1. What is the lecture mainly about?

　　(A) Ways to generate heat for nuclear fusion

　　(B) Differences between nuclear fission and nuclear fusion

　　(C) A controversial theory regarding how to generate nuclear fusion

　　(D) The possibility of establishing sustained nuclear fusion

　　2. According to the students, what are three advantages of nuclear fusion over nuclear fission

　　Click on 3 answers.

　　(A) Nuclear fusion can use a fuel that is more easily obtained.

　　(B) Nuclear fusion can be achieved at lower temperatures.

　　(C) Nuclear fusion produces more energy.

　　(D) Nuclear fusion does not produce hazardous by-products.

　　(E) Nuclear fusion does not require as many natural resources.

　　3. Why does the professor mention isotopes of hydrogen?

　　(A) To correct a student's comment about how fusion takes place in stars

　　(B) To help answer a student's question about temperature requirements for fusion reactors

　　(C) To explain what happens to hydrogen atoms during fusion reactions

　　(D) To justify the need for superconducting magnets in nuclear fusion reactors

　　4. According to the professor, how will the ITER reactor differ from earlier experimental fusion reactors?

　　Click on 2 answers.

　　(A) It will be transportable to different locations.

　　(B) It will sustain nuclear reactions through heat that it generates on its own.

　　(C) It will heat the fuel mixture to a higher temperature.

　　(D) It will confine the plasma in a more energy-efficient way.

　　5. What does the professor say about the international effort to develop ITER?

　　(A) The participation of many countries may cause ITER to be delayed even more.

　　(B) The research orientation of ITER has encouraged international collaboration.

　　(C) ITER will make use of equipment made in many different countries.

　　(D) The lack of international cooperation on earlier fusion projects has hurt ITER.

　　6. What does the professor imply when he says this:

　　(A) He prefers to work on projects with more immediate results.

　　(B) He believes that research in the physical sciences requires strict time lines.

　　(C) He thinks it will take less time to develop ITER than most researchers expect.

　　(D) He is more skeptical about the future of nuclear fusion than most researchers are.

　　Script:

　　Narrator:Listen to a discussion in an environmental policy class

　　Professor:So, today we’re going to wind up our discussion of alternative energy sources and we’re going to talk about one that often gets overlooked. That source is nuclear fusion as opposed to nuclear fission, which is already discussed. In nuclear fission, the centers of atoms, the nuclei, are broken up. This is the reaction today that drives today’s nuclear-powered stadiums. Nuclear fusion, on the other hand, is pretty much the opposite. It occurs when two atoms collide and then nuclei combine, or fuse, to form a heavier nucleus. This is the reaction that powers the Sun, all stars. So, who can tell me what makes fusion more attractive than fission as an energy source. Julie?

　　Julie:Well, it releases more energy, for one thing.

　　Professor:Yeah, a lot more energy than fission.

　　Julie:Oh also, it can use hydrogen as a fuel source. And hydrogen is abundant and easily available in water. Fission uses uranium, which is way more difficult to find.

　　Male：Plus, fission is more dangerous. With fusion, you wouldn’t have to worry about radioactive waste, right?

　　Professor: Another good point.

　　Male：But still, I remember from my physics class, to fuse the nuclei of two hydrogen atoms require temperature found similar to the sun, like over 100 million degrees Kelvin. How can we possibly recreate those temperatures here on Earth?

　　Professor:Well, we can’t yet. Not sustainably. But maybe we don’t need to. See, right many countries around the globe are cooperating to realize the potential of nuclear fusion. And the project they’re putting the most resources into is called ITER. ITER stands for International Thermonuclear Experimental Reactor, a large fusion reactor that’s being built in southern France. It’s designed to create the first sustained nuclear fusion reaction, meaning the energy it will release is greater than the energy we’ll use to start it up. And I’ll get back to this point in a moment. But let’s back up.

　　You asked about how we generate the tremendous temperature required for fusion. Well, that’s not really the problem. There are heavier isotopes of hydrogen, deuterium and tritium that will undergo fusion at lower temperatures than regular hydrogen. And when we tend to do deuterium, tritium mixtures that much, around 40 million Kelvins, it generates what’s called a plasma, which is a cloud of ionized gas.

　　So what is the problem? Well, it’s twofold. First, the plasma, this cloud of plasma, is way too hot for any solid container to hold. Fortunately, high temperature plasma conducts electricity, which means we can use an electromagnetic force to hold the plasma in place to confine it. Unfortunately, that requires a lot of energy, more energy than we’d ever be able to get from the resulting fusion reaction. And this brings us back to the point I mentioned before. Creating a sustained fusion reaction, because up to now experimental fusion reactors have never been able to achieve this, this break-even point, the point where the energy output is as great as the input for more than a fraction of a second.

