Please note the following report is for informational use. It may not be cited as a scientific reference nor may it be quoted in publications without permission. Contact Jim Terry (terry@psfc.mit.edu) with comments or questions.

The primary activities at Alcator C-Mod during the fourth quarter of FY97 were: continued analysis of C-Mod data from previous run campaigns, preparation for the run campaign which began October 30, execution of ITER-relevant experiments on the electron-cyclotron-resonance-heated discharges used for wall cleaning, continued work on major systems upgrades (the RF transmitters and the Diagnostic Neutral Beam), management of the repair of the alternator which powers most of the machine magnets, and continued participation in the critical assessment of fusion science. A more detailed account of these activities follows.

Scientific Results

Analysis of Alcator C-Mod data has continued and led to a number of new results.

Core Confinement Results

Dimensionless Scaling

Experiments were carried out to determine the scaling of the normalized confinement time, Bt_E , and normalized thermal diffusivity, c_E/c_Bohm, with r^* and n^*. With a fixed ICRH frequency of 80 MHz, these experiments compared deuterium discharges heated via first harmonic hydrogen minority at 5.3 T to those heated at second harmonic hydrogen minority at 2.6 T. In the first set of experiments, heating power, plasma current and density were adjusted to match the profiles for q, b, and n^* while varying r^* by a factor of about 1.6. Further experiments matched b and r^* while varying n^* by almost an order of magnitude. Global scaling was observed to be gyroBohm like; that is, Bt_E was found to be proportional to (r^*)^-3.1. The error in the r^* coefficient was estimated conservatively to be ±0.6. The ratio of normalized thermal diffusivity between a high field discharge and a low field discharge was consistent with gyro-Bohm scaling across most of the profile. The uncertainties in this measurement are large, and separation of the ion and electron channels is probably not statistically significant. These results are similar to those reported by DIII-D and JET. Surprisingly, even with all three experiments, C-Mod, DIII-D, and JET, showing gyro-Bohm scaling, scaling between these machines gives a result closer to Bohm. The collisionality scans showed a surprisingly strong dependence. Both global and local analysis gave approximately a linear dependence on n^*.

Critical Gradient/Marginal Stability Behavior

Edge temperature and core confinement are tightly correlated for L and H-modes in C-Mod over a wide variety of regimes including ELMfree, and ELMy/EDA H-modes, ordinary L-modes, and enhanced L-modes which are achieved by strong heating of reversed field plasmas. The improved confinement is not merely the result of adding a temperature and density pedestal to an L-mode discharge. The core gradient, defined as an average over the region outside the sawteeth and inside the edge transport barrier, increases linearly with edge temperature. This behavior is qualitatively consistent with critical gradient-length transport models (for example, ITG turbulence). Simulations from one such theory, the IFS-PPPL model, were compared to experimental data. The model gives fairly good agreement for ion temperatures in C-Mod H-modes (though it consistently underpredicts T_i in L-mode). The electron temperature is often overpredicted. There are a number of possible reasons for this. First, Dorland's nt code, which is used for the simulations, does not have a sawtooth model and sawteeth are very strong in C-Mod discharges. The result of adding an ad-hoc sawtooth mixing model to the simulation substantially reduces the discrepancy. Second, the model only includes effects on the electrons from the ITG mode and additional sources for electron energy loss may be present. Finally, it is worth noting that the C-Mod collisionality falls outside the range of validity assumed by the IFS-PPPL model.

In the area of H-mode thresholds, a new collaboration with Jim Drake and Barrett Rogers of the Institute for Plasma Research, University of Maryland, was initiated this summer. C-Mod threshold data have been recast in terms of the dimensionless variables a (the ballooning parameter) and a_diam (the ion diamagnetic parameter) proposed by Rogers and Drake. The results show that our L-mode edge parameters, measured at the 95% flux surface, are indeed in the same range as those considered in their model. Their 3-D numerical simulations of drift-ballooning turbulence and transport should thus be applicable. We find that the L-H transitions do exhibit thresholds in these dimensionless parameters which are close to the critical values a_crit and a_diam,crit predicted by the simulations. Furthermore, the 5.3 T and 8 T points in this dimensionless space overlap, despite having quite different global and local threshold parameters. We find the level of agreement of the predicted and measured thresholds very encouraging, and will pursue further comparisons. These results, as well as a summary of experimental threshold results, were presented at the H-Mode Workshop in Kloster Seeon, Sept. 22-24.

