Introduction to particle accelerators using a CRT

This is an unusual experiment using an oscilloscope CRT found in an old college text book on Physics and Electricity. A conventional CRO, or in my case, WWII radar tube can be used to calculate the charge to mass ratio for an electron. This can be extended to examine the relativistic nature of mass with high electron speeds. The cathode ray tube is set-up as it would be in an oscilloscope for beam current and focused to a central spot. An ac voltage is then applied to the Y-plates to create a vertical line on the screen and this is adjusted to give a full with deflection on the screen. The frequency is unimportant for the experiment and 50Hz is used, as it can be taken directly from the mains via an isolation transformer and a Variac for control.
The complete CRT is housed in a solenoid to produce a linear magnetic field parallel to the electron beam. This will not deflect the straight-line beam but will twist and interact with the deflected beam causing it to spiral and reduce as it travels towards the screen.
The current in the solenoid is adjusted until the line displayed rotates and shrinks in diameter to appear as a spot on the screen. At this critical point the magnetic field has rotated the beam 180 degrees and the field strength would be calculated from the coil current. If the anode voltage is adjusted at this point, the deflection line will start to reappear before and after the zeroed point on the screen. Adjusting the anode voltage changes the speed of the electrons and hence the point in time when they hit the screen with reference to the Y-plate deflection.
The experiment was obtained from Electricity and Modern Physics (2nd edition) by G.A.G. Bennet (page250)
The calculation for electron velocity and charge /mass ration is normally demonstrated in schools and colleges using special educational cathode ray tubes where fluorescent screen is placed along the beam path showing the direction of electron travel rather than the landing spot as in a screen. This is demonstrated in another of my videos at: https://youtu.be/o69t9QNhOOM (2:39)
CONTENT:
00:00 - Intro
01:10 - CRT being used
01:57 - Set-up
03:17 - Experiment
06:29 - Explanation

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