johan frenje

Research Scientist
	MIT Plasma Science & Fusion Center Email: jfrenje@psfc.mit.edu Phone: (617) 452-4941 Ad0dress: Room NW17-235 Related links: High-Energy-Density Physics Division

Biographical Sketch

Johan began his Ph.D. studies at Uppsala University, Sweden. His graduate work, which was funded by the Swedish Natural Science Research Council, involved the development of a novel neutron spectrometer for the Joint European Torus (JET) at Culham Laboratories in UK. The spectrometer was installed in 1996 and subsequently used during many deuterium (D₂) campaigns and the first high-power deuterium-tritium (DT) campaign in 1997. Time-resolved neutron spectra from triton burn-up in strongly transient D₂ plasmas were obtained for the first time and compared to simulations. During the high-power DT campaign, information about toroidal plasma rotation, fast-ion components in radio-frequency and neutral beam heated plasmas was also obtained for the first time using neutron spectrometry. Overall, his work has according to many experts in the field been instrumental for the development of neutron spectrometry for Tokamak fusion plasmas.

At MIT, his research focuses on studies of ICF plasmas. He was the lead scientist in developing a novel burn-history diagnostic [the proton temporal diagnostic (PTD)] for studies of capsule-implosion dynamics previously unattainable. Utilizing this diagnostic together with other nuclear diagnostics, accurate time-resolved studies of the nature of the D³He and the DD burn were performed. In particular, studies of the shock-bang time and evolution of ion temperature (T_i) were conducted for the first time. This work resulted in an invitation to present these results at the American Physical Society Division of Plasma Physics held in Albuquerque in 2003.

He is currently the responsible scientist for two neutron spectrometers [called Magnetic Recoil Spectrometers (MRS)], one at OMEGA and one at the NIF, for measurements of the absolute neutron spectrum in the range 5 to 30 MeV, from which areal density (ρR), ion temperature (T_i) and yield can be directly inferred for cryogenic DT implosions. Using the MRS, high ρR cryogenic DT implosions were probed for the first time using down-scattered neutrons at OMEGA. The ρR data obtained with the MRS have been essential for understanding how the assembly of the fuel occurs, and for guiding the cryogenic program at LLE to ρR values up to ~300 mg/cm². The MRS on the NIF has also provided data that have been essential to the progress of NIC. Recent data obtained with the MRS in September 2011 indicate that the implosion performance, characterized by the Experimental Ignition Threshold Factor (ITFX) has improved about 50 times since the first shot a year earlier. Overall, this work has resulted in six invited talks since 2008.

For the first time, he measured the differential cross section for the elastic neutron-triton (n-³H) and neutron-deuteron (n-²H) scattering at 14.1 MeV by using an Inertial Confinement Fusion (ICF) facility. In these experiments, which were carried out by simultaneously measuring elastically scattered ³H and ²H ions from a deuterium-tritium gas-filled ICF capsule implosion, he measured the differential cross section for the elastic n-³H scattering with significantly higher accuracy than achieved in previous accelerator experiments. The results compare well well with calculations that combine the resonating-group method with an ab‑initio no-core shell model, which demonstrates that recent advances in ab-initio nuclear theory can provide an accurate description of light-ion reactions. This work is ushering in a new and exciting field of research, Plasma Nuclear Science, blending the separate disciplines of plasma and nuclear physics.

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