As she slipped out of the room, Rogers explained that the electrodes were fitted into the channel of the MHD generator.

“The plasma goes through the channel at supersonic speed. It’s more than five thousand degrees Fahrenheit. It’s loaded with potassium salts to buck up its conductivity and a lot of sulfur compounds from the coal.”

With a nod of understanding, Jake said, “So the channel takes a beating.”

Rogers shook his head. “The problem’s not with the channel. It’s lined with ceramic tiles, like the heat shield material on the space shuttle. The channel’s okay. It’s the damned electrodes.”

Jake looked down at the blackened tubes.

“The electrodes have to be electrical conductors. We can’t make them out of ceramic. They have to tap the electrical power in the plasma and carry it out to the transformer.”

“I get it,” said Jake. “If they don’t work well you can’t get the power out of the plasma.”

Rogers nodded glumly as he hefted one of the tubular objects in one hand. “They stick out into the plasma stream while it’s roaring down the channel, five thousand degrees hot and in supersonic flow, with megawatts per cubic inch of electrical power crackling in there.”

“Like lightning rods,” Jake muttered.

“Exactly!” said Rogers. “Lightning rods that’re getting zapped constantly, as long as the generator’s running.”

“They erode,” said one of the young men.

“A lot,” added the student beside him.

Jake picked up one of the electrodes. It was much lighter than he had expected, judging from its size. But he could see that one end of it had been melted as if it had been stuck into a blast furnace.

“And the erosion rate is too damned high,” Rogers said.

“How long do they last?” Jake asked.

“That one in your hand was in the little rig downstairs for just over a hundred hours.”

“They’re all from the little rig?”

“Yep. These are all from low-power runs. We haven’t even tried any long-duration runs on the big rig yet.”

One of the other students said, “We’re moving the separator from downstream of the channel to upstream, between the combustion chamber and the channel.”

The young man beside him said, “That’ll let us separate out the sulfur compounds before the plasma streams into the channel.”

“Which is where the electrodes are,” Jake said.

“Right.”

Rogers took up, “Separating out the sulfur upstream of the channel will help reduce the erosion rate. Lowers the plasma’s enthalpy a bit, but we can live with that.”

Before Jake could ask about enthalpy, Glynis pushed through the door with the big stainless steel coffeepot in one hand and a tower of Styrofoam cups swaying in the other.

“Coffee break,” she announced.

After a sip of the scalding-hot coffee, Jake asked Rogers, “How serious a hang-up is this electrode business?”