　　How will the ITER project overcome this? First, by creating a larger plasma. Twice as large as any previous generated. The advantage of this is that once the initial fusion reaction occurs, the larger plasma will generate enough energy to keep itself hot, to keep the fusion reaction going. And second, ITER will use super-conducting magnets to form the magnetic field, magnets that consume less electrical power than those used in previous attempts. So, less energy goes in. More energy comes out. Theoretically, it should do the trick.

　　Now, keep in mind, the ITER reactor has been in the works for about twenty years and it will probably take another decade to build. And even then, of course it will be used for research purposes. Commercial fusion won’t be feasible for at least another twenty years after ITER is built. So that’s a long timeline, right? Not something I’d be comfortable in my own work. I need shorter term goals to motivate me. But for those who can handle it, well, it means this project is not about short term economic competition or gains. So in a way, it’s easier to get countries to work together on it. If we cooperate, we’ll get there sooner because we know how much difficult it is to do it alone.

　　今天我們將討論替代能源的話題我們將討論一個經(jīng)常被忽視的問題。這個來源是核聚變，而不是核裂變，這已經(jīng)被討論過了。在核裂變中，原子中心，原子核，被分解。這就是今天驅(qū)動核動力體育場的反應(yīng)。而核聚變則恰恰相反。它發(fā)生在兩個原子碰撞，然后原子核結(jié)合，或融合，形成一個較重的原子核。這是太陽，所有恒星的能量反應(yīng)。所以，誰能告訴我什么使核聚變比裂變更有吸引力，而不是能源。朱莉?

　　朱莉:嗯，一方面，它釋放出更多的能量。

　　教授:是的，比裂變更多的能量。

　　朱莉:哦，它還可以用氫作為燃料。而且氫很豐富，在水中很容易獲得。裂變使用鈾，這是很難找到的。

　　男:另外,裂變更危險。有了核聚變，你就不用擔(dān)心放射性廢料了，對吧?

　　教授:另一個很好的觀點。

　　男:但是,我記得從我的物理課,融合兩個氫原子的原子核要求溫度發(fā)現(xiàn)了類似的太陽,就像在1億開爾文。我們怎么可能重現(xiàn)地球上的溫度呢?

　　教授:好,我們不能。不是可持續(xù)的。但也許我們不需要。看，世界上許多國家正在合作實現(xiàn)核聚變的潛力。他們投入最多資源的項目叫做ITER。ITER是國際熱核實驗反應(yīng)堆，一個在法國南部建造的大型核聚變反應(yīng)堆。它的設(shè)計是為了制造第一個持續(xù)的核聚變反應(yīng)，這意味著它釋放的能量大于我們用來啟動它的能量。一會兒我會回到這一點。但是讓我們后退。

　　你問我們?nèi)绾萎a(chǎn)生聚變所需的巨大溫度。這不是問題所在。有較重的氫、氘和氚同位素，在較低的溫度下會比普通的氫進(jìn)行聚變。當(dāng)我們傾向于氘，氚混合物的時候，大約有4000萬，它產(chǎn)生了所謂的等離子體，這是一團(tuán)電離氣體。

　　那么問題是什么呢?這是雙重的。首先，等離子體，這團(tuán)等離子體，對于任何固體容器來說都太熱了。幸運的是，高溫等離子體導(dǎo)電，這意味著我們可以使用電磁力來控制等離子體，以限制它。不幸的是，這需要大量的能量，比我們能從核聚變反應(yīng)中得到的能量還要多。這讓我們回到我之前提到的觀點。創(chuàng)造一個持續(xù)的聚變反應(yīng)，因為到目前為止，實驗聚變反應(yīng)堆從來沒有能夠?qū)崿F(xiàn)這個，這個收支平衡點，能量輸出和輸入一樣大的點，超過了一秒鐘的時間。

　　ITER項目將如何克服這個問題?首先，創(chuàng)造一個更大的等離子體。是之前的兩倍大。這樣做的好處是，一旦最初的聚變反應(yīng)發(fā)生，較大的等離子體就會產(chǎn)生足夠的能量來保持熱，以保持聚變反應(yīng)的繼續(xù)。第二，ITER將使用超導(dǎo)磁體形成磁場，磁體消耗的電能比之前嘗試的要少。所以能量減少了。更多的能量。從理論上講，它應(yīng)該奏效。

　　現(xiàn)在，請記住，ITER反應(yīng)堆已經(jīng)運行了大約20年，可能還要再花10年才能建成。即使這樣，它當(dāng)然也會被用于研究目的。在ITER建成后，至少再過20年，商業(yè)融合是不可能實現(xiàn)的。這是一個很長的時間軸，對吧?在我自己的工作中，我不會感到自在。我需要更短期的目標(biāo)來激勵我。但是對于那些能夠應(yīng)付的人來說，這意味著這個項目不是短期的經(jīng)濟(jì)競爭或收益。所以在某種程度上，讓各國一起合作更容易。如果我們合作，我們很快就會到達(dá)那里，因為我們知道單靠它是多么困難。