156: Chapter 156 Visit

Lunch was a simple affair at the research institute's cafeteria.

The food was affordable and tasty; most of the people sitting around were Researchers in overalls or white coats, and their conversations mostly revolved around experiments, data, and project progress.

After the meal, Academician Yang Zhenyu had an important coordination meeting to attend, so he took his leave first, saying to Chen Youhua before he left:

"Youhua, I'll have Engineer Yang accompany you on a tour this afternoon."

"Our research institute isn't just about the nuclear fusion device; there are many intricacies in the various supporting disciplines built around it. If there's anything you want to know, just ask Engineer Yang."

"Please go ahead with your work, Chief Engineer Yang. It will be great to have Engineer Yang accompany me." Chen Youhua stood up to see him off.

After seeing off Academician Yang, Engineer Yang asked with a smile.

"Professor Chen, is there any particular direction you'd like to see first this afternoon?"

"We have a specialized Materials Research Institute, a Low-Temperature Technology Center, a Power Supply Technology Research Office, a Microwave Heating Laboratory, and various teams responsible for diagnostics and measurement..."

Chen Youhua said almost without hesitation.

"Let's go to the Materials Research Institute first. One of the ultimate challenges in confining plasma at hundreds of millions of degrees is the materials."

"I'm very interested in the plasma-facing materials and superconducting materials you use."

"No problem! The Materials Institute is indeed the key among keys. Follow me."

Engineer Yang was clearly very familiar with the place, leading Chen Youhua toward another building.

Unlike the grandeur of the main experimental hall, the Materials Research Institute was filled with laboratories of various sizes.

In some labs, Researchers were operating massive vacuum melting furnaces to prepare samples of special alloys.

In others, high-power electron beam welding equipment emitted a blinding light, welding components that needed to withstand extreme heat loads.

Engineer Yang first took Chen Youhua to a High-Temperature Mechanical Properties Testing Laboratory.

An elderly Researcher with graying hair and safety goggles was intently staring at a changing stress-strain curve on a computer screen, while a complex machine nearby was applying high temperature and pressure to a small piece of tungsten alloy material.

"Engineer Zhao," Engineer Yang called out softly.

Engineer Zhao's body paused for a moment; he didn't turn around immediately but first completed the final fine-tuning movement, confirming the sample was clamped correctly before straightening up and turning his head.

There was a layer of fine sweat on his forehead, and his eyes behind the goggles shone with a sharp light.

Seeing Chen Youhua beside Engineer Yang, he froze for a moment, then wiped his hands on his slightly oil-stained work clothes.

"Engineer Yang? This is... Professor Chen?" His tone carried uncertainty and surprise.

"Hello, Engineer Zhao. I am Chen Youhua. I'm sorry to interrupt your work." Chen Youhua stepped forward.

"Oh, it really is Professor Chen! Hello, hello!"

Engineer Zhao seemed somewhat pleasantly surprised and instinctively wanted to wipe his hands again.

"I didn't expect you to come for a visit. Please, come in. The place is a bit cramped and messy."

He pointed apologetically at the samples, fixtures, and thick logbooks scattered on the nearby table.

"You're too kind. We're just here to learn."

Chen Youhua's gaze turned toward the massive testing machine.

"Engineer Zhao, the one you just installed is..."

"A candidate material for the Divertor target plate—a Tungsten-copper composite material," Engineer Zhao answered immediately.

"We're preparing for a transient thermal shock test to simulate the extreme heat loads during a large ELM or plasma disruption."

Chen Youhua stepped closer, carefully observing the small metal piece and the complex heating and loading devices on the testing machine.

"In this kind of test, what's the peak heat flux density you can simulate?"

"Depending on the experimental requirements, we can simulate up to over twenty megawatts per square meter, with durations ranging from milliseconds to seconds."

Engineer Zhao pointed to an extremely steep heat load curve set on the computer screen.

"You see, it's like this—a sudden climb followed by a rapid decay."

"Many materials crack, melt, or even sublimate under just one such impact."

"Twenty megawatts per square meter... millisecond level..."

Chen Youhua repeated the numbers, lost in thought.

"This means the microstructure of the material's surface undergoes a phase transition from solid to liquid or even gaseous state almost instantaneously."

"How do you capture the damage mechanism during such a rapid evolution in real-time? For instance, the initiation and propagation of micro-cracks?"

Engineer Zhao adjusted his glasses, not expecting Chen Youhua to ask such specific questions.

"We combine several methods, mainly using ultra-high-speed photography to record instantaneous changes in surface morphology, and a laser acoustic emission detection system to listen for internal micro-fracture signals."

"Immediately after the test, we perform micro-area X-ray diffraction and scanning electron microscopy analysis on the sample to observe lattice changes and crack paths."

"But to be honest, capturing all the details in real-time is still very difficult; much of it is inferred after the fact."

"Crack paths..." Chen Youhua pressed further.

