physics of hadronic matter at extreme temperature and density. To sustain and extend its discovery potential, the LHC will need a major upgrade in the 2020s. This will increase its luminosity (rate of collisions) by a factor of five beyond the original design value and the integrated luminosity (total collisions created) by a factor ten. The LHC is already a highly complex and exquisitely optimised machine so this upgrade must be carefully conceived and will require about ten years to implement. The new configuration, known as High Luminosity LHC (HL-LHC), will rely on a number of key innovations that push accelerator technology beyond its present limits. Among these are cutting-edge 11-12 tesla superconducting magnets, compact superconducting cavities for beam rotation with ultra-precise phase control, new technology and physical processes for beam collimation and 300 metre-long high-power superconducting links with negligible energy dissipation. The present document describes the technologies and components that will be used to realise the project and is intended to serve as the basis for the detailed engineering design of HL-LHC.

Comprehensive studies with the MARS15(2016) Monte-Carlo code are described on evaluation of prompt and residual radiation levels induced by nominal and accidental beam losses in the 5-MW, 2-GeV European Spallation Source (ESS) Linac. These are to provide a basis for radiation shielding design verification through the accelerator complex. The calculation model is based on the latest engineering design and includes a sophisticated algorithm for particle tracking in the machine RF cavities as well as a well-established model of the beam loss. Substantial efforts were put in solving the deep-penetration problem for the thick shielding around the tunnel with numerous complex penetrations. It allowed us to study in detail not only the prompt dose, but also component and air activation, radiation loads on the soil outside the tunnel, and skyshine studies for the complicated 3-D surface above the machine. Among the other things, the newest features in MARS15 (2016), such as a ROOT-based beamline builder and a TENDL-based event generator for nuclear interactions below 100 MeV, were very useful in this challenging application.

Electrons of dark current (DC), generated in high-gradient superconducting RF cavities (SRF) due to field emission, can be accelerated up to very high energies-19 GeV in the case of the International Linear Collider (ILC) main linac-before they are removed by focusing and steering magnets. Electromagnetic and hadron showers generated by such electrons can represent a significant radiation threat to the linac equipment and personnel. In our study, an operational scenario is analysed which is believed can be considered as the worst case scenario for the main linac regarding the DC contribution to the radiation environment in the main linac tunnel. A detailed modeling is performed for the DC electrons which are emitted from the surface of the SRF cavities and can be repeatedly accelerated in the high-gradient fields in many SRF cavities. Results of MARS15 Monte Carlo calculations, performed for the current main linac tunnel design, reveal that the prompt dose design level of 25 μSv/hr in the service tunnel can be provided by a 2.3-m thick concrete wall between the main and service tunnels.

The Booster Beam Notch is a beam gap needed to allow extraction kickers to reach full field strength for a single turn extraction scheme. The Notch is created at injection energy by kicking 3 out of the 84 bunches to a dedicated absorber. The kicker voltage, pulse length and geometry of the absorber must be optimized to minimize the beam loss due to the notch creation. Beam studies, simulation and implementation as well as the optimization and improvement of the notch system will be discussed in this paper. PROTON IMPROVEMENT PLAN (PIP) The notch system task was one of 35 PIP tasks identified for the Proton Source to address the need to increase proton beam flux. A more than doubling of proton per hour rate is required to meet the Fermilab HEP program. A significant effort to increase the flux went to increase Booster beam cycles from 7Hz to 15 Hz. The doubling of Booster beam cycles consequently would incur increased integrated beam loss at various phases of beam operations, including notch formation and extraction time. Reduction in extraction losses and better managed notch formation losses need to be optimized [1]. THE SWITCH FROM VERTICAL TO HORIZONTAL NOTCH SYSTEMS A dedicated absorber was designed and then installed in the Booster ring, in the 2012/13 upgrade maintenance period, to contain the notched beam (Fig. 1). The kicking plane was changed to the horizontal plane as there is more aperture to separate notched beam [2]. Previously, notching was achieved with 2 kicker magnets in two different regions of the Booster ring. The kick was in the vertical plane. The kicked beam was deposited into the collimation region and 2 small mask absorbing elements 6 cells away to clean up the tails of the notched bunches. Simulation is seen in Fig. 2a. This change would reduce the activation levels in the circulating beam collimation region significantly (see on Fig. 2a.) and allow for a more controlled deposition of the removed bunches to create the three-bucket notch in the new absorber (Fig. 2b). Fig. 3 depicts this this new layout. Initially, the same notching equipment was relocated to the new physical locations in the Booster ring and equipment galleries with the addition of a third old kicker system until the new equipment could be built. Simulations indicated that a third kicker would be needed for the horizontal kick scheme to work at 400-700MeV. The new consolidated power supply system and faster filling magnets where implemented in phases. This Fermilab RR/NOVA style pulser would drive 6 half meter long kickers with two CX2610 thyratrons [3]. This would provide faster fill time than the previous 1.08 meter long kickers and power supply. Our rise time improved by about 10 nsec, giving a flatter notch pulse. Figure 1: Hor. Notching kickers and absorber. Figure 2: Loss sim. vert. (a) and hor. (b) notching. Figure 3: Notched beam region. 700MEV TO 400MeV NOTCH Beam notching was initially implemented in the horizontal plane at two energies, 400MeV (Booster injection) and 700MeV. The later energy was required to establish notch synchronization when utilizing the RF cogging method, required for MI/RR batches 2-12, which could not be initiated earlier than approximately 600-700MeV [4]. With the advent of a new magnetic cogging technique, horizontal dipole corrector magnets are used to achieve this goal thus enabling an earlier notch creation time for the cogged cycles to Fermilab’s Main Injector and Recycler Ring [5]. The notch time has been optimized to occur just after recapture of the Linac beam via paraphrase method in Booster. Now all 12 notched beam events are fixed to 400MeV. For a 12 batch MI/ RR injection, this helped reduce the notch losses on the later cogged 11 batches. ___________________________________________ *Operated by Fermi Research Alliance, LLC under Contract No.DeAC02-07CH11359 with the United States Department of Energy. † chaurize@fnal.gov TUPIK117 Proceedings of IPAC2017, Copenhagen, Denmark ISBN 978-3-95450-182-3 2002 Co py rig ht © 20 17 CC -B Y3. 0 an d by th er es pe ct iv ea ut ho rs 04 Hadron Accelerators A17 High Intensity Accelerators Notching beam early highlighted the fact that the separation between the circulating beam and notched beam was less, due to lower energy and larger emittance beam. There where losses due to broader tails on the bunches. Losses were still lower overall due to the reduced notch beam energy. This required more work on beam orbits to find an ideal operating point. Beam size and orbit trajectories were simulated. Beam measurements were also made looking at beam position and losses through the notch region and ring wide. We took measurements looking at the kicked bunches using raw BPM data. We could see the effective aperture and relative beam positions of the two beams (Fig. 4). Figure 4 : Notched/circulating beam orbit.

The shielding calculations for the Booster Notcher absorber were performed in order to predict the surface water activation around the absorber and effective dose at the nearest public places (in Booster gallery and atop the berm).

Results of detailed Monte Carlo energy deposition and radiological studies performed for the LBNF hadron absorber with the MARS15 code are described. The model of the entire facility, that includes a pion-production target, focusing horns, target chase, decay channel, hadron absorber system - all with corresponding radiation shielding - was developed using the recently implemented ROOT-based geometry option in the MARS15 code. Both normal operation and accidental conditions were studied. Results of detailed thermal calculations with the ANSYS code helped to select the most viable design options.