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Date: Thu, 28 Jun 2001 09:21:38 EDT
Subject: Re: Beamer rennovation
To: jad@texas.net
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In a message dated 6/28/01 1:12:54 AM Eastern Daylight Time, jad@texas.net 
writes:

<< Subj:     Beamer rennovation
 Date:  6/28/01 1:12:54 AM Eastern Daylight Time
 From:  jad@texas.net (John Dormer (Automatic_Jack))
 Sender:    jad@idoru.austin.mdn.com
 To:    f.knuettel@worldonline.de (Franz Knüttel)
 CC:    DMBoss1021@aol.com, jay@rootaction.net (Jay Bolton)
 
 File:  mvc-423f.zip (125912 bytes)
 DL Time (45333 bps): < 1 minute
 
 Wow, Stan, you were right. The new beamer configuration is >lots< stronger
 than the old one with the rectangle magnets.
 
 I measured the old South Pole beamer and the new North Pole beamer several
 times in several orientations (to eliminate stray flux from reinforcing bar
 which might have been in the concrete below the test area).
 
    Test #      Beamer      Deflection Dist, inches
    1       old S       11.75
    2       new N       19.25
    3       old S       13.25
    4       new N       19.0
    5       old S       13.25
    6       new N       18.5
 
    avg     old S       12.75
    avg     new N       18.92
 
    18.92 / 12.75 = 1.484
 
    
 The magnetic field decays at a rate of 1/d^3. From the ratio, the new beamer 
 strength is:
 
    1.484^3 = 3.27
 
 times the strength of the old beamer. I'm assuming that the polarity didn't
 matter (which it wouldn't at the coarseness of my measurement tools).
 
 The old beamer's strength relative to a single 0.38T disc is:
 
    12.75 / 10.925 = 1.17
 
    1.17^3 = 1.589
 
 and its rough field strength is:
 
    1.589 * 0.39T = 0.62T
 
 The new beamer is 3.27 times that, which is:
 
    3.27 * 0.62 = 2.03T
 
 The two opposite-polarity beamers really like to attract each other, probably
 with half a pound of force when they meet. The old beamers' attraction was
 barely noticeable. 
 
 Stan, does this field strength make sense? I was using a deviation of the
 compass which was five times as great (compared to the ring magnet strength
 test recently done), but the ratio should still hold as it is dimensionless.
 
 The first attached photo is the detail of the 3/8" brass tubing in the middle
 of the magnets, which holds them in a neat line. The brass screw and its
 upside-down finishing washer are in the foreground. The shoulders of the
 washer make a nice nesting of the screw central to the opening in the top of
 the magnets.
 
 The second photo is of the old beamer, left, and the new beamer, right. I
 hadn't done the strength tests on the beamers by the time the photo was 
taken,
 but I did keep the camera a little bit away (about a meter). :) All those
 nice, pointy things should be interesting to observe in a 100KV field. 8P
 
    John
  >>

John:

Cool! - I didn't mean replace all of the magnets, only the axial ones, with 
the larger round ones.  But that's OK.

I must have misled some with my incorrect reporting of the PVC pipe size in 
my Hexbeamer stats - I used 3" pipe cap, which is about 4" dia actual.

Looks like you used 4" pipe size, which is larger than 4".  that's OK, just 
that the 3" pipe allows tigh fitting rectangles for radial magnets, and then 
round for axial, and their edges touch - and the rectangles then are more 
space filling.

But your mod works too.

I modeled it in FEMM quickly just now, and used actual ceram5 grade 
parameters, and drew them to scale (30 mm O/D.; 10 mm I.D; and 6 mm thick)  
Not sure if I got the relative spacing correct of the stacks.  I used 12840 
nodes here.

Attached are two images of the plots.

Remember that the 0.4T Br is for closed core, long magnets - these end up 
around 0.23T internally, while ceram1 grade ends up about 0.09 to 0.1T.

First plot (a) is close up of the beamer - REMEMBER - this is only a cross 
section down the middle, and cannot account for the extra three radial 
stacks!  they will add significantly to the flux output in the 3D beamer. 
(the max B will not be more than the internal amount of the magnets, but the 
extent of the higher flux region will be further out in reality)

Also mentally you have to revolve this plot around the beamer axis for a true 
3D picture of the field shape.

The polarity shown is all inwards (N in) (FEMM has no way to display the 
vectors, but they are specified that way in the block labels)

Field lines are set as they appear by default, and set at 29 lines for the 
range that shows up.

Image -b - this shows a full scale plot, with the flux density shown at a 
small scale range - 0 to 0.05T (0 to 500 gauss)

AND the flux lines are shown filtering out high flux isolines - so only the 
low flux lines are displayed (QF can't do this)

This reveals some VERY interesting properties of the structures!

These lines extend out of the boundary, and loop around and return at the 
opposite side - so lines near the beamer axis (the x axis of the plot), loop 
around for several feet to the left, to return at the right, and there is 
VERY little divergence in this axial "beam" zone.

Also the overall region of influence of this altered flux area [space 
warpage] is QUITE large, once you account for all 6 radial magnet stacks, and 
would be frankly huge for NIB magnets that are 2" dia x 2" long as Bushman 
specified.

Stan