The next generation of experiments on charged lepton flavor violation demands higher muon rates. To achieve this, one of the existing target stations at the Paul Scherrer Institute's high-intensity proton accelerator, along with its two connected beamlines, will be dismantled and rebuilt as part of the High Intensity Muon Beams (HIMB) project, under the Swiss Roadmap for Research Infrastructures initiative, IMPACT. The new MuH2 and MuH3 beamlines will rely on 15 large-aperture solenoids and 5 dipoles for muon beam transport, designed to handle a large phase-space beam. Our estimates of the absorbed dose levels indicate that five transport solenoids and two dipoles must be radiation-resistant, requiring the use of mineral-insulated cables, whilst the other magnets can utilize epoxy-impregnated coils. Currently, the design of transport beamline components is based on standard resistive magnets, which suffer from high power consumption. This study aims to explore an alternative using Nb-Ti superconducting coils to reduce power consumption. The paper focuses on the design study of transport solenoids and includes a thermo-economic analysis, considering radiation exposure at three positions relative to the target.

We determined the ultracold neutron (UCN) production rate by superthermal conversion in the solid deuterium (sD$_2$) moderator of the UCN source at the Paul Scherrer Institute (PSI). In particular, we considered low amounts of less than $20\,$mol of D$_2$, deposited on the cooled moderator vessel surfaces in thin films of a few mm thickness. We measured the isotopic ($ c_\text{HD} < 0.2 \, \% $) and isomeric ($ c_\text{para} \le 2.7 \, \% $) purity of the deuterium to conclude that absorption and up-scattering at $5\,$K have a negligible effect on the UCN yield from the thin films. We compared the calculated UCN yield based on the previously measured thermal neutron flux from the heavy water thermal moderator with measurements of the UCN count rates at the beamports. We confirmed our results and thus demonstrate an absolute characterization of the UCN production and transport in the source by simulations.

Solid deuterium (sD(2)) is used as an efficient converter to produce ultracold neutrons (UCN). It is known that the sD(2) must be sufficiently cold, of high purity and mostly in its ortho-state in order to guarantee long lifetimes of UCN in the solid from which they are extracted into vacuum. Also the UCN transparency of the bulk sD(2) material must be high because crystal inhomogeneities limit the mean free path for elastic scattering and reduce the extraction efficiency. Observations at the UCN sources at Paul Scherrer Institute and at Los Alamos National Laboratory consistently show a decrease of the UCN yield with time of operation after initial preparation or later treatment ("conditioning") of the sD(2). We show that, in addition to the quality of the bulk sD(2), the quality of its surface is essential. Our observations and simulations support the view that the surface is deteriorating due to a build-up of D-2 frost-layers under pulsed operation which leads to strong albedo reflections of UCN and subsequent loss. We report results of UCN yield measurements, temperature and pressure behavior of deuterium during source operation and conditioning, and UCN transport simulations. This, together with optical observations of sD(2) frost formation on initially transparent sD(2) in offline studies with pulsed heat input at the North Carolina State University UCN source, results in a consistent description of the UCN yield decrease.

Changing the configuration of the cold neutron source during a planned extended shutdown of the Swiss Spallation Neutron Source (SINQ) is being considered for improving performance of instruments at SINQ that use cold neutrons. The cold neutron source consists of a 20 L volume of liquid D-2 at approximately 25 K. This study includes making the re-entrant hole external, redesigning the re-entrant hole geometry, adding a Pb-208 reflector, replacing the zirconium safety hulls, adding cryogenic beryllium reflector/filters, and incorporating an active ortho-D-2 conversion loop. The optimization methods and the effects of the best-case modifications at all six neutron guides are presented. The best case design is predicted to yield a maximum gain factor of 1.5 in cold neutron intensity.

