Soreq Applied Research Accelerator Facility Research Articles

Characterization of the LEBT based neutron source

Neutron generation by implantation and subsequent beam interaction of 40 keV deuterons at Soreq Applied Research Accelerator Facility (SARAF) low energy beam transport (LEBT) section was measured and characterized. The generation of 2.45 MeV neutrons by a deuteron beam of several mA was verified by a neutron spectrometer. Relative neutron yields were studied as a function of beam energy and beam spot size using two types of available implantation surfaces. The buildup of neutron yield was studied at long and short time scales. Absolute neutron yield was measured via activation at several conditions. The maximum neutron yield that could be obtained at the SARAF LEBT is of the order of 107 n/s, which presents a convenient source for testing neutron instrumentation in DC or pulsed mode.

Opportunities for high-energy neutron- and deuteron-induced measurements for fusion technology at the Soreq applied research accelerator facility (SARAF)

The Soreq Applied Research Accelerator Facility (SARAF) will be based on a 40 MeV, 5 mA CW (continuous wave) proton/deuteron superconducting linear accelerator, currently under construction at Soreq Nuclear Research Center in Yavne, Israel. It is planned to commence operation during 2025. Experiments at SARAF could provide data on high-energy deuteron- and neutron-induced cross-sections, yields and radiation damage, which are invaluable for the design and operation of the International Fusion Materials Irradiation Facility-DEMO-Oriented NEutron Source (IFMIF-DONES), and fusion technology in general. Pulsed beams (∼1 nsec) of variable energy deuterons will irradiate a lithium target and generate pulsed neutron beams with energy up to ∼55 MeV, which will be used to measure energy-dependent neutron-induced differential cross-sections, utilizing time of flight techniques. Impinging continuous wave (CW) 40 MeV deuteron beams on a unique gallium-indium (GaIn) liquid-jet target, will generate a neutron rate of more than 1 × 1015 n/sec, with energies up to ∼45 MeV. We plan to use this high rate to measure integral neutron-induced reaction yields of all channels simultaneously, employing an original novel method that will identify the reaction-produced nuclei via accurate mass measurement. The neutron-energy dependence of the yields could be deduced by combining measurements at various deuteron energies. The measured cross-sections and yields at SARAF may predict the activation characteristics of construction materials of IFMIF-DONES and future fusion reactors. The deuteron beams will also be used directly to measure cross-sections via in-beam and offline methods. The high neutron and deuteron rates will extend SARAF’s reach to rare materials. The deuteron beam power density on the liquid GaIn target will be 100 kW/cm2(similar to IFMIF-DONES) on a 2 cm2spot. The resulting neutron flux on small secondary samples will be in the 1013 n/cm2/s level, only an order of magnitude less than IFMIF-DONES. Therefore, SARAF may serve as a pilot facility for fusion-related radiation damage studies, providing important information towards the design of IFMIF-DONES.

Optical Measurements of the thickness of the Gallium Indium free surface jet for the SARAF beam dump and neutron source

The Soreq Applied Research Accelerator Facility (SARAF) is a proton/deuteron RF superconducting linear accelerator. Phase II of the project is underway and includes the development of the accelerator to its final specifications: energy of 40 MeV proton/deuteron, and a current of up to 5 mA. A beam dump and a neutron source will be required for the commissioning stage, daily operation, and basic physics experiments. A liquid metal target based on a high-velocity windowless gallium–indium jet has been designed to absorb a beam of 200 kW by generating a stable 6 mm-thick film flowing at a velocity of up to 5 m/s into a concave supporting wall (nozzle). The main goal of the present research was to demonstrate that the thickness and variations of the Ga–In flow satisfy the design requirement in the area corresponding to the beam footprint. This research also presents a novel method for optical non-contact measurements of the liquid Ga–In thickness by using a chromatic confocal sensor. The advantage of our system is that it uses an “off the shelf” non-expensive product, non-contact, very accurate, and with very high resolution.The results show that the average Ga–In thickness was 5.6 ± 0.3 mm at a flow speed of 5 m/s. These results are in agreement with the expected thickness of the nozzle.

