CERN's CMS Detector

The Compact Muon Solenoid (CMS) detector is one of the big four experiments of the Large Hadron Collider (LHC), the world’s largest and most powerful particle accelerator. The LHC is part of CERN's accelerator complex in Geneva, Switzerland. The detector is located 100 meters underground near Cessy, France, at the opposite end of the LHC from ATLAS detector. It is 15 meters high and 21 meters long, and it weighs 14,000 tonnes.

This 120:1 scale model shows CMS' most important components. It is based on the original Technical Design Reports and the SketchUpCMS project. It was originally modeled by James Wetzel, W.G. Wetzel and Nick Arevalo with a grant from Don Lincoln. Some parts have been modified by me for ease-of-printing or cosmetics.

If you like this model but it seems too complex to print, check out the mini version!

Objective of CMS

CMS is a general-purpose detector with a broad physics programme ranging from studying the Standard Model (including the Higgs boson) to searching for extra dimensions and particles that could make up dark matter.

Components

The CMS detector is shaped like a cylindrical onion, with several concentric layers of components. These components help prepare “photographs” of each collision event by determining the properties of the particles produced in that particular collision.

Particle collisions occur at the very center of the detector, within the LHC accelerator's beam pipes. Inside the accelerator, two high-energy particle beams travel at close to the speed of light before they are made to collide. The beams travel in opposite directions in separate beam pipes – two tubes kept at ultrahigh vacuum. They are guided around the accelerator ring by a strong magnetic field maintained by superconducting electromagnets.

The CMS detector is built around a huge solenoid magnet. This takes the form of a cylindrical coil of superconducting cable that generates a field of 4 tesla, about 100,000 times the magnetic field of the Earth. The field is confined by a steel “yoke” that forms the bulk of the detector’s 14,000-tonne weight.

CMS acts as a giant, high-speed camera, taking 3D “photographs” of particle collisions from all directions up to 40 million times each second. Although most of the particles produced in the collisions are “unstable”, they transform rapidly into stable particles that can be detected by CMS. By identifying (nearly) all the stable particles produced in each collision, measuring their momenta and energies, and then piecing together the information of all these particles like putting together the pieces of a puzzle, the detector can recreate an “image” of the collision for further analysis.

Here is a brief description of each component represented in the model, as seen from the inside out:

Barrel_6_Tracker.stl
The Silicone Tracker is made of around 75 million individual electronic sensors arranged in concentric layers. When a charged particle flies through the Tracker layer, it interacts electromagnetically with the silicon and produces a hit -- these individual hits can then be joined together to identify the track of the traversing particle.

Barrel_5_ECAL.stl
The Electromagnetic Calorimeter (ECAL) measures the energy of electrons and photons by stopping them completely.

Barrel_4_HCAL.stl
The Hadron Calorimeter (HCAL) measures the energy of “hadrons”, particles made of quarks and gluons (for example protons, neutrons, pions and kaons).

Barrel_3_Solenoid.stl
The solenoid magnet, formed by a cylindrical coil of superconducting fibres. When electricity (18,500 amps!) is circulated within these coils, they generate a magnetic field of around 4 tesla. This solenoid is the largest magnet of its type ever constructed.

Barrel_2_Yoke.stl
The steel yoke that confines the high magnetic field to the volume of the detector.

Barrel_1_Muons.stl
The muon chambers, one of the most important components of CMS. There are two different types of muon detectors in the barrel, Drift Tubes (DTs) and Resistive Plate Chambers (RPCs).

Endcap_Full.stl and Endcap_Quarter.stl
The endcaps "close" the ends of the barrel. They are made of alternating layers of steel yoke and muon chambers, composed of Cathode Strip Chambers (CSCs) and Resistive Plate Chambers (RPCs).

HF_Full.stl and HF_Quarter.stl
The Hadronic Forward calorimeters (HF), part of the HCAL system, pick up the myriad particles coming out of the collision region at shallow angles relative to the beam line.

Airpad-16.stl
A compressed-air powered piston system to lift the endcaps when moving them into position. Each pad can lift ~350 tonnes!

Barrel_Feet-2.stl, Endcap_Feet-2.stl, HF_Riser-8.stl and HF_Table-2.stl
Support structures.

Print instructions

5% infill is good enough, there's no need to waste more plastic. I recommend honeycomb infill pattern at least for the endcap pieces, otherwise the top layers may not come out too well.

The following parts need to be printed with supports (on build plate only):

• Barrel_Feet-2.stl
• Endcap_Feet-2.stl
• Endcap_Quarter.stl and Endcap_Full.stl
• HF_Quarter.stl and HF_Full.stl
• HF_Table-2.stl

For a full model, print one of each file except for:

• Airpad-16.stl, print 16
• Barrel_Feet-2.stl, print 2
• Endcap_Feet-2.stl, print 2
• HF_Riser-8.stl, print 8
• HF_Table-2.stl, print 2

This model looks best when printed with at least 6 different colors, preferably at least 8. Different components should have different colors to be able to differentiate them properly. Here's how you should allocate the colors:

• Barrel_1_Muons.stl: color1
• Barrel_2_Yoke.stl: color2
• Barrel_3_Solenoid.stl: color3
• Barrel_4_HCAL.stl: color4
• Barrel_5_ECAL.stl: color5
• Barrel_6_Tracker.stl: color6
• Endcap_Quarter.stl and Endcap_Full.stl: color2, color1, color4 and color5
• Barrel_Feet-2.stl and Endcap_Feet-2.stl: color2
• HF_Quarter.stl and HF_Full.stl: color7 or color4 (if you must reuse)
• HF_Riser-8.stl: color8
• HF_Table-2.stl: color8 or color9
• Airpad-16.stl: color8 or color10

If you want to make it look more like the real thing, color1 should be white, color2 should be red, color8 should be yellow, color10 should be orange and the rest are up to you. Feel free to look at photos of the real thing for inspiration.

The two endcap pieces have alternating layers, so you should print them with color switches. Assuming a 0.2 layer height, 100% scale and the 2.0 parts, here are the color change points:

start with color2
2.6 : color1
6.0 : color2
8.6 : color1
11.8 : color2
17.6: color1
21.0: color2
26.8: color1
31.4: color2
34.8: color4
56.4: color5

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