1
Tests of a diamond quadrant detector at Hasylab (DESY) using the Libera Brilliance
J Morse European Synchrotron Radiation Facility, France
H Graafsma Hasylab, DESY, Germany
B Solar Hasylab, DESY, Germany
ESRF
B Solar Instrumentation Technologies, Slovenia
2
Acknowledgements
Eleni Berdermann GSI Darmstadt
Michal Pomorski CEA-Saclay
Harris Kagan Ohio State Unversity
Muriel Salomé ESRF Grenoble
Liam Gannon University of Bath
3
Talk Outline
Objectives:
- evaluate the feasibility of using RF readout with diamond beam position monitors;
- compare performance, practical issues… with the (usual) electrometer read-out approach.
1. X-ray Synchrotron beam monitoring requirement why diamond?
2. some background: tests at ESRF
3. the Libera Brilliance system
4. DESY F4 beamline measurements/results
4
global application scale
2009: about 50 synchrotrons in the world…
infra-red to MeV photon beams, but main interest 5 ~ 50keV
ESRF-Grenoble
4
5
‘local’ application : ESRF
European Synchrotron Radiation Facility ESRF
~5000 external user experiments / year
with high intensity, coherent
X-ray beam probes 0.5 ~ 500keV
basic and applied research in
biology (protein structures…)
materials science
chemistry, catalyisis…
(coherent) imaging
-- at micro, nano, molecular & atomicscales …
6
3rd generation synchrotrons
ESRF Ø300m
~ 50 beamlines
Beam position - intensity monitors
white/pink beam 0.2~2kW
monochromatic beam ~mW
undulator source
50 ~100m
source to end station
7
3rd generation synchrotrons
ESRF Ø300m
~ 50 beamlines
Beam position - intensity monitors
white/pink beam 0.2~2kW
monochromatic beam ~mW
undulator source
50 ~100m
source to end station
8
X-ray beamline monitoring requirements
required beam stability ~10% of beam size 0.1 ~ 50µm, nanofocusing goals 10nmmeasurement rates required dc ~ 1kHz (acoustic vibrations !)
Position
accuracy & linearity requirement ≤ 0.1%Intensity:
synchronization with optical lasers in ~psec pump probe experiments (X-ray photon bunches ~50psec at 105~108 pulses/sec
Timing:
minimal beam interference: absorption, scattering, coherence loss beamline compatibility:
package size, operation in air, dirty-vacuum, clean-UHVionizing radiation load >104 Gray/sec
device…
max. absorbed X-ray power: ≤ few mW monochromatic beamsbut ≥100W in ~mm2 ‘white’ beam applications: ONLY possible with diamond
9
why diamond ?
0 10 20 30
10
100
1000
Thic
knes
s fo
r 5%
abs
orpt
ion
(mic
rons
)
X-ray energy (keV)
Diamond (Z= 6) Silicon (Z= 14)
~practical limitssingle crystal CVD
…and short range of photoelectric- or Compton electronZ = 6 low specific X-ray absorption / beam scattering…
- ‘zero’ leakage currentcan use high E-field nsec response
- simple devices can be radiation hard
- outstanding thermal conductivity diamond 2000, cf. Si 150 (Wm-1ºK-1)
10
XBIC, Poly- and single crystal response
XBIC: signal current maps made from x, y raster scan of micron X-ray beam
Polycrystalline:grain-boundaries
trapping and local field distortions, signal response lagX-ray scattering…
Single Crystal:excellent spatial uniformity…‘unity gain’ charge collection with blocking contacts
1σ signal variation 0.103%over 100 point row
11
signal lag with fine-grain polycrystalline
10 secCharge collection increases (prompt + detrapped) with E field 1…5v/µm
beam 15 x 100µm2 ,1.3 x 1012 ph/sec at 12keV
Ralf Menk, 2006 SLS data on polycrystalline ~10µm thick (sourced by Diamond Materials??)
