Sorry I have very few Sams. Not to throw more confusion into this, but this is a video that goes over the concept of O'scope bandwidth, and is good for your problem.
http://www.youtube.com/watch?v=oZ1Dv2dVGkU
After the 2:50 point he starts getting into the "ringing" on an otherwise low frequency oscillator, and the bandwidth you will need to find your problem.
This video shows a little about roll off and why your scope should have a bandwidth well above what you actually want to be able to measure. And it all comes down to what makes up a wave form. He does not go into it here, but a square wave of 1khz actually needs a bandwidth multiple times that 1khz to be accurately displayed on an oscilloscope.
http://www.youtube.com/watch?v=pGwL6FadC9U
Your oscillation is about 10X horiz scan rate, easy to see as you have at least 10 visible vertical bars on the screen, As stated, around 200K, so you will need a scope that has a 1mhz bandwidth to see the ringing clearly. The above video explains the roll off of the scope, and why partly the bandwidth should be 1mhz. He is correct in this.
Another person asks if the bars get darker if the contrast knob is turned. With the same white screen, no signal, when turning the contrast knob through its range, does the bars change in their appearance? If not the noise is getting in other than the video amplifier circuit, (power supply because of bad decoupling cap) if they change significantly then the noise is being amplified by the video amplifier. So its a signal level noise.
Regardless of how the noise gets in, its source is likely at some point in the horizontal section. It is possible it can come from your corona source, does it intensify as you do something to cause the field to come close to arcing?
Other than that, there are two attached pictures from a tv I own, its not yours, but it shows parts near the horiz. area that can be culprits of your problem. Suspect any parts near the red dots, resistors, caps, inductors. You should go to the Sams website and buy your tv schematic, look around in the same parts of the tv, Horiz Osc, Driver, and output stages. There are two red arrows on one of the pictures, they point to waveforms that are capable of generating the "ring" because they are a pulse, and are squared. If a part that is designed to filter out overshoot in the pulse rise is bad, then the circuit, or following stage will momentarily oscillate at a higher frequency and give you that ring, and go into another part of the tv and give you those vertical bars...... Do not overlook shielding, of any parts, picture tube, or grounds.
This is a likely description of what could be causing those bars, its your job to look for a bad part in those areas, you will likely need the Sams, and possibly a good scope, and (2) 1mhz - 5mhz 10X to 1X probe with capacitance trimmer built in. There are good, inexpensive 20mhz - 100mhz Tektronix scopes and cheap starter grade probes that can be had for around $100. + Shipping, sometimes less. (Yes go for more than a 1mhz scope) You may need a second probe to connect to a horiz sweep sync source, as stated be another, so you better get two.