Upper Divertor Cryopump Quarterly Progress Report Presented by B. LaBombard for the Cryopump Team July 26, 2007

Transcription

1 Alcator C-Mod Upper Divertor Cryopump Quarterly Progress Report Presented by B. LaBombard for the Cryopump Team July 6, 7

2 Recent Accomplishments Alcator C-Mod Pumping Slots Gas Baffle Gas Cuffs (for laser access) Periscope Cryopump is Operational Cool-down to LHe attained on May 5 => factor of reduction in base pressure Cryogenic control system works well Easy to operate - technician Seamless integration of cryopump operation with C-Mod shot cycle cool-down, pumping, regen ~ min. Only 6-9 liters of LHe consumed for a run heat exchanger LHe line stepper control valve LN line LHe Dewar PLC Rack

3 Recent Accomplishments Alcator C-Mod Cryopump Startup Experiments Performed (MP#475) - Cryopump meets D Pumping Speed Benchmark Torr-l/s 6 4 D Injection Rate - D injection at ~35 torr-l/s mtorr Torus Pressure - Chamber ~ 3.5 mtorr liters/s System Pumping Speed Pumping speed = 9.6E+3 liters/s - Pumping speed ~ 9,6 liters/s 3 4 seconds

4 Recent Accomplishments Alcator C-Mod - Pumping slot/baffles work as planned USN upper divertor pressures ~ LSN lower divertor pressures. Upper Null - Red Lower Null - Blue MA.5 Plasma Current. m - mtorr mtorr.8.4. NL4 Upper Divertor Pressure Similar neutral pressures Lower Divertor Pressure seconds

5 Recent Accomplishments Alcator C-Mod - Pumping slot/baffles work as planned USN upper divertor pressures ~ LSN lower divertor pressures. Forward Field Direction Upper Null - Red Lower Null - Blue. Reversed Field Direction MA.5 Plasma Current MA.5 Plasma Current m - mtorr mtorr NL4 Upper Divertor Pressure Lower Divertor Pressure Similar neutral pressures seconds m - mtorr mtorr NL4 NL4 Upper Divertor Pressure Lower Divertor Pressure Similar neutral pressures seconds.5. - Divertor pressures and pumping throughputs are found sensitive to magnetic field direction

6 ..5 seconds seconds seconds seconds..5. Recent Accomplishments Alcator C-Mod - Effect of SSEP on pumping throughput explored SSEP jog from LSN to USN is being used as a tool to promptly turn on cryopumping - Excellent L-mode density control has been demonstrated Example of SS operation with large pump & puff throughputs: m - Torr-l/s mtorr NL4 UDIV Pressure Injection Rate seconds - Very flat NL4 trace = density control - Steady state fueling rate of ~ 4 torr-l/s ~, liters/s pumping speed at pump entrance

7 Remaining Activities Alcator C-Mod Semi-Automatic Cryopump Control - Cool-down & regen initiation based on C-Mod states Continued Development of Cryopump as an Operational Tool MP#498 Density peaking at low collisionality MP#56 H-Mode with cryopumping in upper single null topology...

8 ..5 seconds seconds seconds..5. Remaining Activities Alcator C-Mod Semi-Automatic Cryopump Control - Cool-down & regen initiation based on C-Mod states Continued Development of Cryopump as an Operational Tool MP#498 Density peaking at low collisionality MP#56 H-Mode with cryopumping in upper single null topology... m - mm Challenge: H-mode density control NL4 3 SSEP & 9 L-H density rise L-mode reference plasma NL4 9 SSEP seconds L-H density rise is faster than pumpout - Jog in SSEP controls pumping rate Potential remedy: Evolve H-mode into ELMy regime, apply cryopumping...

9 C-Mod FY7 Campaign Status presented by R. Granetz Alcator C-Mod quarterly review 6 July 7

10 C-Mod JOULE target is 5 weeks of research operation in FY7 Budgeted for 6 research days plus 4 startup & conditioning days So far we have completed about 75% of the planned weeks of operation, and we anticipate meeting the 5 week research target around the end of August. We are currently running two run weeks in reversed B T and reversed I p configuration. Remainder of campaign is heavily oversubscribed, as always. It will include operation at several different ICRF frequencies.

11 C-Mod 7 run utilization through 5 July (in run days) Topic/Group Run Days Original Allocation Pre-Physics* LH H-mode Scenarios MHD. 6 Divertor/Edge Transport 5.38 AT Scenarios.5 7 ICRF.9 6 Operations Diagnostics Total Research Startup/Condition Total Operating 5.76 (~ weeks) *Note that some of the research runs, especially under the LH and Diagnostics topics, were actually done during the pre-physics time (tentatively before 74), so these aren't really overrun. We have actually used 8.5 days for official "Startup and Conditioning" activities, out of 4 budgeted, so at this point we get about six bonus days available for research and/or operations (i.e. frequency switches, etc.)

