MS-Word (Annual Report, Appendix1, Appendix2)
The Large Tokamak Collaboration has continued successfully in 2003, with personnel assignment program, workshop, task assignment program, and IEA/ITPA coordinated experiments. The Implementing Agreement functioned efficiently to promote improved understanding of tokamak physics and development of fusion technologies.
I-1 Executive Committee Members
Dr. J. Pamla : EFDA Associate Leader for JET
Dr. S. Clement-Lorenzo : DG Research, CEC
Dr. M. Watkins : Head of Program, EFDA-JET CSU
Mr. M. Cox : Head of the Machine Operations Department
Dr. E. Oktay : Office of Fusion Energy Sciences, DOE
Dr. N. Sauthoff : Head of Off-site Research Department, PPPL
Dr. J. Willis : Director, Research Division,
Office of Fusion Energy Sciences, DOE
Dr. R. Stambaugh : Key Advisor of International Collaboration in U.S., GA
Dr. M. Kikuchi : Deputy Director, Department of Fusion Plasma
Dr. Y. Miura : General Manager, Large Tokamak Experiment and
Diagnostics Division, Department of Fusion Plasma
Dr. K. Ushigusa : Senior Staff, Office of Planning, JAERI
Dr. S. Ishida : General Manager, Tokamak Program Division, JAERI
I-2 Streamlining / enhancing the coordination of activities, and increasing
At the last IEA FPCC meeting in 30th January 2003, action items emerged to request IEA fusion IAs that "they should be reconsidered in order to improve 1) Co-ordination and internal coherence between IEA IAs, the FPCC, the CERT, and the international fusion R&D programme, and 2) Visibility of the FPCC and fusion IAs inside and outside the IEA, and communication to the public and policy makers".
In response to above request, at the 18th Executive Committee Meeting held at JET, 4-5 June 2003, the Executive Committee discussed and decided to streamline and enhance the coordination of activities within the IEA Large Tokamak IA as well as across IEA IAs and ITPA. The committee also discussed how to increase IEA fusion activities visibility. A number of decisions were made along these two lines that will be implemented in the frame of this IA. (As a result of interaction with IEA IAs for the poloidal divertor experiments and the plasma wall interactions in TEXTOR, a letter was jointly sent from chairs of the three IAs to IEA FPCC dated 30th July 2003.)
There were two major decisions as follows;
1) The executive committee decided to make a restructuring of the Tasks to align it with the structure of ITPA Topical Groups. This should help streamlining the processes of implementation, monitoring and reporting.
2) The Executive Committee agreed to construct Large Tokamak home page to increase visibility of IEA Large Tokamak IA. JT-60 member offered to construct Large Tokamak Home Page at JT-60 site (http://www-jt60.naka.jaeri.go.jp/lt/). This proposal was unanimously agreed among the Executive Committee members. This home-page contains, objectives and scope, historical achievements of large tokamaks, annual reports, Executive Committee Meetings, Tasks, Workshops, ITPA coordinated experiments, etc. Its first version was open to the public in November 2003 and was announced to Dr. G. Simbolotti of IEA and FPCC chair.
I-3 Personnel Assignment Program, Workshop, and Executive Committee Meeting
The total number of personnel assignments carried out in 2003 was thirty-two (U.S.<-->JET (20), JET<-->JT-60 (7), and JT-60<--> U.S. (5)).
Four workshops were held as follows.
(1) W51 "In-vessel Tritium Inventory" (March 2003, JET); tritium behavior in large tokamaks was discussed in relation to ITER.
(2) W53 "Management of Wastes from Fusion Facilities" (March 2003, JET); Radioactive waste management was discussed for TSTA, TFTR, JET, JT-60 in relation to ITER.
(3) W54 "Implementation of the ITPA Coordinated Research Recommendations"(Nov. 2003, JT-60); see section I-5.
(4) W55 "Physics Needs for High Beta Steady State Tokamak" (Nov. 2003, JT-60); Physics issues of high beta steady-state operation as most likely operation mode of DEMO was discussed covering steady-state operation in ITER and US, EU, JA, RF approaches toward this scenario.
The Eighteenth Executive Committee meeting was held at JET on 4-5 June 2003. The coordinated assignments in the year were reviewed, and the annual strategic work program was discussed in this Meeting. Those activities in 2003 were summarized in Appendix 1.
I-4 Task Assignment Program
As mentioned in Section I-2, the Task assignment program has been restructured to align it with the structure of ITPA Topical Groups. They are now; Task 1 - Transport physics, Task 2 - Confinement database and modeling, Task 3 - MHD disruptions and control, Task 4 - Edge and pedestal physics, Task 5 - SOL and divertor physics, Task 6 - Energetic particles, steady state operation, and Task 7 - Tritium and remote handling technologies. Task 7 is a continuation of one of the former tasks in the IEA Large Tokamak IA. The first reports, which cover the period from July to December 2003, for the new tasks are included below. Then the final reports from the former tasks up to June 2003, which were submitted to the last Executive Committee Meeting, are included in Appendix 2.
As reported below, significant progress has been made as a result of the ITPA high priority physics multi-machine experiments coordinated through IEA Large Tokamak IA and other IAs.
