Alcator C-Mod Quarterly Progress Report - October 2001

The primary activities at Alcator C-Mod during the fourth quarter of FY01 were:continuation of the run campaign, wherein Milestones 76 and 77 were completed, and disassembly/inspection of the tokamak.

Science Results

Core Confinement and Transport

Visual Imaging of Turbulence

Analysis of the edge turbulence data continues (MIT/PPPL collaboration). Using the Princeton Scientific Instruments "ultra-fast" camera, that takes 12 sequential 4 msec images in D_a light from the separatrix region, we are able to follow the temporal evolution of the "blobs" of emission that have been seen previously in the C-Mod edge plasma. We believe that they reflect the blobby nature of the density there. The characteristic size of the brighter blobs is slightly less than 1 cm in both the radial and poloidal dimension (they have much longer characteristic wavelengths along the magnetic field). The characteristic lifetime of the brighter blobs is 10-50 mseconds. The time-sequenced images show clearly that these blobs move both radially and poloidally. Outside the separatrix the dominant radial propagation direction is outward. Characteristic outward speeds for the some of the brighter blobs are as much as 400 m/s, which means that they move a distance similar to their size during a lifetime. In contrast, some blobs move very little during their lifetimes. The poloidal velocities for the features that move poloidally are also as much as a few hundred m/s. Eddy-like motion of some features has also been observed. Examples of data from this diagnostic may be viewed at:

http://www.psfc.mit.edu/people/terry/edge-turbulence-movies.html

Theoretical simulations of edge turbulence in C-Mod were made with a 3-D nonlinear electromagnetic two-fluid model which was developed specifically to treat the collisional edge plasma of tokamaks. It was developed by our collaborators Barrett Rodgers of Dartmouth University and Klaus Hallatschek of IPP Garching. The model is based on the Braginskii equations and has diamagnetic and toroidal curvature effects but does not have particle orbit effects. The simulation described below was done in a "local" geometry with shifted-circle closed field lines but with no magnetic separatrix or limiters, which may be appropriate for the very collisional C-Mod edge plasma.

The simulation domain is 5.2 cm radially by 10.4 cm poloidally, i.e. has many wavelengths in both the poloidal and radial direction, with boundary conditions periodic in the poloidal direction, and "hard walls" in the radial direction. The code was started from an initial noise level, progressed through a linear instability phase dominated by the resistive ballooning mode, and reached a saturated steady-state after about 100 microsec.

The poloidal correlation length of the density fluctuations in this simulation was Lpol=0.6 cm, which is consistent with the experimental Gas Puff Imaging (GPI) result of Lpol=0.85 cm. However, it is also clear from comparing the simulation results with the image data for the same shot that the simulation contains more small-scale structure than does the GPI images.

Thus the initial comparison of the theoretical simulation with the measured edge turbulence in C-Mod is encouraging in several respects; namely, the average length scales, time scales, fluctuation amplitudes, and diffusion coefficients in the local simulation agree to within a factor-of-two with the local measurements just outside the separatrix. This suggests that resistive ballooning modes may be the dominant instability in this region, similar to a recent study of edge turbulence in ASDEX Upgrade. Clearly more work needs to be done to verify and extend this agreement; for example, by adding to the code more realistic magnetic and limiter boundary conditions, by extending the code to include ionization and non-local profile effects, and by many more detailed comparisons with experiment.

Double Transport Barrier Plasmas

Milestone 76 was completed in August, 2001.

**** 76. Investigation of ITB control with multiple frequency ICRF.

(Baseline target AUG 2001)

Plasmas with Internal Transport Barriers (ITBs) show promise as the goal for future advanced tokamak steady state reactor operation. Plasmas with dual edge and internal, energy and particle barriers have been formed in Alcator C-Mod with auxiliary radio wave heating, in the absence of the usual neutral beam particle and momentum sources (which will be unavailable in future reactors). The prescription for achieving these ITBs is to lower the magnetic field, which causes the radio waves (at 80 MHz) to be concentrated in the inner portion of the plasma, off-axis. Further heating power at 70 MHz will be concentrated at the core of the plasma to increase the temperature of plasma center, inside of the ITB, to hold the density profile steady and to arrest impurity accumulation. The fundamental role of plasma rotation in the ITB formation will also be investigated.

