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Nuclear Science Division

Graphene Amplifier & Sensor Development

In the early development of the LEGEND-200 low-noise readout electronics (cf. July 2023 NSD newsletter), researchers in the NSD Neutrinos Program realized a supply issue of the junction field-effect transistors (JFETs) implemented in the design. The vendor that manufactured these low-noise devices has stopped making them, as have many of their competitors. NSD Senior Scientist Alan Poon’s group then embarked on a journey to find an alternative to these high-quality devices.    In the summer of 2021, a Science Undergraduate Laboratory Internships (SULI)  student, Jeremy Fleishhacker, from Carleton College, MN, was tasked with simulating the electronic response of a graphene field-effect transistor (GFET). His early findings showed that GFETs could be a viable alternative to JFETs.

This past summer, another SULI student, Phoebe Andromeda, from Oregon State University, joined the research team to investigate the actual device performance; in particular, the variation of electronic performance for graphene of different sizes, which acts as the “channel,” between the drain and the source of the GFET. They also measured the electronic characteristics at room and liquid nitrogen temperatures. Working with electronics in cryogens was a highlight of Andromeda’s summer term, as “running electrical tests on the GFETs was the culmination of all the hard work earlier in the internship.”

During the early development of this project, Marcos Turquetti, a staff engineer from the Lab’s Engineering Division, saw an increase in noise when he exposed the GFET device to light in the laboratory. He has since verified that GFETs are indeed sensitive to optical light.  Lisa Schlüter, a postdoctoral fellow in the Neutrino Program since summer 2023, is now investigating the spectral response of GFETs over a broader wavelength spectrum, exploiting its utilities in other photo-sensing applications.

The team is exploring other practical uses of GFETs.  For example, Lucas Brouwer of the Lab’s Accelerator Technology and Applied Physics  (ATAP) Division is developing a magnetic sensor that exploits graphene’s high charge mobility. The goal is to develop a magnetosensor with nano-Tesla sensitivity for superconducting magnets operating at liquid helium temperature.  

In 2022, the Department of Energy’s Office of Nuclear Physics funded this GFET development work as a two-year project under its Micro-electronics Initiative.  

Figure 1.  Layout of a Graphene FET (Image from Graphenea GFET-S31 datasheet).

Figure 2: SULI undergraduate Phoebe Andromeda presenting their GFET work at the Conference Experience for Undergraduates (CEU)  poster session in Hawaii in November 2023.  Andromeda summed up their poster presentation nicely: “It went exceedingly well. I spoke to many people in the nuclear science community during my presentation who were very interested in my research as it was new and cutting edge!”

Empowering Detector Development: Introducing the Upgraded Scintillator Library

Until recently, the compilation of scintillator properties has largely proceeded as a side project to detector development efforts for fundamental physics and applications. The recently launched modernized version of the Berkeley Lab Scintillator Library is poised to change this landscape. 

This database provides measured properties of many scintillating materials along with citations to published papers in which the original measurements were reported. The recent expansion features an Organic Scintillator Library with a current focus on scintillator response to protons and heavy ions. These quenching data are required for modeling scintillator-based detector response to neutrons and charged particles [1] and are useful inputs for kinematic neutron image reconstruction algorithms [2]. The initial library release also includes tabulated data on recoil ion response for EJ-309, a widely-used liquid organic scintillator. The longer-term vision is to provide data on scintillation properties for an array of commercial and custom organic scintillators to facilitate comparison between measurements, provide a basis for theory development, and lay the foundation for future evaluation. 

This site is an extended version of a library focused on inorganic scintillators originally created by Stephen Derenzo, Martin Boswell, Marvin Weber, and Kathleen Brennan at Lawrence Berkeley National Laboratory (LBNL) with support from the Department of Homeland Security (DHS). The site is currently maintained by Bethany Goldblum and Thibault Laplace at LBNL and the University of California, Berkeley with support from the Nuclear Data Program within the Department of Energy, Office of Science, Nuclear Physics and the Department of Energy, National Nuclear Security Administration, Office of Defense Nuclear Nonproliferation Research & Development via the Nuclear Science and Security Consortium. 

In 2023, the site was visited by more than 1000 unique users from 47 countries around the globe. Figure 1 shows a world heat map illustrating country demographics of library visitors. 

For suggested additions to the library, contact Bethany Goldblum at bethany@lbl.gov. 

Figure 1: Heat map (using a sequential blue scale from the least to the most opaque shades representing low to high values) of visitors to the Scintillator Library by country since January 2023. 