Stellar s-process neutron capture cross sections on ASe and ACe

We report on experiments at the Soreq Applied Research Accelerator Facility Liquid-Lithium Target (SARAF-LiLiT) laboratory dedicated to the study of s-process neutron capture reactions. The kW-power proton beam at 1.92 MeV (1-2 mA) from SARAF Phase I yields high-intensity 30 keV quasi-Maxwellian neutrons (3-5 1010 n/s). The high neutron intensity enables Maxwellian averaged cross sections (MACS) measurements of samples with short-lived decay products. Neutron capture reactions on natSe and natCe were investigated by activation in the LiLiT neutron beam and γ-spectrometry measurements of their decay products.

Upgrade of SARAF fast beam chopper and its applications in Phase I and Phase II of SARAF linac

A fast chopper system has been developed for single-bunch selection for Phase I of the Soreq Applied Research Accelerator Facility (SARAF) in Israel. Further upgrade of the fast chopper system has improved its performance by enabling single-bunch selection for protons and deuterons at a repetition rate up to 220 kHz, with bunch transmission of up to 65% and with neighboring bunch contamination of less than 15%. The upgrade included (1) the redesign of the chopper deflection plates to minimize the electric-field asymmetry and provide more effective single-bunch selection, (2) a new trigger system with better trigger time resolution and better control capabilities, (3) an upgrade of the chopper electronics to increase the repetition rate, (4) the design of the chopper machine protection system, and (5) a general upgrade of the chopper concept to allow for operation in fast and slow modes. The implemented upgrades and the performance of the upgraded system are described. In addition, examples of the first experiments using the neutron time-of-flight (TOF) technique are presented. A fast neutron TOF facility, based on the upgraded fast chopper, is planned for SARAF Phase II. The high neutron flux at SARAF Phase II combined with the upgraded fast chopper system will make SARAF competitive with other advanced neutron research facilities.

The liquid-lithium target at the soreq applied research accelerator facility

The liquid-lithium target at the soreq applied research accelerator facility

High-power inductive coupler with a high-voltage DC blocker

The authors of this study developed a high-power inductive coupler with a high-voltage DC blocker that is capable of delivering up to 100 kW of CW RF power at 176 MHz and 4 kV DC. The high-power indictive coupler was developed at the Soreq Nuclear Research Center for the radio-frequency quadrupole of the Soreq Applied Research Accelerator Facility. The purpose of the DC blocker is to enable the application of high-voltage DC bias to the inner conductors of the couplers in order to prevent the multipacting phenomena. A new, mechanically and thermally improved, version of the RF coupler is designed and implemented in conjunction with the DC blocker. The underlying design principles, indigenous development, and results of tests of the coupler are presented here.

Upgrade of the 4-rod radio frequency quadrupole for SARAF Phase II Linac

The 176 MHz 4-rod radiofrequency quadrupole (RFQ) is the crucial part of the Soreq Applied Research Accelerator Facility (SARAF) injector and must be able to operate at RF powers up to 190 kW continuous wave and transport 5 mA proton and deuteron beams. The SARAF Phase I RFQ is planned for use in Phase II. The period between the termination of Phase I and the installation of Phase II provided an opportunity to introduce RFQ improvements to fully meet the Phase II requirements. These upgrades and improvements are presented in this report together with the results of the recent conditioning campaigns.

High power high voltage bias-T for half wave resonators and radio frequency quadrupole couplers

High power high voltage bias-T units capable of delivering up to 100 kW CW RF power at 176MHz and up to 4kV DC were developed at the Soreq Nuclear Research Center for the Soreq Applied Research Accelerator Facility linac. Two separate bias-T units with different requirements were designed for the radio frequency quadrupole couplers and the half wave resonator couplers. The purpose of this bias-T is to prevent multipacting phenomena by application of a high voltage DC bias to inner conductors of RF couplers. Underlying design principles, indigenous development, and successful off-line and on-line tests results are presented.