Task 1: Transport Physics
International collaborative experiments coordinated through IEA IAs have made significant progress and expanded multi-machine data sets for further analysis on transport properties. For improved physics understanding of QDB/QH-mode operation, a long ELM free phase with edge harmonic oscillations (EHO) was produced in JET (with US participation). Analysis of previous JT-60U data has revealed strong evidence for QH-mode like behavior as co/counter-beam balance is varied and this behavior was reproduced in 2003 experiments with detailed measurements on magnetic fluctuations and pedestal structures in collaboration with US scientists.
A US scientist participated in the study of impurity transport in JET and completed the validation of the JETTO/SANCO/NCLASS coupling. Analysis shows that impurity behavior is in quantitative agreement with the neoclassical transport.
The US collaborator for the Motional Stark Effect diagnostic on JET worked with EU scientists to plan a trace tritium experiment designed to observe energetic ion confinement in discharges with zero core current density. This experiment was successfully carried out in October.
Task 2: Confinement Database and Modeling
Substantial progress has been made in resolving differences between the beta () scaling of confinement as determined from global databases and from dedicated machine parameter scans. Joint experiments on JET (with US participation) and DIII-D (with EFDA-JET participation) showed no confinement degradation with increasing beta. New scaling relations have been derived from the ITPA confinement database and found to be electrostatic and gyroBohm-like. These scalings predict that the fusion performance in ITER will be improved at high beta, yielding twice the fusion power as compared with operation at the nominal value.
Task 3: MHD, Disruptions and Control
JET (with US participation) and JT-60U studied the applicability of noble gases in reducing VDE forces and divertor heat loads, and in avoiding runaway electron generation; DIII-D (with EFDA-JET participation) demonstrated the benefits of high gas jet pressures for disruption mitigation; ASDEX Upgrade (AUG) showed reduced disruption forces and heat loads at lower gas jet pressures.
Closely co-ordinated experiments on JET, DIII-D, and AUG focused on the scaling of the marginal , below which 2/1 and 3/2 NTMs become unconditionally stable. Sawtooth control to avoid NTM seeding has continued on JET, DIII-D, AUG and TCV.
The control of Resistive Wall Modes and correction of error fields to maintain the stabilising plasma rotation have progressed on DIII-D using the 6 new internal control coils (I-coils). These data, together with Resonant Field Amplification experiments on JET (with US participation) which compared favourably with MARS stability calculations, should elucidate the scaling of the relevant damping terms. DIII-D (with EFDA-JET participation) has also used its I-coils to study the effect of error field spectral content on locked mode thresholds.
Task 4: Edge and Pedestal Physics
Validity tests have been carried out on models for the width and gradient of the edge (pedestal) profile in H-mode plasmas, as well as allowing the investigation of regimes with different ELMs.
With matched plasma shapes in JET (with Japanese participation) and JT-60U (with EFDA-JET participation) the pedestal pressure with Type I ELMs in JT-60U is ~60-70% lower than in the dimensionally identical JET plasmas, for similar values of *. Differences in aspect ratio and edge rotation, as well as possible effect of ripple losses, may account for the differences in plasma behaviour. Co-ordinated MHD analysis (with EFDA-JET participation at JT-60) of selected pairs of discharges has highlighted possible differences in the access to the second stability regime. On JET and DIII-D the width of the pedestal density barrier may be consistent with a neutral penetration model, but neutrals do not control the width of the temperature barrier. ELM energy losses (WELM/Wped) show a dependence on *. MHD edge fluctuations in JET are suggestive of the Quasi Coherent Mode, identified in C-Mod as responsible for steady losses in the EDA regime, but in JET these fluctuations are not sufficient to produce a stationary ELM-free regime.
Task 5: SOL and Divertor Physics
High priority research issues include the scaling of Type-I ELM energy loss, Tritium co-deposition, disruption and effect on materials choices, scaling of radial transport, and parallel transport in the SOL. These involved comparative experiments between JET, DIII-D and AUG. There is a reasonable agreement between these three devices on dimensionless comparison of Type-I ELM energy loss and in scaling of radial transport. In the study of disruptions and their effect on materials choices, it appears that power to divertor is different in JET than it is on DIII-D and AUG.
Task 6: Energetic Particles, Steady State Operation
Study of an ITER steady-state operation relevant discharges, which have a weak shear q profile, has been carried out in JET (with US and Japanese participation). A discharge which has a large fraction of bootstrap current (~ 50%) in a weakly negative shear discharge with qmin ~ 2, nearly full non-inductive current drive with LHCD was maintained by real time control of the ion temperature gradient. For development of an ITER hybrid scenario, which have a flat q profile with qmin>~1, mapping of operational regime in q95, density and shaping has been studied in JET in collaboration with US and AUG. By matching elongation, aspect ratio, triangularity, q profile and *, all AUG features are recovered in JET: ・H89p ~ 5.9 at q95 ~ 3.9 up to 2.8. The hybrid regime has been achieved at lower * (2.5T/2.1MA) but not yet at the lowest * value (3.4T/2.8MA) (with Japanese participation in data analysis). The required values of ・H89p/q952 to operate ITER at Q=10 have been achieved in JET and exceeded in DIII-D and AUG.
A US scientist has joined the test of N-NBI system on JT-60U to expand beam pulse width and to measure the beam divergence of the improved ion source. The aperture displacement of the beamlet and the space charge repulsion between beamlets have been extensively discussed.