12
operation of diamond XBPM devices
• diamond plate, thin (30…100µm) diamond with ‘X-ray transparent’ <100nm surface contacts Cr, Ti, … Ni, Al (Au, Pt, W))
• in beam, diamond bulk acts as solid state ‘ionization chamber’electron thermalization range ~few microns
• current signal readout ‘DC’ up to synchrotron RF clock frequencies possible
( ) ( )
( ) ( )DCBADCBAY
DCBADBCAX
++++−+
=
++++−+
=
YX
A BC D
position (and intensity) found with…
multiple electrodes:
exploits diffusion splitting (~10µm) of charge
e.g. simple quadrant motif
difference/sum of electrode currents A, B, C, Dgivesbeam 'centre of gravity’
sum of currents gives beam intensity
13
operation of diamond XBPM devices
• diamond plate, thin (30…100µm) diamond with ‘X-ray transparent’ <100nm surface contacts Cr, Ti, … Ni, Al (Au, Pt, W))
• in beam, diamond bulk acts as solid state ‘ionization chamber’electron thermalization range ~few microns
• current signal readout ‘DC’ up to synchrotron RF clock frequencies possible
( ) ( )
( ) ( )DCBADCBAY
DCBADBCAX
++++−+
=
++++−+
=
YX
A BC D
position (and intensity) found with…
multiple electrodes:
exploits diffusion splitting (~10µm) of charge
e.g. simple quadrant motif
difference/sum of electrode currents A, B, C, Dgivesbeam 'centre of gravity’
sum of currents gives beam intensity
Packaged device, ID09B, ID11, Desy F4 tests
14
operation of diamond XBPM devices
• diamond plate, thin (30…100µm) diamond with ‘X-ray transparent’ <100nm surface contacts Cr, Ti, … Ni, Al (Au, Pt, W))
( ) ( )
( ) ( )DCBADCBAY
DCBADBCAX
++++−+
=
++++−+
=
YX
A BC D
position (and intensity) found with…
multiple electrodes:
exploits diffusion splitting (~10µm) of charge
e.g. simple quadrant motif
difference/sum of electrode currents A, B, C, Dgivesbeam 'centre of gravity’
sum of currents gives beam intensity
• in beam, diamond bulk acts as solid state ‘ionization chamber’electron thermalization range ~few microns
• current signal readout ‘DC’ up to synchrotron RF clock frequencies possible
Packaged device, ID09B, ID11, Desy F4 tests
duo- and tetra-lateral devices
linear position response over several mm
(but less precise)
15
operation of diamond XBPM devices
• diamond plate, thin (30…100µm) diamond with ‘X-ray transparent’ <100nm surface contacts Cr, Ti, … Ni, Al (Au, Pt, W))
( ) ( )
( ) ( )DCBADCBAY
DCBADBCAX
++++−+
=
++++−+
=
YX
A BC D
position (and intensity) found with…
multiple electrodes:
exploits diffusion splitting (~10µm) of charge
e.g. simple quadrant motif
difference/sum of electrode currents A, B, C, Dgivesbeam 'centre of gravity’
sum of currents gives beam intensity
• in beam, diamond bulk acts as solid state ‘ionization chamber’electron thermalization range ~few microns
• current signal readout ‘DC’ up to synchrotron RF clock frequencies possible
Packaged device, ID09B, ID11, Desy F4 tests
duo- and tetra-lateral devices
linear position response over several mm
(but less precise)
ID06 tests– see Pomorski talk !
16
metal contacted devices, X-ray response
I-V curves under steady-state X-ray beam illumination (7.2 and 6.0 keV)
-150 -100 -50 50 100
-50
50
100
150
20010nm Ti (annealed)
130nm Au30nm Pd10nm Ni
cur
rent
(nA
)
bias (V)
0.5V
/µm
bias
333µm C*30nm Pd
130nm Au
-300 -200 -100 100 200 300
-6-5-4-3-2-1
123456
~100nm Al
curr
ent (
nA)
bias (V)
~100nm Al
0.5V
/µm
bias96µm C*
Shadow mask, sputtered contacts(GSI Darmstadt)
Lift-off litho’ evaporated contacts(Glasgow University)
current ‘gain’
Si beam flux calibration εDiamond = 13.05 +/-0.2 eV/e-h pair
(ESRF, MI-885)
Blocking contact(s) give saturated current response for >0.3Vµm-1
applied E field:
‘overbias’excellent area response uniformity
17
quadrant devices: position response
Line scan @ 7.2keV
For large beamsize (> 50µm), device ‘crossover response’ is simply the line integral across the beam intensity profile
For a small beam (< 10µm), crossover response is convolution of photoelectron thermalizationrange and lateral charge diffusion ocurring during drift
5.16 5.18 5.20 5.22 5.24 5.26 5.28 5.30 5.32 5.34
-1.6
-1.4
-1.2
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
focussed X-beam 0.4 x 1.2 µm2 FWHM
sig
nal (
nA)
position (mm)
bias -40V
50%
isolation gap between quadrants ~120um
signal slope ~5% /micron
…beam focused <1um
Isolation gap ~120µm
1 2
4.9 5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8
-50
-40
-30
-20
-10
0
isolation gap betweeen quadrants ~120µm
dia
mon
d si
gnal
(nA
)
position (mm)
upper left quadrant lower left quadrant
50%
parallel X-beam through 0.2mm pinhole
signal slope ~0.5% /micron
ID21 data, beam collimated 200µm
1 2
!! This data from 0 - 10Hz bandwidth electrometer measurements, i.e. charge integral measurements…what about the time domain??
