Breakdown energy balance

&

Preliminary data analysis

Jan Kovermann, team meeting 24.09.2008

Overall damage of the surface:

Estimations (O.o.M.):-10cm2 of surface affected by -100um2 breakdown spot size-10kBDs per power test

1/1000 of the surface would be damaged…

But: Total damage looks bigger

Are there any ‘crater’ or other spots where one can locate a breakdown event?

Further SEM observations done (thanks to Samuli!)

Befo

re ru

nAft

er ru

n

Damage by ions from Coulomb explosion:

Measured by Magnus&Roger with FC: - ~10E10 ions per event on FC, 1/200 of solid angle 10E13 ions in Coulomb explosion- Ion energies (ToF) ~100eV - 1keV or 2*10-17- 10-16J per ion), secondary electron emissions from FC (bias voltage!) support these values

Estimation: -Radial expansion of the coulomb explosion- 4mm to next iris5E11 ions/mm2 on the other side of the iris~50uJ/mm2 of energy depositedIn 1ns, this is 10kW/mm2Max. 1mJ in total

Seems that the ions cannot heat up the surface tomelting point (pulsed surface heating is 7kW/mm2for 68ns, ΔT is only 60K… (by Juoni))

But: One ion impact each 10x10atoms2, sputtering?

Electrons:Measured:-High currents (5V in 50Ohms, 100mA) of electrons hit the FC in each BD event, X-rays are produced by these electrons

X-rays pass vacuum window and Al-foils at least 10keV to be detectable, for 10E13 electrons (from singlecharged ions) dissipated energy is around 20mJ

X-rays pass 14mm Cu and 5mm Fe at least 100keV to be detectable

In total: 10E13 electrons with 100keV carry

160mJ

New experiments: 1. Precise time measurementof FC pulse (interferes with power tests…)2. Magnetic spectroscopy (1cm bending Radius in 0.01T field)3. Calorimetry of X-rays

Very preliminary analysis of 30GHz structure test dataDistribution of missing energy and FC charge

C30 SB (2185BDs)HDS4thick (1705BDs)

Very preliminary analysis of 30GHz structure test dataStrange pulses…

Incident

Transmitted

Reflected

FC

Pre-pulse? Starting time?

50%

10%

Very preliminary analysis of 30GHz structure test dataDistribution of refl. signal starting times

C30

SB (2

185B

Ds)

t after inc. pulse start[ns]

10%

50%

t after inc. pulse start[ns]

HDS4

thic

k (1

705B

Ds)

10%50%

Very preliminary analysis of 30GHz structure test dataDistribution of FC signal starting times

C30

SB (2

185B

Ds)

t after inc. pulse start[ns]

10%50%

t after inc. pulse start[ns]

HDS4

thic

k (1

705B

Ds)

10% 50%

Conclusions

• Surface is obviously more damaged than expected by number of BDs•Energy carried by electrons during a breakdown is in the order of magnitude of the missing RF energy• Ions do not seem to play a significant role in the energy balance• Ions can probably change the surface state (smoothing by sputtering??)

• Starting time of the BD is not equally distributed during the pulse• There is a ‘pre-reflection’, is it the source of the electrons collected by the FC?

Still some work to do, especially for old test!