Horn current monitor

1
Horn current monitor

• H. Kubo, A. K. Ichikawa (Kyoto university)
• E. D. Zimmerman (KEK Colorado university)
• T. Sekiguchi (KEK)

2
History

• 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
3
Present 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.

4
Purpose 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.

5
Principle
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
6
Assumption 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
7
Field calculation by Poisson/Superfish

• apply 250/4 kA for each pair.
• m1 is assumed for aluminum

8
Required 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.)
9
1st option with compensation coil
Compensation coil using fine-met core
stripline
field
10
2nd option with RC circuit
A-out
stripline
field
11
Compensation 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.)

12
What 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.

13
Raw 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?

15
What 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.

16
Pick-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)

17
Radiation 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.

18
Calibration 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.

19
Hall 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

20
Field probe measurement at stripline

• (Done and being analyzed by Kubo-kun now.)

21
Horn field measurements

• Used probe holder and positioning tool from Univ.
  of Colorado
• Data read by KEK differential-input dataloggger

22
Horn 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

23
Horn 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
24
Horn 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
25
Horn 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
26
concern

• 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.

27
Supplement
28
1st 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??????????????
  ????????????

29
2nd 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 ????? ?????????? ????????????????????
  ???????????????????????????????
  ????????????????????????????

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