Virtual Tour
	Part Five

	A. Vault Interlocks We have now descended to the basement level - 15 metres below the cyclotron vault roof. An electrically operated interlock system guards the entrance to the vault. In order to enter the vault, a key must be removed from the interlock panel and used to open the door. If the key is removed, an electric circuit is broken, preventing the cyclotron from operating. The key release has to be requested via a telephone link to the main control room. These precautions are all taken to ensure that no one is in the cyclotron vault while "the beam is on" or shortly after it has been turned off. It takes several hours for the radiation levels to drop low enough before a team of TRIUMF's designated Atomic Radiation Workers (ARW's) can enter the cyclotron itself to perform maintenance work.
	B. Entry to the Cyclotron Vault Upon entering the vault all persons must put on overshoes. On exiting, the overshoes are removed and a frisker is used to check for radioactive contamination. It is a good idea to leave any credit cards, etc. at this station since the intense magnetic field from the main cyclotron magnet will delete their megnetic information.
	C. Underneath the Cyclotron Accelerator Chamber Looking underneath the cyclotron accelerator chamber we first notice a yellow magnet sector. The magnetic field here is so strong it disrupts the electronics in our camera equipment. The pictures shown here were taken in manual mode. The magnetic field presents a severe safety hazard, since steel tools and even heavy compressed gas bottles are attracted with great force to the magnets.
	D. Tie Rods Another noticeable feature is the tie rods on the underside of the cyclotron tank. During operation, the inside of the tank is almost a perfect vacuum. The rods, present both below and above the accelerator chamber, prevent it from collapsing due to atmospheric pressure. See Cyclotron Facts for more details.
	E. The Cyclotron Superstructure The superstructure which surrounds the cyclotron supports the magnets (total weight: 4000 tonnes) and prevents the accelerator chamber from imploding due to atmospheric pressure. Beside the giant cyclotron we see stairs leading to the top of the structure. Situated above the stairs is the moveable crane used for maintenance.
	F. Top of the Cyclotron From the top of the stairs, we have a good view of the cyclotron. Twenty-four jacks, evenly-spaced around the cyclotron, have been used to carefully lift the lid of the chamber (after releasing the vacuum) and the upper magnet (2,000 tonnes) to a height of 1.2 m (4 ft). To eliminate any warping of the accelerator chamber, computers are used to control the rate of lift of each jack to within 1 mm of each other (the thickness of a dime!).
3816x2522 JPEG	G. The Vacuum Tank About twice a year the cyclotron is shut down for maintenance. At these times the accelerator chamber is pressurized and opened. Remote-control robots enter the chamber first and are used to assess the radiation levels. Once the level and location of the radiation "hot spots" are determined, workers enter the chamber to check for worn or damaged components and to replace them. The process to seal, clean and empty the chamber of all particles, including water vapour and air, requires tremendous heat and vacuum pressure. Any foreign particles left in the chamber can disrupt the free motion of the hydrogen ions and reduce the quality of the ion beam. The worker shown in this picture is kneeling on one of the lower "dees" - so called because they are shaped like the letter "D".
	H. Dees The dees (a model shown) are the "electrodes" used to accelerate the hydrogen ions. The individual elements are the radiofrequency resonators. If you look closely you will see a small gap between the dees (centre horizontal line). By alternating the voltage in the dees from positive to negative and back to positive in a cyclic pattern (23 million times per second!), a positive polarity dee is always presented to approaching negatively charged hydrogen ions as they cross the gap. The other dee, having the opposite polarity, doubles the voltage difference across the gap. The maximum voltage difference is 186,000 volts. Hence the hydrogen ions are boosted in energy on each half turn in the cyclotron. Only those ions crossing the gap during the polarity change will be accelerated. Thus, the hydrogen ions are injected into the centre of the cyclotron in bunches, move through an increasing orbit, and leave in bunches. This method of accelerating particles permits TRIUMF to constantly inject ion "packets" into the cyclotron thus providing a constant high intensity output. While other particle accelerators may produce faster beams, few can produce as an intense a beam as TRIUMF.
	I. Beam Line Extraction Magnets After the electrons are stripped from the hydrogen ions, the remaining protons follow a predetermined curved path out of the cyclotron and into one of the three main beam lines. This picture shows beam line 1 at its emergence from the cyclotron. From here this proton beam is guided by a group of huge electromagnets into meson hall. Magnets are used to bend a beam's path. Also, because the protons in the beam are all positively charged and repel each other, the proton beam spreads and therefore must be "focused" from time to time using a set of magnets. (Next stop: outside south side.)

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