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CVD diamond window development at IAP/GYCOM
Institute of Applied Physics, Nizhny NovgorodGYCOM Ltd., Nizhny Novgorod
A.Litvak, A.L.Vikharev, V.N.Ilin, et al
Presented by G. Denisov
IAP RAS GYCOM
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Motivation
Windows based on a CVD diamond are very expensive but today they are the only option for megawatt CW windows. Calculations show that the windows based on the best discs are capable to transmit 2-3 MW power. Diamond windows allow edge cooling of discs by water at room temperature. This makes their use much more comfortable as compared with some windows operating at cryogenic temperatures or using sophisticated coolants.
Last years significant efforts were done by IAP/GYCOM in order to solve the whole scope of problems associated with the use of CVD diamond windows in gyrotrons: growing of discs, their cutting and polishing, and then high-temperature brazing and mounting to a tube.
IAP RAS GYCOM
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IAP RAS GYCOMDiamond disks grown from the gaseous phase in microwave discharge plasma
Industrial reactorCVD technology for growing polycrystalline diamond disks 75 mm in diameter and up to 2 mm thick has been mastered to create output windows for 1 CW gyrotrons. The disks has low loss tangent~ (1−2)·10-5 at the frequency of 170 GHz and are grown at the rate of 1.5-1.6 µm per hour.
Studies of the ways to speed up the growth of diamond disks in the CVD reactor
Application of the pulse-periodic regime of discharge maintenance
growth speed-up by 1.5-3 times
Application of the discharge produced by millimeterwaves
growth speed-up by 7-10 times
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MPACVD reactors
1
2
3
4 56
7 8
9 10
4
1
23
5
MSU IAF ASTEX
Operation frequency 2.45 GHzMicrowave power 6 kWGas pressure 50 - 150 Torr
Gas mixture H2 + CH4+O2Deposition area 20 - 50 cm2Growth rate 0.5 - 2 µm / h
Operation frequency 915 MHz Gas mixture H2 + CH4+O2Microwave power 20-60 kW Deposition area 70 - 150 cm2
IAP RAS GYCOM
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Growth rate of diamond films
1014
1013
1015 1016 1017
1014
1015
1016
[H], cm-3
[CH 3
], cm-
3
DCarcjet
CombastionTorch
Hot filamentMicrowave
RFTorch
10 3 µm/h10 2 µm/hG = 10 µm/h1 µm/h
X d ef
= 1 0
2
1
1 0- 2
1 0- 4
Growth rate
Relative defect density
K≈ 2
where concentration of H atomand CH3 radical at the substrateare in cm-3
[D.G. Goodwin, J. Appl. Phys. 74(11) (1993) 6888]
GCH Hcm H
∝⋅ +−[ ][ ]
[ ]3
15 33 10
XGHdef K∝ [ ]
CH H CH H4 3 2+ ↔ +
IAP RAS GYCOM
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Diamond growth in CW 2,45 GHz reactor at IAP
Operation frequency 2.45 GHzMicrowave power 6 kWGas pressure 100 - 150 Torr
Gas mixture H2 + CH4+O2Sample diameter 50 - 75 mmGrowth rate 1-2 µm / h
IAP RAS GYCOM
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Nucleation side Growth side
Non-polished diamond disk of 75 mm in diameter and 1.4 mm thick at center
IAP RAS GYCOM
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Non-polished diamond disk of 75 mm in diameter and 1.65 mm thick at center
1000 1100 1200 1300 1400 1500 1600 1700 1800 1900Raman shift, cm-1
I, a.u.
1000 1100 1200 1300 1400 1500 1600 1700 1800 1900Raman shift, cm-1
I, a.u.
