Thrice upon a Time (16 page)

It was a world fashioned and shaped by the uncompromising dictates of high-voltage engineering. Banks of transformers larger than any that Murdoch had ever seen reared upward amid an intricate, three-dimensional tapestry of superconducting busbars and coolant pipes. Between them were batteries of insulator stacks ten feet high and more, carrying lines to immense torroidal windings built around sections of partly visible cylindrical constructions that stretched away through labyrinths of steel structural frameworks.

Mike led them down a series of metal staircases through several levels of railed catwalks and maintenance platforms, and onto a walkway surrounding the base of what looked like a huge, round, steel tank, bristling with insulators and wrapped in cables; a long cylindrical structure emerged from one side of the tank and disappeared through concrete casemates in the approximate direction of the primary, two-mile-diameter storage ring.

"This is one of the injectors," Mike told them, gesturing upward at the tank. "Inside that are high-voltage arcs for peeling off electrons to give us our ion supply. That tube is the first of a series of initial accelerating stages. Initial acceleration is up to a million volts. The accelerators are charged from a capacitor bank located on the next level down."

"What ions do you use?" Lee inquired.

"Mercury."

"How many injectors are there altogether?" Murdoch asked.

"Sixteen," Mike replied. "There are four like this at each corner. This whole arrangement is duplicated by a second system running parallel to it on the other side of that wall." He pointed behind them, and then started to lead the way along a catwalk that followed the wall of the tube, which was at least ten feet high, through the concrete supporting structure and out onto a fairly wide observation platform. They found themselves looking along a vast, brightly lit tunnel in which relays of steel supports carried the tube away into rapidly shrinking perspective. A few hundred feet farther on, they could see the point where the other tube, running almost parallel, emerged from one side to join the first at a fine angle.

"This stretch is the first booster stage," Mike informed them. "From here to the junction along there, the beam is pushed up to ten million volts. Exactly the same thing happens to the beam from next door. The two are then merged to give one double-current beam."

Murdoch leaned his elbows on the parapet surrounding the platform and gazed for a while at the intricate webs of piping and windings that encased the gleaming surface of the tube wall for as far as he could see. "What kind of current are we talking about?" he asked.

"Oh, not much at this stage," Mike said cheerfully. "Even after the two beams merge, it's still only on the order of tens of milliamps—but that's at ten megavolts already, don't forget."

"I thought you said there were four beams at each corner," Lee remarked.

"There are. Come on, let's take a walk. I'll show you where the other two come into the act."

They descended to the floor of the tunnel and followed it to the junction, where they were able to stand and look up at the two massive tubes coming together over their heads. Beyond that point the tunnel became higher, and soon opened out into a huge vault, encircled by more catwalks and platforms, where the tube merged with one angling downward from somewhere above. The combined tube was even thicker than before, and marched away relentlessly into a wider tunnel that continued on in the same direction.

"The whole double-beam setup you've seen is only half of it," Mike explained. "There are two more injectors on a higher level, and their beams are merged in the same way to produce another double-density beam. The two double-density beams come together here."

"So you've got a quad at this point—combining the outputs from all four injectors," Lee observed.

"Quite."

"Still at ten million volts?" Murdoch queried.

"At this point, yes." Mike pointed across to the other side of the wide bay in front of them, which went down several levels deeper and separated them from the mouth of the larger tunnel that continued from there. "That's the beginning of the second booster chain. The first stage of it is another garden-variety linear accelerator that shoves things up to twenty-five megavolts. The other end of the chain is a fair distance away. In fact it's at that primary storage ring, which you must have noticed as you came over the hill."

"We did," Murdoch said. "So what's the beam up to when it reaches the ring?"

"One hundred billion volts," Mike replied.

Murdoch whistled.