The ITBs, formed in conjunction with a reversal of the co-current central toroidal rotation velocity, are apparent for both particle and energy transport, and are confirmed by a dramatic reduction in the core thermal diffusivity inferred from TRANSP modeling. Prerequisites for forming ITBs with off-axis ICRF heating are that the density of the target plasma be above 1.4 x 10²⁰/m³, that the plasma be in EDA H-mode and that the wave resonance be located outside of r/a = 0.5. Among the unique features of the C-Mod ITBs are the presence of sawtooth oscillations, the monotonic q profile (with the ITB foot location near q=1.5) and that they form in the absence of external momentum input. For ITBs formed with single frequency ICRF waves, the particle and impurity densities continue to increase at the plasma axis until the central radiation exceeds the central input power (which is lower with the off-axis heating used to create the ITB) and the barrier collapses. Additional central heating power from a second frequency ICRF antenna has been found to arrest the particle and impurity build-up at the same time as increasing the core temperature, and double transport barrier plasmas have been held in steady state for as long as ten energy confinement times. Simultaneously with the arrest of the core density and impurity buildup, the toroidal rotation reappears in the co-current direction. By varying the timing of the on-axis heating, the density of the steady state ITB plasma may be adjusted, as shown in Fig.1. Steady state double barrier plasmas have been achieved both at 4.5 T (with 80 MHz ICRF on the high field side to form the ITB and 70 MHz ICRF for the core heating) and 5.4 T (with 70 MHz ICRF on the low field side to form the barrier and 80 MHz ICRF for the core heating). This final result shows that the triggering of the barrier formation is not explicitly related to high-field side ICRF heating, but rather the transition can be triggered by strong off-axis heating on either the high- or low-field side. This, in turn, rules out the primacy of ICRF-induced ion orbit effects, which formed the basis of some of the theories proposed to explain the phenomenon.

Transient transport analysis of sawtooth perturbations has begun for ITB discharges. The analysis is based upon a time-to-peak technique described in Fredrickson et al., Nucl. Fusion 26, 849 (1986). The primary data are from soft x-ray measurements since the ECE is often cut off for the discharges of interest. The radial profile suggests a discontinuity in the time-to-peak data when an ITB is present. The analysis also suggests that the barrier is initially near the plasma edge and moves into the core stopping near r/a~0.5 and that these discharges may have a notch-shaped transport coefficient profile (c_e). Further study is underway to check the ballistic effects in the heat-pulse study. The fluctuation data measured by the phase contrast imaging diagnostic shows no significant change in the density fluctuation level from 2 to 500 kHz. Since the PCI is a chordal measurement, we conclude that the fluctuations are not suppressed over a large cross section of the plasma during the ITB.

Fig.1 The central electron density (top) and ICRF (bottom) waveforms

for two 4.5 T ITB discharges formed with 2 MW of 80 MHz power

injected between 0.7 and 1.5 s. 600 kW of on-axis power at 70 MHz

stabilized the central density at different values, depending on the

delay time: 250 ms (green) and 550 ms (red).

