LHC即将刷新高能记录，但是，又出问题了……

上月底，LHC开始接收质子束并注入能量，而本月底，将达到创纪录的 7TeV 的能量。

Full steam ahead!

Following the completion of the campaign to improve the reliability of the cabling for the new Quench Protection System, the main dipoles and quadrupoles of the eight LHC sectors have now been commissioned up to a current of 6 kAmps. In the early hours of Sunday 28 February, the beams were circulating again in the LHC: the longest run in CERN's history has just started!

                               
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One of the first beam shots in the LHC on Sunday 28th February early morning.

During the campaign that the LHC teams carried out over the last few weeks to ensure the correct functioning of the LHC magnets at high current, the several thousand channels of the new Quench Protection System were verified and the resistance of the 10,000 splices connecting the magnets was precisely measured, showing no unacceptably anomalous values.

In order to operate the LHC without risk to the magnet system, it must be possible to switch off the magnets and extract the stored energy in about ten seconds at all times. At the same time, efforts have been concentrated on correctly tuning the parameters of the Quench Protection System in order to avoid it triggering the beam dump when not technically necessary.

Having completed the magnet-powering tests at 6 kAmps, the hardware commissioning team has handed the machine over to the operation team. The initial operations have included tests without beams to verify the correct functioning of all the systems (magnets, radiofrequency, collimators, injection and beam abort systems, etc.) in unison.

By midnight on Saturday 27 February the machine was ready to receive the beams, and injection started. By early the next morning both beams were circulating again in the LHC (see figure). Sunday was then dedicated to the optimization of the beam trajectory and of the other optical parameters, as well as to the control of the beams by the radio-frequency cavities that keep the protons bunched.

In the CERN Control Centre, the operators are now working on optimising the beam parameters and improving the beam lifetime. The energy of the proton beams is currently 450 GeV. The first energy ramp-up is expected in the next few days. High-energy collisions are planned for the end of March.

by [email=Bulletin-Editors@cern.ch?subject=About%20your%20article%20at%20http%3A//cdsweb.cern.ch/journal/CERNBulletin/2010/10/News%2520Articles/1246745%3Fln%3Den]CERN Bulletin[/email]

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LHC计划将质子碰撞的中心能量提高到14TeV，即上述创纪录能量的两倍。不过，根据BBC的一则消息（我刚才未能在CERN官网上找到相关内容），因为一些结构设计的缺陷，为保证安全，LHC将在2011年底再次长时间关闭检修。唉，别等到国际直线加速器建好了LHC还没能达到14TeV。

LHC to shut down for a year to address safety concerns

By Judith Burns Science reporter, BBC News

                               
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The damage that occurred in 2008 took 14 months to repair


A director at the Large Hadron Collider in Geneva has told BBC News that some mistakes were made in construction.

Dr Steve Myers said these faults will delay the machine reaching its full potential for two years.

The atom smasher will reach world record power later this month at 7 trillion electron volts (TeV).

But the machine must close at the end of 2011 for up to a year for work to make the tunnel safe for proton collisions planned at twice that level.

The machine only recently restarted after being out of action for 14 months following an accident in September 2008.

Dr Myers said: "It's something that, with a lot more resources and with a lot more manpower and quality control, possibly could have been avoided but I have difficulty in thinking that this is something that was a design error."
He said: "The standard phrase is that the LHC is its own prototype. We are pushing technologies towards their limits."

"You don't hear about the thousands or hundreds of thousands of other areas that have gone incredibly well.

"With a machine like the LHC, you only build one and you only build it once."

登录/注册后可看大图 The CMS detector can be put through its paces at reduced power

He said the second problem is not with the most complex technology but involves the copper sheaths around the superconducting joints in the tunnel.

The copper sheaths are a failsafe mechanism designed to take up the current if one of the magnets in the Large Hadron Collider warms up - an incident known as a "quench".

The 2008 accident caused one tonne of helium to leak into the tunnel and resulted in a series of "quenches" and a 40m Swiss franc (£24m) repair bill.

Engineers believe the machine is now safe to run at 7TeV but are anxious to avoid another breakdown.

So they have taken the decision to run the machine for 18 to 24 months at half-maximum power before switching it off for a year to carry out improvements to the 27km tunnel.

Dr Myers said the decision was taken jointly with the physicists working on the four giant particle detectors on the LHC.

He said they appreciate the chance to test their own equipment while the machine is running at half its maximum power.

Collisions at enormous energy

The Large Hadron Collider sends beams of protons in opposite directions around the tunnel at close to the speed of light. These cross and collide, smashing into each other with enormous energy.

The ultimate aim is to collide particles head on at 14TeV to recreate the conditions in the moments after the Big Bang.

Scientists hope they will see new subatomic particles in the debris and gain insights into how the universe came into being, billions of years ago.

The machine is buried 100m below the French-Swiss border.

Cern officials say running the LHC at 7TeV will enable physicists to explore another secret of the universe, namely the nature of the "dark matter" that accounts for most of the mass in the observable universe.

http://news.bbc.co.uk/2/hi/science/nature/8556621.stm

晕！又要停工？

回ＬＳ，貌似是的。