Princeton Plasma Physics Laboratory

About: Princeton Plasma Physics Laboratory is a facility organization based out in Plainsboro Center, New Jersey, United States. It is known for research contribution in the topics: Tokamak & Plasma. The organization has 2427 authors who have published 4475 publications receiving 106926 citations. The organization is also known as: PPPL.

Stability of alpha particle driven Alfvén eigenmodes in high performance JET DT plasmas

Abstract: The stability of alpha particle driven Alfven eigenmodes (AEs) is analysed in high fusion power DT discharges on JET. Both hot ion H mode and shear optimized discharges are considered. Unstable AEs are not observed in hot ion H mode DT discharges even at the highest fusion power with alpha particle beta βα (0) ≈ 0.7%. Theoretical analysis shows that the AE stabilization is caused by the large plasma pressure, which prevents the existence of core localized AEs at peak fusion performance. Kinetic toroidal AEs (KTAEs), which persist at high plasma pressure, are found to be radially extended and subject to strong damping. The stability analysis based on the CASTOR-K code confirms that AEs cannot be driven unstable by alpha particles in high performance hot ion H mode discharges performed at JET. Alfven eigenmodes in shear optimized regimes are more unstable than those in the hot ion H mode mainly due to the elevated central safety factor q, which increases the efficiency of AE interaction with energetic ions. As a consequence, AEs are observed in shear optimized DT discharges when ion cyclotron heating as low as 1 MW is applied.

The Twisted Configuration of the Martian Magnetotail: MAVEN Observations

Abstract: Measurements provided by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft are analyzed to investigate the Martian magnetotail configuration as a function of interplanetary magnetic field (IMF) BY. We find that the magnetotail lobes exhibit a ~45deg twist, either clockwise or counterclockwise from the ecliptic plane, up to a few Mars radii downstream. Moreover, the associated cross-tail current sheet is rotated away from the expected location for a Venus-like induced magnetotail based on nominal IMF draping. Data-model comparisons using magnetohydrodynamic simulations are in good agreement with the observed tail twist. Model field line tracings indicate that a majority of the twisted tail lobes are composed of open field lines, surrounded by draped IMF. We infer that dayside magnetic reconnection between the crustal fields and draped IMF creates these open fields and may be responsible for the twisted tail configuration, similar to what is observed at Earth.

The ITER core imaging x-ray spectrometer

Abstract: The core imaging x-ray spectrometer (CIXS) is one of several ITER diagnostic systems planned for measurements of the central ion and electron temperature profiles and of the toroidal and poloidal rotation velocity profiles, Ti, Te, v, and vθ respectively. The diagnostic is based on precision determinations of the Doppler broadening and centroid shift of the lines of highly ionized heavy impurities using a curved Bragg crystal spectral disperser and imager. In a departure from earlier designs, the CIXS employs a novel imaging geometry utilizing spherically bent crystals operating at a Bragg angle near 45°, which spatially and spectrally resolves the x-ray emission from the plasma. In addition, the working radiation will be the L-shell emission of highly charged tungsten ions. Particular emphasis is placed on the strong 3d5/2 → 2p3/2 electric dipole transition in neon-like tungsten W64 +. Here we present the conceptual design of the instrument, which may include an x-ray calorimeter, and discuss the spectral features used in future measurements.

First Direct Observation of Runaway-Electron-Driven Whistler Waves in Tokamaks.

Abstract: DIII-D experiments at low density (${n}_{e}\ensuremath{\sim}{10}^{19}\text{ }\text{ }{\mathrm{m}}^{\ensuremath{-}3}$) have directly measured whistler waves in the 100--200 MHz range excited by multi-MeV runaway electrons. Whistler activity is correlated with runaway intensity (hard x-ray emission level), occurs in novel discrete frequency bands, and exhibits nonlinear limit-cycle-like behavior. The measured frequencies scale with the magnetic field strength and electron density as expected from the whistler dispersion relation. The modes are stabilized with increasing magnetic field, which is consistent with wave-particle resonance mechanisms. The mode amplitudes show intermittent time variations correlated with changes in the electron cyclotron emission that follow predator-prey cycles. These can be interpreted as wave-induced pitch angle scattering of moderate energy runaways. The tokamak runaway-whistler mechanisms have parallels to whistler phenomena in ionospheric plasmas. The observations also open new directions for the modeling and active control of runaway electrons in tokamaks.