ECR BREAKDOWN OF A LOW-PRESSURE GAS IN A MIRROR CONFINEMENT SYSTEM WITH A LONGITUDINAL MICROWAVE-POWER INJECTION

The effect of the gas pressure and location of the ECR region (at a co nstant level of the microwave power) on the initiation of the ECR disc harge in a mirror device is studied. The microwave (MW) radiation is i njected in the longitudinal direction. Good agreement is demonstrated between experimental results and theoretical estimates for the breakdo wn threshold in a low-pressure gas; these estimates take into account losses of electrons in their resonant interaction with the MW pumping. It is found that a dielectric window positioned in the magnetic mirro r region and intended for the injection of the MW radiation into the v acuum chamber greatly affects the discharge.