A/N: My apologies if this conflicts with whatever canon exists for how lightsabers actually work. Backstory for the Happily Ever After chapter 'Dirty Laundry'.
A lightsaber was essentially a circle. Hux was sure that had some deep philosophical meaning to Force users, but he considered that bullshit. There were more practical elements of interest.
A lightsaber functioned by sending a beam of energy into the kyber crystal, which then projected it outward as dictated by the configuration of the crystal lattice. Color and other properties were determined by the presence of impurities and the precise arrangement of the lattice. Again, Force users ascribed all manner of mystical hokum to this, saying it had to do with personality and attunement. It was no better than astrology.
When the energy left the kyber, it existed mostly in hyperspace. This sounded thoroughly exotic but had no practical effect unless you contained it somehow or projected a great deal of energy that way. In order to contain it, lightsabers were equipped with regulators that warped the field, flipping the beam back onto itself at a distance set in the construction of the device. That distance dictated the length of the blade. The energy shot back into the crystal and due to the properties of kyber, cycled back out to create a continuous circuit that manifested as a field of hyperspace no wider than a beam of light.
That circuit was almost impossible to interrupt. Not even clashing with another, similar field would do it. It didn't have much of a loss rate, so the hilt of the weapon was a manageable size, assuming one didn't intend to run one's lightsaber for hours of continuous use. It would cut through almost anything that did not also exist in hyperspace. Powerful gravity fields could effect it, but by the time that happened, the wielder would have long since perished, or the hilt collapsed.
If you left the regulator off, then you had what amounted to a hyperspace beam cannon. It degraded rapidly in the presence of a gravity well and it wasn't as efficient as conventional weaponry. You only saw kyber used for weapons on capital ships or mobile bases like the Death Star. But the simple transmission of energy into hyperspace was useful for communications relays and ship navigation systems. There were synthetic crystals used for cost reasons when one could get away with it, but nothing matched the real thing.
Hux's idea was to take this beam of energy, ramp it up to absurd power levels, and project it through a focusing collar at a gravity well. Like, say, a planet. It was the opposite goal of previous kyber weapon development, where great effort was put into minimizing the effect of gravity on the beam. If enough energy was channeled that way, the beam would travel through hyperspace the same way a ship did and, just as a ship, would fall out of hyperspace after gravity deflected it sufficiently. You couldn't use it to target ships (unless they were the size of planet), but if you wanted to blow up entire planets, then this would work fine. It became a feature instead of a bug. Even the developers of the Death Star had not been crazy enough to make a weapon which could only be used to blow up entire planets.
How to convey this to a being like Snoke? Hux's life depended on convincing him it would work. He had no idea of Snoke's level of technical expertise, but he did know Snoke could use the Force. It seemed reasonable that he would be familiar with lightsabers and how they functioned. Using the lightsaber as a starting point for the discussion seemed, also, reasonable.
As it turned out, Hux's father had happened upon a cache of laser swords in the personal chambers of Emperor Palpatine, on his flagship, the Eclipse. They were probably leftovers from the execution of Order 66, but who they'd belonged to originally mattered not. All Hux cared about was that he'd inherited his father's assets, these among them, and he'd been toying with them off and on for several years as he refined his ideas for Starkiller.
They were nothing special to him – less useful as weapons than the blaster he routinely wore on his hip (it was a regulation part of officer's dress uniform) or the knife up his sleeve. He'd worn both to his first interview with Snoke. He wore both to the second. But he was also carrying a lightsaber hilt in his hand. Armitage Hux strode into Snoke's sanctum with the determination of a man intent on leaving the room alive no matter what he had to do to achieve that.
He never again saw the look on Snoke's face that he did that day, as though for a moment, Snoke realized he was looking death in the face. It was only a moment, a quick flash of expression that Hux had seen before on humans right before they died, as they realized what he was up to. It was so unexpected – with Hux's thoughts having been solely focused on the presentation he was about to give – that he stopped as soon as he saw it.
For a long moment, he and Snoke stared at one another. A slithering feeling coiled around Hux's mind, foiled by the inscrutable mechanics of hyperspace projection and gravity well calculations that he'd been dwelling on. The presence dug for something more. It was wary. Suspicious. Afraid.
