Effects of electron-anode interactions in applied-B ion diodes
- Sandia National Labs., Albuquerque, NM (United States)
The transverse magnetic field in an applied-B ion diode is designed to minimize electron loss to the anode. However, 3-D particle-in-cell (PIC) simulations show that electron loss escalates once the ion current is sufficiently enhanced such that the ion mode instability dominates. Thus the transition from the diocotron mode to the ion mode is accompanied not only by an increase in ion beam divergence, but also by an increased flux of high-energy electrons striking the anode surface. Coupled electron-photon Monte Carlo simulations have been used in conjunction with PIC diode simulations to assess electron reflection, energy deposition leading to anode heating and thermal desorption of contaminants, enhanced ionization of desorbates due to secondary electron emission, and photon production. Electron reflection is included in the 3-D PIC simulations, and although no macroscopic diode effect is seen in the present model, the anode heating profile is affected by high-energy reflected electrons, and low-energy secondary electrons may enhance the effective electron-impact ionization cross-section by factors of 7--10 for desorbed contaminants. The high spatial non-uniformity in the predicted electron loss profile leads to local hot spots on the anode surface which exceed 300--400 C soon after the ion mode transition. Thermal and stimulated desorption results in complete desorption of contaminants with 15--20 kcal/mole binding energies during the power pulse in high-dose regions of the anode surface. Predicted time-dependent photon distributions from electron-anode collisions are available for comparison with X-ray detector measurements.
- Research Organization:
- Sandia National Laboratory
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC04-94AL85000
- OSTI ID:
- 323594
- Report Number(s):
- CONF-970559--
- Country of Publication:
- United States
- Language:
- English
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