A workshop on "Physics Needs for High Beta Steady State Tokamak" (W55) was held on Nov. 24 at JAERI. This workshop was motivated to discuss physics issues of high beta steady-state operation as most likely operation mode of DEMO. The Workshop covered steady-state operation in ITER and US, EU, JA, RF approaches toward this scenario. Presentations were given on the standard and low aspect ratio approaches as well as profile optimization including current hole.
Task 7: Tritium and Remote-Handling Technologies
In view of the importance of tritium retention in ITER, the successful tests of laser de-tritiation at PPPL of samples from JET MkIIA divertor tiles (reported in the Annual Report for 2002) continued in 2003 with preparations for a technological demonstration of in-vessel laser de-tritiation in JET during the 2004 shutdown. Remote Handling was to have been used to treat limiter tiles in-situ using equipment developed by PPPL from their laboratory equipment. Unfortunately, restrictions on the US budget will prevent this demonstration in 2004. Instead the tiles will be treated using a photon cleaning technique developed in the EU.
Through the coordination with IEA ESE Agreement, JT-60 carbon dust has been collected using INEEL collection tool and sent to INEEL for the analysis. The 24 dust samples were collected in poloidal direction on the vessel surface. The total amount of dust collected was 25 mg.
Concerning the characterisation of carbon flakes, 1g of flakes from JET were sent to FZK. An average BET surface of (4.50.6) m2g-1 were found in agreement with previous values measured for PTE flakes in TLK (7m2g-1) or with the INEEL measurements for DIII-D dust particles (30.2) m2g-1 and TFTR dust particles (6.9 to 26.5) m2g-1.
In order to test the performance of a cryosorption pumping panel, a prototype was installed in JET during June 2003 and used during the Trace Tritium Experiments. In the near future, it will be exposed to highly tritiated gases in a parametric test programme. The cryopanel will then be sent to other EU laboratories for detritiation treatments.
I-5 Workshop on "Implementation of the ITPA Coordinated Research Recommendations" (W54), Nov. 23, 2003, JAERI-Naka
This was the second workshop on Implementation of the ITPA Coordinated Research Activities.
In response to the IEA FPCC recommendations in March 2003 for closer interaction among the fusion related IAs, the Executive Committee members of the three tokamak related IEA IAs (LT, PD, and TEXTOR) agreed to jointly organize the W54 workshop. The First Announcement for the W54 workshop was circulated widely in the international tokamak community, and attracted a large number of participants to the workshop. The representations included from the following tokamak related organizations:
- ITPA Coordinating Committee and Chairs/Co-Chairs of Topical Groups
- ITER International Team (IT)
- Executive Committees of IEA IAs on LT, PD, and TEXTOR
- Leadership from the international tokamaks that are currently operating:
The workshop carried out its work in four sessions in one day:
Session 1: Status of Joint Experiments for 2002/2003 developed at the previous workshop held at MIT in November 2002
Session 2: Overview of ITPA proposals for Joint Experiments in 2004
Session 3: Operational Plans for tokamaks in 2003/2004
Session 4: Planning of joint experiments among the tokamak programs.
A general status of the 2003 proposals planned for implementation at the MIT workshop was discussed; The workshop had identified 39 proposals, of which about 30 were designed for joint experiments (E), and nine were considered as programmatic activity (P) that did not require joint experiments. There was activity in almost all of the 39 proposals during the past year. The ITPA Chair summarized the technical results from these joint experiments, which involved extensive scientific exchanges, carefully designed experiments, and data analysis. This response to the joint experiments was considered very successful, as also shown by the increased level of participation at this Naka Workshop for the planning of the 2004 program.
The tokamak program leaders made brief presentations on their operational schedules and their process for planning the 2004 experimental program plans.
The proposals for 2004 were then presented by the TG Chairs/Co-Chairs. The workshop identifies 44 proposals of which 30 are continuation from 2003, 14 are new. Nine proposals are completed in 2003. Among 44 proposals, 28 were regarded as joint experiments (E), and six were considered as programmatic activity (P) that did not require joint experiments, and six were regarded as proposals needed further details (D). Distribution among Tasks are 6 for CDB, 6 for TP, 12 for PEP, 7 for DSOL,
The tokamak leaders wanted to limit the list only to joint experiments. It was decided that the programmatic proposals are carried out by the TGs anyway without the necessity for coordinating joint experiments, or by analysis of existing data, or single-machine data. The emphasis for the Joint Experiments was to focus on those proposals that would benefit from joint experiments and requires scientific exchanges that can be facilitated by the IEA implementing agreements or bilateral exchange programs. It was also agreed that results of joint experiments should be circulated for both ITPA TG chairs and concerned facility leaders.
These information are on the IEA LT Workshop web-page.
II Present Status of Each Party
During 2003, JET continued to focus strongly on ITER needs, concentrating on the optimisation/development of plasma scenarios to increase the lifetime of ITER plasma facing components, to reduce the extrapolation to ITER, to progress towards high performance and steady state, and to prepare for burning plasma physics. The reinforced partnership in the Experimental Programme, Facility Operation and Enhancement under the contractual/financial framework of EFDA provides valuable experience for the organisation, construction and operation of ITER. International collaboration with Japan and the US concentrated on the ITPA ITER high priority physics multi-machine experiments (with JT-60U, DIII-D, C-Mod, AUG), coordinated through IEA IAs. The active involvement of scientists from the Russian Federation and the Peoples Republic of China was established under International Agreements.
