CN104241061B - Device for suppressing secondary electron emission - Google Patents
Device for suppressing secondary electron emission Download PDFInfo
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- CN104241061B CN104241061B CN201410507722.6A CN201410507722A CN104241061B CN 104241061 B CN104241061 B CN 104241061B CN 201410507722 A CN201410507722 A CN 201410507722A CN 104241061 B CN104241061 B CN 104241061B
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- carbon fiber
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Abstract
The invention relates to material for suppressing secondary electron emission. The material comprises a graphite wall and carbon fibers. The carbon fibers are vertically and evenly distributed on the surface of the graphite wall. Electrons are applied to bombard the graphite wall to generate secondary electrons, the secondary electrons are emitted at different angles from the surface of the graphite wall, very few of the secondary electrons return to vacuum after multiple emission and absorption of the carbon fibers, emission coefficient of the secondary electrons is less than 1 and close to zero, secondary electron emission is suppressed, wall potential is significantly increased since the secondary electron emission is decreased, heat flux of the electrons from plasma to the graphite wall is decreased, wall heating, wall evaporation and plasma cooling are suppressed, and features of the graphite wall and properties of the plasma are unchanged.
Description
Technical field
The present invention relates to a kind of device of suppression secondary.
Background technology
When the electron bombardment material surface with certain energy or speed, electronics can be caused from the material surface for being bombarded
Emit, this phenomenon is referred to as secondary.The electronics of bombardment material is commonly referred to incident electron, from by bombardment material
The electronics that material is emitted then is referred to as secondary electron, and the incidence that directly ejection is returned from material surface is also included in secondary electron
Electronics, the ratio of the number of secondary electron and the number of incident electron is referred to as secondary electron yield, and conventional δ is representing this
Amount.
Secondary can produce harmful effect in some vacuum devices.Such as in grid-controlled vacuum tube, grid
Secondary can destroy the normal work characteristic of electron tube.In high-voltage electrical tube, secondary can cause insulation
Part punctures.In super high frequency tube, there is secondary electron covibration.Plasma and wall with secondary is mutual
Effect（PWI）When, in the plasma electron temperature is more than the dielectric wall of 20 eV, and more than the metallic walls of 50～100 eV
In the case of, affected by strong secondary：Hall thruster and Helicon wave plasma propeller, High-Power Microwave electricity
The hollow cathode of sub- device, micro discharge punctures and surface-discharge, space plasma and dust plasma, fusionplasma
And the corona treatment electric discharge of radio frequency/Dc bias.Can change PWI from the strong secondary of suspension wall and wait
Ion volume property, strong secondary can significantly increase the electronics heat flux from plasma to wall, so as to cause：
（1）Wall is heated and evaporated；（2）Plasma is cooled down or even extinguished.The strong and weak plasma that plasma interacts with wall
Parameter has a major impact, and sheaths characteristic parameter (such as sheaths potential drop) directly control plasma and interact this with wall
One important physical process.Sufficiently strong secondary enhances energy loss of the electronic deposition in wall, and this is due to two
The increase of secondary electron emission coefficiency reduces wall potential, reduces the ion energy for depositing to wall, but increased gross energy in device
The deposition of wall.Result of study shows, as the increase of secondary electron yield, wall potential absolute value and sheaths thickness reduce,
Sheaths intermediate ion and electron number densitiy increase.Theoretical modeling shows that the sheaths that there is strong secondary disappear, such electronics
That just has no obstruction goes to wall so as to cause substantial amounts of loss.The secondary electron emission characteristic of many materials is not especially clear
Chu, lacks complete experimental result, especially in incident electron energy than in the case of relatively low, while we do not know outgoing
The composition of electronics, then the accurate description to main plasma and the interior secondary of transitional region (sheaths) of wall is very
It is important and necessary, in such some occasions, just must try to suppress secondary.
