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Can Megawatt Gyrotrons Can Megawatt Gyrotrons Achieve an Efficiency > 50%?Achieve an Efficiency > 50%?

Presented by Richard Temkin, MIT

on behalf of VLT ECH Research Group:Comm. Power Industr. (CPI) , General Atomics, MIT, Univ.

Maryland, Univ. Wisconsin, Calabazas Creek Research

VLT Research Highlight, June 21, 2006

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Motivation / GoalsMotivation / Goals

Demonstrate high efficiency in a depressed collector gyrotron.Design cavity and depressed collector for efficiency enhancement.Implement research results in industrial gyrotrons.

Motivation

Goals

High gyrotron efficiency (> 50 %) is necessary for multi-megawatt gyrotron systems, such as DIII-D, W7-X or ITER.

Need to understand both physics and engineering issues.

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ITER Gyrotrons Have Low Efficiency

170 GHz, 1 MW JAERI GYROTRON

32 % Efficiency at 1 MW

50% needed!

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The W7-X 140 GHz Gyrotron: CPI

CPI-Gyrotron VGT 8141

-

200

400

600

800

1.000

70 71 72 73 74 75 76 77 78 79 80 81

Beam Voltage (kV)

Cavity Magnet Current = 47.88 ATaper Magnet Current = 5.6 AGun Magnet Current = 24.0 ABeam Volt. = Cath. Volt. + Body Volt.Beam Current Varies from 44,5 A to 31,5 APuls Length > 10 min

Test results at IPP:0.9 MW for 30 min

World Record!

Efficiency = 36%

Pow

er (k

W)

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1.5 MW Depressed Collector Gyrotron

Cavity Cathode

Collector

Prime Power = 4 MWEfficiency = 38%

96 kV, 41 A

-96 kV0 kV

+25kV

71 kV, 41 A

0 kV -71 kV

25 kV, < 10 mA

Prime Power ≈ 2.9 MWEfficiency = 52%

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VLT Gyrotron ResearchVLT Gyrotron Research

Build gyrotrons at CPI for long pulse and CW operation.Test gyrotrons at CPI in 10 s pulses to limit of CPI supply, <500 kW.Ship gyrotrons to GA for testing to full power and use for ECH.

Basic Research Experiments at MIT

Industrial Research Program at CPI / GA

Build and test gyrotrons to investigate output power, single mode operation, internal mode converters, efficiency, tunability, etc.

Operate in short pulses, 3 microseconds; avoid thermal engineering.Provide pioneering results on physics and microwave engineering issues.

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MIT Experimental Setup MIT Experimental Setup

4.3 TMagnetic field3 µsPulse lengthTE22,6Mode40 ACurrent96 kVVoltage

1.5 MWPower110 GHzFrequency

Design parametersDesign parameters

launcher

M1

M2

M3M4

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4.3 4.4 4.50.0

0.5

1.0

1.5

2.0

Pow

er (M

W)

Bmain (T)

ResultsResults: P = 1.5 MWEfficiency = 37 %

w/o depr. collectorResults labeled

Axial show higher power; IMC is only 90% efficient.

Vk = 96.6 kV, I = 41.9 A

Power vs. BPower vs. B

Axial V-2005IMC V-2005

Internal Mode Converter (IMC) vs. Axial Configuration

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Experimental results with Dep. Coll.Experimental results with Dep. Coll.

50% efficiency was achieved at Vdep = 25 kV.

0 10 20 30 400.0

0.5

1.0

1.5

2.0

0

10

20

30

40

50

602.0

1.5

1.0

0.5

0.00.0 10 3020 40

0

10

20

30

40

50

60

Vdep (kV)

Pow

er (M

W)

Efficiency (%), Ibody (m

A)

Vk = 96.6 kVIbeam = 42 A

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IEEE Award to Ms. Choi

• Ms. Choi won the Student Paper Award at the IEEE Intl. Vacuum Electronics Conf. (IVEC) in April, 2006

• Her paper was on “Experimental Study of a High Efficiency 1.5 MW, 110 GHz Gyrotron.”

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• 110 GHz

• 96 kV, 40 A

• 25 kV Collector Depression

• Uses older cavity design, not as efficient as MIT cavity

• 500 kW for 10 sec at CPI (power supply limited)• 1.3 MW in short pulses at 42%; Efficiency is low!• Now at GA for long pulse testing

110 GHz, 1.5 MW CPI Gyrotron

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ConclusionsConclusions• An internal mode converter experiment has been done successfully at MIT on a 110 GHz gyrotron.

• 1.5 MW of output power was achieved.

• Efficiency > 50% achieved with depressed collector.

• Industrial 1.5 MW tube built by CPI will be tested for long pulse operation soon at GA.

• Achieved 500 kW for 10 seconds at CPI.

• Short pulse operation only reached 1.3 MW and 42 % efficiency.

• Gyrotron development at CPI needed to finish optimized designs and demonstrate full 1.5 MW for use at DIII-D.

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0 10 20 30 40 50 60 70 80 90 100

0 20 40 60 80 100Spent beam energy (kV)

Dis

tribu

tion

(arb

.)

Future plansFuture plansDep. Coll. experiment

analysis using MICHELLE 3D

Improved internal mode converter

Studies of low frequency (100 MHz) oscillations in gyrotrons.

An improved cavity design

Improved 110 GHz industrial tube to demonstrate full 1.5 MW output power and efficiency > 50%.

Deliver to GA for final testing and use in heating DIII-D.