Another of the papers written for the H-mode Workshop was ``ELMs and fast edge fluctuations in Alcator C-Mod'' by J. A. Snipes, R. S Granetz, M. Greenwald, A. E. Hubbard, I. H. Hutchinson, et al. Just above the H-mode threshold power at low density, small amplitude high repetition rate (1 - 5 kHz) Type III Edge Localized Modes (ELMs) are observed. At higher input power, the H-modes become ELM-free. At high density and high input power ( [`n]_e > 2.2 ×10²⁰ m^-3, P_in > 2 MW), the plasma often enters a new H-mode regime now called the Enhanced D_a H-mode, which is a steady-state H-mode often without distinct ELMs but with high levels of D_a emission. Enhanced D_a H-modes are accompanied by persistent high frequency broadband (50 - 400 kHz) density and magnetic fluctuations. Above about n_e > 3 ×10²⁰ m^-3, the Enhanced D_a H-modes may also exhibit bursting or continuous low m, n coherent magnetic fluctuations with frequencies from 60 - 90 kHz. In H-mode, steep edge gradients are observed with a nine channel ECE polychromator and a 38 channel high resolution edge soft x ray array. The soft x ray pedestal width remains around 3 to 4 mm in ELM-free H-mode and between Type III ELMs. The pedestal collapses within 100 msec during an ELM. Calculations indicate that the plasma in H-mode is often near ideal ballooning first stability limits, but no Type I ELMs have yet been identified. Edge micro-tearing modes, destabilized by the steep temperature gradient, are also considered as a possible explanation of the observed fluctuations during Enhanced D_a H-mode.

The chord-integrated data from the edge x-ray array have been inverted to get edge x-ray emissivity profiles as a function of time. Preliminary results during ELMy H-modes show a very narrow pedestal width, which can be as narrow as 3-4 mm. The pedestal is located inside of the nominal separatrix by about 7 mm. The x-ray pedestal is momentarily destroyed during ELM events, but recovers quickly. The heat pulse from the ELM's is observed well beyond the limiter radius.

Analysis of H-mode results from the last campaign continues. H-L back-transitions have been examined for precursor-like signals on the magnetics. Coherent 150 kHz signals were observed only on outboard coils, which might indicate that the instability is localized to the outer edge. A toroidal mode number of 7 has been found. The poloidal mode number could not be determined because of poor signal coherence from the inboard coils. Such characteristics are very similar to those of Type III ELMs, and the triggering mechanism for the H-L transition may be similar.

In collaboration with K. L. Wong from PPPL, we have been analyzing what appear to be Toroidal Alfven Eigenmodes (TAE) in some reversed shear discharges with early ICRF heating during the current rise. Magnetic pick-up coils at the wall observe a very narrow feature in frequency space that changes frequency rapidly from about 200 to 400 kHz within about 15 msec. This is shown in Fig. 1. The q profile is evolving during this phase of the discharge. If these modes are indeed TAE modes, the change in frequency would suggest a factor of two change in q at the region of steepest gradient in the fast ion pressure profile during this time. Calculations using neoclassical resistivity, however, indicate that the q should not be able to change that quickly. About a factor of four increase in resistivity would be necessary for dq/dt to be that large.

Edge and Divertor Research

Research on the role of neutrals in establishing an H-mode-confinement edge pedestal has continued using a number of new diagnostics. Measurements of ``radiated'' power through escaping neutral particles were obtained during our last campaign. Preliminary analysis made by comparing two measurements, one by normal foil bolometers, the other by the newly installed AXUV diodes, which measures photon radiation only, indicates a significant source of ``radiation'' loss is carried by neutrals immediately inside the separatrix. Effects are being quantified for different conditions such as L vs H mode discharges. The difference in the total light edge profiles during L- and H-mode are shown in Fig. 2. These profiles are inversions of the high resolution, chordal measurements, whose horizontal fan is shown in Fig. 3.