"Have you observed whether the cracks tend to propagate along grain boundaries or through transgranular fracture? This is crucial for understanding the material's brittle behavior and the direction for improvement."

"We've observed both!" Engineer Zhao's demeanor instantly became scholarly as he pondered.

"Tungsten itself is very brittle and prone to transgranular fracture. We added the copper phase in hopes that it would act to bridge cracks and dissipate energy, encouraging crack deflection or even termination."

"But the difficulty lies in the fact that under high-cycle thermal fatigue, the copper phase itself softens and oxidizes, which can instead become a weakness."

"We are experimenting with different tungsten-copper ratios and sintering processes to see if we can find a better balance."

He picked up several discarded samples from nearby that had obvious cracks or erosion marks to show Chen Youhua.

At that moment, the testing machine began to run, emitting a louder noise.

Engineer Zhao immediately turned back, focusing intently on the data stream and monitoring screen.

After the test ended, he carefully removed the slightly warm sample, which seemed to have a slight color change on its surface, and placed it under a stereo microscope.

"Tsk... it lasted five cycles this time, better than last time, but it still started cracking from the edge in the end..."

He recorded his observations in a low voice while looking closely.

"It seems the edge polishing treatment and the connection method with the substrate still need optimization..."

Chen Youhua also leaned in to look at the tiny crack through the microscope.

"Can the origin of the crack be localized? Is it a defect in the material itself, or is it caused by thermal stress concentration?"

"We'll need further metallographic analysis to be sure."

Engineer Zhao looked up and sighed.

"But thermal stress concentration is definitely one of the main triggers."

"So we don't just study the material itself; we also have to work closely with the design department to optimize the geometric shape of the divertor modules and the layout of the cooling channels to reduce the stress concentration factor as much as possible."

"This is another difficult cross-departmental coordination problem."

Chen Youhua nodded, expressing his understanding.

After gaining satisfactory insights from the High-Temperature Mechanical Testing Lab, they proceeded to the Superconducting Material Preparation Laboratory.

A young female Researcher was intently operating a complex winding device, winding an extremely thin Niobium-tin Superconducting tape onto a mold.

Engineer Yang whispered to Chen Youhua, "This is Dr. Xiao Liu."

"Winding a qualified primary sample of a superconducting coil requires seven or eight hours of continuous work without any interruptions or mistakes."

"If the tension of the tape fluctuates or the winding angle deviates even slightly, it could lead to a significant drop in final performance or even failure."

Dr. Xiao Liu clearly noticed them, but she only gave a very quick glance; her fingers remained as steady as a Rock while she controlled the equipment, without any distraction.

Chen Youhua did not disturb her and instead asked Engineer Yang in a low voice.

"Engineer Yang, I've seen in the literature that the critical current density of this kind of Superconducting tape is very sensitive to mechanical strain."

"When winding large coils, how do you ensure the performance uniformity of several kilometers of tape, and how do you control the residual stress introduced during the winding process?"

Engineer Yang nodded and also replied in a low voice, "That's a core challenge."

"First of all, the production process of the tape itself is extremely demanding; any fluctuations from substrate treatment to coating will affect performance."

"During winding, we have a precise tension control system and guidance mechanism to ensure the tension and bending radius of the tape always stay within a safe range."

"After winding is complete, it must undergo a strict heat treatment process to release some stress and optimize superconducting performance."

"Even so, after each coil is made, it must undergo comprehensive performance testing in a low-temperature environment. If any local area's performance doesn't meet the standard, it could mean the entire coil needs to be reworked or even scrapped."

"What Dr. Xiao Liu is doing now is winding a verification sample for a newly designed coil."

Chen Youhua looked at the slowly moving, ultra-thin tape with its special metallic luster, lost in thought.

"In other words, the performance of the final large-scale coils depends largely on the precision and stability of these basic process steps."

"Exactly," Engineer Yang affirmed.

"If any tiny link gets out of control, it can be catastrophic when scaled up to the entire device."

Chen Youhua didn't disturb her; he just quietly watched the ultra-thin tape, with its special metallic luster, as it moved slowly under the guidance of the precision mechanism for a while, then quietly stepped out.

Subsequently, Chen Youhua visited various other laboratories. If the Researchers weren't busy, he would step forward and ask many questions; if they were constantly busy, he would just ask Engineer Yang for a general overview of the content.

No one talked grandly about ideals or dedication; everyone was buried in solving the specific and tiny technical problems right in front of them.

When leaving the Materials Institute, Chen Youhua encountered Engineer Zhao again at the entrance.

He was holding a large tea mug, leaning against a corridor window to rest and looking outside.

"Professor Chen, finished your tour?" Engineer Zhao greeted with a smile.

"I've benefited greatly," Chen Youhua said sincerely. "It's much more intuitive than reading papers."

Engineer Zhao took a sip of tea and smiled. "Our work is just like this—very dull, just constant repetition, using a method that's half experience and half physics to push technology forward slowly."

He didn't say more, just took another sip of tea.

Chen Youhua nodded and didn't ask further.