RF, DAQ, and Instrumentation Requirements for the ILC Vertical Cavity Test Stand at IB1 ILCTA_IB1_VT

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RF, DAQ, and Instrumentation Requirements for the
ILC Vertical Cavity Test Stand at IB1
(ILCTA_IB1_VTS)

• Basic Requirements for Vertical Cavity Testing
• Provide stable RF power to the cavity, with
  control of amplitude, phase, and frequency
• Measure incident, reflected, and transmitted
  power of the cavity (including transmitted power
  from HOM couplers)
• Provide interlocks for both personnel and system
  safety
• Provide automated data acquisition and control
  (reproducibility)

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• Our Approach
• System to be used for PRODUCTION cavity tests, as
  part of the cavity process development program.
  We are interested in understanding and
  quantifying cavity performance, over the course
  of many years, and many tests. This means system
  must satisfy the four Rs
• Robust, Reliable, Reproducible Results,
• This is not an RF system development project. The
  object of the exercise is to test cavities, not
  develop control systems.

Therefore the system should be based on
established technology/designs and use
off-the-shelf components as much as possible. Our
Solution Replicate the production cavity
vertical test system in use at JLab, w/
appropriate modifications/improvements for 1.3GHz
operation.
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Specifications/Features of the RF system -
general Adjustable frequency range 1.2-1.4 GHz,
using coarse and fine manual adjustment allows
investigation of other than p mode, cavity
frequency differences due to BCP amounts, manuf.
tolerances, temperature, etc. Frequency stability
of 1Hz. Adjustable phase range of 360. Maximum
amplifier output of 500W at 1.3GHz. Maximum loss
between amplifier and cavity 3dB. Amplitude
adjustment of RF output to provide 1-35MV/m when
cavity nearly critically coupled (.5 ? b ?
2). Switchable between 500W and 1W (built-in)
amplifier - for cable calibration, Q0 vs T
measurements, coupling determination, etc. High
power SPDT switch to divert RF to 500W load when
interlock fault condition detected.
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Specifications/Features of the High Power RF
system High power amplifier - 500W, 1270-1310
MHz (OPHIR RF). Dual directional couplers -
30dB directivity _at_ 1.3GHz (Narda). RF load -
capable of 500W CW (Microwave Devices). SPDT
switch - 500W, 80dB isolation, 0.2dB max
insertion loss (Narda). High power circulator -
500W, 1.1-1.4 GHz BW, (UTE Microwave).
Cables/connectors ½ Heliac w/ N connectors,
except inside Dewar SiO2 insulated SS
hermetically jacketed cables in Dewar (Meggitt
Systems). ? breakdown potential at connectors,
even using Meggitt cable? ? JLab to test He
pressurized (gt triple point) jacketed
cable AC power 208V/3 f, connected to interlock
system.
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Specifications/Features for the LLRF
system Based upon VCO/PLL design. External RF
source used as VCO (Agilent E4422B). Coarse and
Fine frequency adjustment via 10-turn
pots. Manual phase shifter (?190 phase shift at
1.3GHz, Narda 3752). Vector Modulator for
amplitude/phase control (GT Microwave Model
SA-39-AR or similar). Adjustable loop gain
(variable gain amplifier) prevents oscillation
over wide dynamic range. Crystal (diode)
detectors for observing signals, atten.
adjustment (Omni Spectra 2086, Agilent 8472). PIN
switch to control RF on/off during decay
measurements or pulsed RF processing (American
Microwave 2184).
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The transmitted power network has a switchable
LNA and variable attenuator, both can be
controlled by the computer. The 6 dB pad before
the LNA ensures that there is a minimal gap in
the continuous gain control settings. Without it
there would have been a 12 dB dead band. The
phase shift associated with the PIN attenuator
was measured and included as a lookup table in
the program. The compensation values are
factored into the vector modulator
algorithm. Circulators are used to reduce the
mismatch and ensure more stable power meter
calibrations. The 10 dB attenuators used in the
incident and reflected power path also serve that
purpose Only low drift fixed devices are used
between the power meters and the cavities to
ensure calibration stability/validity.
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The VCO is located externally. This allows the
use of stand-alone commercial RF sources as VCOs.
The 50 dB attenuator may be necessary due to the
excessive tuning sensitivity of the VCO, which is
5.6 MHz/V. Crystal detector gain set to reduce
the square law errors while maintaining a 1V
amplitude at the DAQ input. Manual phase
shifter in addition to VM, used for initial
tuning, finding cavity. Computer controlled
vector modulator is used for amplitude and phase
control. All crystal detector signals are
buffered and available for observation using an
oscilloscope. Computer controlled and automatic
data acquisition ensures repeatable data and
methods independent of operator.
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Specifications/Features of the DAQ HW
Instrumentation Power meters for measurement of
Pi, Pr, Pt, and HOM power (Agilent 4418B/4419B,
w/ 8482A sensor heads). Frequency counter to
measure cavity frequency (Agilent 53132A)
. Oscilloscope w/ Roll feature to allow
observation of cavity signals in RT (Textronix
TDS3024B). Dewar pressure transducers (MKS
Baratron), thermometry (Lakeshore Cernox w/ Model
218 monitor) , and LHe level sensor (AMI Model
135-2 sensors). Radiation detectors (ion
chambers) RadCon supplied or ? Also part of
interlocks/safety system.
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Transmitted power network module
Basic system components and DAQ PC
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• Specifications/Features of the DAQ SW
• DAQ SW available from JLab
• SW is written in LabView environment, and
  provides
• Automatic Pt decay measurement
• Automatic calculation of b
• Interactive cable calibration routine
• CW display of E, Q0, Rad
• Online display of Pi, Pr, Pt, and correction
  factors
• RF output power control
• Phase control/optimization
• Display of cryogenic status (LHe level, temps,
  dewar pressure(s))
• Calculation of Q0, Qext fp, Qext in, Qext HOM1,
  Qext HOM2, Eacc
• Logging of all data
• Graphic display of Q0 vs Eacc
• Graphic display of Rad vs time, Rad vs Eacc

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Status where are we Developing
instrumentation, equipment, and component list
50-60 complete. Can place orders when assured of
availability (after cryostat design is
finalized, RFQ issued, and quotes received). 2
amplifiers (500W) ordered, one for JLab, one for
FNAL. Beginning to assemble documentation/schemati
cs in preparation for design finalization. LV SW
downloaded to FNAL. Rack and cabling layouts
begun. Coordinating efforts w/ similar program of
modifications to JLab 805MHz system (? 1.3GHz).
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Status where are we Developing
instrumentation, equipment, and component list
50-60 complete. Can place orders when assured of
availability (after cryostat design is
finalized, RFQ issued, and quotes received). 2
amplifiers (500W) ordered, one for JLab, one for
FNAL. Beginning to assemble documentation/schemati
cs in preparation for design finalization. LV SW
downloaded to FNAL. Rack and cabling layouts
begun. Coordinating efforts w/ similar program of
modifications to JLab 805MHz system (? 1.3GHz).
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Plan where we are headed/open issues Continue
information transfer re schematics, etc. Trips
to JLab planned for ILC EP cavity testing later
in summer, perhaps trip earlier to collaborate on
RF system design. Finalize design, subject to
review. Begin involvement w/ AD Interlocks and
Rad Safety Groups re interlock system design,
fabrication, etc. This must be integrated with
the RF system at an early stage. Need to
determine type/availability of radiation
detectors (needed for DAQ as well as Safety
System). Finalize and prioritize equipment lists,
MS budget, begin procurement of FY06
items. Prepare more formal (MPP) project plan.