Data from the prototype divertor cryopump run is now being analyzed to investigate its effect on impurity transport and pumping. Pumping speeds in the range of 1000-1500 l/sec for D₂ were determined. In nitrogen injection experiments, pump operation reduced nitrogen concentrations in the core by about a factor of two. In the private flux region of the divertor the reduction was even greater. The cryopump also pumped the puffed recycling impurities, Ar and Ne. The core electron density was also affected by the pump, since slightly larger puff rates were required to obtain the same density during the flattop portion of the discharge when the pump was on. In addition, the density pump-out (occurring during the ramp-down phase) was faster with the cryopump active. These results were obtained with a single prototype pump, representing about 10% of the ultimate pumping speed, once the full cryopump system is installed. These experiments complete milestone 61, Initial Evaluation of Cryp-pump Operation.

Opacity of D₀ Lyman Line Emission

Both the ionization/recombination balance within the divertor and the interpretation of the D₀ spectrum from the divertor are affected by trapping of Lyman series emission. The importance of the problem has been pointed out and considered in the literature. The primary effect on the ionization/recombination balance is to lower the temperature at which the ionization rate equals the recombination rate for n_e = N₀. Experimental observations of trapping of Ly_b in the JET divertor plasma have been reported previously. Because of its importance to the ionization/recombination balance and to the determination of amount of recombination occurring in Alcator C-Mod plasmas, the trapping of Ly_a,b has been investigated experimentally. The brightnesses of Ly_b and D_a were measured by VUV and visible instruments whose views were co-aligned to end at the ``nose'' of the inner divertor. If Ly_b is optically thin, the brightnesses of these lines should be in the ratio of their spontaneous emission coefficients, i.e.

B_Lyb = B_Da×A_3®1/A_3®2,

where the brightnesses are in units of photons/s/sr/unit-area. An example of a constant ratio being maintained between Ly_b and D_a is shown in Fig. 4(a). However, if Ly_b is trapped, its brightness will decrease relative to that of D_a. An example of Ly_b trapping is shown in Fig. 4(b), where at higher D_a brightness, Ly_b falls below the value given on the RHS of the equation above. As evidence that this is in no way an instrumental effect, the time history of Ly_g, which is measured in the same spectrum as Ly_b, and which should not be trapped in these plasmas, is compared in Fig. 4(c) to the same D_a time history. Ly_g tracks D_a where Ly_b does not. In these cases Ly_a emission is strongly trapped, since its absorption mean-free-path is about a factor of 7 smaller than that for Ly_b.

Based on recent understanding of volume recombination occurring in the C-Mod divertor and on new diagnostic tools for studying this phenomenon, we are now reviewing older data with spectrometer views of the outer divertor for information about the role of recombination at the outer divertor. We have found that a significant amount is occurring before detachment. At the onset of detachment we observe pressure peaking at the divertor plate that moves away from the separatrix into the common flux region, leaving low plasma pressure regions behind (detachment). The recombination increases during this period and follows the detachment up the plate. The amount of recombination (integrated over the plate) is less than the integrated current loss during detachment, indicating that an appreciable fraction of the current loss is due to a decrease in ionization.

Preliminary results using the new ``helium probe'' on C-Mod have now been obtained. The helium probe follows a technique developed at TEXTOR, where local values of electron density and temperature can be derived from the ratio of three near-IR lines of HeI. In the case of C-Mod, a crude ``beam'' of helium gas is formed using a capillary that injects through the AB limiter at the outside mid-plane. The capillary nozzle is at the leading edge of the limiter, typically within 10 mm of the separatrix. The helium atoms cross the SOL, penetrating several mm's inside of the separatrix. The helium emissions are observed with a tangentially-viewing fiber array. Initial results indicate a relatively robust signal level, with low background interference (1%). Local conditions at the limiter location as deduced with the technique are T_e = 10 eV to 20 eV and n_e = 2 to 8 ×10¹⁹ m^-3 in Ohmic discharges. A thorough comparison with the fast scanning probe has not yet been made, but these values are consistent with earlier probe measurements. These initial results were presented in Sept. at the ITER Diagnostic workshop in Varenna, Italy.

