A METHOD TO MEASURE THE PRESSURE PROFILE INSIDE EVACUATED TUBES WITH HIGH-VOLTAGE ELECTRODES

We developed a method to determine the pressure distribution in the el ectrode region of electrostatic accelerators. Direct measurement of th is distribution is not possible: the electrodes are maintained inside a high pressure vessel and the presence of vacuum gauges would disturb the beam optics. The method is based on measuring the energy distribu tion of the atomic ion beams and identifying features associated to co llisions with residual gas molecules. The procedure is also applicable to any other evacuated tube in the presence of a static longitudinal electric field. The feasibility of the method was verified ill a 1.7 M V commercial particle accelerator using its facilities (accelerator tu bes, particle beam, stripper, etc.). The measurements also revealed ch aracteristics of the field structure inside the accelerator tube and t he occurrence of leaks.