LEVITATED DIPOLE EXPERIMENT

SUMMARY OF ACTIVITIES (JANUARY - MAY, 1998)

1. OVERVIEW

Our primary tasks have been completion of the design specifications for the levitated ring, control and safety systems, and vacuum chamber.

The design/engineering group consists of J. Minervini, J. Schultz (Team Leader), R. Camille, P. Michael, L. Myatt, B. Smith, A. Radovinsky, S. Pourrahimi, P. Thomas, P. Wang, A. Zhukovsky, D. Hale, and S. Cochin. The design team is assisted by the scientific team consisting of Darren Garnier, Jay Kesner, and Mike Mauel. John Schmidt from PPPL has guided our design specifications for the levitated ring position feedback control system. Leslie Bromberg has guided our investigations of dipole-based fusion power systems.

2. DESIGN OF THE LEVITATED RING

A major activity of the design/engineering team has been the detailed specification of the levitated ring. The levitated ring is made of two counter-wound, high-current, self-supporting superconducting coils enclosed by a toroidally-shaped cyrostat. The design objectives of the coil included high reliability and relative ease of operation.

After consideration of several options, an advanced Nb3Sn superconducting strand was selected for LDX having a high critical current density and critical temperature owing to its relatively low copper/noncopper fraction of 0.428. The strand will be cabled into two lengths and then heat-treated. This cable will then be soldered into a 7.95 mm by 2.01 mm, C-shaped, half-hard copper channel to provide structural integrity for the coil.

Bids for Nb3Sn strand and cable were solicited from several companies, Oxford, Mitsubishi, IGC, Supercon, and Vacuumschmelze. The most promising bid came from IGC since this bid was the lowest and IGC was the only company willing to do the cabling.

On May 12, Joel Schultz, Brad Smith, and Darren Garnier conducted a site-visit of the IGC Advanced Superconductors division in Waterbury, CN to discuss fabrication of the superconducting strand and conductor for the LDX F-coil magnet. This fabrication will include fabrication of a short length of trial cable and channel. Since IGC has an operating solder line, the time required for fabrication of the completed conductor meets with our proposed schedule.

A detailed Statement of Work (SOW) for Production of LDX F-Coil Strand and Cable was completed and sent out to IGC on 5/28/98.

The detailed design specification for the cyrostat for the levitated ring is nearly complete. Design calculations have shown the cryostat will keep the magnet temperature between 5 and 11 Deg K during at least 8 hours of levitated operation. The titanium alloy helium vessel is surrounded by a radiation shield with a large thermal mass made from lead foil. This was a design innovation used by the FM-1 levitron. The shield is wrapped with a super insulation (MLI), which is surrounded by a stainless steel room temperature vacuum shell. The LDX ring will be inductively energized.

We have developed a novel He cryostat design which greatly simplifies ring operation. This concept should significantly reduce the down time associated with ring maintenance and cooling. A patent application is presently pending for this cryostat concept.

3. DESIGN OF THE RING CATCHER AND CONTROL SYSTEMS

Conceptual design of the launch and catcher system is continuing and calculations are being carried out to minimize the forces present in the floating coil during a fall. The launcher is used to position the ring near the center of the plasma vacuum vessel prior to energization of the levitation and control coils. The ring catcher system consists of a stainless-steel "web" which is lifted away from the vacuum chamber walls in the event of a loss-of-control accident.

General specifications of the levitation position control system have been made. A small permanent magnet has been levitated using an active feedback control system which controls the current in an overhead levitation coil as will be used in the initial phase of LDX. For this table-top system, the position of the levitated magnet was detected by the interruption of a light-beam as proposed by John Schmidt.

4. PRESENTATIONS AND WORKSHOPS

During the past few months, we have participated in several workshops, made presentations at various meetings, and conducted two internal design meetings. These are listed below:

5. MIT STUDENT REACTOR STUDY

A graduate course, titled "The Engineering of Fusion Reactors", NE22.63, was taught by the MIT Nuclear Engineering Department this spring. The course was taught by by R. Ballinger, L. Bromberg and E. Chaniotakis, and J. Kesner and there were 8 students enrolled. The course focused on a class project of a design of a levitated dipole reactor that utilizes a high temperature super-conductor and was based on a D-He3 cycle. The base case design had a ring of 2.5 m radius and produced 80 MWe electric. (A major advantage of a dipole based reactor is the ability to ignite advanced fuels in relatively small size units). The design included a particularly creative approach to an internally refrigerated ring that utilizes near term technology that has been developed within the space program.

6. SITE PREPARATION

The preparation of the experimental hall is well underway. The preexisting Plasma Arc Furnace has been removed, and the floor and cable trench covers have been repaired and painted. The control room, shared with the Pulse Test Facility (PTF) and the Versatile Toroidal Facility (VTF), is being renovated with new flooring and computer stations. Setup laboratory space is being made available in adjacent rooms.

7. THE LDX WEB PAGE

The LDX web page provides an introduction to the LDX research program. This site will be periodically updated with news and progress. The LDX web site is located at http://www.pfc.mit.edu/ldx/

8. DESIGN DOCUMENTATION

Detailed documentation of the LDX design are contained in the following technical memos: Last modified June 5, 1998