They skirted the bay by way of a railed walkway running around its edge, and came to a concrete apron from which rose the massive steel supports that carried the accelerator tube into the next section of tunnel. From this vantage-point the tube looked like a gigantic gun-barrel converging away into the far distance. The tunnel was wide enough to accommodate an underground roadway that ran along below and to one side of the tube itself. One side of the roadway was flanked by the steel structural work supporting the tube and its coil assemblies, the other by white, tiled wall lined with layers of cable; looking along it, Murdoch felt like a mouse that found its way into a wiring conduit.

A local control center looked out over the bay from a point above the apron and next to the tube. Mike took them up there to meet some of the engineers who were responsible for that section of the plant and able to answer Murdoch's and Lee's more detailed questions. After that the three of them returned to the apron and boarded a small, electrically powered car to continue their tour toward the central zone of the site.

On the way, Mike explained that the same thing happened at all four corners of the plant, yielding four identical beams that entered the primary storage ring at four equispaced points around its circumference. Each corner-battery of four injectors was designed to produce two hundred and forty quad-current-density ion pulses every second, which were then boosted up to virtually the speed of light. Each pulse lasted for just under a half a thousandth of a second, which meant that a pulse would be some sixty-three miles long; obviously, therefore, its leading edge would arrive at the primary ring long before its tail end had emerged from the injectors. The ring drew the pulse in and wrapped it around on itself ten times, rather like a length of string being coiled onto a reel, and in the process multiplied the ion current by a factor of ten. At the same time it merged the compressed pulse with the ten-times-wrapped-around pulses from the three other injector batteries, achieving a final combined current of the order of amperes circulating in the primary ring.

The tunnel opened into a long, wedge-shaped space, again going down to deeper levels, one side of which was formed by the curving wall of the primary ring itself. Above it, the final, one-hundred-billion-volt booster section of the tube continued, suspended amid girders and latticework, to merge into the structure of the ring, thus forming the pointed end of the wedge. From the ends of the chamber, a brightly lit gallery curved away out of sight in both directions to carry the roadway along the ring's periphery, no doubt connecting with other, similar tunnels coming in from the other corners of the site.

"There are four places like this around the whole ring," Mike said as he halted the car to allow them a few minutes to take in the scene. "Every one is an entry port where a combined beam from four injectors is sucked in. There are four exit ports as well, situated between the entry ports. Every time the ring is pumped up, it unloads a full charge through each of the exit ports in turn."

"Like dealing out four hands of cards," Murdoch said. "Yes, we've come across it before."

"You've got it," Mike said, nodding. "Would you like to see one of the exit ports?"

"Sure. Why not?"

"Let's drive round the ring a little way and have a look at one."

They made a U-turn around the blunt end of the wedge to enter one end of the curving gallery, and followed it around until it opened out into another wedge-shaped chamber similar to the one they had just left. The difference here was that the tube disappearing into the tunnel that terminated in this chamber carried the ion pulses away from the ring instead of into it.

They turned off the ring-road and followed this tunnel for a long distance back out toward one of the corners of the plant; exactly which corner, Murdoch was by now no longer sure. It brought them to yet another similar, but smaller, chamber where the same story was repeated on a smaller scale. The tube from the primary ring fed a secondary storage ring, which was one tenth as large; obviously the secondary was one of the four one-fifth-mile-diameter structures located at the corners of the site that Murdoch and Lee had spotted earlier from the road. Each secondary ring achieved a further wraparound current-multiplication of ten, ending up with a trapped, circulating load of sixty amperes. The primary discharged two hundred and forty times every second, feeding each of the secondaries in turn; thus every secondary was pumped up to full load sixty times per second.

They drove around the secondary ring until they came to its single exit port, which pointed back to the central part of the plant. A diverter enabled the concentrated pulse coming from the ring to be channeled away through any one of four tubes, which diverged from each other across a long, fan-shaped vault before disappearing into the mouths of four separate tunnels. Mike drove them to the far end and into one of the tunnels to reveal yet another seemingly endless procession of lamps and struts marching away to a distant vanishing point. Murdoch was beginning to wonder just how much there was of this incredible subterranean network.

