# Presentation: 407868

## Advanced fueling system for use as a burn control tool

- Roger Raman
- University of Washington, Seattle
- Workshop (W60) on Burning Plasma Physics and Simulation
- 4-5 July 2005
- University Campus, Tarragona,Spain
- Work supported by DOE grant No. DE-FG03-02ER54686

-        Supported by

- Raman, BPW (W60) 4-5 July 2005

## Acknowledgements

- Dr. Henry W. Kugel (PPPL)
- Prof. Thomas R. Jarboe (Univ. of Washington)

- Raman, BPW (W60) 4-5 July 2005

## Outline of Talk

- Burn control in a Burning Plasma Device
- Present systems may be inadequate
- Pellets sizes are large & injection is shallow
- No plan at present for density & pressure profile control (essential for steady burn control)
- CT injection system has potential for density profile control and momentum injection
- Status of current work
- Open issues
- Plans and suggestions

- Raman, BPW (W60) 4-5 July 2005

## Flexible fueling system may be the only choice for burn control

- A burning plasma device has no need for neutral beam injection for plasma heating and alphas are isotropic → no momentum injection
- Initial density peaking via. core fuelling provides more flexibility to reach ignition
- In a device with high bootstrap current fraction, optimized density and pressure profiles must be maintained → fueling system must not adversely perturb established density and pressure profiles
- Other than a system for current drive, a fueling system is all that a burning plasma system may be able to rely on to alter core plasma conditions and for burn control
- Density and temperature profiles determine fusion power output

- Raman, BPW (W60) 4-5 July 2005

## Fueling profiles from present systems

- Pellets (< 1km/s, HFS)
- Large pellets increases density over a large radius
- Capability of small pellets for profile control yet to be established
- Supersonic gas (~ 2-3 km/s)
- Fuels from the edge with improved fueling efficiency
- Capability for profile control not known yet
- Plasma jet (~ 30km/s)
- Similar to supersonic gas, bulk fueling at present
- Penetration into large cross-section plasmas not known

- Raman, BPW (W60) 4-5 July 2005

## In a CT injection system a CT is accelerated to high velocity and injected into the target plasma to achieve deep fueling

- CT Penetration time: few μs
- CT Dissociation time: < 100 μs
- Density Equilibration time: 250 - 1000 μs
- Variable Penetration depth: edge to beyond the core

- Raman, BPW (W60) 4-5 July 2005

## A CT Fueler forms and accelerates CTs in a coaxial rail gun in which the CT forms the sliding armature

- Amount of gas injected controls CT density
- Applied voltage controls CT velocity
- Control system specifies fuel deposition location for each pulse

- Raman et al., Fusion Techn.,** 24**, 239 (1993)

- Raman, BPW (W60) 4-5 July 2005

## Status of current workTdeV tokamak discharges beneficially fueled by CTs, without causing any adverse perturbation

- TdeV
- R = 0.86m
- a  = 0.25m
- BT = 1.4T
- Ip = 160kA

- Raman, BPW (W60) 4-5 July 2005

## JFT-2M results (IAEA 2002)

- K.Tsuzuki et al.,
- EX-C1-1,
- Proc. IAEA 2002,
- Lyon, France

- Raman, BPW (W60) 4-5 July 2005

## Conceptual study of a CT system for ITER yields an attractive design

- R. Raman and P. Gierszewski, ITER Task D315 (1997), Fusion Engin. & Design **39-40** (1998) 977-985

- <1% particle inventory perturbation, 20 Hz operation

- Raman, BPW (W60) 4-5 July 2005

## ITER CT Injector parameters 

- 		CT radius			0.1 m
- 		CT length			0.2 m
- 		CT density (D + T) 		9 x 1022 m-3
- 		CT mass			2.2 mg DT (2.6 T2)
- 		Fueling rate (D + T)		5.3 x 1020 / pulse
- 		Fueling frequency		≤ 20 Hz
- 		CT velocity			300 km/s
- 		CT kinetic energy		100 kJ (120 kJ T2)
- 		Momentum inj. rate		13.2 kg.m/s DT, 15.6 T2,
- 		Power consumption		8 MWe (10 T2)
**(Raman and Gierszewski, Fusion Engin. Design 39-40 (1998) 977 & ITER Task D315)**

