DIAGNOSTIC SYSTEMS ON ALCATOR C-MOD N. P. BASSE,*† A. DOMINGUEZ, E. M. EDLUND, C. L. FIORE, R. S. GRANETZ, A. E. HUBBARD, J.W. HUGHES, I. H. HUTCHINSON, J. H. IRBY, B. LaBOMBARD, L. LIN,Y. LIN, B. LIPSCHULTZ, J. E. LIPTAC, E. S. MARMAR, D.A. MOSSESSIAN, R. R. PARKER, M. PORKOLAB, J. E. RICE, J.A. SNIPES, V. TANG, J. L. TERRY, S. M. WOLFE, S. J. WUKITCH, and K. ZHUROVICH Massachusetts Institute of Technology, Plasma Science and Fusion Center, Cambridge, Massachusetts 02139 R.V. BRAVENEC, P. E. PHILLIPS, andW. L. ROWAN Fusion Research Center, University of Texas,Austin, Texas 78712 G. J. KRAMER, G. SCHILLING, S. D. SCOTT, and S. J. ZWEBEN Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 Received September 15, 2005 Accepted for Publication January 14, 2006 An overview of the diagnostics installed on the Al- cator C-Mod tokamak is presented. Approximately 25 diagnostic systems are being operated on C-Mod. The compact design of the machine and the cryostat enclos- ing the vacuum vessel and magnetic field coils make access challenging. Diagnostics are used to study four focus areas: transport, plasma boundary, waves, and macrostability. There is significant overlap between these topics, and they all contribute toward the burning plasma and advanced tokamak thrusts. Several advanced and novel diagnostics contribute to the investigation of C-Mod plasmas, e.g., electron cyclotron emission, phase-contrast imaging, gas puff imaging, probe measurements, and ac- tive magnetohydrodynamic antennas. KEYWORDS: diagnostics, Alcator C-Mod, tokamak NOTE: Some figures in this paper are in color only in the electronic file. I. INTRODUCTION Alcator C-Mod 1 is a compact ~major radius R 0 = 0.67 m, minor radius a = 0.21 m a !, diverted tokamak with the ability to run high toroidal magnetic field B f ~8T !, high plasma current I p ~2 MA!, and high elec- tron density n e ~1.5 10 21 m -3 ! plasmas. The walls are covered by Mo tiles, and boronization is used regularly to reduce the impurity content of the plasmas. Auxiliary heating presently consists of ion cyclotron radio fre- quency ~ ICRF ! minority heating using two 2-strap an- tennas at 80 MHz and one 4-strap antenna with a variable frequency between 50 and 80 MHz. Additionally, lower hybrid current drive ~ LHCD! at 4.6 GHz is being brought online, mainly to drive current, but also to heat. Approximately 25 diagnostic systems are being op- erated on C-Mod ~see Table I!. Some diagnostics are mentioned in the table but not described in the paper, such as the neutral pressure gauges shown in Fig. 1. The compact design of the machine and the cryostat enclos- ing the vacuum vessel and magnetic field coils make access challenging. Ten horizontal ports exist on the out- board side, along with top and bottom ports at the same toroidal positions. Ports are named A through H and J and K; two outboard limiters are installed, a full limiter in the GH sector and a split limiter in the AB sector. We group the C-Mod diagnostics into four focus areas: Transport ~Sec. II !, plasma boundary ~Sec. III !, waves ~Sec. IV!, and macrostability ~Sec. V!. There is *Current address: ABB Switzerland Ltd., Corporate Research, Segelhofstrasse 1, CH-5405 Baden-Dättwil, Switzerland †E-mail: nils.basse@ch.abb.com a Typical values, depend on the magnetic configuration of a given plasma. In this paper, plasma radius mapped to the outboard midplane is labeled using two main types of nota- tion: major radius, identified as either R or R mid , and normal- ized minor radius r = r0a. For standard geometry, 0.67 m ~axis!  R  0.88 m ~outboard midplane edge!, and by def- inition 0.0 ~axis!  r0a  1.0 ~edge!. 476 FUSION SCIENCE AND TECHNOLOGY VOL. 51 APR. 2007