TRIM code

The reflection of carbon atoms and ions at the limiter or divertor surfaces in the ERO modeling is determined by TRIM [29], However, the binary collision approximation used in the TRIM code is no longer valid at small energies of the incoming particles where chemical effects start to influence the interaction of the particles with the solid. To take this into account reflection coefficients calculated with a molecular dynamic code MolDyn [55] were implemented. 

A computer simulation based on a binary collision approximation (BCA) code MARLOWE was used to investigate the evolution of collision cascades in monazite (Robinson 1983). As with the TRIM code (Ziegler et al. 1985), the trajectories of the ions are divided into distinct binary or two-body encounters. The TRIM code, however, does not account for crystal structure and the atoms are placed randomly whereas, MARLOWE is designed to handle atomic-scale periodicity. Using MARLOWE, Robinson (1983) found evidence for amorphization via overlap of amorphous domains that formed within the cascade. 

The binary collision approximation (BCA) model was the first to be used in computer simulations of ion-solid interactions (Bredov et al, 1958). The usefulness of computer simulations was further demonstrated by Robinson and Oen (1963) during their discovery of the channeling effect. Computer simulations based on the BCA model in essence fall into two categories, those that assume a crystalline structure of the solid and those that, as in calculations based on the TRIM code, assume a randomized or structureless target. 

F[G. 10. Projected trajectories for 10-keV H ions on carbon and gold (100 trajectories each) calculated with the TRIM code (after Eckstein, 1991). 

Fig. 13.3 Concentration depth profiles of boron atoms implanted at 100 keV into polyimid for different boron fluences (in atoms cm ). Rp (TRIM) is a projection of the ion path length on the original ion direction as simulated by TRIM code.

FIGURE 6 Oxygen depth profile for polyethylene implanted with 5 x 10 B /cm at 100 keV. The nuclear stopping power depth distribution csJculated by means of the TRIM code is shown for comparison. 

FIGURE 7 Boron depth profiles for polyethylene (PE) and polyamide 6 (PA) implanted with 5 X 10 B /cm at 100 keV. Theoretical depth profile for boron implanted in polyethylene is shown by the histogram (calculations were performed with the TRIM code is the theoretical projected range). 

Each kind of irradiation was carried out for 4 ion fluences 10 10 , 10 , and 10 cm the fluence is the number of ion by surface unit. The Table I gives some irradiation parameters determined by the TRIM code ". 

The code requires internal ahgnment within the dimensional limits specified in the welding procedure and the engineering design without specific dimensional hmitations. Internal trimming is permitted... 

Removal of a few base pairs at V(D)J junctions occurs frequently. An early suggestion to account for this truncation was that an exonuclease trims the coding ends before they are joined (Alt and Baltimore, 1982), but the enzyme responsible has not yet been identified. Lewis (1994a) has pointed out that it is even possible that trimming results from endonucleolytic rather than exonucleolytic activity. The imprecision in junctional joining, as well as the removal or addition of bases not... 

It is important to mention that gas and vapours have different release characteristics than liquids, and that what is being discussed here is typical for gas, vapours and steam. Until 1985, the code allowed for liquid applications to have an overpressure of 25%. Until then, the same valve trim was used for both gases and liquids, resulting in the release characteristics shown in Figure 5.7. 

However, since 1985, the code has also required a maximum overpressure of also 10% on liquid valves. This meant manufacturers had to redesign many trims so that the same valve could be fitted for both gas and liquid. So it is important to know the age of a liquid valve in order to determine whether it will flow full capacity at 10% or at 25%. Also, blowdown on liquid spring-operated valves was and is still rather unstable, and can be as high as 30% depending on the design. The code does not specify a blowdown requirement for liquid valves. 

It was a positive development when the code insisted on special liquid trim designs besides the fact that the standard gas valve did not reach rated capacity at 10% for liquid, it was also demonstrated that the valve became very unstable during the opening cycle, as can be seen in Figure 5.9. 

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