In a cyclotron-based proton therapy facility, the energy changes are performed by means of a degrader of variable thickness. The interaction of the proton beam with the degrader creates energy tails and increases the beam emittance. An accurate model of the degraded beam properties is important not only to better understand the performance of a facility already in operation, but also to support the development of new proton therapy concepts. The precision of the degraded beam properties, in terms of energy spectrum and transverse phase space, is influenced by approximations in the model of the particle-matter interaction. In this work the model of a graphite degrader has been developed with four Monte Carlo codes: three conventional Monte Carlo codes (FLUKA, GEANT4 and MCNPX) and the multi-purpose particle tracking code OPAL equipped with a simplified Monte Carlo routine. From the comparison between the different codes, we can deduce how the accuracy of the degrader model influences the precision of the beam dynamics model of a possible transport line downstream of the degrader.

A novel design of a gantry for proton therapy is investigated in which a degrader and emittance limiting collimators are mounted on the gantry. Due to the interactions of protons in these components there will be an additional neutron dose at the location where a patient is positioned during a proton therapy. The results of numerical study of this additional dose are presented. Neutron prompt dose at the patient position is estimated through the Monte Carlo simulation using the MCNPX 2.7.0 particle transport code. Secondary neutron and photon fluxes from the distinct beam loss points are taken into consideration and the resulting dose is calculated using realistic estimates of beam losses. The dependence of the dose on the beam energy and individual impacts of each loss point on the total dose at the patient position as well as on critical beam line components are estimated and potential design constraints are discussed. It has been found that compared with a conventional gantry the expected additional dose is higher but the optimization of the beam line configuration and additional shielding shall help to reduce the dose to an acceptable value.

Changing the configuration of the cold neutron source during an extended shutdown of the Swiss Spallation Neutron Source (SINQ) at the Paul Scherrer Institut is being considered for improving performance of the instruments that use the cold source. Proposed plans include making the REH external (ensuring that it is not filled with liquid D2) and using a REH that has been optimized to provide maximum gains between 3 and 6 Å. The optimization study was done using the MCNP Monte Carlo particle transport code, but was made tenable by developing a quick flux reconstruction technique that allows the neutron guide reflectivity to be approximated and accounted for in the optimization figure of merit. Ultimately, a wedgeshaped REH that penetrates the D2 volume to about 4 cm from its center was determined to be optimal, and should provide an average gain of 24% from 3 and 6 Å and a peak gain of 29% at 5.5.

The Paul Scherrer Institut operates two meson graphite targets, Target M and Target E, for creating the world’s most intense pion and muon beams by using 590 MeV protons and c.w. beam currents of up to 2.4 mA (=1.4 MW). The energy deposit on Target E is 20 kW mA −1 . The proton beam feeds also the spallation neutron source SINQ, which operates in DC mode and produces thermal and cold neutrons. The SINQ target consists of a bundle of lead filled Zircaloy tubes. In this report the continuous developments of both target facilities and their operation are presented.

We report on gold foil activation measurements performed along a vertical channel along the tank of the ultracold neutron source at the Paul Scherrer Institute. The activities obtained at various distances from the spallation target are in very good agreement with MCNPX simulations which take into account the detailed description of the source as built.

The proton channel of the PSI high intensity proton accel- erator (HIPA) transports the beam from the extraction point of the ring cyclotron through two meson production graphite targets up to the SINQ spallation source. After many years of continuous improvement, the HIPA accelerator complex has now reached the remarkable beam power of 1.4 MW. The next power upgrade is foreseen for the near future. In order to achieve this further step, an optimization of the beam transport in the proton channel is required with the goal of keeping the beam losses at a reasonable extent and, at the same time, improve the beam distribution on the SINQ target.

The Swiss spallation neutron source (SINQ) at Paul Scherrer Institut (PSI) provides beams of thermal and cold neutronstodifferentneutroninstruments. Inaviewofapotential SINQ upgrade, an experimental program characterizing the current performance of SINQ neutron beams was started in 2013. We present experimental results of the irradiation of imaging plates and gold foils at one of SINQ thermal neutron beam lines that hosts the high resolution powder diffractometer (HRPT) and compare the experimental results to the numerical MCNPX simulations of the neutron flux from the SINQ target-moderator system.