Li Pellet Imaging

Further experiments have been done using the li-pellet ablation trail technique to measure internal magnetic field pitch angles. The pellet position is monitored using a downward imaging photodiode array located at the same toroidal location as the pellets (C port), which gives the radial position as a function of time. The images of the Li II ablation trails are taken with the PSI-3 ultrafast camera, in collaboration with PPPL and Princeton Scientific Instruments, which provides 12 sequential 2-d snapshots (64 x 64 pixels each) with time resolution as fast as 0.5 microseconds. For the pellet images, 30 microsecond imaging was used, which yields a spatial resolution of about 2 cm in the major radius direction. Several techniques are being investigated to measure the angle of the ablation trail, which is aligned with the local total magnetic field, and to evaluate the uncertainties. One technique, which appears to be very promising, involves taking the 2-d Fourier transform of the image, and then measuring the angular properties in k-space. A typical set of images from one discharge, along with an inferred pitch angle profile, can be seen at

http://www.psfc.mit.edu/people/marmar/li_theta_1010731004.pdf

Typical error bars range from +/-0.15 degrees to +/-0.4 degrees. These measurements can be used to constrain the EFIT reconstructions and thus yield important q-profile information.

Edge/Divertor Physics

Main Chamber Neutrals

A series of experiments was undertaken aimed at quantifying the relative contribution of divertor leakage and radial ion transport on neutral pressures surrounding the core plasma. Variations in the divertor geometry, magnetic equilibrium, divertor bypass leakage and confinement mode give evidence that cross-field transport competes with, or dominates, parallel transport in such a way that plasma exists far out in the Scrape-Off Layer (SOL) shadow and recycles on main chamber surfaces. Based on a simple neutral flow model we estimate that neutrals escaping from leaks in the lower (closed) divertor during lower X-point operation contribute a smaller fraction (~10-30%) of the midplane pressure than main chamber recycling. The inferred leakage is much larger from the upper (open) divertor during upper X-point operation. Most neutrals escaping from either divertor do not directly travel to the midplane. Instead, they are redirected, most likely by ionization and/or collisions (elastic, charge exchange). We are able to infer toroidal and poloidal neutral attenuation lengths for this leakage of ~ 20 and ~50 cm respectively. Relatively high divertor pressures are found in upper-null (unbaffled) discharges. This suggests that the SOL plasma may take the place of the mechanical structure present in the lower divertor.

Particle Inventory

Analysis of the total particle inventory and main-chamber fueling for a of series helium discharges has been performed. In these discharges, a constant plasma density was maintained after the helium gas puff was turned off, as one would expect for a 100% recycling gas species. The measured amount of helium injected into the vessel roughly agrees with total inventory of helium ions in the plasma and helium neutrals in the main chamber and divertor. The agreement was found to persist over the full set of discharge parameters. These results suggest that the present array of neutral pressure measurements roughly captures the full inventory of neutrals in the vessel. Also during these discharges, a set of 3 outer divertor flappers was repetitively opened and closed at 100 msec intervals. From the resulting rate of plasma and neutral density rise in the main-chamber, the transient neutral flow rate through a single flapper when it was initially opened appears to be about 3 Torr-l/s. This flow rate is about an order of magnitude lower than that expected from the vacuum conductance and the pressure under the flapper at the time of opening. These results suggest that plasma-neutral and/or plasma-wall interaction at or above the flapper opening may limit the effective neutral conductance.

RF Research

Milestone 77 was completed in August, 2001.

**** 77. Evaluate operation of the modified J-Port 4 strap antenna.

(Baseline target AUG 2001)

Operate the modified 4-strap antenna at 78 MHz with improved arc detection and additional diagnostics up to the maximum power that can reasonably be achieved. Using heating phase, evaluate the heating efficiency, power handling, reliability, and impurity generation of the 4-strap antenna.

The operation of the modified J-Port antenna (see description below) was quite successful in the past campaign, concluded at the beginning of August, 2001. The modified strip lines were in excellent condition (no indication of arcing on the strip lines or vacuum vessel) after the campaign. Furthermore, arc damage was predicted to be located at the ground bridge between the bridge and the strap because E||B and estimated to be ~15 kV/cm when the maximum voltage on the transmission line was 25 kV @78 MHz (~50% higher than during the last campaign) and 30 kV @70 MHz (consistent with expected frequency scaling). Arc damage was found at this location, particularly on straps #2 and #3. The modified J-Port antenna was operated at 70 and 78 MHz and at power levels up to 3.0 MW without significant RF-plasma edge interaction at the antenna corners in H-mode plasmas. From camera data, damage was expected on the BN tile fasteners and this damage was found to be generic to all antennas where a BN-metal interface was exposed to the plasma. This result suggests further modifications to be implemented before the FY2002 run campaign, based upon the empirical observations of limiting the E||B field to <15 kV/cm and removing the plasma facing BN-metal interfaces.

