Plasma potential measurements with a new instrument.
An efficient and fast instrument to measure the plasma potential of ECR ion sources (ECRIS) has been developed at the Department of Physics, University of Jyvaeskylae (JYFL). The operating principle of the instrument is to measure the energy of the ion beam by applying a decelerating voltage to a mesh located in the beam line after mass analysis. The plasma potential is determined by measuring the current at the grounded electrode situated behind the mesh as a function of this adjustable voltage. The measurements were performed with ECR ion sources at JYFL (6.4 and 14 GHz) and at Argonne National Laboratory (14 GHz). The plasma potential was measured as a function of different source parameters such as microwave power, gas feed rate (with different gases), voltage of the biased disk and magnetic field strength. The effects of gas mixing and double-frequency heating were also studied. The energy of the ions extracted from an ECRIS plasma comes from the source potential, plasma potential and the thermal energy of the ions. In order to distinguish the effect of the ion temperature on the measured curve simple computer simulations were performed. With the aid of the simulation and assuming a certain potential profile and Maxwellian velocity (energy) distribution of the ions, it was seen that the ion temperature should affect the shape of the measured curve in the region where the adjustable deceleration voltage is close to the value of the plasma potential. In the measurements it was observed that the shape of the curve in this region changed dramatically when gas mixing was used. However, the effect was typical only for low charge states of the heavier element while the curves measured with higher charge states remained almost unchanged. The effect of gas mixing on the ion temperature will be discussed based upon the obtained results.
- Research Organization:
- Argonne National Laboratory (ANL)
- Sponsoring Organization:
- SC; FOR
- DOE Contract Number:
- AC02-06CH11357
- OSTI ID:
- 925236
- Report Number(s):
- ANL/PHY/CP-115990
- Country of Publication:
- United States
- Language:
- ENGLISH
Similar Records
Effect of the gas mixing technique on the plasma potential and emittance of the JYFL 14 GHz electron cyclotron resonance ion source
A new plasma potential measurement instrument for plasma ion sources