Questions about the practical construction of a Linac

[John Futter]

Noah
It is funny thing with magnets that field strength is proportional to pole gap and power in watts in.


the formulas uses ampere turns but in the end because of the copper resistance this equates to watts or in this case kilowatts. 220 volts at 30 amps is about right ie 6.6 kW for a magnet of 0.8T and 75-100mm gap.
Most modern magnets are wound with copper tape with figures such as 260Amps @30 volts with the coils capped with aluminum plates with a serpentine watercooling channel to keep it cool.
Thicker coils mean less insulation in the coil space which aids getting more turns on and better cooling as more copper means better heat spread.

[Dennis P Brown]

Oops, incorrect post!

[Rich Feldman]

Noah C Hoppis wrote:
> Sadly not much of any tolerance! the whole thing will have a Capacitor to smooth ripple
How can you choose a capacitor without a quantitative ripple current requirement? I have doubts about the practicality of that solution. With no capacitor, your current draw from the mains will be a resistance-limited steady current (average rectified voltage divided by R), rapidly reversing direction twice each cycle.

Noah C Hoppis wrote:
> and the current will be limited by an inductive ballast from previous experiments.
I know you want to set a record for low cost cyclotrons.
How much (number, please) is your magnetic field strength allowed to vary as the coolant inlet temperature changes, and as the mains voltage wanders from second to second and minute to minute, for reasons you can't control? A DC power supply might be easier to control.

Noah C Hoppis wrote:
> The 1 inch gap concerns me though, the gap between the pole faces is 2".
Can we see your calculations that suggested 18,000 ampere turns?

Noah C Hoppis wrote:
> I should mention that for every 5 turns there is one 1/4" copper coolant tube. As far as I remember I over engineered the thing to take 30 C before dropping below .8 Tesla.
Good plan, but be sure to compute the thermal drop between copper hot spots and the coolant at outlet.

[Noah C Hoppis]

The cap was to avoid the lump from the rectification process, and a DC Power supply *would* be nice, and so would a new RF amp, and a new oscilloscope... (the point is for now, I am picking and choosing my battles and the tolerances in the acceleration cavity seemed to at he time take precedence. Though I have no objection to spending others money... (ah sponsorship)). I think a new DC supply might be feasible but I just don't see where it's going to come from. This is also why I have trouble looking directly at the ~12in magnets on ebay without noticing the $4000+ price tag. I also think it is interesting to hear that the newer coils are flat ribbon. would that at all be plausible for a 8 in magnet? Does anyone know of any recently dismantled / decommissioned accelerator facilities in washington state or the surrounding states?

[Rich Feldman]

Noah,
I'm about to send you a direct email & hope to start a dialog that won't pile more stuff onto this unwieldy forum thread. Offer is to be an electromagnet coach. If you make a good electromagnet & then lose interest, I bet you could sell it for more than the cost of materials you put into it.

Practical hint #1, to preserve flexibility as to power supplies. We see your coil is in two sections. It's easy to switch them between series or parallel. In fact, if you make them as 4 identical windings, you get 3 choices of operating voltage. Might facilitate conversion from an initial design (e.g. to run from rectified 120 VAC) to a DC regulated system using a simple switch-mode buck regulator, with no new coils on cores.

Practical hint #2, to acquire big iron at low cost. Does your metropolitan area have a used-metal dealer? Often associated with a places that buy scrap metal. Is there a machine shop that makes big parts and has a stock of leftovers? Poke around and look for pieces of steel that would fit your plan.

Used or new, parts with smaller cross section might be easier to find, and to finish at a home or school shop. For example, a rectangular bar with 8 x 3 inch cross section could be made by stacking 1/2 x 3 inch bars, or 1 x 1 inch bars. An 8" diameter pole piece could be made by stacking circles cut from thick plates. This has nothing to do with lamination for AC applications. Steel costs, new or used, are generally by the pound, so there's no big cost penalty.