CLIC meeting 14.3.2008 Jan Kovermann

Task:Task:

• Analysis of the light which is emitted by a breakdown

• Study the breakdown time dependence of the BD light emission

• See possible differences between DC and RF BDs

• Draw conclusions about BD physics, plasma temperatures and densities, development of the breakdown, ignition process, precursors

I am using the DC sparc setup to optimize the spectrometer with the goal to have comparable measurements for DC and RF. Since the setup is much more accessible than the setup later in RF, it is a very good opportunity to tune the system and to study DC breakdown. Thank a lot to Sergio, Mauro, Antoine and Yngve!

The new spectrometer setupThe new spectrometer setupPMT, Hamamatsu R7400U-01, 300-

850nm, 0.78ns rise time

Rotational stage, servo controlled,

250steps/nm

Linear gauge, 1micron resolution, absolute position

Ruled diffraction grating, 300

lines/mm, blazed at 500nm

achromatic focusing lens

50micron input slit

Fiber input with collimator

The light pickup inside the DC-setupThe light pickup inside the DC-setup

1mm glass fiber without optics

Some specificationsSome specifications

• Motor, scope (PMT readout) and linear gauge readout are controlled by a standard PC

• ~5nm resolution (higher resolution increases measurement time)

• LabView based software for calibration, alignment an spectroscopy operation

• Scope acts as ADC for the PMT(s), 1GHz bandwidth and 2.5GSa/s

• System takes data autonomous (~5h to take full spectrum in DC setup)

• Optical rails foreseen to integrate more PMTs resp. other detectors

• Fiber or free path optical input

• HeAr-reference light source for calibration

• very flexible design for future upgrades

… a spectroscopy multitool!

Goal: To have a working spectrometer that can be installed in CTF2!Goal: To have a working spectrometer that can be installed in CTF2!

First results in chronological orderFirst results in chronological order

Still in 2007… first cw spectrum from an old fluorescent lamp:

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 20000 40000 60000 80000 100000

motor position

PM

T v

olt

ag

e [

Vo

lts]

First results in chronological orderFirst results in chronological order

… and time resolved!

Latest results Latest results

Last calibration done on Wednesday this week:

After alignment:

Calibration with OceanOptics HgAr-lamp delivers four points for calibration.

Setup is linear as expected!

position

inte

nsi

ty

0.

ord

er

58

8.5

nm

61

9.5

nm

47

8.5

nm

44

7.5

nm

Calibration 11.3.2008

y = 0.0041x - 64.774

0

100

200

300

400

500

600

700

0 50000 100000 150000 200000motor position

wa

ve

len

gh

t [n

m]

DC-breakdown light (pink) and current (blue)

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

-5.00E-07 5.00E-07 1.50E-06 2.50E-06 3.50E-06 4.50E-06

time [s]

PM

T s

ign

al

an

d c

urr

en

t [a

rb.u

nit

s]

Measurements of overall light emission with time resolution in the DC setup:Measurements of overall light emission with time resolution in the DC setup:

0.order of grating focused on PMT, molybdenum under test

Measurements of overall light emission with time resolution in the DC setup:Measurements of overall light emission with time resolution in the DC setup:

0.order of grating focused on PMT, molybdenum under test, more detailed

DC-breakdown light (pink) and current (blue)

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

-2.00E-07 3.00E-07 8.00E-07 1.30E-06 1.80E-06

time [s]

PM

T s

ign

al

an

d c

urr

en

t [a

rb.u

nit

s]

Measurements of overall light emission with time resolution in the DC setup:Measurements of overall light emission with time resolution in the DC setup:

0.order of grating focused on PMT, molybdenum under test, even more detailed

DC-breakdown light (pink) and current (blue)

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

-2.00E-08 3.00E-08 8.00E-08 1.30E-07 1.80E-07 2.30E-07 2.80E-07 3.30E-07 3.80E-07 4.30E-07

time [s]

PM

T s

ign

al

an

d c

urr

en

t [a

rb.u

nit

s]

~50-100ns width in 70% of all sparcs, probably correlated to voltage…

Measurements of DC sparc light emission with time resolution in the DC setup:Measurements of DC sparc light emission with time resolution in the DC setup:

time [ns]

wa

vele

ng

th [

un

cal.]

Limited by quantum efficiency of PMT…

broadband light emission at the beginning of a sparc?

Measurements of DC sparc light emission with time resolution in the DC setup:Measurements of DC sparc light emission with time resolution in the DC setup:

… but there is also the white light:

time [ns]

wa

vele

ng

th [

un

cal.]

Clustering?Clustering?

Measurements of DC sparc light emission with time resolution in the DC setup:Measurements of DC sparc light emission with time resolution in the DC setup:

A preliminary spectrum (analysis ongoing):

wavelength [nm]

inte

nsi

ty [

un

cal.] 46

5nm

Cu

I

48

3nm

51

5nm

Cu

I

51

0nm

Cu

I

49

1nm

Cu

II

Conclusion:Conclusion:

• Too early to draw conclusion about DC-BD-physics, there might be still some problems in the setup

• New achromatic optics have been used for the last measurements, transmission spectrum unknown right now (coated)

• System can be used for the RF-BDs as it is after optimization, the setup will be in the gallery, light transport via fiber from CTF2

• There is still a lot to do!

Optimization of the spectrometer with the DC setup will reveals new Optimization of the spectrometer with the DC setup will reveals new information about DC breakdowns and prepares the spectrometer for the information about DC breakdowns and prepares the spectrometer for the

use in CTF2!use in CTF2!