Stellar s -process neutron capture cross sections of Ga69,71

The stable gallium isotopes, $^{69,71}$Ga, are mostly produced by the weak slow ($s$) process in massive stars. We report here on measurements of astrophysically-relevant neutron capture cross sections of the $^{69,71}$Ga$(n,\gamma)$ reactions. The experiments were performed by the activation technique using a high-intensity ($3-5\times10^{10}$ n/s), quasi-Maxwellian neutron beam that closely mimics conditions of stellar $s$-process nucleosynthesis at $kT \approx$ 40 keV. The neutron field was produced by a mA proton beam at $E_p=1925$ keV (beam power of 2-3 kW) from the Soreq Applied Research Accelerator Facility (SARAF), bombarding the Liquid-Lithium Target (LiLiT). A 473 mg sample of Ga$_2$O$_3$ of natural isotopic composition was activated in the LiLiT neutron field and the activities of $^{70,72}$Ga were measured by decay counting via $\gamma$-spectrometry with a high-purity germanium detector. The Maxwellian-averaged cross sections at $kT$ = 30 keV of $^{69}$Ga and $^{71}$Ga determined in this work are 136(8) mb and 105(7) mb, respectively, in good agreement with previous experimental values. Astrophysical implications of the measurements are discussed.

MeV proton irradiation damage in Ta: Measurements, characterization and comparison to W

The effects of high-energy proton irradiation on tantalum and its properties, were studied at the Soreq Applied Research Accelerator Facility (SARAF) using a high-flux 2.2 MeV proton beam. Samples were characterized by optical interferometry, nano-indentation and Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS), to study the effect of radiation damage. The experimental data on the penetration depth of 2.2 MeV protons in tantalum was found to be in good agreement with simulations and an increase of the irradiated sample’s hardness was measured. The volume expansion was found to be correlated to the total proton fluence. With the aid of density functional theory estimates of the point defect formation volumes, we suggest that hydrogen occupies mainly interstitial sites in the Ta lattice. We observed extensive diffusion of the hydrogen into the material. Thus, no blistering was observed up to a total fluence of 1.9•10 20 P/cm 2 , extending the lower bound for blister formation in tantalum to one to three orders of magnitude above the critical fluence for blistering in tungsten. A reaction-diffusion model was employed to analyze the spatial distribution of the point defects, to assist in the interpretation of the results in comparison with tungsten, and to identify the role of the hydrogen diffusion. We conclude that tantalum is a promising structural material in proton radiation environments.

Stellar 78,80,84,86Kr(n,γ) Reactions Studied by Activation at SARAF-LiLiT, Atom Trap Trace Analysis and Decay Counting

We report on (n,γ) neutron capture experiments performed with the Liquid-Lithium Target (LiLiT) and the mA-proton beam at 1.92 MeV (2-3 kW) from the Soreq Applied Research Accelerator Facility (SARAF). The setup yields high-intensity 30-keV quasi-Maxwellian neutrons (3-5 × 1010 n/s) closely reproducing the conditions of s-process stellar nucleosynthesis. The 78,80,8486Kr(n,γ) reactions at the border between weak- and strong- s-process were studied. A Ti sphere filled with 107.7 mg of natural Kr gas was placed in an irradiation chamber downstream of LiLiT with a gold foil used as a neutron fluence monitor during the activation. The activities of the short-lived Kr isotopes (7985m87Kr) were measured by γ decay counting with a HPGe detector. The long-lived Kr isotopes (81,85gKr) were measured by atom counting via Atom Trap Trace Analysis (ATTA) at Argonne and Low-Level Counting (LLC) at Bern.

Study of Astrophysical s-Process Neutron Capture Reactions at the High-Intensity SARAF-LiLiT Neutron Source

We report on recent experiments at the Soreq Applied Research Accelerator Facility Liquid-Lithium Target (SARAF-LiLiT) laboratory dedicated to the study of s-process neutron capture reactions. The kW-power proton beam at 1.92 MeV (1-2 mA) from SARAF Phase I yields high-intensity 30 keV quasi-Maxwellian neutrons (3-5×1010 n/s). The high neutron intensity enables Maxwellian averaged cross sections (MACS) measurements of low-abundance or radioactive targets. Neutron capture reactions on the important s-process branching points 147Pm and 171Tm were investigated by activation in the LiLiT neutron beam and γ-measurements of their decay products. MACS values at 30 keV extracted from the experimental spectrum-averaged cross sections are obtained and will be discussed. The Kr region, at the border between the so-called weak and strong s-process was also investigated. Atom Trap Trace Analysis (ATTA) was used for the first time for the measurement of a nuclear reaction cross section. After activation in the quasi-Maxwellian neutron flux at SARAF-LiLiT, isotopic ratios were determined for 81Kr(230 ky)/80Kr and 85gKr(10.8 y)/84Kr. The latter ratio was confirmed both by low-level β counting and γ spectrometry. The shorter-lived capture products 79,85m,87Kr were detected by γ -spectrometry and the corresponding neutron-capture MACS of the respective target nuclei 78,84,86Kr were determined. The MACS of the 80Kr(n, γ)81Kr and 84Kr(n, γ)85gKr reactions are still under study. The partial MACS leading to 85mKr(4.5 h) measured in this experiment has interesting implications since this state decays preferentially by γ decay (79%) to 85Rb on a faster time scale than does 85gKr and behaves thus as an s-process branching point.

