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I'm disappointed that the average current from that device is apparently only a few microamps
where you got that number - are you reading kanji? : ) there is written here - "30 kV，パルス幅 2μs，繰り返㗠1 kHz ã®ãƒ‘ルス高電 圧を発生ã•ã›ã‚‹ IGBT", so apparently 5a peak current for 2us pulse at 1khz - that would be 2.5ma average - too good to be true. but in first paper they show oscillograms, from which you can tell, that acceleration time is 200us, and in second paper from the graph of core field you can clearly see, that extraction time = acc time, so 200us too. tho that would mean 250ma average current which is insane : D
For one thing, it seems that as the frequency increases you'd have less time to inject charge. And the amount of injected charge that would actually be trapped would depend on the type of focusing, the accelerating gradient (volts/turn) and the injection energy, so there are a few variables involved.
need english version of that 2010 paper. seems like this type of acceleration (ffag) is very popular in nippon, for a big machines atleast, and they describe rf acceleration instead induction too - wanna read bout that more.
btw, guys - i wanna build me such a machine not just for fun and giggles - i wanna see cherenkoff radiation from it, in water. so the question is - are human eyes capable of seeing microsecond pulses with high repetition rate (more than 50hz) or not? coz if the latter is true - i am doomed.
no, it's written there - "Electron gun high voltage power supply is voltage 30 kV, pulse width 2 μs, repetitive pulse 1 kHz"
"The size of the power supply includes the electromagnetic power supply for incident and emission, 35×60×45 cm and weighs less than 40 kg"
"electrons flying 20000 laps", so about 50kev gain for one turn
"The vacuum chamber is made of machinable ceramic. if the electron beam collides with the inner surface of the chamber, to prevent the electric charge accumulation Conductive coating (ITO film) used. The thickness of the vacuum chamber is 1 mm at the thinnest position. external turbo molecular pump was uses int the prototype"
"A vibration damper ( black part in Fig. 5) was attached. Without a damper, when exciting the bending magnet at 1 kHz vibrations that occur are transmitted to the X-ray target"
Figure 12 shows an oscilloscope with four acceleration cycles (4 ms)
The magnetic field strength of the deflection electromagnet is about 0.2T, and the acceleration The magnetic field strength is about 0.6T.
pulses of 100A-200V for the main coil of the bending magnet at 1kHz. for cw a 20kW large electromagnet power supply is required, resulting in high costs. Almost no power is lost in the deflection magnet coil, place a capacitor in parallel with the coil. LC resonance circuit and deflecting electromagnet Resonance type power supply electromagnetic power supply of less than 1kW
I'm disappointed that the average current from that device is apparently only a few microamps
where you got that number - are you reading kanji? : )
damn - it's written in the first english document - "Average beam current is estimated about 5 micro A".
but - there is another japanese paper -
they build 300mm in dia device, 6MeV and 430 R/min at the distance of 1m - that's some serious power already. injection time - 20us.
Fixed field betatrons have potentially a much higher intensity than conventional betatrons. Beam can be injected for a considerable fraction of a cycle, if extra accelerating flux is available, rather than the few tenths of a microsecond presently possible. The only beam current limitation appears to be space charge at injection, and this may be decreased by such techniques as high voltage injection. An FFAG betatron has no problems of tracking a pulsed guide field with the accelerating flux, and has also other engineering simplification
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"they build 300mm in dia device, 6MeV and 430 R/min at the distance of 1m - that's some serious power already. injection time - 20us."
Wow that's somewhat more radiation than I would expect.
On page 176 of the book by Kapitza and Melekhin is given an empirical equation for calculating the "bremsstrahlung intensity" (apparently from an optimally thick tungsten target):
r (roentgens/minute @ 1.0 meter from the target) = 0.04 * W^3 * I (where W is the electron energy in MeV and I is the electron current in uA).
So if r = 430 and W = 6, solving this equation suggests average current I = 49.77 uA (unless I made a mistake which is very possible).
Does the paper give any numbers for the circulating current and the radius of the beam's orbit at the target? If so it seems we should be able to calculate the trapped charge, q, and then multiply by the frequency, f, to determine the average current I.
I could be wrong, but I see it like this:
q = coulombs/second * seconds (where coulombs/second = circulating current; and seconds = circumference of electron beam orbit/electron velocity)
I don't know what these numbers actually are in this case but just to get a ball park idea let's say that circulating current is 8 amps; the beam radius where it strikes the target is 12.5 cm; the velocity of the electrons is roughly 3 x 10^10 cm/sec; and the frequency is 1 kHz.
Then I = (8 coulombs/sec) * (2 * pi * 12.5 cm)/(3 * 10^10 cm/sec) * 1000/sec = 21 uA
I don't know why these two numbers differ so much. Perhaps the bremsstrahlung formula in the book is wrong, or needs some additional qualification or something, or maybe my thinking is wrong somewhere.
Anyway, if I could find a cheap 5 MW pulse magnetron somewhere or a section of an S-band accelerator tube on ebay I might be tempted to try to build a small RF linear accelerator; otherwise the cost and complexity would be a show stopper for me.
So my presently held belief is that the only practical approach to a low end (a few MeV) accelerator (for someone with my limited resources) is the use of fast DC HV pulses. As I see it, this could possibly be in the form of a modified "Multibeam accelerator"; or in the form of pulse driven resonant cavities; or in the form of a Marx generator driving a coaxial transformer (where the Marx generator current pulse is in the Z direction and the magnetic field is in the theta direction in cyl. coordinates); or where a fast Marx generator drives a (possibly magnetically insulated) tapered line transformer, etc.
Does the paper give any numbers for the circulating current and the radius of the beam's orbit at the target?
yes - 8a and 0.125m, and i don't see any errors in your calculations. can you help me with evaluating some basic parameters of that 6 mev machine, like expected coils currents and so on? why they're feeding electromagnet with sinusoidal current in the prototype, when according to their graph "bending field", there has to be times with constant field?
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particle accelerators