The overall heating efficiency of the J-Port antenna is similar to that of the D and E antennas. A phase scan showed that the nominal [0,p,0,p] was the most effective heating phase and had little or no negative edge interaction. An outer gap scan was also completed and suggested a gap of 1-1.5 cm was better than larger outer gaps. Antenna performance was insensitive to toroidal field from 5-5.6T.

The modified J-Port antenna differed from the previous version in the design of the strip line components, front tiles, and back plate. Due to arc damage found after the previous (winter 2000) campaign, the radial strip lines elements were aligned with the magnetic field to eliminate as much as possible E parallel to B arc paths. In addition, the electrode spacing was increased from 1 cm to 1.5 cm. S-parameter measurements of this new configuration indicated that the antenna was not significantly modified with respect to RF electrical characteristics. These measurements confirm our attempt to maintain a 50 Ohm transmission line while eliminating E parallel to B-field arc paths. During the winter 2000 campaign, a strong RF plasma edge interaction limited the injected power to ~2.5 MW into H-mode and the interaction appeared to follow field lines. The BN tiles were aligned and all metal surfaces except the Faraday screen were covered or removed. Measurement of the antenna tile position on all antennas confirmed that the J-Port antenna is at the same radial location as the D and E-Port antennas. In order to interrupt long field lines across the antenna, an insulating septum was installed. The back plane feedthrus were also modified to reduce the E-field parallel to the B-field. In addition, four optical arc monitors, six B-dot probes, and an MKS pressure gauge were installed. These modifications have all contributed to the successful operation and understanding of this antenna.

The optical arc monitor signals had recorded large transient signals that correlated with reflected-to-forward power arc detection during some vacuum conditioning shots. In plasma operation, the optical arc monitor signals did not correlate with most arc detect faults. This result suggests that faults were occurring outside their field-of-view. In addition, the optical monitors detected signal when the D and E-Port antennas were active. Comparisons with the voltage data indicate the induced voltage from D and E-Port antennas are low when the light signal is detected and high when no light is observed. This result suggests that the low induced voltage is sufficient to initiate multipactoring. This low power multipactoring does not impact plasma operation, nor does it affect the subsequent operation of the J-Port antenna.

The new B-dot probes indicated that the current in strap 4 was equal in both the top and bottom half of the antenna strap. They also proved to be the most sensitive diagnostics to arcs in the antenna.

The new 200 kHz and 1 MHz digitizers allowed direct monitoring of the arc protection system. During a particular experimental day, the fast data indicated that some arcs survived for 30-80 micro-sec. Up to 100 J could be available to dissipate in these arcs; therefore, we reduced the reflected-to-forward power ratio necessary to generate a trip by 25% for all subsequent experiments. This change successfully limited the arcs to ~15 micro-sec or ~15 J per MW injected.

