The effect of magnetic field strength on the time evolution of high energy bremsstrahlung radiation created by an electron cyclotron resonance ion source

An electron cyclotron resonance (ECR) ion source is one of the most used ion source types for high charge state heavy ion production. In ECR plasma the electrons are heated by radio frequency microwaves in order to provide ionization of neutral gases. As a consequence, ECR heating also generates very high electron energies (up to MeV region) which can produce a vast amount of bremsstrahlung radiation causing problems with radiation shielding and heating superconducting cryostat of an ECR ion source. To gain information about the time evolution of the electron energies in ECR plasma radial bremsstrahlung measurements were performed. JYFL 14 GHz ECR ion source was operated in pulsed mode and time evolution measurements were done with different axial magnetic field strengths with oxygen and argon plasmas. Bremsstrahlung data were analyzed with a time interval of 2 ms yielding information at unprecedented detail about the time evolution of high energy bremsstrahlung radiation from an ECR ion source. It was observed, for example, that reaching the steady state phase of the plasma bremsstrahlung requires several hundred milliseconds and the steady state time can be different with different gases. (C) 2008 Elsevier B.V. All rights reserved.