Thursday, August 30, 2007

Processing Power

As you know I like FORTH a lot for control applications. I was estimating that with standard off the shelf hardware we might get a PID loop interval in the 4 KHz range.

However, there is a new kid on the block. The SEAforth 24B.

This kid is a screamer. It has 24 cores that each run at 1 G instructions per second (Ips). Peak of course is 24 G Ips.

For a PID loop that means loop cycle times in the 10 MHz to 50 MHz range. But that is not all:

* Static/dynamic memory interface
* Eleven SPI I/O ports
* Two 18-bit A/D converters
* Two 9-bit D/A converters
* 32 Parallel I/O lines

C18 Processor Features

* 18-bit stack oriented engine
* Runs VentureForth™ programming language as native code
* Executes 1 VentureForth instruction / ns
* 512 words RAM / 512 words ROM
* Hardware 18x18 multiply/accumulate
* Automatic sleep mode at <1mW dissipation

The multiplier will be very handy for PID loops. If you design your PID loops correctly they will consist of adds, subtracts, and a few multiplies.

Update 02 Sept 007 1023z

The A/D is a VCO and a counter. Which means conversion times on the order of 15 to 20 uSec. The D to A is a VCO type device as well.

What that means is that for actual high speed operation the SPI ports will probably be required.

In any case for low speed signals these ports should be fine.

Also the multiplier is actually a 9 bit by 9 bit bitwise hardware multiply. Nine or more clock cycles to complete a multiply. Some stack manipulation will be required to to do an 18 bit by 18 bit multiply. It will probably be somewhat slow. Probably 50 to 100 clock cycles. Meaning about 1E7 multiplies per second for each core. Which means that if you have one core for P one for I and one for D you could probably do a PID loop at a bit better than 5 million loops a second. If you cut down the number of bits to 12 or 14 you could tune the multiplies to make them faster.

Update 03 Aug 007 0743z

It appears the 24B is not currently being offered. The A version has the following specs:

* Twenty-four C18 core processors capable of combined sustained 24 Billion operations / second
* Completely asynchronous for faster processing and lower power
* Static/dynamic memory interface
* One SPI I/O port plus a broad set of serial and parallel ports
* Two 18-bit A/D converters
* Two 9-bit D/A converters

C18 Processor Features

* 18-bit stack oriented engine
* Runs VentureForth™ programming language as native code
* Executes 1 VentureForth instruction / ns
* 64 words RAM / 64 words ROM
* Automatic sleep mode at <1mW dissipation

A more detailed look at the chip can be found at SEAforth 24A.

Update: The SEAforth 24a pdf is no longer available by direct link. The above link now takes you to the page where you can order a copy.

Thursday, August 23, 2007

Bussard Reactor Funded?

I just received an e-mail claiming that the Navy has funded Dr. Bussard to complete his WB-7 fusion reactor experiment. In addition the e-mail claims the Navy is on board for the full up power demo if the WB-7 results are positive.

If I get further confirmation on this and permission to post it, I will. ASAP!

Update: 30 Aug 007 1436z

I can confirm the above facts. I'm not at liberty to disclose my sources. Expect a confirmation from the Navy in the coming weeks. I am just as anxious for a public announcement as you are.

Wednesday, August 8, 2007

The Inflationary Universe

Michael Turner of the University of Chicago talks about the Big Bang and the Inflationary Universe. A deep subject given a light hearted treatment. You might want to get up to speed on the physics idea of "time horizon" in relation to the speed of light before digging in. Or keep repeating the section from about 7 1/4 minutes in on the first video until it makes sense. His "view graphs" owe a lot to Batman Comics. The videos require "Real Player".

Michael Turner - video 1

Michael Turner - video 2

More Cosmology Videos

H/T Commenter Cynthia at The Reference Frame

Monday, August 6, 2007


ITER plans to use Ansys Software for various simulations.

Here is a press report.

Weld It Shut

I have been giving a lot of thought to sealing the electromagnets. It will be difficult to do a seal with fasteners that will keep the leak rate low enough.

It may be necessary to weld a cap over the seams or do some other kind of welding or perhaps silver solder if an appropriate metal is used for the coils. Electron beam or laser welding may be an option.

The coil design should be well tested before we seal them to make sure that unbuttoning them is not a regular occurrence.