This tunnel led back to the center, all the time following a gentle incline that took it beneath the structure of the primary ring, passing en route through a lower level of one of the wedge-shaped chambers that housed the entry and exit ports; for all Murdoch knew, it could have been one of the two that they had already passed through higher up when they were going in the opposite direction.

The tunnel ended in a low, circular space a hundred feet or so across, which contained one of the tertiary storage rings. The tube they had been following entered the ring at a tangent in a way that was by now familiar, and the exit tube led away at another tangent from the same side. There were sixteen such tertiary rings in all, Mike informed them, lying edge to edge in a belt around the heart of the plant like a circle of coins. Each of the secondary rings at the corners fed four tertiaries in sequence via a diverter arrangement like the one they had seen in the fan-shaped vault. Since a secondary ring discharged sixty times every second, every tertiary was pumped up fifteen times per second. Further wraparound in the tertiaries gave another current-multiplication factor of ten, producing six hundred amperes in each.

Thus, fifteen times every second, a point was reached where there were six hundred amperes of multiply ionized mercury atoms moving at relativistic speed inside every one of the sixteen tertiary rings. When the plant eventually went to full power, all sixteen rings would be discharged simultaneously, and a total of ten thousand amperes would converge in the final rush along the three-quarter-mile-long guides that climbed gently upward to the target chamber. The compression achieved at that stage would be such that the pulse delivered from sixteen directions at once would last only for nanoseconds.

The power that smashed into the target pellet in those nanoseconds would be in excess of a thousand trillion watts.

Murdoch and Lee gazed out through a long, glass wall at the place where the beams ended their brief lives in a flash of fusion plasma. They had arrived at last in the Main Control Room below the Reactor Building, which was the large building dominating the cluster at the center of the site. Beyond the glass lay a vast, circular cavern in which the thirty-foot-diameter, steel-clad bulk of the reactor vessel reared up through tiers of access levels and maintenance platforms. Around its base and below the level of the control room, a circle of massive steel yokes carried the beam tubes from the tertiary rings into the reactor wall.

Mike waited a while for them to digest the view, then moved forward to stand beside them and gestured with his arm.

"That's where it all happens. The target chambers are in there, of course. Actually they're not as big as you might think. Most of what you can see from the outside is due to shielding for neutrons and radiation."

"How come 'chambers'?" Murdoch asked. "How many are there?"

"Three. The first phase of full-power testing will be to run one of them flat-out. If it all goes okay, we'll go the whole hog and double the firing rate of the injectors. Then the accelerator system will deliver thirty full packets a second. That will drive two reactors in parallel. The third is a standby, so the plant will always be capable of chucking out two reactors' worth."

Murdoch looked out at the forest of girders and pipes encasing the reactor vessel, scattered among which a dozen or so technicians were making final adjustments and measurements in preparation for the coming Monday's tests. "How long before you try running two chambers in parallel?" he asked.

"Practically straight away," Mike replied. "Every section of the system has already been tested through individually, and the whole thing has been run up to moderate power lots of times without any major snags. On Monday we'll run two chambers at full-blast individually. Then, if all goes well, we'll double up on Tuesday morning. After that it will be solid testing for at least a few months."

"On-line by summer then, huh?" Murdoch said.

"With luck. Tentatively we're saying by the middle of July."

Lee looked down at the sample target that he was holding in his hand, one of two that Mike had presented as souvenirs. It was a thin-walled, hollow glass lens over half an inch across, filled with a mixture of deuterium and tritium. Inside one of the reactor chambers, a stream of pellets at a precise spacing of fifteen per second would be directed through the beam focal point like machine-gun bullets to be hit on the fly by the titanic bolts of energy from the accelerators. The inner surfaces of the target chambers comprised "waterfall" screens of liquid lithium metal, thus affording no solid area to be eroded by the particles and debris generated in the fusion process. The fast neutrons produced were slowed down in the lithium blanket, where their kinetic energy was transformed into heat to be carried away by the liquid and used to generate power in another part of the plant. As an alternative, the fusion plasma could be directed out of the chamber and its energy tapped directly via magnetohydrodynamics, but that capability would be added later.