T. Rinckel

Use of microparticles as internal targets for nuclear physics with storage rings

Abstract We report on the development of ultrathin (1014 to 1016 at/cm2) internal targets for storage rings using microparticles. A “dust beam” is created by a gas-particle mixture flowing through a capillary into vacuum. In a laminar flow, the viscous drag accelerates the particles in the direction of the gas flow, while the Bernoulli force concentrates them near the axis of the tube. At the exit of the tube the gas diffuses, but the particles, due to their inertia, continue with small divergence. This property will allow us to differentially pump the carrier gas along the dust beam axis before the microparticles enter the high vacuum of the storage ring.

Uniform beam intensity redistribution in the LENS nonlinear transport line

The Low Energy Neutron Source (LENS) at Indiana University is producing neutrons by using a 7 MeV proton beam incident on a Beryllium target. The Proton Delivery System is currently being upgraded [1], [2]. A new AccSys Technology,Inc. DTL section [3] will be added to increase proton beam energy from 7 to 13 MeV. A 3 MeV RFQ and 10 MeV DTL will be powered by two 1.25 MW klystrons. The goal of this upgrade is a 13 MeV,25 mA proton beam with duty factor greater than 3%. At this power level it becomes increasingly important to make a proton beam that is uniformly distributed to prevent excessive thermal stress at the surface of the Be- target. To achieve this goal two octupole magnets are being implemented in each LENS beam transport line. In this paper we discuss the experimental results of the beam intensity redistribution as well as some features inherent in tuning of the nonlinear beamline and our operational experience.

Upgrade of the LENS Proton LINAC: Commissioning and results

The Indiana University Cyclotron Facility is operating a low energy neutron source which provides cold neutrons for material research and neutron physics as well as neutrons in the MeV energy range for the neutron radiation effects studies. Neutrons are being produced by a 7 MeV proton beam incident on a beryllium target. Since the first commissioning of the LENS Proton Delivery System (PDS) in December 2004 its performance has been significantly improved. The RF system of the accelerator has been upgraded by replacing 350 kW 425 MHz 12 tube amplifiers with two Litton 5773 klystron RF tubes capable of running at 425 MHz and 1.25 MW. Since the commissioning of the klystrons, a proton current of 25 mA at 7 MeV and 0.6% duty factor has been successfully delivered to the beryllium target. A future part of this upgrade will introduce a new 6 MeV DTL section to increase proton beam energy from 7 to 13 MeV. The 3 MeV RFQ and 4 MeV DTL will be powered by one klystron and the 6 MeV DTL will be powered by the second klystron. The expected output is 25 mA and 13 MeV of proton current at 0.6% duty factor. A second target station has been added to allow separate source optimization for the two primary research programs (cold neutrons and radiation effects). Other upgrades include increasing the RF duty factor to 3% through the installation of a new power supply for the klystrons. In this contribution we discuss the results of the commissioning of the new RF system, second beamline and second target station, as well as improvement in the beam parameters after these upgrades. The future plans will also be outlined.

Dielectronic recombination in He+ ions

Abstract Dielectronic recombination involving 1s + e− → nln′l′ transitions has been investigated for He+ ions. This work was done using the ion storage ring and electron cooler at the Indiana University Cyclotron Facility. Resonant maxima from DR were observed, but the energy resolution was insufficient to identify individual transitions. The magnitude of the measured cross sections appears to be about a factor of two lower than theory.

Dielectronic recombination from the ground and excited states of Li

Abstract Dielectronic recombination (DR) was investigated for Li + + e − collisions using the electron cooler at the Indiana University Cyclotron Facility (IUCF). For Li + (1s 2 ) ions, DR is expected to occur for relative energies E rel between 50–60 eV, and for metastable Li + (1s2s) DR should occur for E rel E rel near zero, radiative recombination (RR) (inverse photoelectric effect) is expected. This work is an extension of our previous work for He + ions. These light He + and Li + ions pose stringent tests of DR theory because the electron-electron interaction, which mediates DR, is stronger compared to the electron-nucleus interaction than is it for heavier ions. Additionally, the electron coupling in two-electron Li + gives rise to angular momentum configurations different from those in He + . Preliminary results of recent measurements at IUCF, where DR was observed for both ground-state and metastable Li + ions, are presented.