Title: Horn current monitor
1Horn current monitor
- H. Kubo, A. K. Ichikawa (Kyoto university)
- E. D. Zimmerman (KEK Colorado university)
- T. Sekiguchi (KEK)
2History
- K2K used CTs for each striplines.
- The stripline structure was different at the CT
position. This looked that it is adding
inductance and also that it is weak against the
Lorentz force. (c.f. T2K Lorentz force is 1.7
times larger than that for K2K.) - So we started a project to monitor the current
flowing the stripline with pick-up coils, which
is small enough that there is no need to change
the stripline structure. - K2K has a analogue interlock module looking at
the valance among four CT outputs. Its maximum
rating was 300kA. We have decided to make a new
digital interlock system using PLC.
K2K CTs
K2K CT Interlock module
3Present status
- The progress of the RD was not so quick. This is
partially because trial and debugging cannot be
done by the power supply problem. We have only
three opportunities to actually see signal before
this March. - So it is still debugging process.
- With the experiences in this April and June run,
it should be modified if necessity found.
4Purpose and requirement
- Monitor the current of each stripline
pulse-by-pulse during throughout experiment. Both
magnitude and timing should be monitored. - From purely physics point of view, required
precision for total current is 5. - See http//jnusrv01.kek.jp/internal/t2k/nubeam/rep
ort/Spitz.05/HornCurrent.spitz.ppt - http//www.t2k.org/docs/technotes/004
- To monitor the stripline or cable status,1
sensitivity for stability monitoring is required. - So we set the requirement for the monitor as
- A few tenth of 1 sensitivity for stability
monitoring - lt5 for the absolute current determination
- See p.? for other facility horn occurences.
- This monitor will be also used to tune the horn
fire timing against beam. Required timing
precision is 80micro seconds. (1 current drop
from the peak) - Note that this monitor was intended to be used to
protect horn, striplines and cables, but not to
protect the power supply. If lt0.1 pulse-by-pulse
sensitivity is required in order to protect the
power supply, this monitor would not work for
that. - Because it will be installed in radiation
environment, it should be fully passive in the
area.
5Principle
Proportional to field change
Ground level control tent
Integration circuit
A-out
Interlock PLC ADC
Peak Hold module
A-out
Isolation amp
Pick-up coil
Copper FADC
An integration circuit is necessary In order to
deal the signal with the peak hold module and PLC.
stripline
field
6Assumption of this method
- The field at the coil position is approximately
uniform. Or the coil has to be small compared to
the stripline width(40cm). - The field at the coil position is dominantly
determined by the current of the striplines
sandwiching that coil. - The magnitude of the current of the striplines
sandwiching the coil is approximately same.
2cm
40cm
7Field calculation by Poisson/Superfish
- apply 250/4 kA for each pair.
- m1 is assumed for aluminum
8Required Time constant of the integration circuit
- Since the horn pulse width is 13ms, ideally t
should be gt100ms. - But large t means small output voltage and weak
against noise. - Simulation study was done.
- Still pulse shape with 20ms integrator dose not
exactly reproduce the original pulse shape. But
considering the purpose of this monitor, we
decided to use t20ms in order to achieve
sufficient pulse height for the production. - Optimization of t may still need some study. Peak
timing should be also checked.
Blue Horn current black induced voltage Red
integrator output (Absolute pulse height depends
on the coil inductance. Just see relative
magnitude here.)
91st option with compensation coil
Compensation coil using fine-met core
stripline
field
102nd option with RC circuit
A-out
stripline
field
11Compensation coil v.s. RC
- Both options look promising.
- But we had a some difficulty to produce good
compensation coil, we decided to use the RC
integrator. - (RC integrator is easy and cheap.)
12What we learned in July and August, 08 operation
at Tsukuba.
- Observed 510 field in the gap where field
should be low. - This is same whether the striplines are connected
to the horn or just terminated. In the latter
case, the current in both side of the stripline
pair is exactly same.