12 Facility Status and Plans DoE Quarterly Review 7/6/7

13 Status Alcator C-Mod is currently in operation (details from Bob Granetz) 5 plasma discharges thus far 77% startup reliability Operational activities thus far include Excellent performance of the new upper chamber cryopump Tests of the prototype FFT system Improvements in MSE diagnostic performance Commissioning of new diagnostics and diagnostic upgrades Routine operation of Long Pulse DNB

14 Updates: Lower Hybrid Systems Lower Hybrid Control and Protection Systems Continuing to work with vendor of high speed CPCI data acquisition card to provide programming area for coupler protection upgrade interlock signals Phase I SBIR awarded to design transmitter protection system upgrade (Rockfield Research, Inc.) Lower Hybrid Stainless Steel Couplers Detailed analysis of brazing process is now complete New brazing fixture being fabricated A 4-window braze test will be performed New couplers and windows are in-house 3

15 Updates: Lower Hybrid Systems Design of nd launcher continues New 4-way splitter design may reduce complexity of the jungle gym (8-way systems also under investigation) Prototype splitter fabricated and successfully tested at low power Detailed layouts of E-Plane design underway 4 th Cart Fabrication work also continues Klystrons are being refurbished Circulators on order and on schedule for Fall delivery 4-way splitter 8-way splitter 4

16 Updates: ICRF Systems Continued fast-ferrite-tuner work The power reflection on the match side has been dynamically kept below % for sudden plasma variations, such as L-H transition and pellet injection. For a slowly varying plasma, the power reflection is usually < 3% under feedback control. Low power drivers for transmitters #3 and #4 replaced No saturation Less harmonic generation Reduced performance of J-Port antenna under investigation 5

17 Updates: Diagnostics Upgrades and additions to CXRS, fast scanning probes, x-ray spectrometers, Thomson scattering, bolometry, Penning gauges, and plasma video system are all operational and providing new data Science Surface Station (S 3 ) is providing important new data on boronization deposition profiles as function of fill pressure and vertical field Dual FIR laser for polarimetry diagnostic expected Feb 8 Single chord rotation measurement during next run campaign Quotes being received for detectors Collaborations with PPPL and UTexas underway Beam position feedback system being tested this run campaign (direct application to ITER) 6

18 Boronization Boronization is critical to high performance operation of C-Mod Boronization has previously been done with toroidal field only, using an electron cyclotron discharge to produce the plasma --- particles drift out radially; very little localization The addition of a vertical field can improve the localization of the deposited boron Coat proper surfaces Protect outboard components S 3 has been used to study the deposition profiles as a function of vertical field, diborane pressure 7

19 NSTAR On June st NSTAR reconfigured our 3.8 kv line that supplies power for our LH HV supply, ICRF, DNB, several power supplies, and the alternator drive motor Power was no longer supplied from two stations but just one Remaining station had.5 Ω current limiting reactor in the line that resulted in up to a 35% drop in voltage under load We have reconfigured some of our power systems to use house power (another 3.8 kv source) NSTAR has completed a review and is scheduling removal of the reactor Configuration w/o the reactor will result in acceptable voltage drops 8

20 Liquid Helium There is a shortage of helium (nation wide) Numerous problems at processing plants Suppliers are reducing allocations We have had to carefully work availability of LHe into our operational planning (cryopump, DNB, diagnostics) Now working with multiple vendors We already had plans to reclaim helium gas for reprocessing at the MIT Cryogenics Lab This effort has been moved up in the schedule and will be available before the next run campaign Exhaust gas will be pressurized and returned via an underground line directly to the Cryolab 9

21 Plans Complete 5 week operation (approx run days remaining) Continue design of new E-plane launcher and fabrication of new klystron cart (4 klystrons) Complete brazing of 4 new couplers Preparations underway for up-to-air period. A few items from the work list include Improve high voltage performance of J-Port antenna Add gas puff capability to lower hybrid launcher Refurbishment of LH launcher Numerous diagnostic upgrades Additional marker tiles Magnetics refurbishment

22 Lower Hybrid Experiment Completion of non-joule Milestone: Operate LHRF into L-Mode and H-Mode plasmas, and investigate combined LHRF and ICRF. (June 3, 7) Ron Parker Alcator C-Mod Quarterly Review 6 July 7

23 Coupling of LHRF into ICRH-heated and H-Mode plasmas depends on density at grill no special problems as long as density maintained x 8 m -3 Operation up to MW with E- and J- port antennae and in ohmic H-mode D- and E-port antennae decrease density at LH antenna Magnetically well connected to LH antenna at C-port Less dramatic effect from E- port, especially following boronization Γ Short Pulse Coupling Data 6 o 9 o Solid curves: Brambilla coupling code n grill = 4x 7 m -3 o n [m 3 ] probe x 8

24 Boronization apparently has beneficial effect on n grill ICRF Power RF Power (MW) [kw] [MW] 7698 Post boronization ICRF RF Power (MW) [kw] 7474 Pre boronization I sat [A].. I sat [A].. Top Mid Bot n e bar [m 3 ] x n e bar [m 3 ].5 x I p [MA].8 I p [MA]

