Results of a gas-ionization beam size monitor at the final focus test beam

A new type of gas-ionization monitor, built at Orsay, has been used to opti mize and measure the transverse beam dimensions of the Final Focus Test Bea m at SLAC. This monitor detects the ions created by the beam to probe its s pace charge field and to derive both transverse dimensions. The ultimate va lues measured with the monitor are 1.5 mu m x 60 nm. Moreover, the high sen sitivity of the monitor has been used to detect and cancel out detrimental "banana" shapes of the beam. (C) 1999 Elsevier Science B.V. All rights rese rved.