At present, three aspects are concentrated mainly in the research for suppressing secondary：Groove process, surface coating process
And surface line bombardment processing.（1）Surface groove process：The theoretical research surface of secondary, surface roughness pair
Secondary electron yield has considerable influence, and surface is more coarse, and secondary electron yield is less, theoretical based on this, people
Carry out surface groove to process to increase the research of roughness.Comprehend at surface groove and change the spy that line interacts with cavity wall
Property, that is, affect cavity wall impedance.Therefore in order that impedance is minimized, groove direction is along beam path direction.Exist
Inhibiting mechanism when magnetic field：Parallel to the magnetic line of force, when electronics is got to the side and reflected, it can be horizontally rotated vertical edges
Half-turn gets to again the surface, and the secondary electron for ejecting still can be made convolution fortune by magnetic fields in horizontal plane
It is dynamic.Therefore in theory, vertical edges can completely inhibit secondary, this mechanism with drift section helix tube magnetic
The mechanism of field containment secondary electron is similar to.Inclination angle can not possibly completely inhibit secondary electron for the hypotenuse of α, and part secondary electron is returned
Just depart from surface after rotation collision several times, part secondary electron can directly depart from surface, its effect places one's entire reliance upon α.Secondary electron
The probability for impacting hypotenuse after half rotation again depends on α, and α is bigger, and this probability is bigger, thus inhibitory action is stronger, Fig. 1 institutes
Being shown as surface carries out incised groove process, and Fig. 2 show the electron orbit of secondary electron restriction scheme.（2）At surface coating
Reason：" technical surface " is referred to through grinding process, chemical method cleaning, the surface that economically can be applicable in ultravacuum.Thing
Unavoidably there is layer of oxide layer on this surface on surface in reality, and this causes much higher than base metal of its δ.Some are taken for this
Measure is very important come the adverse effect for eliminating natural oxidizing layer, and one of solution is exactly that surface carries out Vacuum Deposition
Film.Using nanoscale tetrahedral amorphous carbon（ta-C）Film suppresses secondary.Sp in ta-C films2The content of key and thin
The thickness of film has an impact to secondary electron yield, and the secondary electron yield after coating reduces 35%；And when film is thick
More than 5 nm, secondary electron yield is significantly reduced degree, and when thickness is more than 10 nm, secondary electron yield can increase, point
Analysis main cause be film thickness in 5～10 nm, sp2The content of key is larger, and the weak secondary for presenting graphite is special
Property.Result of study shows, although ta-C films can preferably play suppression secondary electron effect, from technological angle
Say, the method high cost, time-consuming and the surface that generates is fragile needs special process.（3）Surface line bombardment processing：It is real
By after air pollution, in adsorption hydrocarbon and water molecule layer, this will substantially increase secondary electron on the cavity wall surface on border
Emission ratio.Even if having carried out coating film treatment to cavity wall surface, but cannot still avoid this impact.Want to greatest extent
Play the effect of film, it is necessary to which its surface is cleaned.That is exactly to use particle beam to bombard sputtering chamber wall surface, removes surface
The impurity of absorption, conventional method has two kinds of electronic beam current and ion beam current.Result of study can be seen that line bombardment can be bright
Aobvious to reduce the ten thousand of sample surfaces, and ion beam becomes apparent from than the effect of electron beam, this will be understood by because with pollution
Thing atomic mass is closer to it is bigger to make the energy that inelastic collision transmitted, the easier desorption of pollutant atom.But the technology
Lack related process research and data report.
It is not isolated that these suppress the method for secondary, and can be and have been obtained for comprehensively should
With, for example, wall can be first corresponded to and be processed into groove surfaces, then plated film is carried out to surface, surface remains after plated film
Groove shapes, are finally toasted and particle beam cleaning to surface, and so last cavity wall surface just has very low two
Secondary electron emission coefficiency.But the method for above-mentioned suppression secondary, the final secondary electron yield of acquisition is still
It is of a relatively high.
The content of the invention
Instant invention overcomes the deficiencies in the prior art, there is provided a kind of material of suppression secondary.
To reach above-mentioned purpose, the technical solution used in the present invention is：A kind of material of suppression secondary, including
Graphite wall and carbon fiber, the carbon fiber Vertical Uniform is distributed on the graphite wall surface.
It is a kind of to suppress the material of secondary to further include the carbon fiber in a preferred embodiment of the present invention
A diameter of 1-50 microns, length be 0.5-5 millimeters.
