Jets and Shock Waves from Cavitation 



Ellis's paper. It is necessary, of course, to have such centers of high com- 

 pression in order to generate strong shock waves. 



Centers of high compression are also required to explain another well- 

 known phenomenon associated with cavitation, namely, the faint luminescence 

 that is emitted from cavitation, otherwise known as sonoluminescence. Cur- 

 rently it is believed that this emission is thermal in origin and is caused by the 

 rapid compression of small traces of permanent gas in the collapsing bubbles. 

 Temperatures as high as 10,000 °K are considered likely. If the effects of heat 

 conduction and vapor condensation are considered, very high compressions in- 

 deed would be required to reach such temperatures. Observations have been 

 made of the luminescence from the cavitation cloud at the end of a magneto- 

 strictive transducer. 



I am indebted once more to Professor Flynn for Fig. D3 that he took of 

 such a cloud through a light intensifier. The intensification factor is of the 

 order of j-O"* and the exposure time is 1/5 sec. The transducer surface is 



Fig. D3 - Intensified view of luminescence 

 emitted from cavitation 



157 