Mechanical design of the superconducting solenoid package for the SARAF-linac project

The Soreq Applied Research Accelerator Facility (SARAF) in Israel will provide an intense source of fast neutrons and radioactive nuclei for neutron applications, to explore rare nuclear reactions and produce new types of radiopharmaceuticals for nuclear medicine. CEA Paris-Saclay is in charge of the design, construction and commissioning of this superconducting linear particle accelerator (linac) to produce the first particle beams in 2022.The superconducting linac is part of the SARAF accelerator and it will be equipped with twenty identical solenoid packages arranged in four 5-metre long cryomodules; they are located between the cavities and they ensure the beam control. The solenoid package is a complex mechanical system and it is designed to operate at cryogenic temperatures. It comprises the main solenoid coil with an integrated square flux density of 3.5 T2 m , two lateral shielding coils to reduce the fringe fields on the cavities as well as two pairs of steering coils. This ensemble is enclosed in a stainless steel helium vessel.In this study, we present the mechanical design of the first prototype of the solenoid package with a particular focus on the main coil, whereby the superconducting wire (Nb–Ti/Cu) is wound and cured on two extremity flanges made of epoxy reinforced with glass cloth (G-10). The modelling of the solenoid components is carried out using Finite Element Analysis (FEA) and the results of simulations are used to assess the structural integrity of the components. Moreover, an extensive literature review is conducted to collect the mechanical properties at cryogenic temperature of the composite materials used for the construction. Finally, the results of the experimental validation of the first solenoid prototype are presented. The experimental campaign is carried out using a cryostat designed on purpose to reproduce both the final operating temperature and magnetic field.

Fracture morphology and mechanical properties of blisters in poly- and single crystal tungsten irradiated by MeV protons

The mechanical properties and the fracture morphology of the inner surface of blisters formed in polycrystalline and single crystal tungsten under MeV proton irradiation, were studied.The tungsten samples were irradiated at Soreq Applied Research Accelerator Facility (SARAF) by 2.2 MeV protons, at various samples temperatures and proton doses. The morphology of the irradiated samples was observed by examining cross sections of blisters obtained by focused ion beam (FIB). The thickness of the blister cap was found to be in good agreement with the irradiating protons stopping range, regardless of sample structure, temperature or total dose. Increased curvature of the surfaces was observed with increased temperature for polycrystalline and single crystal blisters and was interpreted as increased ductility of the blister growth process. The ductility is more substantial in single crystal blisters, pointing to the role of grain boundaries in blisters growth mechanism. The cap of one blister was removed, exposing the inner fracture surface of a blister and supporting the validity of the cross sectional observations.The mechanical properties in the vicinity of a blister formed in a single crystal sample were characterized by nano-indentation. The hardness near the irradiated surface was found to increase both in the vicinity of the blister and beyond. This observation suggests that the elevation of the blister cap does not cause significant strain hardening. For the blister cap, the hardness was found to increase with increasing depth from the irradiated surface, correlating with increased irradiation damage.

Branching Ratio Measurement in 23Ne Beta Decay

We describe the branching ratio measurement experiment performed at Soreq Applied Research Accelerator Facility (SARAF) using the deuteron beam. We successfully produced 107/s 23Ne atoms in the run and used them to measure the branching ratio in 23Ne beta decay to the first excited state of 23Na. We provide some preliminary results of the experiment whose data analysis currently ongoing.