18
Vertical & horizontal position time scans
ESRFMI-885, ID21 microfocus beamline1sec/point: beam shifts
X-ray flux ~108 s-1 at 7keV~ 20fC in diamond per X ray bunch~ 10nA ‘dc equivalent’ signal current)
0 5000 10000 15000 20000 25000 30000 35000
-1.5
-1.0
-0.5
0.0
0.5
1.0
posi
tion*
(µm
)
time (sec)
vertical horizontal
*scaling 'calibration' error possibly ~10%
19
Vertical & horizontal position time scans
ESRFMI-885, ID21 microfocus beamline1sec/point: beam shifts
X-ray flux ~108 s-1 at 7keV~ 20fC in diamond per X ray bunch~ 10nA ‘dc equivalent’ signal current)
0 5000 10000 15000 20000 25000 30000 35000
-1.5
-1.0
-0.5
0.0
0.5
1.0
posi
tion*
(µm
)
time (sec)
vertical horizontal
*scaling 'calibration' error possibly ~10%
30600 30800 31000 31200 31400 31600 31800 32000 32200 32400
-1.5
-1.0
-0.5
0.0
*scaling 'calibration' error possibly ~10%
posi
tion*
( µm
)
time (sec)
vertical horizontal
18 x time zoom
refill30740 30760 30780 30800 30820 30840 30860 30880 30900 30920 30940
-0.15
-0.10
-0.05
0.00
*scaling 'calibration' error possibly ~10%
180x time zoom horiz position
posi
tion
(µm
)
time (sec)
residuals sd 0.0151µm over 145 points/240secs
30740 30760 30780 30800 30820 30840 30860 30880 30900 30920 30940-1.30
-1.25
-1.20
-1.15
-1.10
*scaling 'calibration' error possibly ~10%
180x time zoom
A
residuals sd 0.0204µm over 100 points/166secs (section A->B)
vert position
posi
tion
(µm
)
time (sec)
B
σ =13.3nm rms
σ = 20.4nm rms
20
position timescan and ‘vibrations’, ID09B:
~ 14 keV beam
currents measured with Keithley 485 electrometers, (10Hz BW, mean current/electrode ~10µA
charge generated in diamond ~ 100 fC /pulse
0 5000 10000 15000
0.0
0.1
0.2
0.3
42
43
44
45
46
47
48
sum
of 4
qau
dran
t sig
nals
(µA
)
beam
pos
ition
seconds
ID09B 23 June 2008
1 =
20um
(ver
tical
)1
= 60
um (h
oriz
)
4.4 hours
FFTs using Femto DLPCA-200 current preamps (simultaneous sampling ADCs at 1ksample/sec)
0 50 100 150 200 250 300 350 400 450 5000.0000.0020.0040.0060.0080.0100.0120.0140.0160.0180.020
Ampl
itude
Frequency (Hz)
Average of 10 FFT of 1000 samples
Vertical noise amplitude
10200 10400 10600 10800
0.1
0.2
0.3
42
43
44
45
46
47
481µm
1 =
60um
(hor
iz)
1 =
20um
(ver
tical
)
sum
of 4
qau
dran
t sig
nals
(µA
)
beam
pos
ition
seconds
ID09B 23 June 2008
1µm
Machine artifacts or something upstream on beamline…
21
diamond temporal response
ESRF 4 bunch mode, ID21 beam ~108ph/sec mean flux (very weak beam intensity…)
700ns
<100pS FWHMX pulse duration
DBA-3LeCroy scope LC584A,~1GHz BW
2.3GHz, 38dB
0.5m 5m
Vb=-50V
22
diamond temporal response
ESRF 4 bunch mode, ID21 beam ~108ph/sec mean flux (very weak beam intensity…)
700ns
<100pS FWHMX pulse duration
DBA-3LeCroy scope LC584A,~1GHz BW
2.3GHz, 38dB
0.5m 5m
Vb=-50V
Signal response to crossing of one X-ray bunch
absorption of ~160 photons at 7.2keV (total ~1MeV = 12fC /pulse )
Linear fit to slope gives signal full base width ~2.5ns, e- drift velocity ~40 µm ns-1
at ~1.1 V µm-1
23
wideband position measurements, ID09B
200mV/20ns division(after 10dB attenuator)
20keV beam, incident flux ~1 x 107ph per pulse (1kHz mechanically chopped white beam)~ 5% X-ray absorption in diamond 385µm thick, ~50% photoelectric/50% Compton
~50pC/pulse in diamond (diamond electrode capacity ~ 0.5pF, bias at 500V ‘CV’ charge limit ~200pC)
X-ray beam
signal direct to DSO: poor decoupling and 50Ωmatching signal ‘bounce’
S361-1, sample
TiW contacts processed by Kagan-OSU.
