Appendix 18. Preliminary Solar Polar Magnet Study

  

A18.4 Results

 

A18.4.1 Magnets

 

To compare the various magnets as received from the manufacturer, field surveys were made very early in the game. The magnets were arbitrarily selected and numbered. Field surveys were then made using yoke SST-416/APL along the yoke centerline with consecutive pairs of magnets. The data presented in Table A18-1 is graphically presented in Figure A18-43. The average peak field is 1820 Gauss with variations of ą60 Gauss. This is a variation of ą3%; not insignificant. In all the tests that followed, the same magnet pair--magnets 1 and 2--were used in the same orientation.

 

Figure A18.43 Magnetic Field Intensity Along Central Axis as a Function of Magnet Pairs

 

Because of the time consumed to make the measurements, tests were not made to compare individual magnet field strengths or uniformity of magnetization across each individual magnet.

 

 

A18.4.2 Configuration

 

Tests were run to determine the effect of yoke/pole piece/magnet configuration in the magnetic field intensity in the air gap. As mentioned previously, Configuration I has the magnets adjacent to the air gap and Configuration II has the pole pieces adjacent to the air gap. It can be seen by comparing the projection of the magnets on the Y=0 plane in Figures A18-4 and A18-7 for the two configurations that because of the mechanical orientation, the projection in Configuration I is slightly forward (toward smaller positive X) by approximately 0.060 inches than Configuration II. The result, as seen in the graphical comparison for yoke SST-416/APL (Figures A18-11 and A18-14), is that the peak field intensity for Configuration I is always approximately 0.2 inches forward of the peak for Configuration II. This can also be seen in the comparison of Configurations I and II for yoke C49/Mod I shown in Figure A18-44.

 

Figure A18.44 Magnetic Field Intensity Along Central Axis as a Function of Magnet/Pole-Piece Configuration

 

Another difference between Configurations I and II is the value of the peak field intensity. For some reason, the geometry of Configuration II increases the reluctance of the magnetic circuit, resulting in a greater leakage field and a lower value of field in the air gap. Variations between the peak fields of the two configurations are of the order of 40%.

 

 

A18.4.3 Yoke

 

Presented in Figure A18-45 is a plot of the magnetic field intensity along the centerline for each of the yokes tested. So that they are all on a common basis, only the test data for Configuration I is shown--since for yoke C49/Mod II this is the only configuration physically possible. The effect of moving the magnets to larger positive X for yoke C49/Mod II is obvious. It can be seen that changing the yoke material from stainless steel 416 to the greater permittivity material Carpenter 49 and thinning the wall material down did little change to the peak value of the field intensity and to the general profile of the intensity curve.

 

Figure A18.45 Magnetic Field Intensity Along Central Axis as a Function of Yoke Material and Design

 

 

A18.4.4 Electron Beam

 

Besides the presentation of data obtained by imaging an electron beam on a phosphor after passing through the magnetic field, if similar data was obtained for different magnet parameters, comparisons were made to attempt to determine the effect of the parameter change.

One such comparison, as mentioned above, is for yoke C49/Mod I where similar electron beam data was obtained for electron energies of 40, 80 and ~145 keV and target positions X = 0, Y = -3/16, 0, and +3/16 inches, Z = 0 for the two different magnet configurations, I and II. These comparisons are presented in Figures A18-46, A18-47, and A18-48, respectively. It can be seen that the effect of changing from Configuration I to Configuration II is to move the peak of the magnetic field in the +X direction. This means that the lower value of magnetic field in the target area allows target positions further in the -Z direction--for electrons to image near screen position zero inches. Effectively, Configuration II allows a greater geometric factor.

 

	Figure A18.46 Location of deflected electron beam image. Comparison of Yoke C49/Mod I, Configuration I & II, target: x=0, y=0, z=-3/16.
	Figure A18.47 Location of deflected electron beam image. Comparison of Yoke C49/Mod I, Configuration I & II, target: x=0, y=0, z=0.
	Figure A18.48 Location of deflected electron beam image. Comparison of Yoke C49/Mod I, Configuration I & II, target: x=0, y=0, z=+3/16.

 

Another comparison is between Mod I and II for yoke C49 in Configuration I. The only similar data taken is for electron beam energies of 40 and ~145 keV and a target position of X = 0, Y = 0, Z = 0. This comparison is presented in Figure A18-49. It appears that, at least for this target position, the Mod II yoke design proves more effective in bending electrons nearer the screen zero position (detector position) than the Mod I version. The difference between the 40 and ~145 keV peaks are the same in both cases.

 

Figure A18.49 Location of deflected electron beam image. Comparison of Mod  I and II for Yoke C49, Configuration I, target: x=0, y=0, z=0.

 

Another comparison is between the electron beam image for the same yoke/magnet assembly (in this case, Yoke: C49/Mod I in Configuration II) with the imaging screen at the detector position and moved back from the assembly by 0.375 inches. Similar data was obtained, in this case, for electron energies of 80 and ~145 keV and only target position X = 0, Y = 0, Z = 0; and is presented in Figure A18-50. It can be seen that the peaks in the back screen require a larger incidence angle than for electrons in the peak of the front screen. Derivable from this set of curves and of more interest is the actual electron path between the two screen positions. The electron trajectories between the screen positions for 80 and ~145 keV electrons as a function of incidence angle for target position X - 0, Y = 0, Z = 0 are presented in Figures A18-51 and A18-52, respectively. These figures should be directly comparable to results of an electron trajectory computer program output.

 

	Figure A18.50 Location of deflected electron beam image. Yoke C49/Mod I, configuration II. Target screen moved back 0.375 inches.
	Figure A18.51 Electron trajectories - 80 keV, Yoke C49/Mod I, Configuration II
	Figure A18.52 Electron trajectories - 145 keV, Yoke C49/Mod I, Configuration II

 

Acknowledgements: The author wishes to thank R. E. Thompson (JHU/APL) for obtaining all the magnetic field survey data used in this report. Also, thanks to D. Potter (UCB) and J. H. Crawford (JHU/APL) for obtaining the electron beam data at the NASA/GSFC low-energy accelerator.

 

 

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