o ak r idge n ational l aboratory u. s. d epartment of e nergy 1 iter diagnostic rga's:...
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
ITER diagnostic RGA's: background and current design status
Walt Gardner
Task Leader, ITER Diagnostic RGA
U.S ITER Project Team
26 March 2007
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
W. L. Gardner 26-Mar-07
ITER diagnostic RGA’s
Prior to becoming a part of the U.S. package the diagnostic RGA’s were ill defined at best
RGA’s were thought to be straightforward. This is not true in the ITER environment
The diagnostic RGA systems are considered to be “group 1a* diagnostics: those needed for machine protection and basic machine control”
* The machine is unable to operate without a working diagnostic providing every group 1a parameter (1b for advanced operation). -- ITER PID v3.0 [adopted from the ITPA diagnostics WG]
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
W. L. Gardner 26-Mar-07
Seventeen potential locations were identified at a kick-off meeting in Cadarache (11-Oct-06)
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
W. L. Gardner 26-Mar-07
RGA measurement specifications taken from Table 4.22-2 of the ITER Project Integration Document
RESOLUTION
MEASUREMENT PARAMETER CONDITION RANGE or
COVERAGE Time
or Freq.
Spatial or Wav e No.
ACCUR ACY
16. Divertor
Operational Parameters Gas Composition
Before, during and after discharge
A = 1 – 100 amu 1 s A = 0.5 amu Several points
20% during pulse
18. Gas Composition in Main Chamber Gas Composition
During conditioning; prior to, during and after discharge
A = 1 – 100 amu 10 s A = 0.5 amu
Several points 50% during pulse
19. Gas Composition in Ducts Gas Composition
Before, during and after discharge
A = 1 – 100 amu 1 s A = 0.5 amu Several points
20% during pulse
RESOLUTION MEASUREMENT PARAMETER CONDITION RANGE or
COVERAGE Time or Freq.
Spatial or Wave No.
ACCUR ACY
16. Divertor Operational Parameters
Gas Composition
A = 1 – 100 A = 0.5
TBD 1 s Several points
20% during pulse
18. Gas Composition in Main Chamber
Gas Composition
A = 1 – 100 A = 0.5
TBD 10 s Several points 50% during pulse
19. Gas Composition in Ducts
Gas Composition
A = 1 – 100 A = 0.5
TBD 1 s Several points 20% during pulse
Table rearranged to better reflect column headings
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
W. L. Gardner 26-Mar-07
Will need more than one sensor type
Conventional RGAs [quadrupole mass specs (QMS)] Pros: Will cover the specified mass range, readily available, good
general mass spectra libraries, adequate time response in multiplex mode
Cons: Cannot resolve He & D2 peaks, slow in scan mode, poor resolution of hydrogenic species peaks
Penning Gauge Diagnostic (PGD)* Pros: Good hydrogenic peak resolution (H, D, T), separate He peak,
fast response (few ms) Cons: Sensitive only to species with optical emission peaks, hence,
no information on CxDy, CxTy & CxDy-zTz
Both the QMS and PGD diagnostic are currently being considered as complementary sensors within the diagnostic RGA system.
* Currently part of the Pressure Gauge package (EU)
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
W. L. Gardner 26-Mar-07
Expected measurement capabilities for the two RGA sensor types
Parameter QMS PGD Operating pressure range 10-12 – few x 10-2 Pa (FC &
SEM) Few x 10-4 – few x 10-1 Pa
Minimum partial pressure ≈ 10-7 Pa (FC); ≈10-12 (SEM) ≈ 10-4 Pa Peak resolution 1 AMU (peak width at 10%
height) 0.2 Å
Mass range 1-100 AMU Limited to species with optical emission lines
Time response Up to 0.5 ms/AMU Few milli seconds Magnetic field TBD TBD Operating temperature (max.) 150 ˚C (200 ˚C) 150 ˚C (200 ˚C)
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
W. L. Gardner 26-Mar-07
Issue: Pressure Operating pressures of up to 20 Pa (150 mTorr or
0.2 mbar) in the divertor region are greater than can be tolerated by either a QMS (few x 10-2 Pa) or a PGD (few x 10-1 Pa).
Hence, RGA’s monitoring the divertor must be differentially pumped
Recommend differential pumping for other RGA’s to perform calibration, operate during discharge cleaning, and complement the leak checking system
A preliminary design already exists for a [Type 2] Diagnostic Vacuum Pumping System (T2DVPS)
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
W. L. Gardner 26-Mar-07
RGA system here
Torus service vacuum
Proposed 2nd cryopump system (w/containment)
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..
