Transcript Test_Results_Oct_29Talk0

Summary of Tests of SIC and
SEM as Beam Loss Devices at
CTF3
Anne Dabrowski
Thibaut Lefevre
October 29 2004
SIC as Ionization Chamber
53
52
RAW signal
51
(no amplifier or electronics
– just cable to digitizer)
SIC amplitude (mV)
50
49
48
47
~8 mV
Voltage Dependence on SIC
visible:
46
No polarization
+ 180 volts
- 180 volts
45
44
-4
43
2400
2600
2800
3000
time (ns)
•average of 5 measurements at
each voltage and constant beam
loss
•Signal other than ionization
Dominant
3200
SIC signal isolated (mV)
42
2200
-3
+180 volts
+140 volts
+100 volts
+40 volts
+20 volts
-20 volts
-40 volts
-100 volts
-140 volts
-180 volts
-2
-1
0
1
2
~3 mV
3
4
2200
2400
2600
2800
Time (ns)
3000
3200
Beam Loss Conditions based on
Matthew’s simulation
(CTF3_NOTE_061)
Charged
particles
gammas
Number of particles /
0.25 MeV
Flux (1/cm2 s)
1012
10-2
10-3
1011
10-4
0
Radius (cm)
100
0
Energy
25MeV
Flux of photons ~ order of magnitude
higher than e+e- for E < 5 MeV
t, atomic photoeffect (electron
ejection, photon
absorption);
Total photon cross section in lead, as a
function of energy
Energy Distribution for a beam
energy of 25 MeV at a distance
of 100 cm
Beam Loss: SIC Faraday Cup
Girder 5 beam
energy ~ 20 MeV
Electronics:
Amplification Factor: 20 or 200
Amplifier Saturates at ~1.6V.
read over a 50 ohm resistor
Currently operating at the lower gain or 20
0.05
0.00
-0.05
Intensity
-0.10
-0.15
Faraday Cup (mA)
SIC (mA)
BPM (A)
-0.20
-0.25
SIC, Faraday cup
-0.30
-0.35
2000
2500
3000
t (ns)
3500
4000
Girder 5, beam energy ~ 20 MeV
Sensitivity
0.2
0.0
-0.2
-1
0.8 A of
beam loss
BPM502
BPM590
Intensity (mA)
Intnesity (A)
0
-0.4
-0.6
Fcup
SIC
-0.8
-1.0
-1.2
-1.4
-2
-3
5000
F-cup is
saturated
5250
5500
5750
-1.6
2250
2500
2750
3000
3250
t(ns)
6000
t (ns)
0.2
1
0.0
0.25 A of
beam loss
-1
BPM502
BPM590
-2
Intensity (mA)
Intnesity (A)
0
-0.2
Fcup
SIC
-0.4
-0.6
-3
-0.8
2250
5250
5500
5750
6000
t (ns)
Intnesity (A)
0
-1
Less than
0.025 A beam
loss
[between %
and ‰]
BPM502
BPM590
-2
2500
2750
3000
3250
3000
3250
t(ns)
0.10
0.05
Intensity (mA)
-4
5000
0.00
-0.05
Fcup
SIC
-3
5000
5250
5500
t (ns)
5750
6000
-0.10
2250
2500
2750
t(ns)
Look for linearity between the
Faraday cup and SIC within pulse
On Girder 6, Beam
Energy > 35 MeV
Faraday cup saturated
but not visible from last
bin of -1600 … would
need to go to higher
intensities to check
saturation of SIC
Saturation
of SIC not
visible at ~
40% of loss
of beam
current
Voltage Scan of Chambers at Girder 7 : SIC and SEM give same
signal
with the electronics (50ohm resistor to an amplifier)
200
200
0
0
-200
-400
SIC : Girder 7
0 Volt
+150 Volts
-150 Volts
-600
-800
Signal (mV)
Signal (mV)
Estimate 1 mA/cm2 of current from the beam going through the chambers.
This is a high beam loss region.
-200
-400
SEM
0 Volt
+150 Volts
-150 Volts
-600
-800
2600
2800
3000
Time (ns)
3200
3400
2600
2800
3000
Time (ns)
3200
3400
Z-mapping to localize losses
Girder 6 Setup : 3 SIC’s 1Atm
Middle of first
cavity
Middle of second
cavity
After the
quadrupole
Nominal Beam Optics
Just after the quadruple
Middle of the first cavity
Middle of the second cavity
Huge Loss in the 2nd Cavity
Just after the quadruple
Middle of the first cavity
Middle of the second cavity
Conclusion
• Negatives:
– Since the SIC / SEM is sensitive to X-rays, and X-ray cross
sections depend on energy, the device is difficult to calibrate ...
– There are sources of X-rays in the machine not correlated to
beam loss eg dark current in the cavities
– To go to the ‰ level SIC lacks sensitivity (close to the noise), at
least at the 20 – 30 MeV region.
• Positives:
– SIC, SEM and Faraday cup correlate to the beam loss in
amplitude and pulse time.
– SIC and SEM have same sensitivity since the dominant process
is photo-electric effect, with fast response.
– Can be used to give additional beam loss information, eq z
position of the loss.
Future improvements
• Shielding from noise to improve the actual system
– Seal the shielding boxes
• Question for the future ?
– Detecting the ‰ of beam loss
– Only sensitive to charged particles (calibration)
:important to do reliable quantitative measurements
– Fast time response : important for transient study
(quantitative beam loss measurements)
We need to work on a new detector : (Richardson
? ..)
Response of SIC 1 Torr vs SIC 1
Atm within the pulse
SIC 1 Torr
SIC 1 Atm
SIC 1 Atm
SIC 1 Torr