Preliminary analysis has been made of local impurity dispersal from trace-impurity injection experiments performed during the June '97 run campaign. During these experiments, controlled injections (10 msec duration) of 10¹⁷ to 10¹⁹ molecules of impurity gas (He, N2) were delivered by a modified fast- scanning probe onto targeted flux surfaces in the scrape-off layer. Images of the resultant impurity line-emission `plumes' (NII, NIII, HeI, HeII) emanating from the injection point have been analyzed. Plumes of ionized impurities extended along field lines, closely matching the local field line trajectory as deduced from themagnetic reconstructions obtained from EFIT. A small asymmetry is evident in NIII and HeII plumes, consistent with a reversed parallel flow (Mach number  0.1) near the separatrix. These data appear to corroborate the reversed flows seen by the Langmuir-Mach probe near the separatrix. The spatial extent of the plume along field lines is consistent with DIVIMP simulation results (collaboration with U. Toronto group). However, saturation of pixels viewing closest to the injection point does not allow a comparison with the complete image to be made. DIVIMP modelling shows that images of NIV emission would be more sensitive to parallel flows in these high density (10²⁰ m^-3) and high temperature ( ³ 50 eV) scrape-off layer plasmas. The possibility of looking at a CIV line arising from an acetylene (C₂D₂) injection is also being considered.

RF Research

Analysis of the 40 MHz RF testing and conditioning experiments has shown central direct electron heating consistent with excitation of mode converted Ion Bernstein waves. The peaked profile has a full-width half-maximum of < 0.2 r/a. The analysis was done using a break-in-slope analysis of data from the 9 channel grating polychromator ECE diagnostic. The fraction of total power deposited into electrons as determined by this method is < 0.25. TORIC simulations indicate that approximately 50% of the power is absorbed directly by ions.

Discharge Cleaning Studies

Electron cyclotron resonance heating of low density plasmas might be the only technique for conditioning the thick vessel walls of large fusion reactors with superconducting magnets, like ITER. Electron cyclotron discharge cleaning (ECDC) plasmas operate in steady state, require no inductive currents, and require only small port access for wave-guides. Alcator C-Mod has demonstrated effective first-wall conditioning using ECDC. We recently performed controlled experiments to quantify the plasma conditions of these ECDC plasmas, and their cleaning effectiveness. Typical experimental conditions were: 0.04-0.08 Pa deuterium fill gas, 3 kW microwave power (2.45 GHz), and on-axis toroidal field 0.067 £ B_T (T) £ 0.11. By varying B_T, we swept the cyclotron resonance location between the inner and outer walls of the vacuum vessel. Langmuir probes, a gridded energy analyzer, and visible spectroscopy were used to monitor plasma conditions. Camera views of the plasma showed toroidally symmetric visible light emission which decreased abruptly at a major radius near the cyclotron resonance, yet remained mostly uniform from the resonance location radially outward to the wall. Electron density measurements confirmed this radial structure: density decreased inside the resonant major radius by an order of magnitude over 10 cm while outside the resonance we recorded a uniform, but fluctuating value of n_e » 2 ×10¹⁶m^-3. Typical electron temperatures were T_e » 10 eV outside the resonance, increasing by a factor of two slightly inside the resonance. We measured uniform ion temperatures of T_i » 2 ev. We also measured the removal rate of a 20 nm diamond-like carbon coating on a stainless steel sample which was inserted into the ECDC plasma. By moving the exposed part of the sample relative to the resonance location, we obtained a radial profile of the carbon removal rate. The thickness of the carbon layer remaining after exposure is being measured using proton backscattering by our collaborator B. Wampler at Sandia Nat. Lab.