With reversed magnetic field and plasma current, the plasma flow stagnated throughout much of the Scrape-off-layer (in contrast to the strong net flow, up to M=0.6, from outer to inner divertor observed with forward field/current) and net deposition on the outer divertor was observed for the first time. Trace levels of tritium (<1-2% of the deuterium fuel and injected by gas puffing and/or high energy Neutral Beams, NB) were used for the first time in six years as a precise diagnostic to probe the confinement of the fusion fuels (key physics parameters such as normalised Larmor radius or plasma collisionality were varied), to validate the use of high energy tritium for plasma heating, and to test ITER-relevant diagnostic techniques (neutron detectors, -ray measurements). High power (upgraded NB), high current ELMy H-modes approached conditions in normalised Larmor radius * which were about a factor of two larger than in ITER. Real time control techniques were used extensively: to obtain high performance, steady conditions in impurity seeded plasmas with reduced divertor heat fluxes; to establish long pulse reversed shear discharges with wide ITBs, mild ELMs and close to full non-inductive current drive; and to control both the pressure and q profiles in high power ITB discharges using three actuators, LH, ICRH and NBI. ITBs have been produced with ICRF mode conversion heating (stronger than with minority ICRF heating). Lower hybrid power has been coupled under ITER-relevant conditions of large antenna-plasma distance (0.1m); high quality ITBs were maintained. JET at reduced performance reproduced dimensionally identical AUG long pulse "hybrid" operation, and extended the regime to values of * closer to ITER. Under conditions similar to those established in C-Mod, DIII-D and AUG, mild ELMs with reduced power loading on plasma facing components have been observed but the full benefits found in the smaller machines have not yet been realised on JET. Multi-machine co-ordinated experiments were particularly successful for edge (pedestal) and Neoclassical Tearing Mode (NTM) studies (Section I-4). Confinement degradation due to NTMs was found to be weaker at high when bursts of m/n=4/3 activity interrupted the 3/2 activity. Saddle coils and error field correction coils were used to study Resistive Wall Mode physics below the critical . The stabilisation of sawteeth by fast particles was controlled by ICRF resonant near the q=1 surface.
Low Activation experiments in deuterium, helium and hydrogen in early 2004 will be followed by a major shutdown to install further enhancements, notably an ITER-like ICRH antenna (7.2MW power capability and ELM-resilient coupling; High Power Prototype support tests are being conducted at Oak Ridge National Laboratory), a new divertor target for higher triangularity operation, and 14 new/upgraded diagnostics for both deuterium and D-T operation.
Fusion Technology on JET launched nineteen new tasks, and during 2003/4 the focus will be on water detritiation, waste characterisation and treatment, detritiation of plasma facing components, neutronics and safety. The supporting R&D, detailed design, costing and procurement package for a Water Detritiation System will be defined by the end of 2004.
There have been substantial positive movement towards advancement of Japanese fusion research in 2003. After the integration of STA and Monbusho into the MEXT (Ministry of education, sports, culture, science and technology), a working group (WG) on fusion research was formed under the council for science and technology to discuss future direction of national fusion research when ITER becomes reality. The report was accepted at the Council for Science and Technology in January 2003. The Working Group has defined four centralized programs consisting of three future centralized programs, tokamak research (the National Centralized Tokamak Device Program), reactor engineering research (the Fusion Material Test Facility Program), and laser fusion research (the Laser Fast Ignition Program), and has added the existing helical research (the Large Helical Device (LHD) Program) to these three. The Working Group concluded that this National Centralized Tokamak Device has to be a super-conducting device with break-even-class plasma performance aimed at high-beta values (the normalized beta = 3.5 to 5.5) required for the demonstration reactor with sustained operation longer than 100 seconds under full non-inductive current drive conditions. The Working Group also concluded that JT-60 should continue operation as one of 3 centralized joint research devices (JT-60, LHD and GEKKO-XII) until the start of the National Centralized Tokamak Device Program. After this WG report, a study group was formed under AEC (Atomic Energy Commission) of Cabinet Office to check and review the progress of 3rd phase basic program of Japanse fusion research and development. In the summary of major items reported to Advisory Committee on Nuclear Fusion in Dec. 1, it was noted that tokamak research should be directed to fusion power generation hoping ITER will be sited in Japan while other concepts such as helical and laser fusion are taken as important academic researches.
Following the recommendation of the WG report, number of national collaborators in JT-60 research team is increasing rapidly and becomes 168 in FY2003. Research subjects led by University researchers are increased from two in 2002 to five in 2003.
JT-60 started FY2003 conditioning operation in November and will perform 16 weeks of extensive research operations until mid 2004. During more than 1 year of no-operation phase of JT-60U, extensive efforts have been placed on the improvement of the machine capability, especially on the extension of discharge flat-top from 15 s to 65 s. Pulse length of NBI and LHCD will be extended to 30 s and 65 s, respectively. So far, discharge length was extended from 15 s to 48 s and ELMy H-mode was sustained for 30 seconds. Sustained duration of high ~ 3 is extended to 3.4 second and injected power to plasma in a single discharge is increased to 0.286GJ.
