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Update on TERA C-bandhigh gradient test
A.D. 31-07-2013
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First run - Test stand setup
magnetron
Thermo-chiller unit + temperature sensors
cavity
VE2098 C bandcoaxial magnetronFrequency range: C band (tunable)Peak out power: 2.5MWAnode voltage: ≤50kVAnode current: ≤120ADuty cycle: ≤0.001Pulse duration: 4µs
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Test stand setup
cavity
PMT
FaradayCup
vacuum port
bidirectional coupler
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Acqusition and control system: «C-box»
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Magnetron
Circ. + load
Flange adapter
RFwindow
Bidirect coupler
Vacuum port Splitter
WG
to
cavi
ty
Cavity
Wat
er
cool
ed lo
ad
from
PSI
Line layout
Without load max. pulse length ~ 1 us.
With load max. pulse length ~ 2.1 us.
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Second run - setup
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Test setup and history• Vacuum level: ~ 1 10-7 – 1 10-6 mbar (heavy outgassing of the
load)• Peak power from magnetron: 0.6 – 2.4 MW• Magnetron pulse length: 1.6 – 3.6 µs• Magnetron freq tuning by mech. Deformation (no direct
meas. of frequency)• Repetition rate: 10 Hz (15 HZ)
– Vacuum limited increase in rep rate
• Conditioning time:– 24 hours/day x (21 days (10 HZ) + 7 days (15 Hz) ) (# pulses ~ 30 M)– RF on time ~90% (interlocks due to vacuum and cooling issues)
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C-box screenshot
-- Forward-- Reflected-- Load-- FWD-REF-LOAD
-- PMT
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Some BD pulses – BD1 (1MW-23)
Reflected and load have a signalForward pulse continuesPMT sees something
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BD2 - (1MW-24)
Forward pulse stopsReflected and load drop abruptlyPMT signal noisy
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BD3 - (1MW-27)
Forward pulse stopsReflected and load drop abruptlyPMT signal noisy
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BD4 – (1.1 MW-15)
Reflected increasesForward pulse stopsLload drops abruptlyPMT signal noisy
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Stored energy
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Stored energy - BD
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Stored energy – short BD
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BDR – T_pulse scaling
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BDR- Esurf scaling
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Fowler Nordheim plot
• Beta_FE ~ 90
0.0000000025 0.000000003 0.0000000035 0.000000004
-20.6
-20.55
-20.5
-20.45
-20.4
-20.35
-20.3
-20.25
-20.2
f(x) = − 302236609.311999 x − 19.4132836158282R² = 0.897782054269765
1/E_surf [(V/m)^-1]
log1
0 (I/
Es^
2)
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...to be done
• Validation of splitter calibration• Analysis of BD-time distribution
• Inspection of the cavity surface