It is a kind of to suppress the material of secondary to further include the carbon fiber in a preferred embodiment of the present invention
The density range of Vertical Uniform distribution is 0.5%-5%.
The present invention solves defect present in background technology, and electron bombardment graphite wall of the present invention produces secondary electron, and
Secondary electron from graphite wall surface with different angular emissions out, through the multiple transmitting of carbon fiber with absorb, can return true
Empty number remains little, and the emission ratio of such secondary electron is much smaller than 1, close to zero, then just play the secondary electricity of suppression
The effect of son transmitting, low secondary significantly increases wall potential, reduces the electronics heat flux from plasma to wall,
Wall heating, wall evaporation and plasma cooling are inhibited, the characteristic and plasma properties of wall will not be changed.
Description of the drawings
With reference to the accompanying drawings and examples the present invention is further described.
Fig. 1 is the existing schematic diagram for carrying out surface zigzag groove reason；
Fig. 2 is the electron orbit schematic diagram of the secondary electron restriction scheme of Fig. 1；
Fig. 3 is the schematic diagram that existing electron beam is acted directly in graphite wall；
Fig. 4 is by the design sketch of the secondary obtained by SEM after Fig. 3 effects；
Fig. 5 is the schematic diagram that the material and electron beam of the present invention is acted on material；
Fig. 6 is by the design sketch of the secondary obtained by SEM after Fig. 5 effects；
Fig. 7 is the graph of a relation of the secondary electron yield with incident electron energy of different samples.
Specific embodiment
Presently in connection with drawings and Examples, the present invention is further detailed explanation, and these accompanying drawings are simplified signal
Figure, only illustrates in a schematic way the basic structure of the present invention, therefore it only shows the composition relevant with the present invention.
As shown in figure 5, a kind of material for suppressing secondary, including graphite wall and carbon fiber, carbon fiber is vertically equal
It is even to be distributed on graphite wall surface.Preferably a diameter of 1-50 microns of carbon fiber, length of the invention are 0.5-5 millimeters.Carbon is fine
The density range of dimension Vertical Uniform distribution is 0.5%-5%, namely the gross area and the ratio of graphite wall surface area at the top of carbon fiber
It is worth for 0.5%-5%.
With SEM（SEM）As a example by, explain secondary.When beam bombardment material surface, meeting
Secondary is produced, SEM is exactly that material surface image is provided by the detection to secondary electron, can from the result of SEM
Know, " black " region is that, without secondary, " white " region is secondary.Fig. 3 is existing electron beam direct effect
Schematic diagram in graphite wall, the effect by the secondary obtained by SEM is as shown in Figure 4.Fig. 5 is the material of the present invention
The schematic diagram of material, when electron beam parallel to carbon fiber perpendicular to incident wall when, by the secondary obtained by SEM
Effect it is as shown in Figure 6.As can be seen that the effect of secondary is completely different from Fig. 4 and Fig. 6, shown in Fig. 4
" white " region is substantially more than " white " region shown in Fig. 6, illustrates to inhibit secondary electron to send out well using the material of the present invention
Penetrate.In addition, secondary electron yield can pass through formula δCarbon fiber ≈ δGraphite AIn vain/AAlwaysTo calculate, i.e. the secondary electricity of graphite
Sub- emission ratio is multiplied by white portion area and the secondary electron yield of carbon fiber is obtained with the ratio of the gross area, due to
The secondary electron yield of graphite is less than 1, while learning as can be known from Fig. 6, white portion area is remote with the ratio of the gross area
Less than 1, therefore δCarbon fiber ≈ δGraphiteA is white/and A is total<<1.
In order to verify that material of the present invention suppresses the effect of secondary, entered from following control example and embodiment
Row test.
Reference examples 1：Graphite wall.
Embodiment 1：Graphite wall and Vertical Uniform are distributed in the material of the composition of the carbon fiber on the graphite wall surface, wherein,
The length of carbon fiber is 1.5 millimeters, distribution density is 0.8%.
Embodiment 2：Graphite wall and Vertical Uniform are distributed in the material of the composition of the carbon fiber on the graphite wall surface, wherein,
The length of carbon fiber is 1.5 millimeters, distribution density is 0.5%.
