A Proton Stream, is a stream of positively charged ions which can harness a ghost. The Proton Stream is very dangerous and barely controllable. Egon has also mentioned that crossing Proton Streams will result in total protonic reversal causing all life as we know it to stop instantaneously and every molecule in a user's body to explode at the speed of light.
What a Proton Stream is
The known parts of the Proton Stream:
- Proton Beam (red with a yellow/orange core)
- Electron/Positron Lightning (blue to white)
- Sparks (pink/purple sparks that come off the wand point)
- Emitted Light (partly the sparks, it is usually white)
- Lens Flare (bright streak horizontal and sometime vertical which is mostly blue)
The Proton Stream has noted traits to capture ghosts for possible storage. The Beam acts like a rope and will lasso around the target during the event.
The stream is also noted for being difficult to control and highly destructive to physical objects. Objects hit by the stream tend to blow apart or catch fire, and as the beam tends to undulate wildly the Ghostbusters tend to cause a lot of collateral damage.
The color of the containing electrons/positrons (blue-white) is scientifically accurate for free electrons/positrons 
Difference in Appearance
Explosions were filmed on stage at Entertainment Effects Group then rephotographed with a technique called "pin blocking." The explosions were miniaturized so that the tip of the Particle Throwers appeared to have pyrotechnic explosions and flares. The explosions and flares were laced in with five levels of classical animation which was then manipulated on the optical printer by Optical Supervisor Mark Vargos. Sound designer Richard Beggs did a feedback loop in the harmonizer and generated a sort of rhythmic pulsing sound between the uniform base sound he made first and the Moog synthesizer. Beggs then made a library of raw sounds in six or seven different families of sounds for different situations like whimpery for when the thrower was turned on, the degre of violence or impact, and one distinct sound for each of the Ghostbusters. It was decided the stream would look like rubberized light and hover rather than be straight laser that's been done before in other movies. The imagery of a fishing line was used when designing the stream when it connected with Slimer. It was decided there would be a certain warmth to the stream by using contrasting colors, an amber orange glow wrapped in blue electricity.
At first, the team at Industrial Light and Magic attempted to duplicate the Proton Streams from the first movie. Dennis Muren and Mark Vargo encouraged animation supervisor Tom Bertino and the crew to go in a new direction in order to surprise the audience. John Armstrong and Peter Crossman came up with designs that evolved the Proton Streams to act like cowboy lassos and fishing lines. Muren and Vargo approved then the designs were brought to Ivan Reitman. Reitman loved them and gave the go-ahead to continue. The lasso idea turned out to work very well with the mylar squash and stretch effect used on the Scoleri Brothers. When the streams were supposed to wrangle them, the mylar would be utilized to constrict the ghost. 
The Proton Stream seems to have a different sound effect used in Ghostbusters and Ghostbusters II. In the second installment, the stream seems to make a small cling sound when first fired (similar to when the Proton Pack turns on). Other than that, the sound effects are nearly identical.
- Mueller, Richard (August 1985). Ghostbusters: The Supernatural Spectacular, p. 99. Tor Books, New York NY USA, ISBN 0812585984.
- CERN 12/2016
- Terry Windell (1999). Ghostbusters "SFX Team Featurette" (1999) (DVD ts. 04:36-05:03). Columbia Pictures. Windell says: "And actually took explosions that were filmed on the stage and then rephotographing them with a technique that these guys called pin blocking so we can miniaturize these little explosions so that the tip of the gun had pyrotechnic explosions and flares and things laced in there with five levels of classical animation that was also manipulated on the optical printer by Mark Vargos."
- Wallace, Daniel (2015). Ghostbusters The Ultimate Visual History, p. 56-57. Insight Editions, San Rafael CA USA, ISBN 9781608875108. Richard Beggs says: "There was a liquid part to the sound. I wanted something that sounded splashy but electronic, like a plasma flow. I'd gotten the base sound of it down, but it was too uniform and not very dynamic. So I did a feedback loop in the harmonizer and got this sort of rhythmic, pulsing thing between it and the Moog. I made the sound of the neutrona wand depend on the violence of the shot or the impact. Some were a little whimpery, like what happens when they start up, and at low, medium, and high intensity. I created this library of raw stuff in six or seven different families of sounds, then I would choose one for Bill Murray, one for Dan, and so on, and that would be theirs."
- Richard Edlund (2009). Ghostbusters- Slimer Mode (2009) (Blu-Ray ts. 36:33-36:59). Columbia TriStar Home Video. Richard Edlund says: "And so we came up with an animated style for the neutrona wands, where the beam would shoot out and it would hover. And it was funky-looking, but very kind of funny. And there was something about it. We talked about rubberizing light. It wouldn't have been funny if it had just been a straight beam. It's like a laser beam. Everybody's seen that already."
- John Bruno (2009). Ghostbusters- Slimer Mode (2009) (Blu-Ray ts. 36:26-36:32). Columbia TriStar Home Video. John Bruno says: "And I said, "They'll never point them in the right place so let's just make it crazy, so that once it's connected, it's like a fishing line.""
- Terry Windell (2009). Ghostbusters- Slimer Mode (2009) (Blu-Ray ts. 37:00-37:16). Columbia TriStar Home Video. Terry Windell says: "We wanted a certain amount of warmth and we ended up using contrasting colors. So we had this sort of amber orange glow and then we wrapped it with, you know, cool blue electricity. So, you sort of had the whole spectrum in there."
- Eisenberg, Adam (November 1989). Ghostbusters Revisited, Cinefex magazine #40, page 18, 20. Cinefex, USA.