Design and thermal simulations towards a high intensity radioactive ion source for ISOL@MYRRHA

Abstract

MYRRHA will be the world’s first large-scale Accelerator Driven System project at power levels scalable to industrial systems. ISOL@MYRRHA will produce Radioactive Ion Beams (RIBs) using the Isotope Separation On-Line (ISOL) technique, with increased isotope production by high intensity primary beams over a long period while maintaining a high-quality RIB. Higher atom flux produced prevalently affects the ISOL ion source. A surface ion source is chosen as a first source because of its reliability and simple design. To understand the hot cavity’s behaviour, finite element thermal-electric simulations were performed. To start, a heating system study with experimental results from the SPES project was reproduced. This concept was then modified by: electrically insulating the source from its support, adding a feedthrough, transforming a passive thermal screen into an active part. With this heating system upgrade, the ion source temperature profile can be adjusted, especially at its exit part where high temperature is expected to play a crucial role in ion production and extraction.

First ion source at ISOL@MYRRHA with an improved thermal profile - Theoretical considerations

“…This Ohmic heating results also in temperature gradients along the tube. For our design this was recently calculated using thermal-electric simulations [3]. 1999 1996 1993 1990 1987 1983 1980 1976 1973 1969 1966 1962 1958 1954 1951 1947 1943 1939 1935 1930 1926 1922 1918 1913 1909 1904 Position along the ion source tube [mm] Figure 3: Plasma sheath potential Φ P on a tantalum surface along the ion source tube depending on its surface temperature.…”

“…1999 1996 1993 1990 1987 1983 1980 1976 1973 1969 1966 1962 1958 1954 1951 1947 1943 1939 1935 1930 1926 1922 1918 1913 1909 1904 Position along the ion source tube [mm] Figure 3: Plasma sheath potential Φ P on a tantalum surface along the ion source tube depending on its surface temperature. Temperature values come from a thermal-electric simulation with similar boundary conditions as those adopted in reference [3]. The surface potential is set to Φ s = 0 to better highlight this confinement effect.…”

“…Those two conditions are present at the junction between the ion source and transfer line. The potentials plotted in figures 3 and 4 have been obtained by using an Active Thermal Screen heating system [3], which improves the temperature profile of the ion source, mainly at the exit of the ion source where the extraction electrode is placed, but also at the junction.…”

“…This ion source is currently used at many other facilities to produce RIBs. Our design [3] stems from the SIS of ISOLDE at CERN [4] and of SPES at INFN [5]. At ISOL@MYRRHA, the higher primary proton beam current will result in a higher atom flux through the ion source.…”

Production study of Fr, Ra and Ac radioactive ion beams at ISOLDE, CERN

“…It is known that the temperature distribution inside the transfer line and ion source features colder spots, which has a strong impact on the ionization or can condensate the transiting atoms. In case of longer irradiation and higher intensity, the ion source faces challenges such as saturation and its inability to keep the temperature constant along the tube 27 . Another way of increasing the extractable yield is by using molecular ion beams.…”