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
W. L. Gardner 26-Mar-07
Issue: Radiation
Very high radiation fields can degrade ceramic insulators over time
High radiation fields can degrade QMS solid state femtoamp high-gain amplifiers, which must be located near to the Faraday cup and SEM sensors. [Could use vacuum tubes and other radiation resistant components*]
The fiber optic for the PGD is susceptible to the formation of color centers in a high radiation field, which degrades transmission. Need to continuously anneal the fiber at 250˚C. In high neutron flux areas annealing will not work.
Tritium beta decay will cause a background shift in the QMS secondary electron multiplier; may only be a problem if using it for leak checking purposes
* Demonstrated on JET: R. Pearce, et al., Vacuum, 44(5-7), pp. 643-645 (1993)
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
W. L. Gardner 26-Mar-07
Issue: Magnetic field Theoretical evidence* that the sensitivity of QMS-
based RGA’s degrades significantly while resolution improves in fields > 0.05 T parallel to the mass filter axis
For transverse fields** an increase in resolution is measured for B = 0.017 T. However, enhanced sensitivity was observed and is attributed to flux leakage into the ionizer
There appear to be no studies on the effects of magnetic fields on the PGD [Small R&D activity]
Need to determine smallest acceptable field in relevant quadrupole geometry in order to calculate shielding needed. [Small R&D activity]
* Tunstall, J. J., et al., Vacuum 53, 211-213 (1999)** Srigengan, B., et al., IEE Proc.-Sci. Meas. Technol., 147(6), 274-278 (2000)
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
W. L. Gardner 26-Mar-07
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
W. L. Gardner 26-Mar-07
Time response as a function of length for various diameters and masses
Appears to be adequate response for hydrogenic species when sampling the divertor ducts (length ≈ 5-7 m)
Slower response if sampling the divertor directly (L ≈ 13 m), the equitorial ports (L ≈ 10 m), and the upper ports (L ≈ 12 m). Not so good for higher masses
Response time = pipe vol (l)÷conductance (l/s)
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
W. L. Gardner 26-Mar-07
One proposed area to place an RGA system for monitoring pumping ducts
Cryopump
300-mm diameter pipe
Area proposed for RGA system (on skid or cart?)
●
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
W. L. Gardner 26-Mar-07
Other issues/considerations
Calibration RGA’s require periodic calibration. Once installed it would be
impractical to remove these systems to a central calibration facility. In-situ calibration to known gas mixtures and pressures is the preferred method
Mechanical QMS’s are sensitive to vibration
Electrical/Electronic Tore Supra experience is that their QMS is particularly
susceptible to RF noise from ICRF Thermal management Installation Maintenance
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
W. L. Gardner 26-Mar-07
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
W. L. Gardner 26-Mar-07
Cryopump
Gate Valve
RGA head
Penning diagnostic & pressure gauge cluster
Preliminary design layout of the Diagnostic RGA system
Cryopump Not shown: Tritium containment “box” Magnetic shielding Aperture, pipe from pumping duct, torus
isolation valve, calibration system Various service inputs and outputs
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
W. L. Gardner 26-Mar-07
Can a better diagnostic be developed for measuring divertor gas composition? Desire local measurement of gas
composition at pressures up to ~20 Pa, in magnetic fields of several Tesla, and in high radiation flux
Recent interest from pellet fueling team in knowing T:(D+T) ratio on <100 ms time scale to control firing of T pellets vs. D pellets
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
W. L. Gardner 26-Mar-07
Possible solution: Capacitive RF discharge based device Japanese group has operated an RF glow discharge up
to 2T at P=100 mTorr (13.3 Pa) [Kaneko, T., et al., JJAP, 44(4A), 1543-1548 (2005)]
Optical signal could be collected (mirror array) and analyzed in manner similar to the PGD
Should be able to operate with only 10’s of watts of RF power and pre-discharge voltages of ~100 V.
Because RF impedance changes with pressure, one could use a calibrated impedance monitor to measure pressure (complement to other pressure measurements?)
Simple construction with radiation tolerant materials is possible
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
W. L. Gardner 26-Mar-07
100 mm
RF Cable
Insulator Powered Electrode
Tube for gas and light transmission
RF Discharge-based Optical Gas Analyzer (RFD-OGA)
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
W. L. Gardner 26-Mar-07
Schematic for the RFD-OGA
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
W. L. Gardner 26-Mar-07
Possible location under the divertor dome
Locate RFD-OGA discharge chamber on shelf (200 mm wide x >450 mm long x >200 mm high)
RFD-OGA light output could piggyback on Impurity Monitor mirror system in this case
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
W. L. Gardner 26-Mar-07
Summary
Have had and are having discussions with ITER - Cadarache on nailing down real estate and specifications
Have identified issues and are working to resolve those [no apparent show stoppers, some modest development needed]
Have generated a design schematic and rough layout of the RGA system
Have produced an “advanced” RGA [RFD–OGA] concept for monitoring gas composition in the divertor to control pellet injector firing (isotopic control) [if strong ITER interest, concept needs R&D $’s and place(s) to test concept]