References

[1] T.A. Laplace, B.L. Goldblum, J.A. Brown, G. LeBlanc, T. Li, J.J. Manfredi, and E. Brubaker, “Modeling ionization quenching in organic scintillators,” Materials Advances (2022). https://doi.org/10.1039/D2MA00388K 

[2] J.J. Manfredi, et al., “The Single-Volume Scatter Camera,” Proc. SPIE 11494, Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XXII, 114940V (20 August 2020). https://doi.org/10.1117/12.2569995

MARS-D: Progress Towards 4th Generation ECRIS

The MARS-D project will produce a 4th Generation Electron Cyclotron Resonance Ion Source (ECRIS). MARS-D is expected to outperform the 88-Inch Cyclotron’s world leading 3rd Generation VENUS ECRIS. The transition from a 3rd Generation to a 4th Generation ECRIS means that both higher intensity beams and higher charge state beams can be provided to the 88-Inch Cyclotron for experiments, and this is made possible with stronger plasma confining magnetic fields. In an ECRIS, the plasma confining fields are typically provided by a conventional configuration that uses a combination of solenoids and a set of six racetrack coils. Using this conventional configuration, the upper limits of the superconducting NbTi wire, for use in an ECRIS, have been reached.  MARS-D will be able to achieve stronger fields than VENUS, while also using NbTi superconductor wire, because of its novel magnet configuration that will replace the six racetrack coils which provide the radial confining field. The novel magnet configuration is a closed-loop coil that will provide both a radial confining field as well as solenoidal fields that will add to the axial confinement of the plasma [1].

The 88-Inch ECRIS Group and the SMP group received funding through a DOE Office of Science Funding Opportunity Announcement (FOA) in 2023. The two year project will produce the coldmass (sextupole and solenoid magnets) for the MARS-D ECRIS, to be built at a later date. Recently, the group successfully completed a full size 4 layer test wind using NbTi, shown in Figure 1. The winding of the final coil will begin in January of 2024 and consist of 24 layers. The test wind allowed the group to perfect the winding tooling, test the epoxy impregnation, and observe effects of cooling down on the coil.

Figure 1: The completed NbTi 4 layer test coil is shown after epoxy impregnation is completed.

The success of the test wind is owed to the hard work of the technicians at the 88-Inch Cyclotron and ATAP: Brian Bell, Patrick Coleman, John Garcia, Roman Nieto, Matthew Reynolds, Nathan Seidman, Chet Spencer, James Swanson, Sixuan Zhong, the lead designer Lianrong Xu, and the 88-Inch Mechanical Engineer Jaime Cruz-Duran.

References: [1] M. Juchno et al., Shell-based support structure for the 45 GHz ECR Ion Source MARS-D,” IEEE Trans. Appl.  Supercond., vol. 32, no. 6, Sept. 2022.

Director’s Corner

2023 has been an important year for Nuclear Science in the U.S. with the roll out of the new NSAC Long Range Plan (LRP) on Nuclear Science “A New Era of Discovery”. The research portfolio and strategic priorities developed for LBNL’s Nuclear Science Division, are well aligned with the priorities and recommendations articulated in the LRP, including the Electron Ion Collider (EIC) and Neutrinoless Double Beta Decay as top construction priorities. LBNL plans to make leading contributions to the EIC ePIC detector and is supporting two next generation Neutrinoless Double Beta Decay experiments, CUPID – as lead lab – and LEGEND. The November Division Retreat was a successful occasion to bring the whole division together and discuss not only our strategic goals but also focus on conversations around People Stewardship. It was great to see so many members of the NSD team in person and the engaged interactions during the session and the breaks.

This issue of the NSD Newsletter introduces the newly formed Neurodiversity Working Group, part of the Lab’s AllAccess Employee Resource Group (ERG), which aims to celebrate that diversity, develop community, and influence lab policy to hire, support, and retain neurodivergent employees.

On the technical side, the Newsletter introduces the recently launched modernized version of the Berkeley Lab Scintillator Library, which provides measured properties of many scintillating materials, and will advance modeling of scintillator response in support of a variety of applications. It also summarizes the exciting technical development of a graphene field-effect transistor (GFET) for applications as cryogenic signal amplifier and photo sensor.  

We also learn about the advances in producing a new, innovative closed-loop coil for the MARS-D project, a 4th Generation Electron Cyclotron Resonance Ion Source (ECRIS). MARS-D will be able to achieve stronger fields than the current VENUS source at the 88-Inch cyclotron, further enhancing the already impressive current ion-beam capabilities. The end of the year saw the first delivery of a high-intensity 50Ti beam from the 88-Inch CCyclotron to the Berkeley Gas-filled Separator (BGS), using a new induction oven in VENUS. This sets us up for an exciting year ahead in the heavy element program.

It is great to see these science and technology developments as well as the advancement of our workplace culture. I am looking forward to an exciting year and wish everyone a healthy, safe,  and successful year 2024.