Using of lapping process for optimization of passive surface's resonant cavities of anodic block from power magnetrons.

Pop, Adrian Petru ; Gordan, Mircea ; Ungur, Ana Patricia 等

1. INTRODUCTION

The magnetrons are multiples resonator electromagnetic oscillators of high frequency, as base principle relays on electrons behavior under simultaneous action of electric and magnetic fields with orthogonal field lines. The nonuniformities surface's anodic cavities and angular error between cavities has negative influence about of magnetron working. The high frequency work is going the anode parameters of cavities surface's micro-geometry determination by skip effect. The penetration depth-8 can be estimation in conformity with relation (Simion & Maghiar, 1981):

[delta] = [sup.503][square root of [rho]/[[mu].sub.r] x f] (1)

Where: [delta]-is penetration depth [m], [rho]-electrical resistivity [[ohm]m], [[mu].sub.r]-relative magnetic permeability [H/m], f-current frequency [Hz]. The penetration depth is comparable with surface microgeometry, characterized by the roughness-[R.sub.a] (Ungur, 1999). At cylindrical magnetron with multiple cavities, the current density in dependence of penetration depth is getting by formula:

[J.sub.h] = [J.sub.0] x [e.sup.h(s,z)/[delta]] (2)

, where: [J.sub.h]-current density [A/[cm.sup.2]] at depth-h, [J.sub.0]-current density of conductor surface [A/[cm.sup.2]], h(s,z)-depth function at that is measurement the current density, [delta]-penetration depth [m]. This paper presents a proceeding for achievement of optimized resonant cavity used at magnetrons with multiple cavities, type vane or slit, having a metallic structure of anodic block with metal-metal (MML) or metal-insulation-metal covered layers (MIML) (Maghiar et al., 2001).

2. PHYSICS PHENOMENA

To avoid the Joule effect is required superfinishing process of side surface's resonant cavities to get a new orientation mode of roughness, parallel with direction of skin current and reduced dispersion of electric field on side cavities of magnetron.

[FIGURE 1 OMITTED]

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The proceeding has realized in two variants, in function of position the covered layers on the base structure of anodic block. The plating is doing by non-ferrous paramagnetic layers, such as cooper with high purity, and covered layers being metal-metal type (MML-first variant) or metal-insulation- metal (MIML-variant second) (Maghiar et al., 2003).

First variant has the goal of improved efficiency and reduced the surface resistivity of resonant cavities, on which surfaces the roughness is modeling parallel with direction of skin current. It has realized by the processes of warm galvanization or evaporation in vacuum a metal layer, example Au, with a different potential as metal base of anodic block-Cu, resulted a structure of metal with a good electrical and thermal conduction of covered layer. This layer assured a good thermal transfer outside and a fast decrease of electric current dispersion at surface and without great losses. The quality of resonant cavities surfaces obtained by galvanic plating process is superior as classical cutting processes. The Joule-Lentz effect are more diminished and thermal stability being assured by Peltier, Thomson and Seebeck thermo-electric effects, which occurred at structures with bimetallic layers subjected of potential difference in presence of temperature gradient.

The second variant of achievement has the goal of reduced the magnetron weight, by using of Cu or Al with high purity as base metal structure of anodic block and modeling of resonator cavities surfaces roughness parallel with direction of skin current. After that, the surfaces are oxidation by well-known proceedings: oxidation for Cu and eloxation for Al, due to an insulation oxide layer of Cu[O.sub.2], respectively [Al.sub.2][O.sub.3], with thickness of some microns. These electrical insulations have a stable structure and good thermal conduction, on those are plating by vacuum evaporation a metal layer of Au, with different potential as metal base, obtaining of a structure with MIML.

The insulation layer of oxides assures a better skin current dispersion and high quality of surfaces, which due to of thermal losses by Joule-Lentz effect.

3. OPTIMIZATION PROCESS

A multiple variants of anodic block optimization are showing in Fig.3-Fig.6 (Maghiar et al., 2003).

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The obtaining process of resonant cavities with metal structure by plating of layers MML and MIML, used of magnetron anodic block with multiple cavities type vane or slit presents the following advantages (Maghiar et al., 2003):

--decrease the magnetron power losses by Joule-Lentz effect;

--improved the magnetron efficiency and quality factor;

--reduced the volume and weight aggregate.