Embodiment 3：Graphite wall and Vertical Uniform are distributed in the material of the composition of the carbon fiber on the graphite wall surface, wherein,
The length of carbon fiber is 1.5 millimeters, distribution density is 1.8%.
Embodiment 4：Graphite wall and Vertical Uniform are distributed in the material of the composition of the carbon fiber on the graphite wall surface, wherein,
The length of carbon fiber is 3 millimeters, distribution density is 2.7%.
Embodiment 5：Graphite wall and Vertical Uniform are distributed in the material of the composition of the carbon fiber on the graphite wall surface, wherein,
The length of carbon fiber is 0.5 millimeter, distribution density is 4%.
The step of secondary electron yield is measured be：It is sample from above-mentioned reference examples 1, embodiment 1-5, first to sample
Product surface is cleaned, and then sample is delivered to into analysis room and fixes, then analysis room is vacuumized, when vacuum is up to 10-5During Tort
Residual gas analyzer is opened, leak detection and vacuum condition measurement is carried out, when vacuum reaches 10-7Electron gun is opened during Tort,
Secondary electron yield is measured using current method, experimental data is recorded.Fig. 7 is document（D. Ruzic, R. Moore, and
D. Manos, “Secondary electron yields of carbon-coated and polished stainless
steel,”J. Vac. Sci. Technol. 1982 21, 933.）, reference examples 1, embodiment 1-5 secondary system
The graph of a relation of number and incident electron energy, as seen from the figure, the secondary electron yield of embodiment 1-5 is substantially than document and control
Low many of the secondary electron yield of example 1, wherein, the secondary electron yield of embodiment 4 is minimum.
Under low secondary electron yield material of the Hall thruster wall using the present invention, electron temperature can be with electric discharge
The rising of voltage and raise, the nearly wall electric current of electronics is then basically unchanged, and discharge current concussion is minimum, and efficiency is higher.Low secondary electron
Transmitting significantly increases wall potential, reduces the electronics heat flux from plasma to wall, it is suppressed that wall heating, wall evaporate and wait
Gas ions are cooled down.
It is above enlightenment according to the desirable embodiment of the present invention, by above-mentioned description, related personnel completely can be with
In the range of without departing from this invention technological thought, various change and modification is carried out.The technical scope of this invention
The content being not limited on specification, it is necessary to which technical scope is determined according to right.
Claims (1)
1. it is a kind of suppress secondary device, it is characterised in that：Including graphite wall and carbon fiber, the carbon fiber is vertical
It is evenly distributed on the graphite wall surface, a diameter of 1-50 microns of the carbon fiber, length are 0.5-5 millimeters, described
The density range of carbon fiber Vertical Uniform distribution is 0.5%-5%.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN101365651A (en) * | 2006-01-06 | 2009-02-11 | 独立行政法人产业技术综合研究所 | Oriented carbon nanotube/bulk structure having different density portion, its manufacturing method and usage |
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| TWI404675B (en) * | 2004-07-27 | 2013-08-11 | Nat Inst Of Advanced Ind Scien | Single layered carbon nanotube and oriented single layered carbon manotube-bulk structure, and manufacturing method, manufacturing apparatus and use thereof |
| CN100411866C (en) * | 2005-04-30 | 2008-08-20 | 北京大学 | Carbon fiber composite single carbon nano tube and its preparing method |
| JP2010062071A (en) * | 2008-09-05 | 2010-03-18 | Rohm Co Ltd | Lighting system |
| CN101458225B (en) * | 2008-12-26 | 2012-12-26 | 尚沃医疗电子无锡有限公司 | Electrochemical gas sensors |
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| CN101365651A (en) * | 2006-01-06 | 2009-02-11 | 独立行政法人产业技术综合研究所 | Oriented carbon nanotube/bulk structure having different density portion, its manufacturing method and usage |
Non-Patent Citations (1)
| Title |
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| 抑制多级降压收集极二次电子发射的研究进展;王加梅, 等;《功能材料与器件学报》;20120229;第18卷(第1期);第5-8页 * |
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