Exploratory investigation of the HIPPO gas-jet target fluid dynamic properties

Abstract

In order to optimize the performance of gas-jet targets for future nuclear reaction measurements, a detailed understanding of the dependence of the gas-jet properties on experiment design parameters is required. Common methods of gas-jet characterization rely on measuring the effective thickness using nuclear elastic scattering and energy loss techniques; however, these tests are time intensive and limit the range of design modifications which can be explored to improve the properties of the jet as a nuclear reaction target. Thus, a more rapid jet-characterization method is desired. We performed the first steps towards characterizing the gas-jet density distribution of the HIPPO gas-jet target at the University of Notre Dame's Nuclear Science Laboratory by reproducing results from 20 Ne(α, α) 20 Ne elastic scattering measurements with computational fluid dynamics (CFD) simulations performed with the state-of-the-art CFD software ANSYS Fluent. We find a strong sensitivity to experimental design parameters of the gas-jet target, such as the jet nozzle geometry and ambient pressure of the target chamber. We argue that improved predictive power will require moving to three-dimensional simulations and additional benchmarking with experimental data.

Status of the JENSA gas-jet target for experiments with rare isotope beams

“…At an input pressure of 150 kPa before the de Laval nozzle, a (2.20 ± 0.20)mm wide helium jet with (2.59 ± 0.21) × 10 17 atoms/cm 2 (as weighted arithmetic mean from both methods) was achieved. Ensuing computational fluid dynamics (CFD) simulations [28] were found to be consistent with the scattering experiment.…”

The status and future of direct nuclear reaction measurements for stellar burning

“…High-intensity ion beams for elements up to mass A ≈ 50 are delivered to St. George by the Santa Ana single-ended Pelletron accelerator, which has an electron cyclotron resonance (ECR) ion source in the terminal. The target for (α, γ) reactions with St. George is the HIPPO gas-jet target, which is well characterized [199,200]. St. George is designed to have an angular and energy acceptance of θ = ±40 mrad and ∆E/E = ±7.5%, respectively.…”

Energy acceptance of the St. George recoil separator

“…Several ports are available along the St. George beam line and on the magnets for diagnostic equipment to assess the properties of transmitted ions. For future (α, γ) reaction measurements, St. George will be preceded by the HIPPO gas-jet [11], which will serve as a relatively uniform high-density reaction target [12]. For the acceptance measurements presented here, the primary beam from St. Ana was transmitted directly into St. George, where two 2 mm diameter collimators 20 cm apart were employed just prior to the entrance of St. George to ensure the beam entered St. George on-axis.…”

“…In order to undertake (α, γ) reaction cross section studies at astrophysically relevant energies for nuclei with nuclear mass A ≤ 40, the St. George recoil separator at the University of Notre Dame's Nuclear Science Laboratory (NSL) has been developed [10]. The recoil separator technique generally relies on using inverse kinematics, where a heavy ion beam is impinged on a lighter nuclear target; for (α, γ) reactions with St. George, the HIPPO helium gas-jet produces the desired target [11,12]. Unreacted incident beam particles and nuclear reaction recoils both exit the gas-jet with similar momenta.…”