- Raman, BPW (W60) 4-5 July 2005

## Previous experiments too small to study localized core fueling

- Approximate relative sizes of various target plasmas and CTs.
**A CTF sized CT will do far more localized fueling on a NSTX sized device**
**- Steep B****T**** more precisely determines CT stopping location**
- Ref: R. Raman and K. Itami,  Journal of Plasma and Fusion Research, **76**. 1079 (2000)

**Open Issues**

- Raman, BPW (W60) 4-5 July 2005

## Proposed research Plan

- Injection into a large cross-section, low field device (eg., NSTX) - *using an existing injector*
- Establish localized fueling (~ 2 yr)
- - Perturb core transport
- Establish momentum injection (~ 2 +1 yrs)
- Establish multi-pulse fueling (~3 + 1 yrs)
- Intermediate scale experiments (JT-60U,JET)
- Conduct burning plasma injector design
- Re: design study for JT60U (R. Raman and K. Itami,  Journal of Plasma and Fusion Research, **76**. 1079 (2000))

- Raman, BPW (W60) 4-5 July 2005

## The CTF-II injector (in storage at PPPL)

- Raman, BPW (W60) 4-5 July 2005

## The CT Formation bank power supply (110V AC input)

- Raman, BPW (W60) 4-5 July 2005

## A CT injector could provide profile control capability

|  | CT | Pellet |
| --- | --- | --- |
| Particle invent. perturbation for deep fueling | Few %
- will not destroy optimized profiles, allows precision fueling capability to adjust profiles | Typically 50% on DIII-D
- large pellets needed to deposit small fraction of fuel in core |
| Optimal injector location | Outboard mid-plane
- tangential injection will impart momentum | ‘True’-Inboard mid-plane
- injection at an angle reduces penetration |
| Real time density feedback control capability | Yes -  potential for fuel deposition location specification on each pulse using control system request
- Also a source of momentum injection | Improbable because large pellets fuel entire discharge and mechanical nature of injector reduces fueling flexibility |

- Raman, BPW (W60) 4-5 July 2005

## Conclusions

- A CT injector has the potential to deposit fuel in a ***controlled*** manner at any point in the machine
- In a burning plasma device with only RF for current drive, a flexible fueling system may be the only internal profile control tool
- Inject momentum (in conjunction with current drive) for plasma beta and stability
- Precise density profile control to optimize bootstrap current and to maintain optimized fusion burn conditions
- Perturb core transport in present machines
- Large tokamaks should consider and develop backup options to meet the fuelling and burn control requirements of a burning plasma device
- Large STs are an attractive target for developing CT fueling
- - **Steep B****T**** gradient, large crossection**
**Essential CT data needed for an ITER CT injector design could be obtained on NSTX**

- Raman, BPW (W60) 4-5 July 2005

## No evidence for metallic impurity contamination of TdeV

- Raman, BPW (W60) 4-5 July 2005

## Edge fueling of diverted discharges triggers improved confinement behavior

- Raman, BPW (W60) 4-5 July 2005

## Inductive quality discharge produced by electrode discharge

- Raman, et al., NF 45 (2005) L15-L19

- Raman, BPW (W60) 4-5 July 2005

## CT induced confinement improvement also seen on STOR-M* 

- * Recent similar results on JFT-2M

- STOR-M
- R  = 0.46 m
- A  = 0.12 m
- Ip  = 20 kA
- BT  = 1T

- C. Xiao, A. Hirose, R. Raman, 2001,
- Compact Torus Injection Experiments
- in the STOR-M Tokamak,
- Proc. of 4th Symp. on Current Trends in
- International Fusion Research:
- Review and Assessment
- (Washington D.C., March 12-16, 2001,
- in print)

- Raman, BPW (W60) 4-5 July 2005