Feasibility study of current hole as a reactor core is also studied with respect to the beta limit and energetic particle confinement showing good prospect for the reactor.
Gyro-kinetic turbulent simulation code GT3D of JAERI is benchmarked against PPPL codes giving good agreement.
There have been substantial positive developments in the U.S. Fusion Energy Sciences Program in 2003. The major development is of course the Presidential decision in January 2003 for the U.S. to join ITER negotiations. This decision increases the importance of tokamak research on the major U.S. facilities and through International Tokamak Physics Activity (ITPA) in support of ITER and gives a context for the development of their 5 year Program Plans for the three major facilities (DIII-D, C-MOD, and NSTX). The Office of Fusion Energy Sciences (OFES) peer-reviewed the 5 year Plans for these three facilities, in part to meet their renewal cycles, and in part to improve the scientific quality of their programs. There is also an emphasis to increase the operating times of the major facilities. As a new program, the construction of the National Compact Stellarator Experiment (NCSX) at PPPL has started in FY 2003.
The mission of the U.S. Fusion Energy Sciences Program is still "Advance plasma science, fusion science, and fusion technology - the knowledge base needed for an economically and environmentally attractive fusion energy sources". The program is recognized as a science program with energy goal, not just an energy program or a science program. It derives its strength from its potential contribution to future energy mix, and it is included in the Long Range Energy Strategy of the Administration.
It has been a long road for the Presidential decision to join ITER negotiations. It required both a strong community support and champions at the high levels of government. The U.S. community organized several workshops and held Snowmass summer study during the past 2-3 years to reach a consensus on the scientific merits of burning plasma physics and the need to build a new facility for it. The community plans for the Burning Plasma Physics were reviewed by the Fusion Energy Sciences Advisory Committee (FESAC) and National Research Council (NRC) which supported the decision for the U.S. to join ITER.
The DIII-D, C-MOD, and NSTX 5-year plans were reviewed during April-June, 2003. The DIII-D focus is on Advanced Tokamak, Energy Transport, and Mass Transport. The C-MOD thrusts are Quasi-Steady State Advanced Tokamak, Burning Plasma Support (at high toroidal fields), and to investigate fusion science issues using its unique dimensional parameters. The NSTX focus is on the impact of small aspect ratio on the toroidal physics, which provides a path for high-beta operation.
The U.S. program has made an effort to increase the experimental operating time on the major facilities. In FY 2003 (the period from October 1, 2002 to September 30, 2003), DIII-D operated for14 weeks, C-MOD for 13 weeks, and NSTX for 8 weeks (a problem with the NSTX coil joint in the summer terminated the operations prematurely). In FY 2004, all three facilities are planning for 21 weeks of operations.
There is a strong support in the U.S. for ITER and the related International Tokamak Physics Activity (ITPA), The three U.S. facilities are extensively engaged in the ITPA Joint Experiments and in ITPA/ITER support through theory, modeling, and sharing data.
III Planned Activities in 2004
At present, two workshops such as "Physics of Current Hole (Feb. '04, JT-60)" and "Neutron diagnostics (JET)" are planned.
Personnel exchanges for the first half of the year was agreed already and those for the second half will be proposed at next Executive Committee meeting.
The next Executive Committee meeting will be held in 14-15 June 2004 at JT-60. The coordinated assignments in the year as well as the annual strategic work program will be reviewed in this Meeting. Planning of activities in 2004 will be also discussed in this meeting.
Appendix 2 to IEA LT-IA Annual Report 2003
Report from Task Assignment Programmes for June 2002 - June 2003
(This report was submitted to 18th Executive Committee Meeting held at JET, 4-5 June, 2003.)
Task 1: Transport / Confinement
Research on reversed-shear and optimized shear plasmas with internal transport barriers (ITBs) has continued on JT-60U and JET. Drs. X. Litaudon and H. Shirai have discussed the confinement and transport of double transport barriers in JET and JT-60U. Drs. X. Litaudon and T.Suzuki have compared the formation condition of the internal transport barrier between JET and JT-60U. The newly found equilibrium of Current Hole at the extreme condition of reversed shear plasma has been studied in JT-60U and JET extensively. Drs. T. Fujita and N C. Hawkes have begun the comparison of the Current Hole. Dr. V. Parail stayed Naka three weeks to analyze data for similarity experiment between JET and JT-60U. He found the difference of the edge stability for two very similar discharges and pointed out a number of possible reasons (aspect ratio, mode of instability, heating power, ripple loss, heating scheme of NB or effect of wall).
Significant activity from US collaborators has continued with focusing on analysis of ITB discharges via TRANSP, the NCLASS, FULL and GS2 codes. Dr. K. Hill has presented the analyzed results of JT-60U ITB plasma at 19th IAEA Fusion Energy Conference. Modeling work has continued on all devices to determine the appropriate model for the radial transport of heat and particles. Both transient and steady state techniques have been used to test a large variety of theoretical and empirically based models. Although some models have been eliminated there is as yet no preferred model. Dr. W. Houlberg has continued with his implementation of the FORCEBAL code to aid in the development of transport tools for the analysis of JET plasmas. The NCLASS has also been incorporated into the code JETTO. Dr. L. Baylor has continued his activities on pellet fuelling and modeling of pellets launched from the inside, high field side, and vertical launch tubes of JET.