Operations and Diagnostics

Long Pulse Operation

Two runs were devoted to extending the plasma pulse lengths in C-Mod. These experiments succeeded in extending the end-of-flattop (EOF) from 1.5 s to 3.0 s (3.2 sec for the TF), more than doubling the flattop time in these inductively-driven discharges. The long-pulse experiments were carried out at 5 T, with line-averaged density in the range 0.3x10²⁰<nebar<1.2x10²⁰ /m³, and plasma currents of 800kA. The longest discharges had current flattops of approximately two L/R times. ICRF heating was applied to several of these discharges, with power levels of ~1MW sustained for up to 2.4sec, using all three ICRF antennas run sequentially. The plasma pulse lengths were limited by administrative restrictions on the currents in the PF coils, especially the EF1 coils which are mainly used for X-point control. All power supplies functioned as expected, and magnet and bus heating during the long pulses was measured and found to be consistent with calculations carried out earlier. The maximum rise in TF magnet temperature was 39^oC. The between-shot cool-down time was only slightly longer than for normal length discharges, and in practice the between-shot time was dominated by setup time for the next shot and special measurements and inspections associated with monitoring the operation.

Evolution of the wall particle inventory and recycling was investigated using short gas puffs during the long low-density flattop discharges. We showed that the wall does NOT saturate at a time <3 seconds, at least at the low densities run in this experiment. We also showed that the inventory in the walls is not so large that it will significantly affect our ability to run at low density. These results are relevant to planning for the C-Mod Lower Hybrid/AT Physics Program.

In the course of these experiments we observed H-modes at nebar~0.65x10²⁰/m³ with ICRF power of 1 MW. We also observed, for L-mode cases, a (poorer) confinement mode at these low densities, in which temperature drops, sawtooth amplitude decreases or disappears, and fueling efficiency decreases (as evidenced by the H_a increase). These poorer confinement conditions tended to appear between 1.2 and 1.6 seconds into the discharge, and persisted for the remainder of the pulse.

Divertor heating was observed during the long pulses with the (LANL) IR camera system. We were able to puff N₂ via feedback in an attempt to reduce the heat load on the divertor; analysis of this aspect of the experiment is ongoing.

Ten shots were dedicated to high-field plasma operation. We operated at toroidal fields up to 8.0T for the first time in several years. All systems functioned nominally, and several 1MA plasmas were produced. ICRF heating (D-He³ minority heating scenario) was applied successfully.

Magnet Inspection

On August 6th, following the conclusion of the FY2001 run campaign, we began disassembly of Alcator C-Mod primarily to inspect the TF magnet. This inspection was recommended by our TF Review Committee in 1998 when the machine was last reassembled. By September 7th the cylinder was removed and detailed measurements of the TF joint resistances were begun, along with careful documentation of OH coax resistances. Following these measurements, all of which were within specification, the finger joint spring plates were removed using new instrumentation that allowed force-displacement measurements to be made. These measurements are used to make estimates of feltmetal compression. All joints were found to have acceptable loading on the feltmetal, though some joints showed lower compression than expected. We are developing new instrumentation and insertion tooling that will allow these measurements to be made during assembly. Following removal of the spring plates, the TF horizontal arms and vertical legs were removed. A small number of silver plated TF joint fingers show a frosted appearance that we are investigating. These surfaces had a polished appearance before the last assembly. The frosting indicates either some wear of the plated surface or transfer of silver from the heavily plated feltmetal. We will continue disassembly to reach the lower horizontal arm connections to the TF core and the OH2 lower coax, after which disassembly will be complete.

Both upper OH coaxes have also been removed from the machine after careful measurements of the torque settings of all six bolts securing each coax in place. Analysis of these data is proceeding. The condition of the feltmetal used in the coax connections is in an as installed condition.

Computing

Unix based computing:

A plan is in place to replace OpenVMS computing with unix (linux). This includes both user workstations, and a compute server which will be used for both inter-shot analysis and the running of modeling and analysis codes off-line. Migration of data acquisition, and experiment data storage will be done later, after some experience with these new platforms is gained. The main file/application server and a 36 node beowulf cluster are in place. The first complement of 3 user workstations is on order and we plan on at least 10 by the start of the next run campaign. Inter-shot analysis programs are being ported to the Beowulf cluster, and we intend to run most of these programs on that cluster during the next experimental campaign.