Sunday, August 5, 2007

Superconducting Magnet Advances

Here is an interesting paper on recent advances in elevated temperature (20K) superconductors.
We investigated the effect of nanoscale-C doping on the critical current density Jc and irreversibility field Birr of Fe-sheathed MgB2 tapes prepared by the in-situ powder-in-tube method. The tapes were heat treated at 600-950C for 1 h. Higher values of Jc and Birr were seen for 5 at.%C-doped MgB2 tapes at higher sintering temperatures, where substantial substitution of boron for carbon occurred. The C-doped samples sintered at 950C showed the highest Birr, for example, at 4.2 K, the Birr reached 22.9 T. In particular, at 20 K, Birr for the C-doped tape achieved 9 T, which is comparable to the upper critical field of the commercial NbTi at 4.2 K. This role of nano-sized C particles can be very beneficial in the fabrication of MgB2 tapes for magnetic resonance imaging applications at 20 K.
I sure hope this stuff is available commercially by the time we decide to build WB-100. And think of it. Another good use for Boron.

Considering that we are quite happy (for now) operating at the 1T to 2T range, we might be able to go higher than 20K operation. If higher fields seem useful we can go to lower temperatures.

Thursday, August 2, 2007

Gain And Power Out

I have been mulling over for some time how Dr. Bussard came to the conclusion that power gain scales as the fourth power of the magnetic field times the radius and that power out scales as the fourth power of the magnetic field times the radius cubed.

I think I have the answer thanks to our number magician Indrek. The very first graph is I to v. The I is the coil current. The v is the velocity of the electrons. The coil current is directly proportional to the magnetic field. The energy of the electrons goes up as

1/2 m v2

Where m is the mass and v is the velocity.

That tells us that the energy of the electrons that the magnetic field can confine goes up as the square of the magnetic field. Since the density of electrons that can be confined also goes up as the square of the magnetic field and the density of the electrons determines the density of the two reactants power goes up as the fourth power of the magnetic field as does power gain since the densities are multiplied to get the power output. In addition power gain goes up for the same reason.

The second part of the power equation - r cubed - is easy to figure. The bigger the reaction volume the more power out.

So the last question is why does the gain go up as r ? Easily answered. Electrons only have a chance of escaping the reaction area if they hit a magnetic wall. At a given electron energy (it would be fixed no matter the size of the reactor) the time it takes to go from magnetic wall to magnetic wall depends on the distance the walls are apart i.e. the size of the reactor. Bigger reactors inherently have lower losses or to put it another way - higher gains.

Electron Guns

I have been looking at the electron gun question. How to design them how many amps of current they have to deliver.

Electron Gun Power

Electron Gun Suppliers [pdf]

Electron Beam Welding Primer

Joel, aka Tony Russi had this to say at NASA Spaceflight about expected electron gun currents (edited slightly for clarity):

The drive current in amperes to balance electron losses:
Ia = (Eq x Npcc x Vcc / Ts) x 1/ Gmj, where
Eq = electron charge in coulombs i.e. 1.602E-19,
Npcc = average inside electron density per cubic centimeter,
Vcc = volume of Polywell in cm3 i.e. 1.4E4, (4 π r3/3 )
Ts = electron transit time in seconds across Polywell(R=15cm),
Gmj = recirculation-corrected confinement factor.

The formula describes electron motion in a Polywell. The factor Npcc x Vcc is the total number of electrons inside the Polywell. Dividing this quanity by the time for each electron to cross from one side of the sphere to the other gives the rate at which electrons hit the confining B-field at the edge of the well i.e. the rate at which electrons try to escape. Dividing these factors by recirculaing-Gmj is the same as multiplying by the probability of escape per electron, which gives the rate at which electrons escape. Finally, multiplying all that by the charge on one electron gives the rate of charge loss in coulombs per second. An ampere(A) is, by definition, equal to one coulomb per second.


Joel/Tony - I think that is an excellent first cut!

A Spread Sheet to calculate electron current requirements. It is called Electron Rqmts.xlr

Wednesday, August 1, 2007

Electron Gun Power

The Electron Guns are going to require some hefty filament supplies. I was looking at the EIMAC Catalog to get some ideas on filament power. Several 1 Amp tubes I checked had filament powers on the order of 450 watts. A 7 Amp tube I looked at was over 1.5 Kw.