Climbing through Science: a trip through the firstparticle collider.

Peter FisherAuthor’s Note: We made two different visits to the ISR the sameweek with slightly different teams. The routes and significant eventswere the same each trip, so I have written as if it had been a singletrip. The pictures are all from the second trip.

Particle accelerators create high-energy beams of particles that aredirected at matter in order to learnhow they interact. In the 1970’s,the idea came up to try to collidetwo beams of particles head-on inorder to attain harder collisions(think of the damage of hitting aparked car compared to a head-oncollision with a car going in theopposite direction.) One of theearly colliding beam machines wasthe Intersecting Storage Rings (ISR)at the CERN particle physics

laboratory near Geneva, Switzerland.

The ISR has beenshutdown for many yearsand the magnets that hadguided the particle beamsremoved. The 1 km circularhall has been convertedpartly into work areas forthe new CERN machine, theLHC and partly into a largestorage area. One night,after a long day ofmeetings at CERN, we

Figure 2 - Door 291.

Figure 1 - CERN Meyrin Site map.

decided to infiltrate and see what was being stored.

As we all work at CERN, the rules were strict: no passing signs whichsaid “DO NOT ENTER” in any language, no entry to radiation areasand no entry to work areas. We began by trying the entry doors tothe 1 km circular beam hall, which were of course all locked.However, we did notice a brightly light door labeled “291” with stairsleading up and down.

A quick check revealed the stairs going up dead ended into a utilityspace. However, the going down, we found ourselves in a tunnelleading inward, toward the center of the ISR ring.

The tunnel was lined withcable trays and its usebecame immed i a t e l yobvious: in order to controlthe beams and distributepower to the hundreds ofmagnets and acceleratingcavities which controlled theparticle beams, hundreds ofcables were needed to carrysignals and power to andfrom the main control room.The tunnel we had enteredran around inside the ISR

hall. We reasoned there must be places where the cables passthrough to the ISR hall which we could perhaps use for access.

We began walking down the hall toward the center of the ring.There were sounds of rushing air and running water. After 100m, wecame to a T-junction with a circular tunnel which we then followed.As we made our way around the circular tunnel, radial tunnels backto ISR hall. The first few dead-ended; the cable trays lead tochannels up a sheer hall or conduits through the wall.

Figure 3 - Tunnel lined with cable trays forthe accelerator power and control system.

The sound of running water grew louder and we came upon a largepuddle below the catwalk where it appeared the pipe had rustedthrough. As we moved away from the water, we became aware of abreeze, which grew stronger as we moved along. The breeze, now awind, was coming from the next radial tunnel, which we followed.Coming around a bend, we found a ladder going up along the wall.

The ladder rose about 20mto a room at the top. Theclimb was not difficult, but itwas a long drop so we wentslowly. At the top of theladder was a utility spacewith a large ventilator backfrom the top of the ladder.This was the source of thewind we had followed to theladder and there was a largehole in the floor below thevent i la tor that wassurrounded by a railing.Looking down in the hole,we could see stacks of

boxes on a shelf and, peering around the shelf, about 15 m below, agreen floor with yellow stripes. The room below was followed acurve was about 10 m wide andcould only be the ISR hall. Ifwe could climb down from theventilator, we would achieve ourgoal.

Stepping over the railingsurrounding the hole onto theboxes below, we found theboxes were heavy and largeenough for us to step onto andwork our way to the edge of theshelves. The shelves were

Figure 4 - Ladder at the end of radialtunnel.

Figure 5 - Climbing down the shelves.Ventilation hole is at the top.

spaced about four feet apart and once we reached the edge, wecould climb down them to reach the floor.

Upon reaching the floor, we had alook around. Both sides of the hallwere lined floor to ceiling withshelves hold ing e lectr ica lequipment. After some looking,we realized that the componentswere from the high power radiofrequency system for a lateracce lerator , the 27 kmcircumference Large ElectronPositron (LEP) collider. Theelectrons and positrons in LEP hadbeen driven to very high energies using immense cavities filled withelectromagnetic waves. The electronics would surf along the waveand thus gain energy as they circled around the ring. The cavities,their power supplies and control systems were stored here in the ISRtunnel. They rf system and its related components filled the shelvesfloor to ceiling about 5 m deep on each side of the hall for about 100m of the length of the hall.

We found a few of the original copper cavities: they were sphericalcopper chambers 1.5 m in diameter. The copper surface on theinside was highly polished to prevent electrical losses. The electron

beam would pass through

Figure 6 - ISR Hall lined withshelves holding the LEP RF system.

Figure 7 - Copper RF cavity.

Figure 8 - Inside of copper RF cavity.

along a diameter of the sphere and pick up a little energy from thefields inside. Following along the corridor, we found a radiation areathat held the 350 replacement cavities, along with a giant forklift formoving them. As the area was marker a dangerous, we did notenter past the sign.

A chirping sound down a corridor off the main hall attracted outattention. The corridor ended in large double doors, which led out ofthe ISR. Just by each door, there was a radiation monitor forchecking equipment and people being brought in and out. Thechirping was caused by cosmic rays that the detector picked up.

Figure 9 - Replacement RF cavities in background. Foreground shows largeforklift and radiation sign to the left.

We checked each other using the hand held wand and found wewere clean. We left the hall through the large double doors.

Our excursion through the ISR was immensely interesting: weclimbed through a piece of scientific history. There are six otherlarger accelerators at CERN left to explore.