**5. The control of EBP-modification process**

290 Practical Applications in Biomedical Engineering

particles.

injection window.

(*Ts*) were calculated for various modes of the EB scanning modes and various distances *z*0. The results of the computer simulations were verified experimentally for some modeling plasma-generating gases at pressures 1,0 < *Pm* < 50 Torr and dust materials (103 < *nd* < 106 cm-3). The diagnostic complex containing optical, microwave, calorimetric and some other devices was developed to measure values of *Q*(*x*,*y*,*z*), *Ts*, and densities of the plasma

Figure 2 illustrates the obtained experimental data in comparison with the calculations. It presents the radial distributions of the local power input (curves *1-3*) and steady-state temperature of the dust particles (curves *4*, *5*) in the air-EBP at pressure *Pm* = 4 Torr; *z*0 = 200 mm. All quantities plotted along the axis of ordinates are normalized by their values at the

The best combinations of the EBPR operating parameters were found for various plasmagenerating gases (1,0 < *Pm* < 50 Torr) and dust densities. For the experiments described they were: plasma generating gases – water vapor, oxygen, and helium, *Eb* = 30 keV, *Ib* = 2-5 mA, *Pm* = 9 Torr (water vapor), 4 Torr (oxygen) and 40 Torr (helium). The axis of the injected EB was scanned in *x*- and *y*-directions to form the square raster 13x13 cm2 in the plane of the mixing layer. Both continuous and intermittent modes of the EBP generation were applied. The container with the powder to be treated was located at the distance *z*0= 25 cm from the

**Figure 2.** Radial distributions of the local power input (curves 1-3) and steady-state temperature of the dust particles (curves 4, 5): 1 – simulations, 2 – calorimetric measurements, 3 – optical measurements, 4 – thermo-sensor measurements in the non-scanning plasma cloud, 5 – thermo-sensor measurements in

Both the experiments and simulation showed that the powder is uniformly heated to the temperature *Ts* <50 C and the concentrations of the chemically active plasma particles can reach 109-1011 cm-3 in the vicinity of the material to be treated. The concentrations of the

the plasma generated by the EB scanning along the *x*-axis.

point *x* = 0, *y* = 0, i.e. at the center of the given cross-section *z*0 of the plasma cloud.

In general the following parameters are responsible for the processes (and eventually for the results) of the materials modification:


Special software was developed to simulate the processes of the EBP generation and plasma-powder interaction, predict the effect of the modification under various experimental conditions, and optimize the treatment procedure. The description of the numerical algorithms and physical and plasmachemical models used for the software is beyond the paper involved. Here we demonstrate only the application of the software. Figure 3 presents the incident fluxes of the plasma particles on one cm2 of the container bottom (item *9* in Figure 1) calculated as a function of *x*- and *y*-distances from the container center. The EB axis scans in *x*- and *y*-directions, the amplitudes of scanning being equal to ±13 cm. Figure 3(a) illustrates the bio-material treatment in helium at pressure 40 Torr and Figure 3(b) - in water vapor at pressure 10 Torr. In the first case, four rigid peaks of the incident power appear at the raster corners and a sufficiently flat valley ≈5×5 cm−2 occurs between the peaks. The intensity of irradiation in the valley is about half of that on the peaks. In the EBP of water vapor a flat plateau ≈7×7 cm−2 with a uniform flux of plasma particles is formed. In real experiments the container with the material to be treated was placed in the zones of uniform incident fluxes.

If the container location and scanning parameters are known the values of plasma particles fluxes can be found in terms of local concentrations *n* (cm-3) of these particles inside the container. The functions *n* = *n*(*Pm*, *Ib, U*) were calculated for every plasmagenerating gas used in our experiments. The variations *n* = *n*(*Pm*) of the ion concentration

in the EBP of argon excited by the EB at two different values of the beam current *Ib* = 15 and *Ib* =7,5 mA (curves *1* and *2* respectively) are presented in Figure 4 as the example of numerical simulations. In this figure all concentration values *n* are divided by the maximum value of the particles concentration *n*max for *Ib* = 15 mA. The Figure 3 shows that there are optimal values of *Pm* for given *Ib* and *U*, these optimal values being individual for each gas.

Bio-Medical Applications of the Electron-Beam Plasma 293

1

*Pm* , kPa

**Figure 4.** Concentrations of excited particles in the EBP of argon filling the reaction chamber as a function of the gas pressure, *U* = 25 kV, *z* = 130 mm: *Ib* = 15 mA (curve *1*), *Ib* = 7,5 mA (curve *2*).

**EBP-modification** 

of mammalians.


artificially inserted pyrozolidine cycles; - bovine serum albumin (BSA, *Mr* = 66 kDa)

0,25

0,5

0,75

1,0

n / nmax

weight of 95% and 500 kDa, respectively;


**6. Original substances and methods used to investigate products of their** 

2

The plasmachemical modification of the following natural materials was studied in detail:




The original powders of polysaccharides were additionally ground in the laboratory mill before treatment. Average final sizes of the powder particles were within the range 10-40 m. The proteins were treated both in forms of solid powders (BSA and FM) and thing films (BSA). To form a film BSA was dissolved in distilled water and than water evaporation


under vacuum was performed. The thickness of the formed film was 1 μm.



The following properties of EBP-modified products were of particular interest:

**Figure 3.** a.The incident radiation power of fast electrons on 1 cm2 of the sample surface calculated as a function of *x*- and *y*-distances from the sample center: the treatment in the helium EBP at pressure 40 Torr. b.The incident radiation power of fast electrons on 1 cm2 of the sample surface calculated as a function of *x*- and *y*-distances.

If optimal values of *Pm* are found the total dose of the powder particles irradiation can be calculated. In particular, the treatment durations required to irradiate the powder by equal dozes at variable gas pressures were calculated and relevant experiments in various gases were planned and carried out. Experiments of this kind showed the modification effect in the organic materials under consideration to appear when the accumulated doze exceeded some threshold value.

The material temperature can be controlled by varying the gas pressure value during the treatment. The lower the gas pressure - the higher the sample temperature since the scattering and absorption of the EB in gaseous media are more intensive at higher pressures than at lower ones. If higher sample temperature is required to obtain the desirable modification effect the gas pressure should be reduced. For this reason the polysaccharides were treated at lower pressures than the proteins because the higher temperature (about 400 K) was optimal for effective polysaccharides modification. On the contrary, when the proteins were treated in helium the higher pressures (*Pm* 40 Torr) were required to prevent the sample from overheating. It was because of the restrictions on the material temperature that the working pressures in the reaction chamber of the EBPR sometimes differed from their optimal values found as the maximum of the functions *n* = *n*(*Pm*, *Ib*).

**Figure 4.** Concentrations of excited particles in the EBP of argon filling the reaction chamber as a function of the gas pressure, *U* = 25 kV, *z* = 130 mm: *Ib* = 15 mA (curve *1*), *Ib* = 7,5 mA (curve *2*).