Vertical beam scan 1
42mm
14
electrode signal ~60ns integrals
Qua
dran
t sig
nal
Spatial position (motor scan of diamond)
50µm
‘crossover’ response of electrodes, beam size fwhm 40µm (V), 90µm (H)
‘boxcar’ signal integration
24
i-Tech Libera Brilliance system
1234
X, Y, Σ out
over network
Signals in
~10kHz
High performance if adequate ‘tuned’ RF signal power…
but can it work with diamond signals?
!! developed for stabilization of electron beams
25 ppM
26
what’s inside? performance?
analog stage: tuned filter (352 or 500MHz)
-4000
-3000
-2000
-1000
0
1000
2000
3000
AD
C v
alue
isg/d-bpmlibera/1/ADCChannelA
data with attens set auto ??
0 200 400 600 800 1000 1200
ADC sample #
27
what’s inside? performance?
analog stage: tuned filter (352 or 500MHz)
-4000
-3000
-2000
-1000
0
1000
2000
3000
0 200 400 600 800 1000 1200
ADC sample #
AD
C v
alue
isg/d-bpmlibera/1/ADCChannelA
data with attens set auto ??
-2000
0
2000
AD
C v
alue
data with Libera attens set auto??and ~40mV signal pulse amplitude in)
0 30 60 90
ADC sample #
28
what’s inside? performance?
analog stage: tuned filter (352 or 500MHz)
0 200 400 600 800 1000 1200-4000
-3000
-2000
-1000
0
1000
2000
3000
ADC sample #
AD
C v
alue
isg/d-bpmlibera/1/ADCChannelA
data with attens set auto ??
0 30 60 90
-2000
0
2000
AD
C v
alue
ADC sample #
data with Libera attens set auto??and ~40mV signal pulse amplitude in)
FPGA and µPprocessing buffering, fast I/O
29
what’s inside? performance?
analog stage: tuned filter (352 or 500MHz)
0 200 400 600 800 1000 1200-4000
-3000
-2000
-1000
0
1000
2000
3000
ADC sample #
AD
C v
alue
isg/d-bpmlibera/1/ADCChannelA
data with attens set auto ??
0 30 60 90
-2000
0
2000
AD
C v
alue
ADC sample #
data with Libera attens set auto??and ~40mV signal pulse amplitude in)
FPGA and µPprocessing buffering, fast I/O
Rok Uršič, I-Tech Dec 2004 for Libera Electron
30
what’s inside? performance?
analog stage: tuned filter (352 or 500MHz)
0 200 400 600 800 1000 1200-4000
-3000
-2000
-1000
0
1000
2000
3000
ADC sample #
AD
C v
alue
isg/d-bpmlibera/1/ADCChannelA
data with attens set auto ??
