Cluster target

An internal target should be so thin that it doesn't affect the beam significantly, on the other hand it should be thick enough to reach a reasonable number of the required reactions. These requirements can be fulfilled with a cluster target where cooled gas (e.g. hydrogen) is pressed through a so-called 'Laval'-nozzle.

Cluster generation in a Laval nozzle

Inside the nozzle the gas is cooled by the expansion and molecules freeze together forming clusters. Using skimmers free gas molecules are peeled off the cluster beam. So the rest gas pressure in the target chamber is very low (the COSY beam isn't affected), only in the beam-target interaction region the target density is high enough. After traversing the target chamber the clusters warm up and are pumped away.
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Last updated: 15-December-1997 by T.Sefzick