Operations and Diagnostics

Tokamak plasma operations have just resumed on Alcator C-Mod as of October 30. A 0.8 MA plasma lasting 1.5 s and ending in a successful rampdown was obtained on that day. The C-Mod Operations Calendar and C-Mod Run Schedule have been updated. They can be found on the Web at

http://www.psfc.mit.edu/cmod/cmod_links.htm

under the Experiment Operations heading. We plan 10 operational weeks in the remainder of this campaign.

Repair of the alternator was contracted to Mechanical Dynamics and Analysis, Inc. It entailed disassembly of the rotor, removal, cleaning, refurbishment, and re-installation of all of the field-coil copper. Clean up, bead blasting, ultrasonic testing, mag-particle inspection, and repair of the rotor forging were completed successfully. The rotor wedges were refurbished. The stator was thoroughly cleaned and inspected. A hi-pot test of the stator was performed successfully. The rewind of the alternator rotor was accomplished, and the alternator was completely re-assembled. A review of the alternator instrumentation and protection circuits was held on October 20th at MIT. The alternator was successfully brought up-to-speed on Oct. 24 and is now in use. Re-balancing will be done if needed the week of Nov. 17th.

Two of the major auxiliary systems, the Diagnostic Neutral Beam, our major collaboration with the U. of Texas, and the RF heating system, in collaboration with PPPL, are being worked on and upgraded continually. For the technical details of what has been achieved on these systems, I refer the reader to the C-Mod weekly reports.

A DOE Quarterly Review was held on Oct. 22nd at MIT. Rostom Dagazian represented DOE. Summaries of recent physics results were presented. Plans and progress for the PPPL collaboration were discussed by Randy Wilson and those of the UT-FRC by Bill Rowan. Also attending were Joel Hosea from PPPL and Ken Gentle from UT-FRC.

The Final Design Review for the new Princeton four strap, ICRF antenna array was held at MIT. The antenna fabrication process is beginning. Contracts for the parts which require the longest lead times have been awarded, and a C-Mod port mockup at PPPL has been built. The plan is to have the antenna built and tested in the mockup at PPPL in January 1998. It will then be disassembled and shipped to MIT in February, ready for installation in March.

The 5 channel AM reflectometer has now be re-installed in the C-Mod cell. In collaboration with PPPL, the system has been completely rebuilt, and temperature control of the Gunn diodes has been added to improve frequency stability. The AM modulation frequency has been changed from 500 MHz to 132 MHz so that the spatial range of the demodulator is great enough to avoid fringe jumps. A new baseband 88 GHz receiver has been added with the high phase resolution and good frequency response required for fluctuation measurements.

Collaborations and Participation in the Fusion Science Community

Early this year Alcator C-Mod provided a gross vacuum sample to the Idaho National Engineering and Environmental Laboratory (INEEL) for particle size analysis, SEM/EDS analysis, and BET total surface area analysis. Analysis of this particulate has been completed and results are comparable to similar data collected from the General Atomics DIII-D vacuum vessel. Jon Carmack and Dave Petti who have done this work at INEEL are now preparing a report of this analysis. Alcator C-Mod and the INEEL plan continued collaboration and further analysis of particulate to be collected during the next C-Mod vent. This data is very important for determining environmental safety limits for ITER, particularly since the C-Mod data represents the first data from a machine with metal plasma facing components.

DIII-D is considering a major upgrade of their data system and is planning to use our MDSplus software as part of their new system. Discussions concerning the use of MDSplus for that purpose were carried out during a visit by GA and LLNL personnel - Dave Schissel, Chuck Greenfield, Kathy Greene, Tom Casper, and Bill Meyer. The visit emphasized migration and porting issues. Tom Fredian of MIT visited GA the week of Aug. 5 to give an MDSplus presentation and to work with the GA staff. A ``demonstration'' has been implemented at GA which gives access to PTDATA and EFIT results via MDSplus. NSTX is planning on using MDSplus as well. The advantages of uniform access to experimental data across the whole tokamak program are obvious.