0 30 60 90
-2000
0
2000
AD
C v
alue
ADC sample #
data with Libera attens set auto??and ~40mV signal pulse amplitude in)
FPGA and µPprocessing buffering, fast I/O
Rok Uršič, I-Tech Dec 2004 for Libera Electron
Guenther RehmDiamond Light Source, 2008
synchrotron circulating e- beamposition noise for Libera input signal attenuators 0-28dB
31
RF readout: Doris F4 tests May 2009
ESRF-Desy ‘DIMOX’ collaboration (readout of diamond BPMs using Libera electronics)
DORIS F4 BM white beam exit
slits20 x 20µm2
diamond BPMon motorized x-y stage
Bias (NIM unit)
Libera Brilliance
pre-amps
Si diode0.5mm
Al beam absorber plate(s)0.5…3.5mm
E6 SC diamond in ceramic mount before PCB assembly. 389µm thick, 50µm isolation cross, 3mm hole under the diamond for beam passage. ~100nm TiW contact processing: Harris Kagan, OSU
8mm
32
diamond mounting and RF signal cabling
Bias
Four quadrant Single Crystal Diamond Sensor
RF Signal Impendence Matching Circuit
LiberaBPM Electronics
X-rayBeam
Sample
Control System
Modified Brilliance: new +12dB input preamps after crossbar switch
33
Doris F4 bending magnet X-ray beam
0.0 2.0x104 4.0x104 6.0x104 8.0x104 1.0x1050.0
2.0x107
4.0x107
6.0x107
Initial bending magnet flux after 0.5mm Al and 0.5mm Si after2.0mm Al and 0.5mm Si after 3.5mm Al and 0.5mm Si
Flux
(pho
tons
/s/m
m2 /0
.1%
bw)
Energy (eV)
DesyEnergyProfile.opj
Flux incident on diamond after 0.5mm Al absorber ~1.1 x 1012 ph/sec2.9% of incident beam absorbed (photoelectric and Compton)
‘dc’ equivalent current generated in diamond ~15µA (3pC/ pulse at 5Mpps)
effect of full ‘white’ beam on PCB and diamond…Following measurements shown were made after these “accidents”
34
Three slides of results removed from this presentation (these show data that will be included in a publication in preparation)
Please contact speaker directly for these missing slides([email protected])
35
dynamic position response: jump test
Libera ADC buffer data at 130KHz sampling-average
rms position noise* vs. bandwidth
nb. noise includes real beam-sensor movements etc.
µm
µm
36
device modeling with TCAD Sentaurus
High level modeling software for semiconductor devices: 2 & 3D graphics and script input
to describe simple to complex devices.
Program solves Poisson and charge continuity (finite element methods) equations.
Simulates drift, diffusion, recombination etc. of charge carriers, and signals induced on
electrodes for various external load models
Accurate/well tested for silicon devices: input parameter and model files can easily be
configured for other semiconductor materials.
Following slides show FIRST ATTEMPTS at 2D simulations for diamond using
permittivity = 5.7 band gap = 5.47 eV electron/hole mobility = 2300/1800 (cm2/ Vs)
carrier velocity saturation model??
37
boundary conditions, field map and meshing
anode 1 anode 2200µm
cathode L Gannon, Sentaurus Device Editor
38
Signal development during charge transit
0.0 2.0x10-9 4.0x10-9 6.0x10-9 8.0x10-9
-4.0x10-8-2.0x10-8
0.02.0x10-84.0x10-86.0x10-88.0x10-81.0x10-71.2x10-71.4x10-71.6x10-71.8x10-72.0x10-72.2x10-72.4x10-7
Cur
rent
(A)
Time (s)
0.0 2.0x10-9 4.0x10-9 6.0x10-9 8.0x10-9
-4.0x10-8-2.0x10-8
0.02.0x10-84.0x10-86.0x10-88.0x10-81.0x10-71.2x10-71.4x10-71.6x10-71.8x10-72.0x10-72.2x10-72.4x10-7
Cur
rent
(A)
Time (s)
1. charge created near the cathode2. holes reach the cathode and are collected, so signal current is ~halved
3. electrons drift and diffuse across a region of homogenous electric field.
4. as electrons approach anode 1, electric field gradient increases so a rise in current is observed on this anode.
