update on tera c-band high gradient test a.d. 31-07-2013

Update on TERA C-bandhigh gradient test

A.D. 31-07-2013

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

Test stand setup

cavity

PMT

FaradayCup

vacuum port

bidirectional coupler

Acqusition and control system: «C-box»

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.

Second run - setup

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)

C-box screenshot

-- Forward-- Reflected-- Load-- FWD-REF-LOAD

-- PMT

Some BD pulses – BD1 (1MW-23)

Reflected and load have a signalForward pulse continuesPMT sees something

BD2 - (1MW-24)

Forward pulse stopsReflected and load drop abruptlyPMT signal noisy

BD3 - (1MW-27)

Forward pulse stopsReflected and load drop abruptlyPMT signal noisy

BD4 – (1.1 MW-15)

Reflected increasesForward pulse stopsLload drops abruptlyPMT signal noisy

Stored energy

Stored energy - BD

Stored energy – short BD

BDR – T_pulse scaling

BDR- Esurf scaling

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)

...to be done

• Validation of splitter calibration• Analysis of BD-time distribution

• Inspection of the cavity surface