Selected Domestic Travel

Paul Bonoli visited PPPL during the week of Sept. 8 and worked with Cynthia Phillips, Doug McCune, Randy Wilson, Dan Clark, and John Wright as part of the C-Mod/PPPL RF collaboration. Discussions concerning global issues related to the TRANSP/FPPRF code interface, and the question of passing equilibrium information efficiently between TRANPS and TORIC were held. The IDL postprocessor on the PPPL HYDRA was updated to the latest version developed at MIT. This change will allow 2D electric field contours as well as rf driven current profiles to be displayed. The use of the new finer resolution ECE diagnostic to clarify crucial issues in rf power deposition profiles was also discussed.

M. Greenwald attended an ESnet steering committee meeting Sept. 9-12.

Rejean Boivin was at North Carolina State University in mid-September and gave a talk on the role of neutral particles in a fusion reactor. He also discussed possible collaborations with faculty and students there.

Miklos Porkolab travelled to Washington DC the last week in Sept. He attended a meeting with Martha Krebs and other Lab Directors to discuss the White Paper the Lab Directors and UFA Chair Mike Mauel prepared on planning for the post ITER EDA period. He also participated in a panel discussion with the Grunder Panel on the post-EDA proposal.

J. Irby gave a plenary talk on October 7 at the SOFE97 meeting on Alcator C-Mod and recent results.

Miklos Porkolab attended the IAEA meeting on ``Innovative Approaches to Fusion Energy'', in Pleasanton, California, and chaired one of the sessions.

Earl Marmar and Ian Hutchinson attended the FESAC meeting in Washington D.C.

International Travel

Josh Stillerman visited the RFX experiment at CNR in Padova, Italy, in early August and gave a talk on 'MDSplus Remote Collaboration Support'. Their MDSplus implementation, VME/realtime devices and future software projects were discussed.

Sept. 4-12 Earl Marmar attended the International Workshop on Diagnostics for Experimental Fusion Reactors in Varenna, Italy. He presented an invited paper discussing spectroscopic and other diagnostic techniques. He participated in the ITER Expert meeting following this workshop.

Bob Granetz was in Lausanne, Switzerland, in Mid-Sept., attending an MHD Expert Group meeting. Most of the time was spent writing and editing sections of the ITER Physics Basis document.

Brian LaBombard visited the Tokamak de Varennes facility at the CCFM (Centre Canadien de Fusion Magnetique) and the INRS (Institut National de la Recherche Scientifique) in Quebec in mid-September. At the CCFM, he gave a talk on C-Mod divertor transport physics and discussed C-Mod results with members of the T de V edge physics group. At the INRS, he participated in a thesis defense for a University of Quebec student (James Gunn) as an external examiner.

A. Hubbard, J. Rice, and M. Greenwald attended the H-mode workshop in Seeon, Germany, Sept. 22-24. The papers presented there, which will be published eventually in Plasma Phys. and Contr. Fus., are listed below. After this meeting Dr. Hubbard also participated in an informal ITER workshop at Garching discussing pedestal issues. John Rice visited Asdex-Upgrade for one week as part of a collaboration concerning spectroscopy of high-Z materials.

Bruce Lipschultz was in Japan Oct. 12-18 participating in an ITER Divertor Expert Group meeting.

Near Term Plans

Our near term plans are focussed on the run campaign which has just begun. It is scheduled to be 10 operational weeks, extending until mid-February. Most of the physics staff will attend the DPP-APS meeting Nov. 17-23 in Pittsburgh. Mini-proposals for experiments are being solicited from the community. (Approved MP's can be found at http://www.psfc.mit.edu/server-java/MiniProposals.)

Callen, J.D., Neilson, G.H., Jr., Carreras, B.A., ..., Marmar, E.S., et al., ``The Fusion Science Research Plan for the Major US tokamaks: Advisory Report prepared by major facilities Review Panel, Scientific Issues Subcommittee, and Fusion Energy Advisory Committee, Journal of Fusion Energy 15 No. 3-4 (1997) 207.