5. As electrons are collected at anode 1 the current decreases to zero (tailing caused by transit diffusion)Sentaurus Device Simulator
bias -550V
ball of charge400µm
200µm0V
20µm
1 20V
39
Signal variation with position of incident beam
200µm
400µm
0V 1 0V2
bias=-550V
column of charge
-2x10-9 0 2x10-9 4x10-9 6x10-9 8x10-9
-5.0x10-7
0.05.0x10-7
1.0x10-6
1.5x10-6
2.0x10-6
2.5x10-6
3.0x10-6
3.5x10-6
4.0x10-6
Cur
rent
(A)
Time (s)
-2x10-9 0 2x10-9 4x10-9 6x10-9 8x10-9
-5.0x10-7
0.05.0x10-7
1.0x10-6
1.5x10-6
2.0x10-6
2.5x10-6
3.0x10-6
3.5x10-6
4.0x10-6
Cur
rent
(A)
Time (s)
-2x10-9 0 2x10-9 4x10-9 6x10-9 8x10-9
-5.0x10-7
0.05.0x10-7
1.0x10-6
1.5x10-6
2.0x10-6
2.5x10-6
3.0x10-6
3.5x10-6
4.0x10-6
Cur
rent
(A)
Time (s)
-2x10-9 0 2x10-9 4x10-9 6x10-9 8x10-9
-5.0x10-7
0.05.0x10-7
1.0x10-6
1.5x10-6
2.0x10-6
2.5x10-6
3.0x10-6
3.5x10-6
4.0x10-6
Cur
rent
(A)
Time (s)
-2x10-9 0 2x10-9 4x10-9 6x10-9 8x10-9
-5.0x10-7
0.05.0x10-7
1.0x10-6
1.5x10-6
2.0x10-6
2.5x10-6
3.0x10-6
3.5x10-6
4.0x10-6
Cur
rent
(A)
Time (s)
-2x10-9 0 2x10-9 4x10-9 6x10-9 8x10-9
-5.0x10-7
0.05.0x10-7
1.0x10-6
1.5x10-6
2.0x10-6
2.5x10-6
3.0x10-6
3.5x10-6
4.0x10-6
Cur
rent
(A)
Time (s)-2x10-9 0 2x10-9 4x10-9 6x10-9 8x10-9
-5.0x10-7
0.05.0x10-7
1.0x10-6
1.5x10-6
2.0x10-6
2.5x10-6
3.0x10-6
3.5x10-6
4.0x10-6
Cur
rent
(A)
Time (s)-2x10-9 0 2x10-9 4x10-9 6x10-9 8x10-9
-5.0x10-7
0.05.0x10-7
1.0x10-6
1.5x10-6
2.0x10-6
2.5x10-6
3.0x10-6
3.5x10-6
4.0x10-6
Cur
rent
(A)
Time (s)-2x10-9 0 2x10-9 4x10-9 6x10-9 8x10-9
-5.0x10-7
0.05.0x10-7
1.0x10-6
1.5x10-6
2.0x10-6
2.5x10-6
3.0x10-6
3.5x10-6
4.0x10-6
Cur
rent
(A)
Time (s)-2x10-9 0 2x10-9 4x10-9 6x10-9 8x10-9
-5.0x10-7
0.05.0x10-7
1.0x10-6
1.5x10-6
2.0x10-6
2.5x10-6
3.0x10-6
3.5x10-6
4.0x10-6
Cur
rent
(A)
Time (s)-2x10-9 0 2x10-9 4x10-9 6x10-9 8x10-9
-5.0x10-7
0.05.0x10-7
1.0x10-6
1.5x10-6
2.0x10-6
2.5x10-6
3.0x10-6
3.5x10-6
4.0x10-6
Cur
rent
(A)
Time (s)-2x10-9 0 2x10-9 4x10-9 6x10-9 8x10-9
-5.0x10-7
0.05.0x10-7
1.0x10-6
1.5x10-6
2.0x10-6
2.5x10-6
3.0x10-6
3.5x10-6
4.0x10-6
Cur
rent
(A)
Time (s)
anode 1 anode 2
Sentaurus Device Simulator
40
Conclusions:
‘Proof of principle’ established for position readout using Libera Brilliance systemresolution < 0.1µm demonstrated, but initial DESY tests limited by (white) beam size and beam position noise
Further quantitative tests needed to directly compare narrowband RF vs. electrometer readout, especially signal/noise performance vs. absorbed beam energy
(new test in planning, will use ~10keV monochromatic X-ray beam at ESRF)
Better understanding needed of signal development in multi-electrode device coupled with response of signal processor, e.g. Libera: system ~2MHz passband at 352MHz
(modelling just started with TCAD-Sentaurus)