THEV (Nu-Trek)

Purpose : Model complex diodes

Description : THEV uses a Thévenin equivalent circuit model of a diode with a diode gap model.

A fourth order Runge-Kutta differential equation solver is used to calculate the beam potential & current. Typical diode gap models are based on those developed at NRL and cover diodes immersed in axial magnetic fields, ring beam diodes, and pinching diodes. Current flow starts after the electric field exceeds a threshold value. Initially, the current is based on the Child-Langmuir current limit with a turn on time. The critical current limit is used if the Child-Langmuir current exceeds critical current. An additional constraint exists for initiating the bi-polar flow at the cathode: If the anode surface is heated to 300-400 deg. C, then significant ions are formed & flow to the cathode which neutralizes the negative space charge at the cathode. This + ion formation is the result of de-absorbing gases from the anode surface which are ionized by the electron beam.

The flux of electrons near the anode is enhanced for higher Z anodes because of backscattering. The secondary and backscattered electrons from the anode are returned to the anode because of the diode electric field. For most anodes the surface dose can be approximated by a constant that increases with atomic number. This constant is the product of the dose/fluence ratio by the electron range. E.g., this dimensionless number is 0.973, 1.33, 2.11, and 4.76 for C, Al, SS, and Ta, respectively. These numbers were calculated with ITS CYLTRANM for a 1.0 MeV electrons with a normal incidence angle with 1% accuracy.

ESTRESS (Nu-Trek)

Purpose : Calculate E-field diode stresses

Description :ESTRESS uses the time dependent voltage at the diode insulator and the computed E-field components across the insulator surface to estimate if the design is acceptable in terms of flash over. Normally, the E-field is designed to be 60% of the breakdown field. This is the 1% breakdown probability.

TEMPS3E & TEMPS3P (Nu-Trek)

Purpose : Calculates the in-depth time dependent temperature resulting from e-beam or proton beam deposition. Used to:

• Predict the in-depth melting and rate of cooling during re-solidification.
• Predict the anode temperature in rep-rated machines
• Design survivable anodes

Description : TEMPS3E calculates the in-depth time dependent temperature of a slab with a time dependent electron dose deposition. A finite difference procedure is used with small time increments to calculate the re-distribution of temperature during the energy deposition period. TEMPS3P calculates proton in-depth heating. These codes assume that molten material on the surface remains in thermal contact with the slab and uses the latent heat of fusion during the phase transition. Material is removed from the slab when it starts to boil but the vapor still absorbs the incident energy.

ESTAT, Finite element electrostatic field (Field Precision)

Purpose : Used for calculating 2D or cylindrical geometry electrostatic potentials and electric fields

Description : Finite element electrostatic field code.

BSTAT, Finite element magnetostatic field (Field Precision)

Purpose : Used for calculating 2D or cylindrical geometry magnetostatic fields

Description : Finite element magnetostatic field code.

TRAK, Finite element code for charged particle optics (Field Precision)

Purpose : Used for studying electron and ion trajectories in embedded electric and magnetic fields.

Description : Finite element code for charged particle optics

PRESS (Nu-Trek)

Purpose : PRESS calculates the chamber pressure given the pumping speed S, the volume V, the extra gas leak rate Q, and the ultimate pressure obtainable with a given pump.