Observations of the Formation of Periodic Plasma Shocks from Fast Mode Waves

<p>Collisionless plasma shocks (CPSs), forming when supersonic plasma streams encounter a magnetized obstacle, are invoked to explain the acceleration of ubiquitously energetic cosmic rays. It has long been theorized from magnetohydrodynamics, but not directly observed that the CPSs develop from the growth of small-amplitude, low-frequency plasma waves which excited by reflected ion beams from the obstacle. We present in situ observations of an entire formation sequence of the periodic plasma shocks by the MAVEN spacecraft’s magnetic field and particle instruments. The magnetometer first detected small-amplitude circularly polarized magnetosonic waves that further steepened and eventually evolved into periodic shocks. Moreover, differing from the traditional understanding, characterizations of the fast mode waves show that the free energy of the wave/shock generation is provided by newborn protons, and the increasing sunward proton fluxes provided persistent energy for wave steepening. The unusual evidence presents itself from the combination of two circumstances: radial-aligned (Sun-Mars) magnetic fields and Martian atmospheric atom (hydrogen) photoionization and solar wind pickup. These observations lead to the conclusion that newborn ions play a crucial role in the formation process of some CPSs in the astrophysical and space plasma.</p>

Plasma Driven Shock Tube for Dynamic Characterization of Sensors

The development and evaluation of a small scale plasma driven shock tube is described in the current paper, as a new option to sensor characterization for dynamic flow measurements. The initiation of a high energy plasma discharge at one end of a quartz tube generates a shock wave that travels the length of the tube. The rate of shock generation is governed by the discharge energy and can easily be several tens of pulses per minute, instead of several pulses per day as with traditional diaphragm-based shock tubes. There is no contamination with solid particles at the test location, and rise times of the order of microseconds can be achieved. The energy release is controllable resulting in robust and repeatable operation. Lastly, the overall footprint of the plasma driven shock tube is small and ideal for frequent laboratory bench top operation.