Hi Larry,

 

In your meeting notes (copied below) you say about the DCPS:  

 

"The advantages and disadvantages of running the algorithms in real time is being reviewed and compared to running algorithms ahead of time." 

 

This comment surprises me, since at the meeing I explained why running the algorithms ahead of time makes no sense. 

 

Repeating myself here, there are two possible conceptual approaches to running DCPS algorithms ahead of time, one approach in which the detailed current waveforms for a proposed shot are investigated immediately in advance of that particular shot, and another approach in which all possible current combinations are mapped in advance of NSTX CS upgrade commissioning into a comprehensive computer-based map showing the acceptable safe regions in the 15-dimensional "current hyperspace" (i.e., 12 PF currents, 1 OH current, 1 TF current, and 1 plasma current) that together detemine electromagnetic forces. 

 

The first approach to running DCPS algorithms ahead of time does not work because the actual currents flowing in a particular shot will not be accurately and reliably known before the shot has occurred.  Coil and plasma currents are determined by real-time feedback control, which is subject to changes due to various influences.  For some coils the coil currents themselves are not preprogrammed variables subject to servo-feedback control; instead some plasma current or shape characteristic is being feedback controlled.  For instance, the OH coil current waveform vs. time will be remarkably different for shots whose preprogrammed setup parameters differ only in their gas fueling profiles or in their neutral beam plasma heating profiles.   Furthermore, unplanned misoperations in gas fueling or in neutral beam heating may cause the OH coil current or OH-current-depndent forces to surpass limits that cannot be anticipated by running the DCPS algorithms ahead of time.

 

The second approach to running DCPS algorithms in advance is precluded because it is not practical to make a computer-basd map with enough detail to store the acceptability results of all possible combinations of 15 currents, each one of which can vary continuously over its range from its negative to its positive maximum value.  For instance, if 100 coarse "bins" were used to discretize each current signal (i.e., each 2% of full scale) then 

       (100)^15 = 1,000,000,000,000,000,000,000,000,000,000 bits

would need to be stored just to hold the pre-computed map of safe vs. unsafe combinations of currents.  Such computer memory capacities do not exist today.  In addition, the second approach would entirely ignore the need to track in real-time the heating/cooling internal states of coils, which depend on details of the coil current histories. 

 

I'm curious who is doing the review that your comments state is in progress, and what is the technical concept being considered in that review for running DCPS algorithms in advance.

 

-Bob Woolley

 

 

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From: Lawrence E. Dudek
Sent: Thu 4/15/2010 4:25 PM
To: NSTX Center Stack Upgrade Team
Subject: NSTX CSU Project Meeting Notes from 4/14/10

Notes from 4/14 Meeting:

Update on the TF/PF Structure [Mangra (see VGs) ]
The design of the outer TF leg supports and the Outer PF supports was presented at the project meeting. The latest refinements include reduced parts weight while increasing strength and improved assembly features.

PF 4/5 Lead area stress, Existing PF4/5 Support Weld Algorithm, Lower Umb. Lid [Titus (see VGs) ]
Titus presented the status of the PF4/5 lead block stress analysis. 

The strategy for the implementation of the DCPS is being looked at to minimize the required effort while providing the most useful protection for the hardware.  The advantages and disadvantages of running the algorithms in real time is being reviewed and compared to running algorithms ahead of time.

Diagnostics Impacted by Upgrade [Boales (see VGs) ]
A review of the diagnostics on the NSTX is being conducted to determine what impact the new centerstack and higher power operations may have. Of concern so far are the shutters and activation of G10 materials

Viewgraphs will be posted by B. Simmons at:

http://nstx-upgrade.pppl.gov/Project_Meetings/CenterStackUpgrade/index_Meetings.htm

Outstanding Action Items (last update 4/15/2010)

Action: Structural design criteria has a table with likelihood of failures that is in the NSTX (orig.) GRD.  Structural design criteria needs work to be released such as references 

STATUS: Revision being prepared for signatures. (Status 3/15)

Action: The idea of a Design Load Requirements (Criteria) Document is a good one. Action: Mark Smith to pull this together for the Structures– Need this BEFORE the PDR

Action:  We have a set of Calculations signed off, but not all were checked for the CDR.  These calcs need to be updated and checked (by PDR?). ACTION: Titus

________________

Larry