编号 7 (2023)

This paper is devoted to magnetic trap and extraction system upgrade of ECR ion source GISMO to utilize it as a proton injector for linear accelerator of compact neutron source DARIA. An open permanent magnet (Nd–Fe–B) trap was designed. It was adjusted to place the extraction system inside a part of magnet with larger inner diameter. Then, the three-electrode extractor optimization was made. It was shown that the use of additional magnetic lens allows to produce the proton beam with a low divergence angle. The use of the magnetic trap and the extraction system as a part of the proton injector for DARIA project possibility was shown using computer modeling. The following steps of the proton injector creation are discussed.

In the framework of the DARIA project (neutron source Dedicated to Applied Research and Industrial Applications) the 13 MeV, 162.5 MHz and 100 mA pulse proton linac is under development at the National Research Centre “Kurchatov Institute” – Kurchatov Complex for Theoretical and Experimental Physics. The linac includes RFQ (Radio Frequency Quadrupole) and DTL (Drift Tube Linac) sections. This article is devoted to the development of the DTL. The type of accelerating structure for creating high-frequency fields, which consists of a chain of multi-gap resonators, was determined. The optimal number of gaps in the resonators was selected. The choice of the main parameters and the analysis of various structures of the focusing periods were carried out. The results of the beam dynamics simulation in DTL are presented. The influence of Coulomb forces on particle dynamics in DTL was studied. The growth of the emittance in the DTL section was analyzed. The capabilities of the section for a wide range of input current and input beam emittance were considered.

Stainless steel with galvanic copper coating is often used as a material for ion linear accelerators RF cavities. However, for the cavities with complex inner surfaces obtaining a uniform copper coating becomes technologically challenging. The solution might be found in manufacturing the cavity without copper coating at all, though in that case the amount of power losses in the cavity should be carefully estimated. To make such estimations the experiment was carried out, where the electrodynamic properties of a test cavity with two coupling loops were measured with the stainless steel samples placed inside it. The results of this experiment showed sufficient difference between the simulated and measured Q-factor values for the same 12Х18Н10Т sample steel grade. Thus, an assumption was made the magnetic properties of austenitic steel samples could have changed during the manufacturing process, so the magnetic permeability values for the steel samples were estimated.

With the declining number of neutron sources in the world and the decommissioning of research reactors, projects to develop compact neutron sources are attracting more and more attention. The DARIA project suggests the use of a proton beam accelerated to an energy of 13 MeV, which, hitting a beryllium target, creates a neutron beam through the a nuclear reaction (p, n). The reaction yield is three neutrons per 1000 protons, so in this process most of the proton beam energy is released as heat in the target. Intense heating of a beryllium target in the absence of sufficient heat removal can lead to its destruction. A system has been developed for efficient heat removal from a beryllium target during its irradiation with a proton beam. It is a rotating water-cooled beryllium target and is capable of removing a large thermal power from the inner (water-side) surface of the target. For the proposed system, numerical simulations of the speed and pressure of the coolant were carried out. The limiting pressure leading to the destruction of the target and the flows corresponding to this limiting pressure were calculated. Thermodynamical simulations allowed us to evaluate both the average temperature of the system and the peak local (caused by short high-energy pulses) temperatures.

A conceptual design of a powder diffractometer for a compact neutron source DARIA based on a linear proton accelerator is presented. The proposed concept extends the possibilities of optimizing the device performance not only by varying the diffractometer parameters, but also the neutron source parameters, such as the moderator temperature, repetition rate, and duration of neutron pulses. The results of calculating the spectrum of the target assembly for different types of moderators are presented. The efficiency of the neutron source system for increasing the neutron flux on the sample is evaluated in the McStas software package. The calculation results show the principal possibility of implementing the neutron diffraction method under conditions of limited luminosity of the compact neutron source.

The concept of a two-mode neutron reflectometer with a polarizer, two spin-flippers and an analyzer of polarization after passing through the sample is presented. A reflectometer designed for a compact neutron source DARIA is planned to measure the spectrum of a reflected “white” neutron beam using the time-of-flight method at a fixed glancing angle with the possibility of using both polarized and non-polarized neutrons. The main geometric and physical parameters of the neutron reflectometer are presented. With a neutron pulse duration τ = 100 µs and a total length of the time-of-flight base L = 8 m, the pulse repetition rate can reach f = 165 Hz for the wavelength range Δλ = 3 Å and resolution Δλ ≅ 0.05 Å. The use of polarization analysis elements of a reflectometer at a beam polarization exceeding 96% and an efficiency of spin flippers close to unity makes it possible to study magnetic thin-film nanostructures in detail.

The results of studying thin films and superlattices of rare-earth helimagnets Dy and Ho by neutron reflectometry are presented. It is shown that neutron reflectometry allows studying magnetic phase transitions in these nanostructures and obtain information about periodicity of magnetic helices in them. It is proposed to create a neutron reflectometer capable of conducting polarization analysis on a compact DARIA neutron source, optimized for studying long-period magnetic orderings in rare-earth helimagnets, and possible directions of this optimization are indicated.