M. Greenwald, et al., ``H Mode Confinement in Alcator C-Mod'' Nuclear Fusion, 37 (1997) 793.

J. Irby, R. Granetz, and the Alcator group, L. Myatt, P. Titus, ``The Alcator C-Mod Tokamak and Recent Results'', to be published in the IEEE proceedings.

Jablonski, D., LaBombard, B., McCracken, G.M., et al., ``Local Impurity Puffing as a Scrape-off Layer Diagnostic on the Alcator C-Mod Tokamak," J. Nucl. Mater. 241-243 (1997) 782.

Jackson G.L., Lazarus, E.A., Navratil, G.A., ..., Marmar, E.S., et al., ``Enhanced Performance Discharges in the DIII-D Tokamak with Lithium Wall Conditioning," J. Nucl. Mater. 241-243 (1997) 655.

Kurz, C., LaBombard, B., Lipschultz, B., McCracken, G.M., Niemczewski, A., Terry, J.L., ``Measurements of Neutral Density Based on Ha Emissivity in the Alcator C-Mod Divertor," Plasma Phys. and Controlled Fusion 39 (1997) 963.

LaBombard, B., Goetz, A., Hutchinson, I., et al., ``Experimental Investigation of Transport Phenomena in the Scrape-off Layer and Divertor," J. Nucl. Mater. 241-243 (1997) 149.

B. Lipschultz, Goetz, J.A., McCracken, G.M., ``Modification and Control of Divertor Detachment in Alcator C-Mod," J. Nucl. Mater. 241-243 (1997) 771.

Lumma, D., Terry, J.L., Lipschultz, B., ``Radiative and Three-body Recombination in the Alcator C-Mod Divertor," Phys. Plasmas 4 (7) (1997) 2555.

Matthews, G.F., Allen, S., Asakura, A., Goetz, J., Guo, H., Kallenbach, A., Lipschultz, B., McCormick, K., Samm, U., Stangeby, P.C., Steuer, K.-H., Taroni, A., Unterberg, B., West, P., ``Scaling Radiative Plasmas to ITER," J. Nucl. Mater. 241-243 (1997) 450.

May, M.J., Finkenthal, M., Regan, S.P., ..., Terry, J.L., Goetz, J.A., Graf, M.A., Rice, J.E., Marmar, E.S., et al., ``The Measurement of the Intrinsic Impurities of Molybdenum and Carbon in the Alcator C-Mod Tokamak Plasma Using Low Resolution Spectroscopy," Nucl. Fusion 37 No. 6 (1997) 881.

McCracken, G.M., Granetz, R.S., Lipschultz, B., LaBombard, B., Bombarda, F., Goetz, J.A., Lisgo, S., Jablonski, D., Ohkawa, H., Rice, J.E., Stangeby, P.C., Terry, J.L., Wang, Y., ``Screening of Recycling and Non-recycling Impurities in the Alcator C-Mod Tokamak,". J. Nucl. Mater. 241-243 (1997) 777.

McCracken, G.M., Lipschultz, B., LaBombard, B., Goetz, J.A., et al., ``Impurity Screening in Ohmic and High Confinement (H-mode) Plasmas in the Alcator C-Mod Tokamak," Phys. Plasmas 4 No.5 (1997) 1681.

Pitcher, C.S., Carlson, A.W., Fuchs, C., et al., ``Routes to Divertor Detachment in ASDEX Upgrade," Journal Nucl. Materials 241-243 (1997) 696.

Rice, J.E., Terry, J.L., Goetz, J.A., Wang, Y., Marmar,E.S., et al., ``Impurity Transport in Alcator C-Mod Plasmas," Phys. Plasmas 4 No. 5 (1997) 1605.

Rice, J.E., Bombarda, F., Graf, M.A., et al., ``Multiple Plasma Diagnoses from a Five-Chord, High Energy Resolution X-ray Spectrometer Array," Fus. Engineering and Design, 34-35 (1997) 159.

Takase, Y., Boivin, R.L., Bombarda, F., et al., ``Radiofrequency-heated Enhanced Confinement Modes in the Alcator C-Mod Tokamak," Phys. Plasmas 4 No. 5 (1997) 1647.