13Raw signal
After offline integration
14? at terminator at horn2 connection black
coil A red coil B green coil C blue coil D
45
10
- Difference among coils is small.
- Pattern is same for the termination connection
and horn2 connection. - -gt This phenomenon cannot be explained by
unbalance among pairs. - Many current patterns are investigated using
Poisson/Superfish, but failed. Nominally, the
field should be 24. (Current distribution in
the stripline plate is assumed to be uniform in
this study.) - See http//jnusrv00.kek.jp/jnu/tgt-horn/horn/strip
line/CT/HornCT.0808.kubo..ppt - So 7 is not understood.
- In order to confirm that there is really 10
field, field probe measurement was carried out in
December 08 and the result is consistent. - Possible origin may be dynamical effect?
(Poisson/Superfish is static analysis.) - Or non-uniform current distribution in the
stripline plate?
15What we learned in December, 08 operation at the
target station ground level.
- pick-up coils are set and connected to coaxial
cables. The expected signal size was 1V before
integration and 15mV after integration. - Big noise at the rising edge.
- 200 mV, repetition cycle 5micro seconds
- did not disappear even after integrator or
isolation amp. - Seemed to be on GND Line of the coaxial cable.
- Noise was reduced when the GND line of the
coaxial cable was connected to the earth.
- Coaxial cable was replaced with twisted pair
cables with shieldings. The shielding was
connected to the earth in control tent. -gt Big
improvement. - We have decided to adopt twisted pair cable with
shielding. - We have decided to enlarge the signal size by
increasing the number of turns of the pick-up
coil.
16Pick-up coil specification
- 9ch/module
- 0.25mm wire
- 8mm thickness 48 mm width 40 mm wire region
- (140 turns expected)
- wire resistance 15m/ch, 370ohm/km(JIS) --gt 5.5
ohm - inductance 1.4mH
- At ?1000(3ms pulse) --gt corr. 1.4 ohm calculated
by http//emclab.mst.edu/inductance/rectgl.html - expected signal size
- 30V (before the integrator)
- 300mV (after the integrator)
-
17Radiation Dose
- Expected radiation dose is 100Gy/5years.
- Teflon should be avoided.
- Acrylic would be O.K.
- No active electrical component should be used in
the area.
18Calibration strategy
- Use well-calibrated hall probe at close location
to the pick-up coil. - Read simultaneously pick-up coil signal and hall
probe signal. - Get absolute field value by hall probe and
normalize the pick-up coil signal. - Use FEM calculation to link the field value and
current of the stripline. - 0.194T_at_250kA, 0.248T_at_320kA
- c.f. 0.251T_at_320kA by hand calculation
- See p.6 for the assumption for this method to be
valid. - Since we observed 7 discrepancy at the low-field
gap, the obtainable accuracy for the absolute
current would be 7 unless we can understand
this phenomenon. - Field measurement along the stripline width may
help. - Relative calibration accuracy between coils will
be determined from the noise level. Another way
of relative calibration is to move the pick-up
coils to different gap position and measure. - The absolute normalization can be improved by
doing the field measurement by hall probe in side
the horn conductors while pick-up coil is
measuring the field in the stripline gap. We
expect 2 level accuracy with this method. See
p.2125 - Rogowsky coil suggested by Koseki-san is also
potent to calibrate the pick-up coil.
19Hall probe specifications
- SENIS three-axis magnetic field probe
- Specially ordered model with 25 kHz bandwidth
- Linear range /- 2 T
- Output coefficient is 0.2 T/V
- Field accuracy of probe 0.1
- Temperature sensitivity 0.01/C
- Noise lt2 mV (4 gauss)
- Calibration stability lt1 over 10 years
20Field probe measurement at stripline
- (Done and being analyzed by Kubo-kun now.)
