Breakdown energy balance & Preliminary data analysis Jan Kovermann, team meeting 24 .09.2008
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Breakdown energy balance
&
Preliminary data analysis
Jan Kovermann, team meeting 24.09.2008
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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!)
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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?
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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
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Very preliminary analysis of 30GHz structure test dataDistribution of missing energy and FC charge
C30 SB (2185BDs)HDS4thick (1705BDs)
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Very preliminary analysis of 30GHz structure test dataStrange pulses…
Incident
Transmitted
Reflected
FC
Pre-pulse? Starting time?
50%
10%
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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%
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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%
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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!