New Data acquisition hardware:

CompactPCI data acquisition hardware is being incorporated into the MDSplus data acquisition system. These new digitizers will be used for new high channel count applications, as well as to replace CAMAC modules which are aging or becoming obsolete. A prototype of this system was used during the 2001 campaign to acquire signals from the RF heating system. The main magetics, additional RF signals, and data acquisition for Lower Hybrid development will use this hardware during 2002.

Diagnostic Neutral Beam

The capabilities of, and the prospects for, DNB diagnostics on C-Mod can be inferred from measurements made during the last campaign. Signals have been obtained from all of the diagnostics. Beam density, component mix, and attenuation in the duct have been measured. Here, CXRS and BES signals are estimated for four representative sets of beam parameters. The overall conclusion from this work is that the advertised capabilities of modern beams would be advantageous on C-Mod when compared to the known performance of the present beam.

Beam Parameters

There are four sets of beam parameters. The current beam parameters are those which were available at the end of the last campaign. The best beam parameter set is the best obtained to date and was obtained during tests in February. For comparison, a projected set of parameters is included. This set is based on improvements to the magnetic bucket plasma source. The beam that was constructed by Budker Institute for RFX is included as representative of modern beam performance.

beam	current		E	E/2	E/3	E/18
Current	5.2	ion current	0.07	0.29	0.47	0.17
Best	5.2	ion current	0.27	0.29	0.36	0.08
Projected	5.2	ion current	0.33	0.33	0.34	0.00
RFX	3	neutral current	0.90	0.081	0.019	0.00

Table 1. Sets of beam parameters.

Reionization is omitted from these cases to simplify the comparisons. A pumped duct will reduce the reionization for the next campaign. For reference, the reionization without the pumped duct is included in Table 2.

Component	Energy	Duct Reionization
E	50000	0.37
E/2	25000	0.37
E/3	16667	0.32
E/18	2778

Table 2. Duct reionization

The RFX beam would deliver more beam particles to the plasma core in spite of its lower current. For high density plasmas, the beam clearly has advantages simply due to the larger concentration in the main energy component. The MSE uses the full energy component exclusively.

CXRS Signals

The computation is for 6-7, 4944.65, B⁺⁴. The concentration for B⁺⁵ and B⁺⁴ is derived from a MIST calculation for a similar shot and assumes a 1% concentration of boron. The photon emission cross sections are taken from the ADAS database. Note that the RFX beam may be expected to improve the CXRS signal over that expected from the other cases. Here, the CXRS emission induced by each component of the beam is taken into account.

BES Signals.

Like the CXRS diagnostic, the BES diagnostic uses emission from all three components of the beam. Even so, the modern beam will produce a larger signal than either of the other cases.

Lower Hybrid Project

(see separate report)

Divertor Upgrade

In order to operate with higher elongation and at higher plasma current (and to survive higher current disruptions), the inner divertor nose will be replaced. The old inner divertor has been completely removed from the machine, and measurements of stud and diagnostic positions on the inner wall have been made. A picture of the first fitup of inner divertor backing and c-plates together with some tiles can be found at

http://www.psfc.mit.edu/cmod/operations/EngImages/MACHINE/Divertor/Aug31_08.jpg

A view of the back of the divertor assembly can be found at

http://www.psfc.mit.edu/cmod/operations/EngImages/MACHINE/Divertor/Aug31_10.jpg

The invessel fitup of the new inner divertor has been completed successfully. All measurements have been made needed to complete final machining of the components and to have the inner surfaces silver plated to enhance thermal contact to the inner wall. All components have been delivered to the vendors and are all expected back by the end of the month. Work at MIT will now concentrate on the installation of the studs. Before being shipped out, the inner divertor was assembled in our machine shop as one last assembly test. A picture of the assembly may be seen at

http://www.psfc.mit.edu/cmod/operations/EngImages/MACHINE/Divertor/P0002145.jpg

Mike Demaria on the left, our design engineer, and Jim Zaks, divertor project lead engineer, are shown standing over the divertor. Measurements indicated a variation in the inner ring diameter of less than 0.005", well within the tolerance required to maintain efficient heat conduction into the inner wall.

