Silicon carbide photoconductive switches.

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  • August 22, 2015 at 12:43 am #1679
    mteachman
    Participant

    Diamond switches may take a long time to get here.

    Photo conductive SiC switches are being used by CPAC for dielectric wall accelerators which accelerate protons for cancer treatments. They licensed the tech from LLNL
    https://e-reports-ext.llnl.gov/pdf/759551.pdf
    http://cpac.pro

    They trigger them with nanosecond precision by spiltting a pulse of laser light and sending them through fiber optic cables and through the photoconductive switches which fire very quickly.

    The voltage rating of each switch might not be as high as diamond but a bunch of them in series with precise timimng should work. Even if a solid state solution is not cheaper than constantly replacing spark gaps, it could save money by alowing inductors to be used instead of capacitors or fix the jitter problems.

    August 25, 2015 at 11:15 am #13665
    Henning
    Participant

    Interesting read, although I’ve just skimmed it. Not that I’m qualified by any means.

    They also compare their materials (2H-GaN, 4H-SiC, 6H-SiC) to diamond (page 18).

    The 16 kV stated in the introduction is in the ballpark required for Focus Fusion (about 40 kV), but the current needs to be increased about a thousandfold (1.4 kA compared to about 1 MA for Focus Fusion).

    And I’m not sure, if a minimum resistance of 1 Ohms isn’t too high for a 1 MA current.

    Closing speed is great though: 0.1 ns to 1.0 ns.

    August 26, 2015 at 11:24 am #13668
    mteachman
    Participant

    Can the output of one FF be used as the input to another FF? Only input bank with these switches would be needed to start the first in a long chain of FF at a powerplant and the big output bank only need cheap rectifiers?

    If the Diamond or SiC switches could work with a coil , perhaps a superconducting one, would it make sense to send the ion beam through that coil to directly recharge it or is the geometry wrong for that?

    September 20, 2015 at 10:52 am #13672
    CoolRunner
    Participant

    As I could inderstand they got 1.4 kA with a 1cm2 switch. Scaling this to 1Ma would mean 714 cm2 of switch area. That is 26 by 26 cm. This would also reduce resistance to 1/714 ohm.

    Ofcause this would need a laser pulse of 50MW/cm2 * 714 cm2 = 35GW.

    You would of cause have to stack three to get the proper voltage.

    I am not shure if this is feasable, but it is getting close to the right ballpark.

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