Hux looked down at the lightsaber hilt, remembering in a flash something he'd read (and dismissed) about the symbolic importance of such a weapon to users of the Force. It had a meaning that didn't apply to a blaster or a knife. The thing he had in his hand (because his belt did not come equipped with a ring to hang a lightsaber from, nor was he going to attach one for the single time he needed to show it to Snoke) was not a tool. It was a symbol of power. It occurred to him that he might as well have walked in with his blaster in hand, finger on trigger, and pointed directly at Snoke's head.
He probably should have dropped it. Instead, he looked back up at Snoke and his grip tightened. If he had a thought, he couldn't remember it. Force lightning took him out, just as it had the first time. When he woke up, he was shaking, drooling. He'd wet himself. The lightsaber was in Snoke's hand, who was studying it with casual interest.
What happened next ended up being the most agonizing use of the Force he would ever endure. Snoke ripped open his mind and sliced through everything he was. Snoke was careless in doing it this time, letting his intentions be known more clearly than he had the first time. He sought Hux's motivations in entering the room, dismissed them as trifling, and moved on to pull up everything Hux knew of this lightsaber, lightsabers in general, the Force, Emperor Palpatine, and what else Brendol had scavenged from the estate of the late ruler of the galaxy.
Hux gave up everything, because there was nothing else to do. Information was stripped from him like a thin rope yanked from his hand when he wasn't expected a pull. He didn't even know he should have been gripping and if he had, it would have only burned his skin. Once Snoke had that much, he slowed down. He crawled back through Hux's expectations of today – the presentation, the calculations, the showy display he'd practiced of how Starkiller would work by waving around the lightsaber and talking through it, hoping to keep Snoke's attention with theatrics.
Snoke laughed. It was a good joke. He threw the lightsaber at where Hux had picked himself up to a huddled, angry crouch on the floor. He glared at the hilt where it stopped in front of him.
"Pick it up," Snoke said in a taunting whisper.
Was that an order? Or a challenge? Would he die if he did?
At this point, his urine cooling on his pants and his brain on fire, muscles still spasming, Hux didn't give a damn. He picked the thing up. He was angry and desperate, as much as he'd been that time he'd bitten a mouthful out of his father's leg, twenty years before. If he was going to die, then he was going to go down fighting. He got to his feet, nose wrinkled, chin raised. Unsteady, because his legs kept wanting to buckle.
Snoke's brows rose. He looked amused. "Impressive. The First Order has something of worth in it after all." The praise stiffened Hux's spine. It also gave him second thoughts about charging Snoke and trying to use a blade he had no experience with. Did he have to fight? This was his superior officer. Theoretically, he shouldn't have entertained the prospect at all, but there was a vicious animal deep inside him that cared more about survival than duty. His grip tightened again.
Snoke knew about that animal. "But it won't for long." He raised his brows in theatrical surprise. "Are you going to challenge me?"
The stupidity of what he was doing flashed through his mind – picking a fight with a prepared opponent who had proven twice now that Hux was powerless against him. The whole High Command had apparently bowed before Snoke. There was no way he could fight this. Even backed into a corner, kicked, abused, made to foul himself, and aching in ways he didn't even know he could hurt – there was no way to fight this invisible thing that took him apart with such ease. It wasn't even his duty to fight it. Hux knelt and set the weapon hilt on the floor between them, backing away from it like it was a bomb. "No sir."
Snoke drawled, "Then get on with it. You came here to give a presentation. I am waiting."
Hux swallowed roughly. He blinked and started to breathe again. He tried to pull his thoughts together. It had been a very long two days – no sleep in it, but enough stims to keep him going – the beginning of a six year off-and-on addiction. He turned his mind back to his point in coming in here, which was to get out alive. That involved the presentation. He swallowed again, raised his head, and began.
The walk back from the interview was the worst. He shook so hard he could barely stay upright. The corridors felt like they were spinning around him. His equilibrium was shot. Many people looked at him, most askance but a few with pity. He was alive and he didn't care about their looks. He was thankful his dark uniform hid his loss of control and got himself to his quarters as quickly as he could. It was a full day before he could bring himself to come out. But he had to. The Starkiller project had been authorized and he'd been promoted to colonel. It was time to get started.