In a previous article on science-fiction weapons systems we talked about the Relativistic Kill Weapon: a massive object accelerated to near light speed and carrying colossal kinetic energy. But there is another way to hit an enemy with relativistic firepower: the particle beam weapon.
The Large Hadron Collider is not at first sight an ideal weapon system. First of all it’s physically a 17 mile (27 km) long circular tunnel, buried beneath the French-Swiss border at a depth in some place of over 570 feet (175 m): hard to deploy against an enemy. However, the concept of a beam weapon was explored in the SDI (‘star wars’) programme for ICBM defense and a weaponised LHC would be a formidable anti-spacecraft system.
The LHC is a proton accelerator. It gets its protons from a tank of hydrogen gas and then accelerates them to their peak 7 TeV energy where they circulate in the LHC ring for 10 to 24 hours while collisions occur at the four intersection points.
How fast are the protons finally going? Their velocity is just a jogging pace (7 mph) slower than light but in relativity the factor which measures relativistic effects is the gamma factor (γ) which tends to infinity as v → c. At the LHC the proton gamma is 7,460. At that enormous γ, a starship journey from earth to the nearest star, Proxima Centauri (4.2 light years away) would be just a five hour jaunt for the crew!
The LHC scientists are interested in those protons in the contra-rotating bunches which hit each other: the collisions lead to new physics. But from a weapons point of view we are more interested in the majority which miss. These are completely lethal. In dealing with them, the LHC engineers had to answer the question: how do you stop the fastest objects ever to travel on the earth?
The engineering team simulated the effects of the proton beam hitting a copper tube 4 inches in diameter and 16 feet long. In the top picture of the diagram above we see the situation half a microsecond after beam impact. The beam has already penetrated 7 feet (around 2 metres) into the (purple-colored) tube with a core overpressure of 30 GigaPascals (300,000 atmospheres). The protons and their collision debris are literally gouging out the centre of the target.
The lower picture shows the situation at 9.5 microseconds where the beam has now penetrated the entire 16 feet (5 metres) of the (red-colored) tube. This is a density plot and shows the vaporised core as having less than 1% of the original copper density. Based on this simulation, the entire 89 microsecond beam-pulse of the Large Hadron Collider would penetrate 115 feet (35 metres) of solid copper.
At CERN they take care to defocus the beam first, spreading it over the face of the beam dump. It turns out that carbon is better than copper in stopping the now-defocused beam so the actual LHC beam dump absorber is engineered as a two foot diameter, 23 foot long graphite cylinder contained in an outer steel cylinder. This is water-cooled and surrounded by 750 tonnes of concrete and iron shielding in a dedicated enclosure. The LHC protons finally come to rest in a cascade of secondary particles, deep inside a blazingly-hot carbon tube.
In a future weaponised version, it could have been a missile or spacecraft: stabbed, incinerated and disabled in 100 microseconds.
Note: in a practical weapon we would accelerate both protons and electrons and combine them into a neutral beam. This prevents electrostatic divergence of the beam as well as some (probably ineffectual) defensive options