Beam Interlock System


When in one of the beam areas the beam is going to be switched on, this area becomes a Prohibited Area ("Sperrbereich") due to the radiation. Therefore, the beam areas are protected by an interlock system. At DESY, the doors to interlock areas are colored yellow.

Before setting the interlock of an area, you have to attend the safety instructions by test beam coordinators. The safety briefing is usually offered every Monday at 13:00 in the ATLAS Conference Room (Building 1c/room O1.310, 1st floor). After this, the permisson to set the interlock can be set in the DACHS system.

In hut 21/22, there is a cabinet with keys. Do not remove them from there.
These keys are only for safety during repairs or maintenance work and are not needed for the user operation of the interlock system.

Setting the Interlock and Starting the Beam

The interlock and beam can be controlled via the touch screen -including the hardware buttons below- in the rack in the user hut.

Area Search

The area search is done by a single person only! You start the search with your DACHS card and end it with the same card. This ensures that the person doing the area search has left the area before switching on the beam. This only works if only one person is in the area when the search is done.

To start the search you swipe your DACHS card across the reader at the area entrance. If you have the permission to set the interlock, the reader will light up green.

Then you enter the area and switch on the light barrier at the entrance by pressing the button labeled “Set light barrier" right behind the door. Note that you don't have to close the yellow door during the area search.

After this, the yellow interlock light at the area entrance and the green search buttons in the area will light up. Also, an announcement that the interlock search is going on in German and English will run in the area.

The area search can be stopped by a second swiping of the DACHS card at the reader at the entrance. Also passing the light barrier will break the search. This means you should not enter an area, when the yellow light at the entrance is on.

Now you have to go through the complete area checking that noone is still inside. To confirm you checked in all corners, there are search buttons installed in the areas which you have to press so the green light goes out. Be careful not to press accidentally the red emergency-off, which is next to some of them.

After confirming all search buttons, the “Light barrier muting” button directly at the entrance will light up. To exit the area without breaking the light barrier, press this button. After this you have about 6 seconds to leave the area before the barrier switches on again. This can only be done once.

After exiting the area, close the door behind you and press the now active "Set button main door" at the panel at the area entrance. Then you swipe your DACHS card a second time across the reader to finish the search procedure.

Now the light at the door will switch from yellow to red and a warning in German and English will run for 30 s in the area, that the beam is going to be switched on.

After the warning finished, the door will be locked from outside; from the inside it could still be opened. Then the area is ready to switch on the beam.

Shutter Operation and Breaking the Interlock

When you come back to the hut, you should find now the "Home" display of the interlock control with all items on green.

Switch there to "Logic + Operation" to operate the shutter.

You can open and close the beam shutter (BS) via the two buttons "Open BSXX.Y" and "Close BSXX.Y" on the touch screen, where XX.Y stands for the number of your beam area.

To get beam in the area, you still have to switch on the beam magnet and choose the beam energy.

To break the interlock and access the area again, close the beam shutter and press "Break door interlock Area TXX” on the touch screen. The door to the beam area will be released and the warning light at the entrance switched off.


To open the yellow interlock door in case of an emergency after the interlock has been set and it is locked, you can use the key in the red box next to it.

After the interlock is set and the area is ready for beam, the orange warning lamps will flash while the acoustic warning is running that the beam is going to be swiched on.

In case you are inside the area when this happens, you have about 30 seconcs to save your life. Do not hesitate to hit an emergency-off button or, in case you are close to it, open the interlock door and leave through the light barrier. Both will break the interlock and keep the shutter from being opened.


All areas are equipped with an additional "radiation alarm". In the case the area would not be interlocked but the shutter would be opened, this sign will switch on and there will be a loud warning signal. When this happens leave the area immediately and avoid crossing the beam path while doing so. Keep other persons from entering and call the machine control room (Tel. 3500) to immediately switch of the DESY II accelerator. After this inform the test beam coordinators.