mtof image


The Mass Time-Of-Flight (MTOF) sensor of the CELIAS investigation is actually two subsensors. The MTOF/Main is the primary unit, providing solar wind elemental and isotopic abundance measurements. The MTOF/Proton Monitor is an auxiliary unit designed to measure the solar wind proton parameters, including speed and direction. Both units are housed within a common structure (seen in the figure above), which also contains the low voltage power converter, the high voltage power supplies, the analog electronics, and the digital electronics. The smaller wedge-shaped black region near the top-middle of the figure is the entrance to the Proton Monitor. (The larger wedge-shaped region is the opening to the Main sensor.)

pm schematic The MTOF Proton Monitor was conceptualized, designed, and fabricated by the Space Physics Group of the University of Maryland. The Proton Monitor (PM) is a solar wind Energy per Charge (E/Q) analyzer of a new design, consisting of a three-box deflection system followed by a wedge-shaped MicroChannel Plate (MCP) assembly. The electrostatic analyzer is similar in form and function to the WAVE deflection system used in the MTOF/Main.
in test bracket
Figure Above: The PM mounted in testing bracket: the front of the PM deflection system, showing the entrance to the first box at the top, and the exit from the third box at the bottom. Second box is in the middle. Rear view of first and third boxes, with ruler indicating scale.

pm anode The specially designed wedge-shaped MCP, with its associated ring and sickle anode (shown at left), provides two-dimensional, cylindrically symmetric, position information of the solar wind ions hitting it. The energy-per-charge (and hence speed) of the incident ions is determined from the "R" (radial) position information, while the "theta" position signal allows the determination of the solar wind flow angle in the plane perpendicular to the ecliptic plane.

The MTOF/PM data accumulation is organized within a six-step deflection plate voltage sequence (5 seconds accumulation per step), thereby acquiring an entire E/Q spectrum every 30 seconds.

The MTOF PROTON MONITOR provides solar wind plasma parameters with 30-second temporal resolution:

Solar wind proton bulk speed
Solar wind proton density
Solar wind proton thermal velocity
Science Objectives:
Evaluating solar wind composition measurements
Identification of solar wind flow type
Mapping solar wind to the originating solar longitude
Providing near real time solar wind data to the ISTP community


Example of "mapping" the solar wind back to its origin on the solar disk (heliographic longitude), using the solar wind speed from the Proton Monitor.

return to PM home page Return to Proton Monitor Home Page