NSS Plenary Talks
Instrumentation issues for neutrinoless double beta decay
Giorgio Gratta, Stanford University
I will review the technical requirements and instrumentation needs of modern double-beta decay experiments. Several technologies are implemented in various detectors, ranging from massive use of Ge counters, bolometric detectors and large time projection chambers in liquid and gas phase. The common threads are exquisitely low radioactive background and holistic design of the instrumentation, to fully optimize the detector sensitivity and optimally use the source material that, in most cases, requires isotopic enrichment.
Giorgio Gratta is a professor in the physics department at Stanford. He has worked on collider physics contributing to the first silicon strip detector with integrated readout for Mark II at SLC (SLAC) and to the large BGO electromagnetic calorimeter for L3 at LEP (CERN).
Since 1995 he is at Stanford where he has been active mainly in low energy neutrino physics. He had a leading role in the Palo Verde neutrino oscillation experiment and in KamLAND that provided one of the very first solid proofs for neutrino oscillations and did the first measurements of (anti)neutrinos from the Earth’s interior. In recent times he has led the EXO-200 double beta decay experiment and the larger nEXO experiment, under development. Both these detectors use liquid xenon technology with charge and scintillation readout. Gratta has also developed the first system to detect ultra-high energy cosmic-ray showers in sea water using sonar techniques and is presently perfecting a new technique to measure the force of gravity at sub-100-um distance.
Chasing the signature of a single prolific r-process event in an ultra-faint dwarf galaxy
Anna Frebel, MIT
The heaviest chemical elements in the periodic table are synthesized through the rapid neutron-capture (r-) process but the astrophysical site where r-process nucleosynthesis occurs is still unknown. The best candidate sites are ordinary core-collapse supernovae (deaths of massive stars) and mergers of two orbiting exotic neutron stars.
13 billion year old ultra-faint dwarf galaxies preserve a "fossil" record of early chemical enrichment that provides the means to isolate and study clean signatures of individual nucleosynthesis events. Based on new spectroscopic data from the 6.5m Magellan Telescope, we found seven stars in the recently discovered ultra-faint dwarf Reticulum II that show extreme r-process overabundances.
This enhancement implies that the r-process material in Reticulum II was synthesized in a single prolific event. Our results are clearly incompatible with r-process yields from an ordinary core-collapse supernova but instead consistent with that of a neutron star merger. This first signature of a neutron star merger in the early universe holds the key to finally, after 60 years, identifying the cosmic r-process production site.
Anna Frebel is Associate Professor of Physics at the Massachusetts Institute of Technology (MIT) but works as an astronomer. She has received numerous international honors and awards for her discoveries and subsequent chemical abundance analyses of the oldest stars and how these stars can be employed to gain insight into the early Universe some 13 billion years ago. Prof. Frebel has authored more than 90 papers in various refereed journals, including Nature. She also enjoys communicating science to the public through public lectures, magazine articles, interviews as well as her popular science book "Searching for the oldest stars" (2015, by Princeton University Press).
Smaller and Sooner: Exploiting new superconductor technology to accelerate fusion’s development
Dennis Whyte, MIT Plasma Science and Fusion Center
Rare-Earth Barium Copper oxide (REBCO) superconductor (SC) tapes are a newly available technology that promise to revolutionize plasma and fusion research. REBCO are superconducting at liquid nitrogen temperature, providing easy access to ~1-2 tesla steady-state magnetic fields in the laboratory and, unlike standard SCs, have no degradation of their critical current at high magnetic fields when sub-cooled. These features allow >23 tesla magnetic coils, double the B-field of standard SC such as used in ITER, as well as the design of demountable SC coils. The implications of such coils have been examined in ARC, a conceptual tokamak fusion pilot plant for electricity production, and in SPARC, an extremely compact rapid-prototype burning plasma device. For example, exploiting the B4 dependence in fusion power density, ARC produces >500 MW in a device 1/8th the volume of ITER. Demountable coils permit modular internal components, a simple liquid immersion blanket for fusion energy extraction, and advanced high surface area topologies for heat exhaust. Compact, high-B tokamaks provide for robust steady-state operational regimes with largely demonstrated physics. Critical science and technology R&D issues towards ARC and SPARC are discussed that would enable this attractive path to smaller, more flexible fusion devices.
A recognized leader in the field of fusion research using the magnetic confinement of plasmas for energy production, Professor Whyte’s work in magnetic fusion specializes on the interface between the plasma and materials.
Professor Whyte has over 300 publications and as an educator is heavily involved in student design activities through courses. Recently he has been working with students to advance surface and material measurement techniques of fusion and reactive power plant designs for pilot plants.
He has served as leader of the Boundary-Plasma Interface Topical Group of the US Burning Plasma Organization and is a Fellow of the American Physical Society.