# Presentation: 020691

## DIII-D Program

**Presented by**
**Richard W Callis**
**VLT Meeting**
**Washington DC**
**AUGUST 25, 2005**

## THERE ARE SEVERAL AREAS IN WHICH THE VLT SUPPORTS THE DIII-D PROGRAM

**ECH Technology**
**Fast Wave Technology**
**Fueling with pellets**
**Disruption mitigation**
**Material Sampling and Evaluation Systems**

## To support the DIII-D AT program the ECH system has to be increased from 6 MW to 9 MW
Requires two new 1.5 MW Depressed Collector gyrotron systems 
New dual launcher with long pulse mirrors which can handle 1.5 MW

**To support the DIII-D AT program the ECH system has to be increased from 6 MW to 9 MW**
- Requires two new 1.5 MW Depressed Collector gyrotron systems
- New dual launcher with long pulse mirrors which can handle 1.5 MW

**ECH IS A CRITICAL TOOL FOR THE DIII-D ADVANCED TOKAMAK (AT) PROGRAM**

## THE DIII-D HIGH BETA PROGRAM NEEDS ECH AT LOWER FREQUENCY

**Owing to thermal restriction on the toroidal coil, long pulse length experiments can only be performed at reduced fields.**
**In order to heat the center of the plasma, ECH systems of lower frequencies are needed.**
- The full range of experiments on DIII-D can be supported if step-tunable gyrotrons are available
**95 - 110 GHz in 3 GHz steps is desired**

## FW systems on DIII-D are being upgraded

- Three FW antennas and transmitters operational in 05 (GA/ORNL/PPPL)
- Improvements to the transmitters and arc detection system are underway
- ~15 year old 285/300 antenna will be refurbished during the 05/06 torus opening (2 s max pulse length)
- New long pulse antenna for 285/300 is needed for steady state AT and hybrid H&CD scenarios (install in 07)
- A lower voltage design is desired in order to obtain improved H-mode operation
- Modeling is underway to understand design tradeoffs

**OAK RIDGE NATIONAL LABORATORY**
**U.S. DEPARTMENT OF ENERGY**

## Modeling study underway to examine the performance gains possible with a short strap, close-coupled-tuning design

**Design objectives**
- Improved H-mode performance
- Lower voltages on current straps
- Lower voltages inside antenna box
- Current drive (4xN strap phased array)
**Design options**
- Explore the possibility of an improved concept in the short strap, lower voltage, corner of design space
- N=1, 2, 3 or 4 poloidal straps
- Opaque vs transparent Faraday shield
- Internal vs external tuning
- Fixed frequency (60 MHz) self resonant design

**OAK RIDGE NATIONAL LABORATORY**
**U.S. DEPARTMENT OF ENERGY**

## A new 285/300 FW antenna would allow ITER relevant testing in Advanced Tokamak and Hybrid H-mode plasmas

**New 285/300 FW antenna would likely be a 4x4, 4x3 or 4x2 array**
**Test antenna coupling, power & pulse limits and tuning systems in H-mode **
**Test series of  Faraday shield designs with first the refurbished and then the new long pulse antenna**
**Test antenna specific diagnostics for pressure rise and arc detection**

**Candidate ITER design with 4x6 strap array**

**OAK RIDGE NATIONAL LABORATORY**
**U.S. DEPARTMENT OF ENERGY**

## ELM Mitigation by Pellets Dropped into DIII-D

- Divertor heat flux from infrequent, but large, ELMs is a significant problem for ITER.
- Pellets have been shown to trigger ELMs in H-mode plasmas (i.e. DIIII-D).
- High repetition rate pellets injected in AUG were able to reduce the peak divertor heat flux.  (Lang et al, Nucl Fusion 2005)
- Small high rep rate pellets can increase the ELM rate and reduce the peak heat flux _while not_ increasing the plasma density.
- A vertical pellet dropper device with 50 Hz rates is planned for DIII-D.
- The pellet dropper will be used to investigate the pellet induced ELM mechanism and its scaling to ITER.

**Time (s)**

**OAK RIDGE NATIONAL LABORATORY**
**U.S. DEPARTMENT OF ENERGY**

## Installation of Pellet Dropper on DIII-D

- The pellet dropper is a self contained box that mounts to the existing pellet vertical ports.
- Diagnostics for pellet mass (microwave cavity) and penetration (D monitor) are planned.
- Cryocooler cold head technology will be employed (ITER relevant)

**OAK RIDGE NATIONAL LABORATORY**
**U.S. DEPARTMENT OF ENERGY**

## Avoidance and Mitigation of Plasma DisruptionsAre Critical Issues for Tokamaks

- High-pressure gas injection has been shown to be an effective disruption mitigation technique in DIII-D experiments
**dramatic reductions in localized power deposition and forces to internal components due to reduced halo currents**
**modeling and simulation suggest that the technique maybe scalable to ITER**
**reliable disruption precursor detection needed **
**Uses technology developed from ORNL pellet fueling program**

- P. L. Taylor et al., *Phys. Plasmas* **6**, 1872 (1999).

**OAK RIDGE NATIONAL LABORATORY**
**U.S. DEPARTMENT OF ENERGY**

## DiMES and MiMES at DIII-D

- With the modified DiMES and new MiMES in place:
-  Expose C, Be, W and mixed material samples on DiMES and
-   MiMES to measure erosion and redeposition and to bench
-   mark modeling codes at the lower divertor and first wall.
-  Mirror and tile gap experiments will be performed again at new
-   DiMES configuration and at different surface temperatures
-   to study eroded material deposition.

**DiMES: ****Di****vertor ****M****aterial ****E****valuation ****S****ystem**
**MiMES: ****Mi****d-plane ****M****aterial ****E****valuation ****S****ample**

**DiMES sample raised by ~11 cm**