25 Shot 7695: ICRH-heated L-Mode discharge with LHRF n e bar [m 3 ].5 x I p [MA] Mid n e [m 3 ].5 x V loop [V] LH Bot n LH Mid n LH Top n e [m 3 e [m 3 ] e [m 3 ] ] Mid T e [kev] x x x Time [s] LH Net [kw] GPC ICRF Net [MW] LH Ref Co [%] Time [s]

26 Shot 7673 : ICRH-heated H-Mode discharge with LHRF n e bar [m 3 ].5 x I p [MA] Mid n e [m 3 ] 3 x V loop [V] Mid T e [kev] LH Top n e [m 3 ] LH Mid n e [m 3 ] x x GPC LH Net [kw] ICRF Net [MW] LH Bot n e [m 3 ] x Time [s] LH Ref Co [%] Time [s]

27 Shot 7539 : ICRH-heated H-Mode discharge with LHRF n e bar [m 3 ] x I p [MA] Mid n e [m 3 ] 3 x V loop [V] Mid T e [kev] LH Top n e [m 3 ] LH Mid n e [m 3 ] x x LH Net [kw] GPC ICRF Net [MW] x LH Bot n e [m 3 ] x Time [s] LH Ref Co [%] Time [s]

28 LH plus ICRH applied early in slow ramp discharge (Ip = 6 ka in ms) delays sawteeth Ohmic ICRH ICRH+LH,

29 LH plus ICRH applied early in slow ramp discharge (Ip = 6 ka in ms) delays sawteeth

30 Summary Coupling LHRF and ICRF in L- and H-Mode Plasmas LHRF has been successfully coupled into ICRF heated L-Mode and H- Mode plasmas. No special problem providing adequate density at grill is maintained. (LHRF has also been coupled into Ohmic H-modes and has also triggered them.) LHRF with ICRF has been used as a tool to delay onset of sawteeth during slow rampup discharges. Exploration of synergies between ICRF-heated H-Modes and LHRF will require density control (e.g., upper null, pumped) and higher LHRF power as expected from simulations.

31 Bremsstrahlung Profiles Broaden as n is Increased Dynamic development of Bremsstrahlung profiles obtained by square wave modulating RF with 5 ms period. Spectra averaged over ~ pulses. Count rate for 4 6 kev (s ) 8 x HXR Profiles for 6 o Phasing Shots.5 ms.5 5 ms ms 7.5 ms.5 ms.5 5 ms ms 7.5 ms.5 ms.5 5 ms Count rate for 4 6 kev (s ) 9 x HXR Profiles for 9 o Phasing Shots.5 ms.5 5 ms ms 7.5 ms.5 ms.5 5 ms ms 7.5 ms.5 ms.5 5 ms Count rate for 4 6 kev (s ) 8 x HXR Profiles for o Phasing Shots.5 ms.5 5 ms ms 7.5 ms.5 ms.5 5 ms ms 7.5 ms.5 ms.5 5 ms Viewing Cord Channel Viewing Cord Channel Viewing Cord Channel n =.6 n =.3 n = 3.

32 Bremsstrahlung Emissivity Becomes Peaked Off-axis for Higher n 4 6 kev emissivity (counts/(mm 3 str s)) x 4 Emissivity for 6 o Phasing Shots r/a.5 ms.5 5 ms ms 7.5 ms.5 ms.5 5 ms ms 7.5 ms.5 ms.5 5 ms 4 6 kev emissivity (counts/(mm 3 str s)) x 4 Emissivity for 9 o Phasing Shots r/a.5 ms.5 5 ms ms 7.5 ms.5 ms.5 5 ms ms 7.5 ms.5 ms.5 5 ms 4 6 kev emissivity (counts/(mm 3 str s)) x 4 Emissivity for o Phasing Shots r/a.5 ms.5 5 ms ms 7.5 ms.5 ms.5 5 ms ms 7.5 ms.5 ms.5 5 ms Absorption predicted to occur at lower temperature as n increases, T e ~ ( kev ) 3 n

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34 Alcator C-Mod Contributions to ITER Design Review DoE 3 rd Quarter FY7 Review July 6, 7

35 C-Mod Personnel are Actively Involved in the ongoing ITER Design Review Paul Bonoli Coordinated and drafted the Physics Design Section of the Day Lower Hybrid Current Drive System proposal Currently being evaluated as part of the overall Review Amanda Hubbard and Joe Snipes Sensitivity study for L-H threshold for various proposed perturbations (particularly B T reduction) Recommended more general assessment of threshold, pedestal evolution, hysteresis Report submitted last week Ian Hutchinson, Steve Wolfe, Marco Ferrara Evaluation of vertical stability margins, particularly in light of C-Mod design and operational experience Analysis tools developed for C-Mod being applied Being combined with DIII-D and PPPL proposal to US-ITER for explicit funding Joe Snipes Evaluation of Alfven Eigenmode behavior changes with reduced B T Jim Terry and Jim Irby Evaluation of US credited diagnostics (spectroscopy, polarimetry, interferometry) Josh Stillerman and Tom Fredian Plans and design of the CODAC system for ITER Included participation in recent design review at Oak Ridge Earl Marmar Chairing Diagnostic Design Review for all ITER systems Review at Cadarache, July 9-3 Report is in preparation