21Horn field measurements
- Used probe holder and positioning tool from Univ.
of Colorado - Data read by KEK differential-input dataloggger
22Horn field measurements
- Several sources of error at the 1 level
- Probe radial location position read off from
scale on probe holder precision is only about
0.5 mm - Position is referenced to outer conductor which
(in Horn 2 and Horn 3) may not be round,
introducing more error on radius - Tsukuba horn test facility did not have precise
horn current measurement - Hall probe averages over unknown (probably about
1 mm) area
23Horn 1 and Horn 3
- Measurements were made in 2007 by Z. Butcher and
KEK group - Analysis used peak probe voltage in pulses
- Field agrees with absolute prediction from
Amperes law to within 2 except for expected
dropoff near outer conductor
Horn 1 downstream left port
Horn 1 downstream left port
24Horn 1 and Horn 3
- Horn 3 upstream ports have largest observed
deviations from expected field nearly 2.
Horn 3 upstream left port
Horn 3 upstream top port
25Horn 2
- Measurements made in August 2008 by E. D.
Zimmerman and M. M. Tzanov - Current was 250 kA, not 320 kA analysis used
sine-wave fit of central portion of pulse ten
pulses wereaveraged for each location. - Field is within 1 of nominal at all but one port
25
26concern
- Lorentz force on the wire
- Field 0.2Tesla, Imax1A
- F 0.2 N/m 0.2gW/cm
- 2.5gW per 1 turn.
- In case the force sum up coherently, 300gW.
- Elastical limit of the wire is 400gW.
- Capton tape around may not be robust for 5 years
use. Photo? - We have to see what happen in this april and May
run and improve before autumn.
27Supplement
281st trial with compensation coil
- ??????????????????????????? ??????????????????????
?? 50O???????100mV ??????? (2mA) ??
300?????6cm?????20000 ??? ??????????????? ?
0.04??? ???????????????1.2 ????????60 mA (3V
????? ?)??????? ????????FADC??????????????????????
? ????????????????????? ???CT?????N
??????????????? ??????????N?2?????????????????????
?? ?????? 1/N ?????? ???????3????????????
1.???????????????? 2.??????????
3.??????????????????????1 ???????????????????? ??
10µH ??????? ????????167 Hz ????????????????????10
mO??? ????50O???????????????? ???????2H
(167Hz???????2kO??) ????????????? ????????
?????????????????????????? ???????????????????????
?????? ????????????????????????????
?????????????????????10??????????????
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292nd option with RC circuit
- RC??????????????????? L ???????????????????????
????R , ??????????C, ????50 O???? ????
50RC/(R50) ???????????? ????????????? C ????R
?50 O?????????????????????? ??????????????????????
??? ????????????????????????????? 50/(R50) ?
????? ?????????????????????????
???????????????????????????????????? ?????
???????????????????????????0.5A ??? ???????1V
??????10O???????????????????? ????(??????????)
??? 4.7 mF ???????????????????46 ms ???????
????????????????????? 4.7 mF ??????????10??????3??
???????????? 200?????????????? http//jp.rs-online
.com/web/search/searchBrowseAction.html?methodget
ProductR3654048 ???????????????????????????120
Hz ????? ?????????? ????????????????????
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30- ???? ???????????????????????? FADC
???1V????????????????????????????
???????????????????????????? 10 mV
??????????????????????????????? ?? Atsuko K.
Ichikawa ???????? gt ?????? gt gt
????????????????????????????????? gt
FADC??????????????????????????? gt
?????????????????????????? gt ?????????????????????
??? gt gt Hajime Kubo ???????? gtgt ???? gtgt gtgt ?????
gtgt gtgt ???????????????????? gtgt ????????????????????
?? gtgt gtgt ???????????? gtgt ??????(167 Hz)
????????????????(10 Hz ??? gtgt 100ms)
??????????? gtgt ?????????????????????? gtgt gtgt
?????????????????????????????????? gtgt
?????????????? gtgt gtgt ? ?????????????10?????? ?
????? gtgt ??????100 Hz ?????????????????????? gt gt