Collaborations/Participation in the Fusion Science Community

ASDEX Upgrade

Operation in support of MP287, "ASDEX-Upgrade Similarity Experiments" was undertaken. The goal was to make high density, high power EDA H-modes in a shape identical to that in ASDEX-Upgrade 'Type II ELM' discharges. This regime, which was only recently obtained on AUG, appears rather similar to that obtained on C-Mod when power is increased into EDA H-modes. At reduced powers, AUG sometimes sees a 'quasi-coherent' mode. We wanted to see if the same behavior is observed on the two machines with the same dimensionless parameters. We obtained edge profiles both at threshold and in the steady H-mode period. AUG will then try to match the dimensionless parameters (n*,b, r*) of these discharges. The shape development part of the run went quite smoothly, and we did get shots that were a very close match to ASDEX Upgrade shapes. Compared to our usual operation, these plasmas have quite low triangularity and are very close to being double null. As expected, it was more difficult to get steady EDA H-modes in the lower triangularity ASDEX-Upgrade shape and also that RF coupling is much more difficult (the two effects may be related). On some shots a weak quasi-coherent mode was seen on PCI, but it was not strong enough to cause large particle transport. The optimum density seemed to be nel=9.5x10¹⁹ /m². At higher targets the gas pressure increased substantially, and the H-mode density became steadier, but seemed to exhibit bursts of higher transport, reminiscent of the typical behavior with Type III ELMs and a cold edge, though the ELMs were not immediately obvious. An H-mode shot that was not steady-state but had moderate and steady increases in density and radiation was obtained, which should be suitable for ASDEX-Upgrade to attempt to match. We completed this phase of the experiment by taking a slow power ramp to get the threshold power and edge parameters at identical target conditions. This will be suitable for AUG threshold comparisons.

National Fusion Collaboratory

The remote data access capabilities of MDSplus (http://www.mdsplus.org/) are being enhanced to include secure authentication and authorization. This work is being done under a Department of Energy/Office of Science grant for "Scientific Discovery through Advanced Computing: National Collaboratories and High Performance Networks"(http://www.fusiongrid.org/) Using the security tools of the Globus software under development at Argonne National Laboratory and the secure authorization management tools of the Akenti software under development at the Lawrence Berkeley National Laboratory, the MDSplus package will be extended to use X.509 security certificates to authenticate client/server connections and optionally encript the communications. A prototype MDSplus client and server using Globus secure communications has been implemented and will be demonstrated at the SuperComputing 2001 Meeting (http://www.sc2001.org/) in Denver in November.

Domestic Travel

Earl Marmar was at U. of Wisconsin, Madison, July 10-11 for a meeting of the Next Step Options Program Advisory Committee.

Paul Bonoli visited the Princeton Plasma Physics Laboratory (PPPL) from Monday - Thursday (July 23-26, 2001). He worked with Dr. Cynthia Phillips and Yuichi Takase on HHFW heating in NSTX and he gave a talk at the weekly NSTX Group Meeting titled "Full-wave modelling of HHFW heating in the NSTX device". Paul Bonoli also attended a 2 1/2 day planning meeting for the RF Sci-Dac Initiative (Scientific Discovery Through Advanced Computing). The meeting was hosted by Cynthia Phillips (PPPL) and was attended by representatives from ORNL, Lodestar, PPPL, Mission Research Corp., Comp-X, and MIT. The meeting was extremely productive. A three year workplan was formulated and physics issues related to C-Mod specific problems were discussed in detail.

Tom Fredian and Martin Greenwald travelled to Chicago for a meeting of the SciDAC funded national fusion collaboratory. Participants from MIT, GA, PPPL, ANL and LBNL attended. This was the first face to face meeting of the group and concentrated on developing a detailed work plan for the first year of the project. MIT work on the collaboratory will be focussed on the addition of a certificates-based authentication scheme for MDSplus and SQL server access.

