Summary of SIT Meeting of 8/20/02

From: Hutch Neilson [hneilson@pppl.gov]
Sent: Tuesday, August 20, 2002 3:24 PM
To: wreiersen@pppl.gov; mzarnstorff@pppl.gov; bsimmons@pppl.gov; Brad Nelson; rstrykowsky@pppl.gov; lyonjf@ornl.gov; mioduszewspk@ornl.gov; John A. Schmidt
Cc: hneilson@mailserver.pppl.gov
Subject: Summary of SIT Meeting of 8/20/02

Summary of SIT Meeting of Tuesday, August 20, 2002.


1. How much plasma-to-first wall standoff is needed?


Peter presented a handout with detailed analyses of field lines launched from the inboard and outboard midplane from 0 to 1 cm outside the VMEC boundary. Outside-launched field lines launched from 0 to 1 cm make 20 revolutions and have the desired connection length if there is a 4 cm plasma-wall gap. Inside-launched field lines launched from 1 mm to 8 mm are also relatively well confined if there is a 4 cm gap but field ines launched from 9-10 mm are poorly confined within a 4 cm gap. Since >80% of the inside and outside-launched field lines are contained, a 4 cm gap (increasing to ~8 cm at the divertor) is the minimum acceptable from a divertor point of view. Additionally, particle diffusion and flexibility considerations would argue for providing more than this if possible.


A 4 cm gap appears achievable through the combination of mechanical structure and plasma displacements currently being studied (~2 cm each).


2. Creating more plasma-to-first wall standoff by moving the plasma


Several cases are being healed which have shifts of 2-2.2 cm each. They have not yet converged.
The revised winding surface from Dave W. is urgently needed.


3. Is it OK to have a low-resistance conducting path wrapped around the winding pack, or would the eddy currents be a problem? (Affects decisions on possible cooling solutions.)


Discussion:


Low resistance the short way around the winding pack is probably OK.


Low resistance the long way (parallel to the turns) is the concern. Concerns are: 1) Long time constant would complicate plasma control. 2) Eddy current heating of the copper.


It was noted that the currents in the stainless steel would be comparable to the currents in the copper, based on their relative cross section areas.


Interrupting the copper path with breaks might be ineffective if the copper were attached to the stainless and the breaks were short. Have to worry about the cooling tube too.


The decay time constant should be calculated. Less than 10ms is clearly acceptable, greater than 100ms is probably unacceptable.


4. Getting the GRD approved.


Discussion of some of the comments received so far:
- Clarify those requirements where the first-plasma performance metrics (in PEP) differ from design requirement.
- There is a leak rate metric for first plasma, but not a leak rate requirement. Should there be? Kugel will make a recommendation.
- The disruption handling requirements do not specify a current decay time. This is conservative since only electromagnetic loads are considered, but it would be OK to make it 1 ms.
- Is it critical to complete the heat-up and cool-down at the beginning and end of bakeout within 24 hours? Discussions with NSTX say probably not. We will understand what it drives and consider relaxing to 48 hours.


Wayne will maintain a file of comments received.


Comments are still due Sept. 6.


5. Discussed plans for NCSX PAC Meeting (Dec. 9-10) and QPS Design Assessment (Dec. 11-12), both at PPPL.


6. Next SIT Meeting: Monday, August 26, 2002, 11:00 a.m. EDT.


PPPL participants may meet in my office if they wish. Make arrangements with Pamela.
Dial-in as follows:
USA Toll Free Number: 877-925-0984
PARTICIPANT PASSCODE: 690113 (followed by #)
LEADER PASSCODE: 100800 (Wayne)
LEADER: Mr Hutch Neilson


HAVE A GOOD MEETING AND I WILL LOOK FORWARD TO READING ABOUT LOTS OF PROGRESS IN THE SUMMARY!


Thanks to all,
Hutch

Please forward any questions or comments to mailto:reiersen@pppl.gov

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