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1MW, can 1000Joules source of energy deliver 1M of power in 1 millisecond? $Energy =$ $P$ $x$ $t$ , so does it make sense to have small amounts of energy in large pulses of power? In an extremely short duration of time?

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  • $\begingroup$ Depends on what you want to do with the energy. $\endgroup$ Oct 7, 2014 at 15:26

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The obvious example of this is the laser system at the National Ignition Facility. The energy delivered to the target is only a few kJ, but it's delivered in about a picosecond so the power during that time is around 500 terawatts - that's $5 \times 10^{14}$W.

The power is so great that it heats a hydrogen pellet enough to make it undergo nuclear fusion.

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Definitely yes. Thinking of energy in terms of "work done" might help.

Just take an example: a big Ferrari with $10^3$kW of power,wont do too much if its engine is turn on for just a few milliseconds seconds and then immediately turned of. Hardly any petrol is used and there is no appreciable increase of kinetic energy.

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You can deliver that with a rather small capacitor bank. 1MW is 1000V and 1000A of current into a 1 Ohm load. That's fairly trivial to switch with a few dozen bipolar transistors. To store 1000J of energy, you would need a capacitor of 2*1000J/(1000V^2)=2000uF. That's about $2000 worth of electronics components.

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  • $\begingroup$ It's not that simple. Your example starts delivering 1 MW initially, but will then fall off as the capacitors discharge. Due to the falloff, you're not going to get 1000 J in 1 ms. $\endgroup$ Oct 7, 2014 at 16:13
  • $\begingroup$ Depends on your application. If you need a stable, rectangular 1MW power pulse, then you add a bit more voltage, a bit more capacitance and some regulation. You can buy plenty of industrial solutions for that kind of thing (CERN kicker magnet supplies, for instance, do just that). What do you need this kind of thing for? Are you running an accelerator that has kicker magnets? $\endgroup$
    – CuriousOne
    Oct 7, 2014 at 16:18
  • $\begingroup$ You are missing the point. The OP wanted 1 kJ in 1 ms, which your example doesn't provide. He didn't say anthing about a rectangular pulse, so a exponential decay is acceptable. The problem is your numbers don't work out. 1 kV on 1 mF into 1 Ohm isn't going to deliver 1 kJ in 1 ms. $\endgroup$ Oct 7, 2014 at 16:50
  • $\begingroup$ I wasn't trying to provide the OP with a 100% solution to his problem but merely gave him a starting point for how little hardware is involved in a system that can produce 1MW of peak power. If you need a real design for a stabilized 1MW power supply, I can help (for a substantial design fee, of course). Do you need a real design? $\endgroup$
    – CuriousOne
    Oct 7, 2014 at 16:53
  • $\begingroup$ I don't need anything. I'm just pointing out that this doesn't really provide what the OP asked for. The problem is that you are totally ignoring the exponential nature of the voltage and current. $\endgroup$ Oct 7, 2014 at 16:58
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Depending on how the energy is stored, it is certainly possible to transfer a lot in a short time. Here are several examples of delivering 1000 J in a short time:

  1. A bank of capacitors adding up to 200 mF charged to 100 V holds 1000 J. The right type of capacitor is capable of discharging in 1 ms. Since it may take too long to discharge a capcitor all the way, let's say the capacitor bank is charge to 120 V. That's 1440 J total. We only need to discharge it to 66 V to get 1000 J out, which would take .8 time constants assuming a exponential discharge into a resistor. That makes the time constant 1.2 ms, and the resistance 6.2 mΩ. That's doable, considering internal resistance of the capacitors and plausible interconnects.

  2. Drop a 100 pound weight from a height of 2.2 m or 7.4 feet. If both the weight and the surface it hits are hard but not elastic, all the energy will be released quickly. I don't know if releasing it all in 1 ms is plausible, so drop the weight from somewhat higher of use a larger weight. The point is to show that this level of power transfer for a short time is possible with everyday stuff.

  3. Various explosives. A gram of TNT releases 4.2 kJ when detonated, so 1 kJ only requires 240 mg. I'm no explosives expert, so I don't know whether 240 mg of TNT can complete detonation in 1 ms, but it sounds in the plausible range. To be sure, use more TNT.

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