Jim Irby, Monty Grimes, Dave Terry, Jim Zaks and Ron Parker attended the Lower Hybrid Coupler Final Design Review, the 31st of July, at PPPL. The Review was successful and we concluded that procurements and fabrication could proceed. While at PPPL for the LH launcher design review, Terry met with Nevell Greenough and discussed briefly the demodulator and protection circuitry PPPL is using as well as the new phase feedback system they are implementing.

Parker stayed at PPPL August 1-2 to attend the FESAC meeting.

Dave Terry traveled to Opal-RT in Canada for a demonstration of their RT-Lab software. He discussed three of our possible applications with them, including the Lower Hybrid, Fast Ferrite Tuner, and Hybrid Computer systems.

Martin Greenwald was in Santa Fe the week of Sept. 10 to attend a meeting of the Esnet steering committee and to participate in a review of the Esnet program.

John Rice was at PPPL on Sept. 20-21 to participate in the NSTX review and to present a talk ‘Double Transport Barrier Plasmas in Alcator C-Mod’ at the NSTX physics colloquium.

Miklos Porkolab, Ron Parker, and Earl Marmar attended the Fusion Power Associates annual meeting in Washington, Sept. 25,26. Ron presented a talk entitled "Comparative Overview of Burning Plasma Experiments", and Earl presented a talk on the "Alcator C-Mod National Facility Advanced Tokamak Program."

International Travel

Bruce Lipschultz attended the Int'l meeting on Plasma Edge Issues (July 10-11th) at the JAERI Naka site. There were 5 sessions at this meeting with a number of talks on: high density operation, ELMs, main chamber recycling, SOL flows and high-Z materials experience. Bruce Lipschultz gave a presentation on main chamber recycling work at C-Mod and DIII-D as well as a presentation on high-Z wall operation in C-Mod. He also chaired the main chamber recycling session.

He also spent time (July 10th-13th) with collaborators N. Asakura and T. Nakano at JT-60U on US-Japan collaboration FP3-5, "Comparison of main chamber recycling in C-Mod and JT-60U'. The purpose of this work is to compare and contrast JT-60U and C-Mod SOL data and plan towards joint experiments on JT-60U and C-Mod. Diagnostics and experiments were identified for the September run period on JT-60U.

From Sept 5 to 7, Amanda Hubbard attended the 8th IAEA TCM on H-mode physics and Transport Barrier Physics, at NIFS, Toki, Japan. She presented a poster on "Evolution of Pedestal Profiles through the L-H and H-L Transitions in Alcator C-Mod", and also one on "Double Transport Barriers in Alcator C-Mod" on behalf of John Rice. On Sept 10-12, she attended the first meeting of the International Tokamak Physics Activity (ITPA) on burning plasma transport, also at NIFS.

Bruce Lipschultz was at JET from Sept 5 to 7 to work on JET data related to SOL transport and main chamber recycling. This collaboration is with Guy Matthews, Kevin Erents and Wojtek Fundamenski. Bruce looked at SOL data from a number of JET shots, and discussed improvements in diagnostics and potential joint experiments. He joined Brian LaBombard in Aix en Provence to attend the IAEA Technical committee meeting on Divertor Concepts organized by the Cadarache group. Brian LaBombard gave a talk on cross-field transport in the SOL. Bruce Lipschultz gave a talk on the origin of neutrals in the main chamber of C-Mod.

Near Term Plans

The near term plans include continuation of the magnet inspection, installation of the new inner divertor and reassembly of the machine to resume operation. There are also some modifications to the ICRF antennas, the cylinder and the cryostat

Schedule

The near term schedule calls for reassembly to be complete by mid March 2002 with operation resuming in April 2002.

http://www.psfc.mit.edu/cmod/operations/short_term.pdf