To view the results double click on the thumb-nail and then single-click on the image to shrink again. As seen in the multi-faraday cup models, the best results come from having the two inner rings turned on and the outer ring turned off. Show transcribed image text Assume that the Faraday Cup and Grounding Cage act like coaxial conducting cylinders (ignore that there is a bottom to the Faraday Cup, and allow the height of the Grounding Cage to be equal to the height of the Faraday Cup). The following is presented for those who would like an introduction to the solar wind and how it is monitored. Soviet spacecraft equipped with a€?ion trapsa€? (Konstantin Gringauza€™s gridded Faraday cups) were the first to sample the solar wind. In the three years after Lunik II launched, a number of improved instruments designed to analyze the solar wind either failed to launch or failed to detect the wind. In 1962 a curved plate ion energy analyzer equipped with a faraday cup particle detector was launched as part of the payload of Mariner 2. The solar wind consists of positively and negatively charged particles in about equal numbers so that the bulk charge is about zero (a plasma). Instruments designed to monitor the solar wind usually return data in terms of particle abundance versus particle energy. Below is a spectrum collected by the electrostatic analyzer (ESA) curved plate analyzer (CPA) that was launched on the ESRO HEOS-1 satellite in 1968.
Jumping forward two decades, the SWEPAM-I instrument on the ACE spacecraft was launched in 1997 and is currently collecting spectra of the solar wind ions. The plots shown above differ from the plots of raw data from Mariner 2, ESRO HEOS-1, and ISEE-2 in that the particle flux at each energy is given in units of flux rather than counts.
The speed, temperature, and density of the solar wind are derived from the ion energy spectra that are collected by satellites.
The density of the solar wind is simply the a€?particles per cubic centimetera€™ integrated over all energies in the peak. In addition to varying in its speed, temperature, and density, the solar wind varies in ita€™s angular a€?sizea€™ and direction of flow. SWEPAM-I  is spun and has 16 channel electron multiplier detectors that look at 16 slightly different directions simultaneously so that it can make a full 3-D plasma measurement of protons and alphas over 40 energy levels every 64 seconds. Retarding potential analyzers like the FC instrument have been flown in space to sample the solar wind from many spacecraft. As seen the electric field is sufficiently high over the tip area (where the value is calculated at) for field emission to occur.
It is currently unsure why this is, or even if this happens and will be confirmed or disproved in a future lab experiment. The top part is the multi-farday cup and the bottom "dot" is the array of tips shown as a point source. The inside cylinder is isolated from the outside cylinder with the outside cylinder attached to ground. Those that failed to detect the wind either pointed in the wrong direction or were a€?blindeda€™ by sunlight when they did point in the right direction. Mariner 2 returned an ion energy spectrum of the solar wind almost continuously for 113 days.


