**4. The tests of the EBPR and optimization of the biomaterial treatment procedure**

The computer simulation of the dusty EBP was carried out to preliminary estimate optimal parameters of the biomaterial treatment. The following processes were taken into account:


288 Practical Applications in Biomedical Engineering

**3. The operation modes of the EBPR** 

gas; its chemical composition.

window outlet and mixing layer.

and some others);

The electromagnetic scanning system *12*, which is placed inside the working chamber near the injection window is able to deflect the injected EB axis in *x* and *y* directions and, therefore, to control the spatial distribution of the plasma particles over the plasma bulk. The working chamber is preliminary evacuated to pressure 10-2 Torr and then filled with plasma generating media. The samples to be treated were inserted into the EBPR reaction zone as solid powders with characteristic particle size ~ 100 mcm and as thing films. The powder of the substance to be treated partially fills the glass container *9*. Thin plate *7* made of piezoelectric ceramics is placed on the container bottom. Being fed with AC-voltage the plate vibrates, throws up the powder particles and forms the mixing layer 6 of the treated material. The miniature thermo-sensor *8* is inserted into the container to monitor the material temperature *Ts* during the treatment. To prevent the thermal distraction of the biological material all samples were processed at *Ts*<50 C. In the case of proteins *Ts* was ~ 37 C. The

temperature control was carried out by selecting the EB current *Ib* (1 < *Ib* < 100 mA).

scanning parameters [7], see section "The control of EBP-modification process".

responsible for the properties of the plasma of this kind are as follows.

are displayed on the control panel of the EBP generator.

Special software was developed to calculate irradiation doses as functions of the electron beam characteristics, gas pressure and chemical composition, treatment duration, and beam

The reaction zone (item *6* in figure 1) of the EBPR is the plasma of an aerosol, as it is sometimes called "dusty plasma". In general, the operation parameters of the reactor

1. The beam parameters: the initial electron energy (*Eb*), that is equal to the accelerating voltage of the electron gun, and the EB power (*N*) injected into the reaction chamber. 2. The power *N* is less than the original power of the EB (*Nb* = *EbIb*, where *Ib* is the current of the beam generated by the gun) since the EB is partially absorbed by the injection window. The transparency coefficient of the injection window was specially measured under various conditions of the plasma generation and the data of the measurements were used to characterize the parameters of the material treatment. The values of both *Eb* and *Ib* are measured inside the high voltage power source, supplying the gun, and

3. The plasma-generating gas parameters: the pressure (*Pm*) and temperature (*Tm*) of the

4. The parameters of the dust: dimensions and shape of the dust particles; the dust density, i.e. the number of the dust particles per unit volume (*nd*); physical properties of the dust material (chemical composition, density, coefficients of the electron emission

5. The geometry of the plasma bulk, especially the distance (*z*0) between the injection

In comparison with the plasma treatment of conventional powder materials (e.g. metals, ceramics, carbon, etc.) the biomaterials processing has at least three important peculiarities.


The local EB power input *Q*(*x*,*y*,*z*), densities of charged particles of the EBP in various zones of the plasma bulk (including the mixing layer), and the temperature of the dust particles (*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 particles.

Bio-Medical Applications of the Electron-Beam Plasma 291

charged plasma particles (secondary electrons and ions) were measured by means of an open barrel-shaped microwave cavity [11] and data of the computer simulation can be used to estimate the concentrations of the neutral ones (molecules, atoms, radicals) [6]. The appropriate duration of the treatment procedure was experimentally found to achieve the

In general the following parameters are responsible for the processes (and eventually for the






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

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

required dose of the material irradiation.

results) of the materials modification:

gas.

volume.

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

injection window, the gun accelerating voltage *U*.

amplitude and frequency of the EB scanning.

surface and by the treatment duration.

placed in the zones of uniform incident fluxes.

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

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 injection window.

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

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 charged plasma particles (secondary electrons and ions) were measured by means of an open barrel-shaped microwave cavity [11] and data of the computer simulation can be used to estimate the concentrations of the neutral ones (molecules, atoms, radicals) [6]. The appropriate duration of the treatment procedure was experimentally found to achieve the required dose of the material irradiation.