Dr. J. Hogan and D. Hillis have focused on the optimization of ELM heat flux mitigation on JET using extrinsic impurities. A detailed model for ELM effects on core impurity transport in the pedestal region was developed for use in the SANCO radial impurity transport code at JET, and a study of the comparative utility of using C, N, O, Ne, Ar and Kr for mitigation studies was presented at APS (Orlando, 2002). A 17-species version (D, C, N atoms and ions) of the solps code (B2-Eirene) has been created and used to evaluate the role of ELMs in JET divertor heat flux reduction experiments with N injection (to be presented, EPS 2003). These modeling tools are now being applied to recently conducted JET deuterium-helium change-over experiments (May 16), which use the same 'power step' scenario in DOC-L, in order to better quantify the active exchange processes which determine tritium retention. Dr. D. Hillis has also begun the design and procurement of a new diagnostic for Helium Ash Detection in DT plasmas which will be available for JET-EP. This new diagnostic will be jointly funded from the USA and JET.
During the past year collaborative experiments were completed on DIII-D and JET on the important issue of the scaling of confinement with . Both sets of experiments confirmed the weak scaling of B with observed previously which is in conflict with the IPB98 scaling. Dr. D.C. McDonald of the UKAEA traveled to GA to take part in the experiments on DIII-D. Effort is currently being focused on understanding the apparent discrepancy between these single scan results and the scaling from the database.
As for the future plan from June 2003 to June 2004, the research on reversed-shear or optimized shear plasmas with ITB, and Current Hole found in JT-60U and JET will be continued. The relation among ITB, microinstability, ExB shearing rate and etc. will be studied further. Also continued are the study of pedestal characteristics and its stability. The multi-machine experiments proposed by ITPA Topical Groups will be performed extensively under IEA-LTA framework and the inter-machine collaboration will be extended in the coming new year.
Task 2: Macroscopic Stability
During the past year the collaboration has concentrated on studies related to neo-classical tearing modes (NTMs), error field induced locked modes, edge localized modes (ELMs), resistive wall modes (RWMs) and the stability of advanced operating regimes.
NTM studies have focussed on examining the marginal beta below which NTMs become unconditionally stable. The study of this process gives insight into aspects of the physics of NTMs by avoiding issues of seed island behaviour. Coordinated experiments have been conducted on JET, DIII-D and ASDEX Upgrade and will continue in June 2003 and beyond. Also for NTMs since the sawtooth instability is a principal source of seed islands for their destabilisation, particularly for the m/n=3/2 NTM, the elimination or control of sawteeth can raise the beta limit to NTMs, as shown by previous experiments on JET. Complementary experiments are now planned for 2003 on DIII-D using electron cyclotron waves.
Joint error field experiments between DIII-D and JET have commenced. The 12 new internal coils (I-coils) on DIII-D, and the new external Error Field Correction Coils on JET, give enhanced freedom to vary error field harmonics, making it timely to revisit the issue of the effects of side-band harmonics on error field driven locked mode thresholds. Data has been collected on DIII-D for the error field thresholds using different combinations of I-coil wirings. The related JET experiments are expected to occur in early 2004 and, when combined with existing COMPASS-D data, should improve understanding of harmonic effects on error field locked mode thresholds.
Dr. Sakasai had detailed discussion with Drs. S. Hotchin, S. Pinches and M. Bigi on the error field correction coils (the saddle coils and the in-vessel coils) and their power supply system. The information is very useful for design of the error field correction coils and the power supplies in the JT-60 modification program (JT-60SC).
Collaborative studies of the modelling of ELMs between JT-60, DIII-D and JET have progressed, based on the interpretation of the experiments. The mechanism of the trigger of the ELMs was clarified by the collaborative stability analysis and the model of ELMs was applied in a transport code.
Building on the understanding of RWMs gained on DIII-D, collaborative experiments have commenced on JET to study RWMs. In particular the stability of (stable) RWMs has been probed by measuring the amplification, phase shift and decay rates of applied error fields (following the successful use of this method on DIII-D). These experiments which have yielded good data will continue on JET later this year. The influence of rotation on stability is also important. A collaborative study on the injection of different amounts of momentum commenced between DIII-D and JT-60, and a related experiment will be planned on JT-60.
Research on the current hole was undertaken in collaboration between JT-60 and JET. MHD equilibrium and stability of the current hole were investigated and the formation mechanism was discussed. Collaborative research on current holes was also undertaken at PPPL. Simulations in toroidal geometry, predict that these discharges undergo n=0 reconnection events, "axisymmetric sawteeth", that redistribute the current to hold its core density near zero. Unlike conventional sawteeth, these events retain the symmetry of the equilibrium, and thus are best viewed as a transient loss of equilibrium, caused when a 1/q=0 rational surface enters the plasma.
Task 3: Divertor and Plasma Boundary
A LTA workshop was held at JET in spring 2002 to compare and discuss the ELM behaviour in the three large tokamaks, with 2 participants from JT60 and 3 from US side. A summary can be found under http://www.jet.efda.org/conf/iea-elms02/. An additional workshop was held at JET on Erosion and Deposition and Related Modelling Activities (20-21 March 02) with 4 participants from US side.