Center
Edge
IAP RAS GYCOM
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Polycrystalline diamond disks were polished by mechanical lapping method using homemade machines
Diamond disks after polishing, diameter – 75 mm, thickness - 1.12 mm and 1.35 mm
IAP RAS GYCOM
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IAP RAS GYCOM
Recently grown discs
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100 200 300
tanδ[10-6]5 0 22DB6
54DB1
40050 2 5 0 35 0
5
10
15
20
25
305 0 22DB6
54DB1
40050 2 5 0 35 0
5
10
15
20
25
30
5
10
15
20
25
30
Frequency [GHz]
53DB1
6 3DB1
64DB1
52DB1
IAP RAS 5
150
IAP RAS 6
Comparison with De Beers diamond disks
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Growth of atomic hydrogen density [H]
Increase of specific power
Increase of electron density Ne
Generation of plasma by quasi-optical system
Millimeter wave radiation
GCH Hcm H
∝⋅ +−[ ][ ]
[ ]3
15 33 10
Increase of growth rate
Increase of microwave frequency
IAP RAS GYCOM
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1 – upper focusing mirror, 2 – down focusing mirror, 3 – flat mirror, 4 – wave beam splitter, 5 – substrate, 6 - gas discharge plasma, 7 – circular corrugated waveguide, 8 – miter bend, 9 – gyrotron, 10, 11 – mode converter to wave beam
11
22
3
4
1
1
5
6
77
8
9
10
11
View A
A
Gyrotron-based system
IAP RAS GYCOM
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High-speed growing of polycrystalline diamond filmsReactor
based on a 10 kW/30 GHz gyrotron 11
22
3
4
1
1
5
6
77
8
9
10
11
View A
A
0.2 0.4 0.6 0.80
2
4
6
8
G, µm/h
[CH4], %
IAP RAS GYCOM
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Plasma reactor
11
224
3
8 7
8
6
5
Process parameters:Substrate 60 and 75 mm Si Gas mixture Ar + H2 + CH4Microwave power 5 – 8 kW Gas pressure 100 – 400 TorrSubstrate temperature 600 – 900C Deposition time 1-100 hours
IAP RAS GYCOM
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0.2 0.4 0.6 0.80
2
4
6
8
G, µm/h
[CH4], %
Growth rate versus methane concentration at gas pressure 200 Torr
IAP RAS GYCOM
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Diamond disks for gyrotron windows are brazed to copper cuffs with a high temperature alloy in order a tube can pass the process of baking out. High temperature brazing was developed in Gycom company.The window was tested with 170GHz/0.65MW/20sec microwaves1.4kW absorbed power; 2-3 sec temperature stabilization
Brazing IAP RAS GYCOM
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GyrotronGyrotronGyrotronGyrotron with a circular Brewster window with a circular Brewster window with a circular Brewster window with a circular Brewster window
2006200620062006 ProofProofProofProof----of principle test of a of principle test of a of principle test of a of principle test of a gyrotrongyrotrongyrotrongyrotron with circular with circular with circular with circular Brewster window (0.1 sec, 0.7Brewster window (0.1 sec, 0.7Brewster window (0.1 sec, 0.7Brewster window (0.1 sec, 0.7----0.9MW, 11 modes in 0.9MW, 11 modes in 0.9MW, 11 modes in 0.9MW, 11 modes in the range of 105the range of 105the range of 105the range of 105----143 GHz)143 GHz)143 GHz)143 GHz)
July 2007July 2007July 2007July 2007 ---- 10 sec test of the tube with high10 sec test of the tube with high10 sec test of the tube with high10 sec test of the tube with high----efficient efficient efficient efficient mode converter and Brewstermode converter and Brewstermode converter and Brewstermode converter and Brewster----angle diamond windowangle diamond windowangle diamond windowangle diamond window
BN ceramic, BN ceramic, BN ceramic, BN ceramic, highhighhighhigh----temperature temperature temperature temperature
brazingbrazingbrazingbrazing
IAP RAS GYCOM
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SummaryWindows based on a CVD diamond are very expensive but today they are the only option for megawatt CW windows. IAP/GYCOM solve the whole scope of problems associated with the use of CVD diamond windows in gyrotrons: growing of discs, their cutting and polishing, and then high-temperature brazing and mounting to a tube. Two setups for growing diamond discs are in operation: the first one bought from Aixtron company, is based on a magnetron and conventional receipts for discs growing, the second one is an experimental gyrotron-based setup operating at high frequency 30 GHz and it aims to increase the disc growth rate. Two more setups are under construction at IAP.IAP/GYCOM discs are brazed at near 800°C temperature to metal constructions. One of the brazed window was successfully tested in the transmission line out of the 170 GHz gyrotron with pulses 0.65 MW/20 sec.Multi-frequency gyrotron with a diamond Brewster–angle window will be tested in July 2007.
IAP RAS GYCOM