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| aetherist:
--- Quote from: TimFox on April 08, 2022, 09:24:15 pm ---Yes. There are commercial sources for vacuum-compatible search coils that can sense a pulsed beam of charged particles flowing through the hole in the coil. Here is one commercial source with several different coil configurations built into vacuum flanges: https://www.bergoz.com/products/ A coil senses the time-derivative of the magnetic field around the beam, dBdt, as the pulsed beam goes through it. Here is a tutorial from Fermilab about various "beam diagnostics", including measuring the field induced by the beam current, similar to how clamp-on ammeters measure normal AC through an insulated wire. https://lss.fnal.gov/archive/2000/conf/Conf-00-119.pdf --- End quote --- It looks to me that sensing a pulsed beam is a measure of the change in magnetic field, rather than the measure or detection of a steady magnetic field. However, for a change in magnetic field then there has to be a magnetic field, & if so then mission accomplished i suppose. I will have to have a think. Would one of thems gizmos detect a magnetic field around a wire carrying steady DC? Has one? If u made a steady electric DC circuit including a CRT type of device & wires, then the gizmo should detect the same magnetic field everywhere along the circuit. Has this ever been done? |
| thinkfat:
Well, just expose the steady beam to a magnetic field of known strength and look at how it's deflected. Like, how a CRT works. |
| TimFox:
--- Quote from: aetherist on April 09, 2022, 06:38:32 am --- --- Quote from: TimFox on April 08, 2022, 09:24:15 pm ---Yes. There are commercial sources for vacuum-compatible search coils that can sense a pulsed beam of charged particles flowing through the hole in the coil. Here is one commercial source with several different coil configurations built into vacuum flanges: https://www.bergoz.com/products/ A coil senses the time-derivative of the magnetic field around the beam, dBdt, as the pulsed beam goes through it. Here is a tutorial from Fermilab about various "beam diagnostics", including measuring the field induced by the beam current, similar to how clamp-on ammeters measure normal AC through an insulated wire. https://lss.fnal.gov/archive/2000/conf/Conf-00-119.pdf --- End quote --- It looks to me that sensing a pulsed beam is a measure of the change in magnetic field, rather than the measure or detection of a steady magnetic field. However, for a change in magnetic field then there has to be a magnetic field, & if so then mission accomplished i suppose. I will have to have a think. Would one of thems gizmos detect a magnetic field around a wire carrying steady DC? Has one? If u made a steady electric DC circuit including a CRT type of device & wires, then the gizmo should detect the same magnetic field everywhere along the circuit. Has this ever been done? --- End quote --- The usual clamp-on ammeter or current transformer is useful for AC current measurement. The electrical circuit formed is basically a transformer, where the wire being sensed is the primary and the surrounding coil is a secondary. Of course, transformer response does not extend down to DC. The coils used to sense beam current are used in the same way, with the beam going through the center of the coil, like the wire in the current transformer case. Note that the manufacturer I cited makes different models, one optimized for low frequencies and another optimized for fast pulse response. To measure DC current in a non-contact manner there are two normal methods: Hall effect sensor or flux-gate sensor. The former uses the deflection of the drifting electrons in an external conductor from the magnetic field from the wire, and the latter is similar to a current transformer, but there are extra coils that excite the magnetic hysteresis of a ferromagnetic core and detect the second harmonic of the excitation frequency due to the magnetic flux from the current in the wire. My classic -hp- 428A "clip-on milliammeter" is a good example of the flux gate. |
| aetherist:
--- Quote from: TimFox on April 09, 2022, 02:08:35 pm --- --- Quote from: aetherist on April 09, 2022, 06:38:32 am --- --- Quote from: TimFox on April 08, 2022, 09:24:15 pm ---Yes. There are commercial sources for vacuum-compatible search coils that can sense a pulsed beam of charged particles flowing through the hole in the coil. Here is one commercial source with several different coil configurations built into vacuum flanges: https://www.bergoz.com/products/ A coil senses the time-derivative of the magnetic field around the beam, dBdt, as the pulsed beam goes through it. Here is a tutorial from Fermilab about various "beam diagnostics", including measuring the field induced by the beam current, similar to how clamp-on ammeters measure normal AC through an insulated wire. https://lss.fnal.gov/archive/2000/conf/Conf-00-119.pdf --- End quote --- It looks to me that sensing a pulsed beam is a measure of the change in magnetic field, rather than the measure or detection of a steady magnetic field. However, for a change in magnetic field then there has to be a magnetic field, & if so then mission accomplished i suppose. I will have to have a think. Would one of thems gizmos detect a magnetic field around a wire carrying steady DC? Has one? If u made a steady electric DC circuit including a CRT type of device & wires, then the gizmo should detect the same magnetic field everywhere along the circuit. Has this ever been done? --- End quote --- The usual clamp-on ammeter or current transformer is useful for AC current measurement. The electrical circuit formed is basically a transformer, where the wire being sensed is the primary and the surrounding coil is a secondary. Of course, transformer response does not extend down to DC. The coils used to sense beam current are used in the same way, with the beam going through the center of the coil, like the wire in the current transformer case. Note that the manufacturer I cited makes different models, one optimized for low frequencies and another optimized for fast pulse response. To measure DC current in a non-contact manner there are two normal methods: Hall effect sensor or flux-gate sensor. The former uses the deflection of the drifting electrons in an external conductor from the magnetic field from the wire, and the latter is similar to a current transformer, but there are extra coils that excite the magnetic hysteresis of a ferromagnetic core and detect the second harmonic of the excitation frequency due to the magnetic flux from the current in the wire. My classic -hp- 428A "clip-on milliammeter" is a good example of the flux gate. --- End quote --- But, ignoring AC, ignoring wires, ignoring pulses – has a magnetic field ever been measured around an electron beam? Here i am thinking an electron beam in a long glass tube. |
| TimFox:
Yes: using the appropriate coils around an electron beam in linear accelerators. The vacuum chamber for the beam is usually metallic, not glass, but the coil can be placed inside the vacuum. Note that the manufacturer I cited places his coils inside standard "ConFlat" high-vacuum flanges. Re-reading the Bergoz catalog, I find one unit that goes down to DC, the "NPCT", which I assume is a flux-gate based instrument. Its specs: Full Scale Range ±20 mA, ±200 mA, ±2 A and ±20 A Resolution down to 0.5 µA rms/√(Hz) Output Bandwidth from DC to 10 kHz (-3dB) Linearity error ≤ 0.1 % It can be mounted outside the chamber, or supplied on ConFlat flanges to go inside the chamber. (If outside a metallic chamber, there must be a gap to pass the magnetic field to the coil.) Another unit, the "ACCT" is AC-coupled. Its specs: Full Scale Range from ±1 mA to ±2 A Single Range or 3 Selectable-Range Resolution ≤ 1.5 µArms Droop ≤ 2 %/ms Bandwidth from 3 Hz to 1 MHz (-3dB) The linear accelerator to accelerate electrons to a high kinetic energy is a mature field. Industrial and medical units go up to around 25 MeV kinetic energy, but the big guys such as SLAC (3 km long) go up to 50 GeV. |
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