Measurements of Co59(d,p)Co60m,g,V51(d,p)V52 , and natV(d,xn)Cr51 cross sections in the 2.7–5.4−MeV energy range

The cross sections of the $^{59}\mathrm{Co}(d,p)^{60m,g}\mathrm{Co},^{51}\mathrm{V}(d,p)^{52}\mathrm{V}$, and ${}^{\mathrm{nat}}\mathrm{V}{(d,xn)}^{51}\mathrm{Cr}$ reactions were accurately measured at the Soreq Applied Research Accelerator Facility in the energy range 2.7--5.4 MeV. The obtained results together with other data, available in the same region of the nuclear chart, were used for verifying the theoretical models. The consistent theoretical model calculation successfully reproduces the experimental results.

Reactions along the astrophysical s-process path and prospects for neutron radiotherapy with the Liquid-Lithium Target (LiLiT) at the Soreq Applied Research Accelerator Facility (SARAF)

Neutrons play a dominant role in the stellar nucleosynthesis of heavy elements and the quest for accurate experimental determinations of neutron-induced reaction cross sections becomes more stringent with the refinement of nuclear and astrophysical models. We review here an experimental nuclear-astrophysics program using a high-intensity neutron source based on the 7Li(p, n)7Be reaction with a Liquid-Lithium Target (LiLiT) at the Soreq Applied Research Accelerator Facility (SARAF) Phase I. The quasi-Maxwellian neutron spectrum with effective thermal energy $ kT \approx 30$ keV, characteristic of the thick-target 7Li(p, n) yield at proton energy $ E_p \approx 1.92$ MeV close to its neutron threshold, is well suited for laboratory measurements of neutron capture reactions along the astrophysical s -process path. The high-intensity proton beam (in the mA range) of SARAF and the high power (few kW) dissipation of LiLiT result in the most intense source of neutrons available today at stellar-like energies. The principle, design and properties of the LiLiT device and recent measurements of Maxwellian Averaged Cross Sections (MACS) based on activation of targets of astrophysical interest are described. Decay counting or atom counting methods (accelerator mass spectrometry, atom-trap trace analysis) are used for the detection of short-lived or long-lived activation products, respectively. In a different realm of applications, the 7Li(p, n) reaction is a leading candidate as an accelerator-based neutron source for Boron Neutron Capture Therapy (BNCT). The high neutron yield achievable from a liquid-lithium target, its sustainability of operation under kW-power incident beams and the recent availability of small-size high-intensity accelerators are compatible with a hospital-based clinical facility. An effort towards the characterization and realization of a liquid-lithium target for BNCT is reviewed. Perspectives of pending and future developments towards SARAF Phase II, based on a 40MeV, 5mA CW proton/deuteron superconducting linear accelerator, are summarized.

Fast chopper for single radio-frequency quadrupole bunch selection for neutron time-of-flight capabilities

A fast chopper system has been developed and tested for single bunch selection with the radio-frequency quadrupole (RFQ) accelerating element of the Soreq Applied Research Accelerator Facility (SARAF). The fast chopper consists of a high voltage (HV) deflector just before the RFQ, providing both positive and negative HV deflections and fast HV switching between polarities to enable momentary transmission of a single prebunch to the RFQ. Presently, the system enables single bunch selection for protons and deuterons at a repetition rate as determined by the user of up to 200 kHz, with bunch transmission of up to 50%, and with neighboring bunch contamination of less than 15%. Single bunch selection provides SARAF with fast neutron time-of-flight (TOF) capabilities. Measurements performed with liquid scintillation detectors show clear gamma and neutrons peaks, with TOF resolution of about 1 nanosecond FWHM. Beam dynamics simulations suggest possibilities for further improvements of the fast chopper and single bunch selection characteristics, with a significant lowering or elimination of the neighboring bunches, enhanced TOF resolution, and increased repetition rate to above 200 kHz. Fast neutron TOF capabilities, especially at phase II of SARAF, will provide exceptional opportunities for neutron induced reaction measurements for nuclear technology and fundamental research.

Weak interaction studies at SARAF

We review the current status of the radioisotopes program at the Soreq Applied Research Accelerator Facility (SARAF), where we utilize an electrostatic-ion-beam trap and a magneto-optical trap for studying the nuclear $\beta$-decay from trapped radioactive atoms and ions. The differential energy spectra of $\beta$'s and recoil ions emerging from the decay is sensitive to beyond standard model interactions and is complementary to high energy searches. The completed facility SARAF-II will be one of the world's most powerful deuteron, proton and fast neutron sources, producing light radioactive isotopes in unprecedented amounts, needed for obtaining enough statistics for a high precision measurement.