Dr. A. Sakasai discussed divertor experiments without the septum in JET with Drs. P. Andrew and C. Challis. The septum was removed from MKII-GB divertor to increase flexibility at high- and high-triangularity operation.
Collaborations between the DIII-D and JET programs have continued in the analysis of helium plasma operation. An LLNL scientist from the LLNL/DIII-D collaboration program participated in the helium experiments in 2002, and did UEDGE analysis of the helium plasmas as part of the experimental analysis. This work was presented at the 2002 PSI meeting.
Collaborations has been continued in the field of particle control and helium exhaust in different divertor configurations, and for optimisation of advanced tokamak plasma operation. The helium compression, enrichment and removal depend strongly both on the divertor configuration, and on the plasma conditions such as density, discharge mode and heating scenario. In campaigns C1-C4 these studies have been performed for a number of conditions such as ELMy H-mode, high triangularity plasmas and ITB discharges in the presence of a divertor septum. These studies were repeated in campaign C5 to investigate the effect of the septum removal.
The effect of plasma drifts on the boundary plasma of DIII-D, JET, and JT60-U has been examined using the UEDGE code. The simulation results have been compared with detailed probe measurement, particularly on the JT60-U experiment. The results were presented at the 2002 PSI meeting. The simulated plasma parallel flow was reasonably consistent with experiment on the high field side of the plasma, but somewhat poorer on the top and low field side. Work is continuing to better understand the differences between measurement and simulation. In addition, we have begun a code benchmarking effort to make detailed comparison of simulations of a JET discharge with UEDGE, SOLPS, and EDGE2D.
Various tokamaks observe large cross-field transport in the SOL which can be much higher than expected, possibly leading to radial fluxes competing with flow into the divertor. These processes have been investigated by means of probe measurements and wide angle CCD overview observations under different plasma configurations, wall clearances, and main chamber neutral pressure versus divertor pressure. It has been found that the SOL ne profiles flatten with increasing<ne>, in common with C-Mod, although the effect is less pronounced on JET. The corresponding JET outer SOL ionization source profile shape stays roughly self-similar as <ne> is increased (it broadens in C-Mod). The neutral penetration, as measured by the neutral mean free path normalized to minor radius, is at least a factor of 2 larger in JET than C-Mod. The implications of these differences will be further explored.
Collaboration on QH mode experiments were carried out in connection with Task Force S1 and Task Force E. Two scientists from the US participated in QH mode experiments on JET. (Punit Gohil, C. Lasnier)
Dr. A. Whiteford calculated soft-X ray emission rate coefficients for Kr and Xe. The rate coefficients were used for analysis of Kr and Xe transport at internal transport barriers in JT-60U reversed shear plasmas. The analysis showed that high-Z impurity accumulated inside the internal transport barrier.
Dr. K. Hill analysed thermal transport and microinstability characteristics of high-density H-mode plasmas with and without impurity puffing in JT-60U. These plasmas had a normal divertor configuration and a configuration with the outer divertor strike point on the dome. Mechanisms leading to improvement of confinement in Ar-puffed plasmas were investigated with TRANSP code and GS2 code. The results were presented at the IAEA Fusion Energy Conference in Lyon.
Dr. N. Asakura joined JET experiments conducted by the Task Force-E Group, where the influence of removing the private septum on the divertor plasma was investigated Dr. Asakura had discussions about neutral compression in the divertor and in-out asymmetry of the divertor plasma with Dr. W. Fundamenski. He discussed the SOL plasma flow pattern in JET and JT-60U with Dr. K. Erents. They agreed to make a proposal for multi-machine comparison of the SOL flow and its effect on impurity transport under the IEA-LT/ITPA collaboration.
Task 4: Fast Particle and Current Drive
Alfvn Eigenmodes in AT plasma
Increased understanding of AE modes in reversed and weak magnetic shear profiles has been a major product of collaborative programs this year. Scientists from the US, EU and Japan have been actively cooperating to understand the nature of previously poorly understood chirping mode activity in AT regimes. A new model, the reversed-shear-induced Alfven Eigenmode (RSAE), has been developed in collaboration with PPPL to interpret fast frequency chirping Alfven Eigenmodes (EAs) observed in reversed shear plasmas in JT-60U. The chirping and roll over of the frequency of NNB an RF driven AEs observed as qmin decreases can now be explained by transition from RSAE to the TAE. These results were presented as a joint paper (M. Takechi, et al.) by Japan and US (PPPL) in the 19th IAEA Fusion Energy Conference, Lyon, October 2002. Motivated by this work, PPPL scientists reanalyzed the original description of alpha particle driven instabilities in the Tokamak Fusion Test Reactor (TFTR) in terms of Toroidal Alfven Eigenmodes (TAEs). In a collaboration with JET scientists, the inconsistency with the variation of the mode frequency with toroidal mode number and the anti-ballooning density perturbation of the modes in TFTR have now been resolved. Based on the new interpretation of AEs in reverse shear plasmas in JT-60U and JET (called Cascade modes), it is now shown that the TFTR data can best be explained by the transition form RSAEs to TAEs as q0 decreases. This result, derived in collaboration with JET scientists, has been submitted to PRL. In addition, the interaction with PPPL scientists has led to a reevaluation of the JET Cascade mode theory. These modes were originally thought to be EPMs, but the work at PPPL with the CASTOR and the NOVA-K code has shown that these modes also exist in the Ideal MHD limit. This reanalysis was motivated by the understanding that such modes must necessarily be perturbative in the TFTR alpha TAE experiments due to the very low fast particle drive. In a recent development, Alfvn cascades are now successfully used on JET for diagnosing the so-called "ITB triggering events", by resolving that ITBs are triggered near integer q-surfaces. These ITB triggering events look like sudden increases of electron temperature slope, dTe/dt, from which the ITB starts. Additionally, it has been shown theoretically that Alfvn cascades are consistent with both weak as well as strong fast ion transport. Above the threshold for the onset of resonant EPMs, strong fast ion transport occurs in "avalanches". Future work will address the possibility of using experimental measurements of Alfvn cascades to characterize the fast ion distribution and the power density threshold for the transition from weak to strong fast ion transport.