Mariner 2 data showed that the solar wind blew continuously within the instrumenta€™s field of view, which could not look farther than 10Es from the sun.
Even though ions can be either positively charged or negatively charged, when solar wind scientists speak of a€?ionsa€™ they mean positively charged particles.
For instruments that make a current measurement to determine the flux of particles the plots of the raw data collected (spectra) are usually of a€?current vs. Below is a graphical representation of a solar wind spectrum (this is a spectrum from SWEPAM-I). By measuring the a€?half-width at half maximuma€™ of each peak, the temperature can be determined from the appropriate formula. The SWEPAM-I instrument on the ACE spacecraft and the Faraday Cup (FC) on the WIND spacecraft.
Rather than filter out the desired energy particles by having them follow curved trajectories through an electric field in a curved space, the faraday cup instrument uses a a€?retarding potentiala€™ supplied by a wire grid in front of a conducting plate. Advantages of retarding potential analyzers have been reported as: compact design, large geometric factor, and the ability to retain calibration over space mission lifetimes.
Such spectra would enable unprecedented monitoring of the solar wind for speed, temperature, and density in both protons and alphas. The current density times by the emission area do not quite give a current of 6 milli-amps as produced by the neutraliser that was the motivation for this investigation. Note the silicon tips are out of scale so will be redrawn as a point source in the future for a more accurate model. The use of the term a€?iona€™ to denote exclusively ions with a positive charge is peculiar to field of solar wind science. The spectrometer, shown below, was improved over the HEOS-1 spectrometer in that it contained channel electron multipiers (CEMs) rather than Faraday cup particle sensors. The spectra from SWEPAM-I are analyzed in real-time for solar wind properties such as velocity, temperature, and density. A similar determination is made for alphas by determining the peak energy for alphas and considering the four-fold greater mass of alpha particles.
Both instruments return spectra that are used to determine solar wind speed, temperature, density, and direction and report them on a day-to-day basis. Ambient particle flux and spectrometer geometric factor are important factors to consider when estimating performance characteristics such as speed and accuracy in solar wind velocity, temperature, and density determinations. The Goembel Instruments Solar Wind Monitor offers at least an order of magnitude better performance and would require fewer spacecraft resources (mass and power) than either SWEEPAM-I or WIND FC. However these values do not consider certain environmental factors such as the temperature of the environment.
Determine the following, showing all work: Use values measured for charging the Faraday Cup with the PVC disk. It was designed to explore the nightside tail of the magnetosphere but was often immersed in the solar wind. Researchers learned that the solar wind was organized into high- and low-speed streams, that the streams had steepened leading edges with higher densities due to pileup, and that the proton temperature varied directly with the speed. In chemistry, to avoid confusion, positively charged ions are denoted a€?cationsa€™ and negatively charged ions are denoted a€?anionsa€™.


It is clear that by 1968 better quality spectra were being collected so that characteristics such as speed, density and temperature for the major components of the solar wind could be derived. A a€?double Maxwelliana€™ curve fit of the data, such as is done with data gathered by WIND, can be used to better determine the two peak locations. Therefore, when the solar wind flows in a purely radial direction from the sun, it appears to be coming slightly from the west when observed from a spacecraft sharing the eartha€™s orbital motion. Experimental evidence suggests that the colder the environment the less field emission that occurs. Five data point spectra showed that alpha particles had the same thermal speeds and bulk speeds as protons and showed that the ratio of alphas to protons was highly variable. Throughout this document I will adhere to the convention used in solar wind science: a€?ionsa€™ are cations. The device was able to detect particles at three orders of magnitude lower fluxes (104 cm-2  s-1) than the HEOS-1 instrument.
The beam also has a non-zero solid angle cross section that varies in shape; sometimes narrow, sometimes wide, sometimes circular, sometimes elliptical. It is clear that by 1962 space-borne ion energy analyzers were proving valuable in monitoring the solar wind. The vast majority of solar wind ions are protons (the hydrogen atom with the electron removed, H+). The remarkable increase in sensitivity is not surprising considering the that CEMs are capable of producing a count for each particle that strikes them and Faraday cups must be struck by a large enough flux of charged particles that a net current can be measured.
As a result of the solar wind a€?beama€™ divergence, it is not unusual to see solar wind ion spectral counts in seven (5Es x 5Es) SWEPAM-I sectors. However these results do support theories predicted by papers in the area and have been supported by values calculated from the models and other algebraic methods. The solid line represents the Faraday Cup, while the dashed line represents the Grounding Cage. Chapman theorized that a static atmosphere of the sun extended far beyond the Eartha€™s orbit. Correlations were made between solar wind speed as measured by Mariner 2 and geomagnetic activity as measured at stations on the Earth. Parker predicted that the Suna€™s corona could not remain in static equilibrium but had to be continually expanding since the interstellar pressure could not contain a static corona. Thus, there was direct evidence of the connection between solar wind conditions (solar wind speed) and effects felt on the Eartha€™s surface (geomagnetic field fluctuations).
The negatively charged particles that balance out the charge in the solar wind plasma are almost exclusively electrons.
He predicted that the solar wind was directed radially from the Sun with a supersonic flow of hundreds of km per second. It took evidence from satellites to prove that there was a solar wind, as Parker theorized.



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