Cairo (AFP) - A Russian plane with 224 people on board crashed in a mountainous part of Egypt's Sinai Peninsula on Saturday, with medics at the site reporting casualties, officials said.

Ambulances reached the site and began evacuating "casualties," officials and state media reported, without elaborating on their condition.

The plane took off early Saturday from the southern Sinai resort of Sharm el-Sheikh bound for Saint Petersburg in Russia but communication was lost 23 minutes after departure, officials said.

"Military planes have discovered the wreckage of the plane... in a mountainous area, and 45 ambulances have been directed to the site to evacuate dead and wounded," a cabinet statement said.

Officials and the state MENA news agency later said the "casualties" were being transferred to nearby hospitals.

At Saint Petersburg's Pulkovo airport, anxious family members awaited news of their loved ones.

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Egyptian military planes have discovered wreckage inb a mountainous area of Sinai (AFP Photo/Patrick …

"I am meeting my parents," said 25-year-old Ella Smirnova, a tall young woman seemingly in shock. "I spoke to them last on the phone when they were already on the plane, and then I heard the news."

"I will keep hoping until the end that they are alive, but perhaps I will never see them again."

A senior Egyptian aviation official said the plane was a charter flight operated by a Russian company carrying 217 passengers and seven crew members.

The official said the plane was flying at an altitude of 30,000 feet when communication was lost.

Sergei Lzvolsky, an official with the Russian aviation agency Rosaviatsia told Interfax news agency that the Kogalymavia Russian airline had departed Sharm el-Sheikh at 5:51 am local time (0351 GMT).

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The aircraft set off from Sharm el-Sheikh at 5:51 am local time (AFP Photo/Mohamed el-Shahed)

He said the Airbus 321 did not make contact as expected with air traffic controllers in Cyprus.

- Communication lost -

"Communication was lost today with the Airbus 321 of Kogalymavia which was carrying out flight 9268 from Sharm el-Sheikh to Saint Petersburg," Lzvolsky later told Russian television networks.

"The plane departed Sharm el-Sheikh with 217 passengers and 7 crew members. At 7:14 Moscow time the crew was scheduled to make contact with... Larnaca, however this did not happen and the plane disappeared from the radar screens."

The flight was scheduled to land at St Petersburg at 0912 GMT, he said.

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An Egyptian army post in Sinai at the border with Israel (AFP Photo/Menahem Kahana)

The contents of the plane's last communication with ground crews were not immediately disclosed.

The wreckage was found in a mountainous area roughly 100 kilometres (60 miles) south of the North Sinai town of El-Arish, Egyptian officials said.

State television reported that Prime Minister Ismail Sharif was headed to the site of the accident.

The last major commercial airliner crash in Egypt happened in 2004, when a Flash Airlines Boeing 737 plunged into the Red Sea after taking off from Sharm el-Sheikh.

The 148 people aboard that flight, most of whom were French, were killed.

Millions of tourists, many of them Russian, visit the resort town, one of Egypt's major draws for tourists looking for pristine beaches and scuba diving.

The resort, and others dotting the southern Sinai Red Sea coast, are heavily secured by the military and police as an Islamist militant insurgency rages in the north of the restive peninsula, which borders Israel and the Gaza Strip.

Militants in the north who pledged allegiance to the Islamic State group have killed hundreds of soldiers and policemen since the army ousted Islamist president Mohamed Morsi in 2013.

And they're still dreaming.

But thanks to the efforts of the Max Planck Institute for Plasma Physics, experts hope that might soon change.

Last year, after 1.1 million construction hours, the institute completed the world's largest nuclear-fusion machine of its kind, called a stellarator.

The machine, which has a diameter of 52 feet, is called the W7-X.

And after more than a year of tests, engineers are finally ready to fire up the $1.1 billion machine for the first time. It could happen before the end of this month, Science reported.

The black horse of nuclear reactors

Known in the plasma physics community as the "black horse" of reactors that use nuclear fusion, stellarators are notoriously difficult to build.

The GIF below shows the many different layers of W7-X, which took 19 years to complete:

Only a handful of stellarators have been attempted, and even fewer have been completed.

By comparison, the more popular cousin to the stellarator, called a tokamak, is in wider use. Over three dozen tokamaks are operational around the world, and more than 200 have been built throughout history. These machines are easier to construct and, in the past, have performed better as a nuclear reactor than stellarators.

But tokamaks have a major flaw that W7-X is reportedly immune to, suggesting that Germany's latest monster machine could be a game changer.

How a nuclear-fusion reactor works

(Uploaded by Matthias W Hirsch on Wikipedia)
Schematic of the average tokamak. Notice how it has fewer layers than the stellarator and the shape of the magnetic coils is different.

The key to a successful nuclear-fusion reactor of any kind is to generate, confine, and control a blob of gas, called a plasma, that has been heated to temperatures of more than 180 million degrees Fahrenheit.

At these blazing temperatures, the electrons are ripped from their atoms, forming ions. Under these extreme conditions the repulsive forces, which normally make ions bounce off one another like bumper cars, are overcome.

The ions are therefore able to collide and fuse together, which generates energy, and you have accomplished nuclear fusion. Nuclear fusion is different from what fuels today's nuclear reactors, which operate with energy from atoms that decay, or break apart, instead of fusing together.

Nuclear fusion is the process that has been fueling our sun for about 4.5 billion years and will continue to do so for another estimated 4 billion years.

Once engineers have heated the gas in the reactor to the right temperature, they use super-chilled magnetic coils to generate powerful magnetic fields that contain and control the plasma.

The W7-X, for example, houses 50 six-ton magnetic coils, shown in purple in the GIF below. The plasma is contained within the red coil:

The difference between tokamaks and stellarators

For years, tokamaks have been considered the most promising machine for producing energy in the way the sun does because the configuration of their magnetic coils contains a plasma that is better than that of currently operational stellarators.

(Science Magazine on YouTube)
Schematic of W7-X.

But there's a problem: Tokamaks can control the plasma only in short bursts that last for no more than seven minutes. And the energy necessary to generate that plasma is more than the energy engineers get from these periodic bursts.

Tokamaks thus consume more energy than they produce, which is not what you want from nuclear-fusion reactors, which have been touted as the "most important energy source over the next millennium."

Because of the stellarators' design, experts suspect it could sustain a plasma for at least 30 minutesat a time, which is significantly longer than any tokamak. The French tokamak "Tore Supra" holds the record: Six minutes 30 seconds.

If W7-X succeeds, it could turn the nuclear-fusion community on its head and launch stellarators into the limelight.

"The world is waiting to see if we get the confinement time and then hold it for a long pulse," David Gates, the head of stellarator physics at the Princeton Plasma Physics Laboratory, told Science.

Check out this awesome time-lapse video of the construction of W7-X on YouTube, or below:

Although it’s more audio than video, it’s fascinating to hear the tension as a pair F-14 Tomcats intercept and engage a pair of Libyan MiG-23 Floggers over the Gulf of Sidra. Small segments have been released before of the historical 1989 shoot-down, but this release includes the entire intercept leading up to the dogfight.