NNB current drive on JT-60U
The performance of the NNB system has progressed dramatically in the past year through collaboration between JAERI and PPPL. A 10 second injection of 2.6 MW at 360 keV was obtained by modifying electrodes in the ion source.
Sawtooth control with ICRH
Sawtooth control techniques with ICRF power at the fundamental and the second harmonic of H have been developed on JET. Scans have been made in the resonance location, H concentration and antenna phasing. In these experiments, two of the four ICRH antennas are used to generate on-axis fast particles, to stabilize the sawteeth, whilst the other two drive current at the q=1 surface, to destabilize them. These results are being analyzed with the participation of US fast ion specialists.
Task 5: Tritium and Remote-Handling Technologies
PPPL/EFDA-JET cooperation: The testing of a method for ex-vessel detritiation of JET CFC tiles exposed to tritium plasmas is being developed. The preparatory work has been completed at PPPL and tests will be carried out soon. The aim is to assess the efficiency of tritium removal using decontamination and heating provided by oxygen-methane burner. The fraction of tritium which can be removed from the surface and bulk of the tiles, rate of tritium out-gassing before and after detritiation will be evaluated. Several systems, developed at PPPL and sent to UKAEA, include an Oxidative Tritium Decontamaination System (for which arrangements are being made to permit its testing with JET soft waste samples) and a PIN diode tritium detector (which will be tested by JET Health Physics). A full day of Remote Handling time has been included in the plan for the JET 2004 shutdown to carry out laser de-tritiation of Outer Poloidal Tiles using equipment developed at PPPL.
LANL/EFDA-JET cooperation: The design of a water detritiation facility for JET is being carried out under an EFDA Fusion Technology Project. As a part of this package, columns for hydrogen isotope separation by cryogenic distillation need to be designed and the cost for construction evaluated. Cryogenic distillation columns of overall separation factor 100,000 or larger and with feed flow rate of 100mol/h would be needed. LANL, having a large experience in design, optimisation and operation of cryogenic distillation systems for separation of hydrogen isotopes, could provide a very valuable contribution. This is under discussion. In addition, the key focus of the US tritium program has been to stabilize the Tritium Systems Test Assembly which is scheduled for completion during 2003.
JAERI activities: Tritium analysis and detritiation study of TFTR D-T plasma facing tiles were started comparing JT-60 D-D tiles. High energy density UV laser irradiation is also planned in this study, which has proved to be effective for the removal of co-deposited layer in the experiment with JT-60 H-H tiles. Systematic experiments on the behaviour of tritium in JT-60 have started, and various cleaning techniques of the vacuum vessel have been tested for the removal of hydrogen isotopes. Results of the first series of experiments were presented in IEA LTA Workshop W51. As a second series, the effect of air purge was investigated. Waste management at JT-60 was summarized and presented in IEA LTA Workshop W53.
JAERI/PPPL cooperation: In the area of developing technologies of tritium removal from plasma facing components, the applicability of fiber to YAG laser irradiation for detritiation was successfully verified. The activity was performed in February 2003 based on personnel assignment JU93. Further cooperative activities are planned to include a tritium analysis and detritiation study on TFTR D-T tiles together with JT-60 D-D tiles and a study of behaviour of tritium in JT-60.
JAERI/EFDA-JET cooperation: In the area of developing effective and reliable plasma exhaust gas processing techniques and research on tritium management in tokamaks for the future D-T burning machines, various R&D work is in progress, and useful information exchange to perform this R&D work effectively has been made. The activity was performed in February 2003 based on personnel assignment JE127. A further cooperative activity is planned in this area.
UKAEA/PPPL cooperation: Concrete cores from the walls of the JET Torus Hall have been analysed for tritium by the UKAEA. A comparative analysis by PPPL will allow PPPL to consider whether it will be possible for the concrete to be treated to reduce the tritium content so that it could be free released and whether it would be possible to undertake the necessary detritiation tests. The tritium is only in the boronated concrete on the inside of the Torus Hall and its level is low - typically in the range 1 to 10 Bq/gram.
JAERI/PPPL future co-operation: US developed a technique of carbon dust collection from the vacuum vessel, and this was already applied in TFTR and EFDA-JET. It is planned that JT-60U carbon dust is sent to US (INEEL) and analyzed there. A probable candidate of the analysis is Dr. Phil Sharpe (INEEL).