The superfinishing of copper without oxygen (CuOFHC) is required a special work conditions. The process has been done at Machine-Tools "Infratirea" Co of Oradea, by handle lapping process (Fig.7), (Maghiar et al., 2003; Ungur, 1999). The attempts had done by CuOFHC lamellas samples of resonant cavities, with roughness [R.sub.a]=1.6[mu]m. The material for base plate was gray cast iron with [R.sub.a]=0.4[mu]m. The lapping paste was a mechanical mixed by black silicium carbide-Cn, with added of stearic zinc, oleic acid, oil gas, lubrication oil.

The lapping process of CuOFHC has accompanied with some chemical phenomena: occurring of [Cu.sub.2]O film on workpiece surfaces (chemical-absorption process), which is broken by the asperities parts of workpiece. The lapping process had 5-10min/piece with a pressure of 2.5MPa, double stokes of 60/min and amplitude of 20mm, continuing by the polish or chemical smoother process.

[FIGURE 5 OMITTED]

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[FIGURE 7 OMITTED]

In conformity with first variant of obtain, Fig.3-5, the side surfaces-(b) of resonant cavities are superfinishing by lapping such as to result a roughness-(d) with an orientation-(c) parallel with direction of skin current. On the side surfaces-(b) of resonant cavities is plating by warm galvanic process a metallic layer-(4) of Au, with different potential of metal base structure 3 and a thickness-[delta]' of metallic layer-4 greater that penetration depth-[delta] of skin current (Maghiar et al., 2003). The deposit metallic layer assured a fast thermal outside transfer and diminished the dispersion of skin current.

In conformity with second variant proceeding, Fig.3-4 and Fig.6 [Maghiar et al., 2003], over of metallic base structure-.? (Cu or Al) of side surfaces-(b) of resonant cavity-(a) is getting by oxidation or eloxation process an insulation layer-5 of metallic oxide (Cu[O.sub.2] for oxidation process, or [Al.sub.2][O.sub.3] for eloxation process). Over insulation layer-5 of metallic oxide is plating by vacuum evaporation process a second metallic layer-6 of Au, with a different potential as of metallic base structure 3. and a thickness-[delta]' of metallic layer deposit-6. This thickness is greater that penetration depth-[delta] of skip current, with decreasing role of electric field dispersion by located mode of successive layers metal-insulation-metal, due to reducer of power losses of magnetron by Joule-Lentz effect.

4. CONCLUSIONS

The control and orientation mode of side surfaces roughness for resonant cavities, realized by superfinishing process due to a growing of magnetron efficiency by Joule-Lentz effect minimization.

The plating with a metal-metal layer (MML) of resonant cavities is going a better thermal transfer and reduce power losses by minimization Joule-Lentz effect and skin current.

The plating of resonant cavities with metal-insulation-metal layers (MIML) is going of thermal stability magnetron improved. The insulation oxide layer assures a uniform thermal distribution, reduce Joule-Lentz effect, enhance of magnetron efficiency and reduce the weight and size of anodic block.

5. REFERENCES

Maghiar, T.; Ungur, P. et al. (2001). Anodic Axial Block for High Power Magnetrons, Patent No.RO116934-B

Maghiar, T.; Ungur, P. et al. (2003). Production of Optimization Magnetron Resonant Cavities Comprises Superfinishing of the Anode Block for Controlled Roughness Orientation Increasing Performance, Patent No.RO118237-B1, DPA No 2004-087840

Simion, E. & Maghiar, T. (1981). Electro-Technique, Didactical and Pedagogical Editor, Bucharest

Ungur, P. (1999). Research and Realization about Improving of Electronic Efficiency in Construction and Magnetrons Technology with Power of 800W with [pi] Mode of Oscillation, PhD Thesis, University of Oradea

Ungur, P.; Pop, P.A. et al. (2008). Theoretical and Practical Aspects Regarding of Electronic Efficiency Improving of Power Magnetrons with Continuous Working and Bimetal Anode, Proceedings ofMSEC2008/ICMP2008, pp.1-9, ISBN-0-7918-3836-6, ASME MSEC_ICMP 2008 Conference, October 7-10, 2008, Evanston, IL, USA