L D X :   C o l l a b o r a t i o n s

LDX is a joint effort between Columbia University and MIT Plasma Science and Fusion Center with significant input from PPPL. There is a widespread interest in the theoretical aspects of confinement in the dipole configuration, including theory groups at UCLA, U. Maryland and IFS at U.T. Austin. Internationally, there is an active interest in the physics of dipole confinement in Japan which includes Hasegawa, and we investigating a collaboration with Japanese colleagues.

As LDX is a concept exploration experiment, only a rudimentary set of diagnostics are planned for the initial operation phase. We hope and fully expect to complement this set with other diagnostics from outside collaborators. We welcome your proposal.

Our current plans for diagnostics, which are designed to address the physics of high-beta hot electron dipole confinement at minimum cost include:

1. Magnetic loops and probes provide for magnetic equilibrium reconstruction and as such a measure of the plasma stored energy and beta.
2. A 60 GHz microwave interferometer provides information on core plasma density.
3. X-Ray Diagnostics:
   1. X-Ray Imaging: This diagnostic will gives qualitative information on the plasma density and electron temperature.
   2. Hard X-Ray Energy Analyzer: This diagnostic renders information on the hot electron energy distribution.
4. Spectroscopic diagnostics provide a measure of the ion temperature and plasma composition (Z_eff).
5. Edge particle probes measure the plasma properties in the low density and temperature region far from the dipole.

Diagnostic Development Program

The main goal of the LDX experiment, to measure and document the effects of plasma compressibility, leads to some unique diagnostic challenges.

• We would like to measure a large "dynamic range" in pressure. At the highest compressibility ratios, we want to measure nearly a 10,000 fold increase of pressure from the edge to the core.
• As we apply current to the external shaping coils to change the compressibility, the flux surface geometry will change dramatically.

The particular areas we would like to see further diagnostic development are:

1. Profile Measurements: Determination of the plasma profiles is key to any fusion concept experiment.
   1. Electron temperature: The low magnetic field on the outside midplane of LDX mean traditional ECE diagnostics can only function in very low density operational regimes (Nor is an ECE based diagnostic in the high field inner region useful for profile information as the mapping of field to flux is difficult to establish.) Diagnostics for LDX will also need to measure the large non-thermal electron population.
   2. Ion temperature: Ion temperature profile information is most commonly determined with NB-based CHERS. LDX has no current plans for a neutral beam.
2. Plasma flow: An ideal fusion reactor has low particle confinement while maintaining high energy confinement. Large scale convective cells are seen in dipoles, and may serve to transport ash away while minimally affecting energy confinement. A means of diagnosing these convective cells is desired. (LIDAR is one possible means being considered.)
3. A charge exchange neutral particle analyzer may be used to diagnose the ion energy distribution in the second stage of operation when the plasma is thermalized.

1. LDX is a very large plasma with great diagnostic access. The vacuum vessel is 5 m in diameter with numerous large ports for diagnostics.
2. The LDX magnetic configuration has a unique axisymmetric and shearless field geometry.
3. LDX can develop and test diagnostics for any low aspect ratio fusion concept with large radial changes in magnetic field strength.
4. Finally, we're a warm and friendly group. We'll even help you prepare your proposals.

If you are interested in obtaining more information about LDX please contact:

Mike Mauel <mauel@columbia.edu>
Jay Kesner <kesner@psfc.mit.edu>
Darren Garnier <garnier@psfc.mit.edu>

We hope to hear from you!