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| **NSTX             |                      |       |                 |
| Experimental       |                      |       |                 |
| Proposal**         |                      |       |                 |
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| Title: **H-mode    |                      |       |                 |
| fueling            |                      |       |                 |
| optimization using |                      |       |                 |
| Supersonic Gas     |                      |       |                 |
| Injector -         |                      |       |                 |
| Upgrade**          |                      |       |                 |
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| **OP-XP-742**      | > Revision:          | >     |                 |
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| **PROPOSAL         |                      |       |                 |
| APPROVALS**        |                      |       |                 |
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| ![](media/imag     |                      |       | > Date          |
| e1.png){width="1.1 |                      |       | > 05/04/2007    |
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| height="           |                      |       |                 |
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| 6in"}**Responsible |                      |       |                 |
| Author: V. A.      |                      |       |                 |
| Soukhanovskii**    |                      |       |                 |
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| **ATI -- ET Group  |                      |       | > Date          |
| Leader: H. Kugel** |                      |       | > 05/04/2007    |
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| **RLM - Run        |                      |       | > Date          |
| Coordinator: D.    |                      |       | > 05/07/2007    |
| Gates**            |                      |       |                 |
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NSTX EXPERIMENTAL PROPOSAL

TITLE: **H-mode fueling optimization using Supersonic Gas Injector -
Upgrade**

No. **OP-XP-742**

AUTHOR: **V. A. Soukhanovskii** DATE: **05/04/2007**

# 1. Overview of planned experiment 

The goal of the experiment is to optimize H-mode fueling using the
supersonic gas injector (SGI). A typical H-mode discharge in NSTX is
fueled from a high field side (HFS) gas injector, a system that injects
gas through a small orifice located at z=0 along the center stack. This
enables reliable H-mode access. A drawback of this fueling technique is
the uncontrollable gas feed at a decreasing rate from about 50 to 10
Torr l / s throughout the discharge duration and an uncontrollable
density rise as a result. The goal of SGI fueling experiments is to
replace or significantly reduce the HFS fueling to gain gas fueling
control, without impact on H-mode access and plasma properties.
Experiments in FY 2004-2006 have demonstrated that the SGI can be
successfully used for H-mode fueling. This experiment will use an
upgraded SGI capabilities - a higher gas flow rate (up to 130 Torr l
/s), a higher plenum pressure (up to 5000 Torr), and a multipulse
capability - to optimize H-mode fueling. In parallel, data will be
obtained on fueling efficiency and other characteristics of the SGI.

# 2. Theoretical/ empirical justification

> Recent theory and modeling results \[Rozhansky et. al, NF 46 (2006)
> 367\] suggest that the radial propagation of a high-pressure jet
> through the edge plasma is determined to first order by the fluid
> pressure balance, mainly by the relative magnitude of the plasma
> magnetic and kinetic pressure vs the gas jet impact pressure. Deep
> penetration appears to be inhibited by a high-density ionizing
> plasmoid that forms in front of the jet, blocking it from further
> penetration. Increasing the supersonic jet pressure would promote its
> penetration through the SOL and separatrix. Off-line SGI testing
> demonstrated that the highest available plenum pressure of 0.33 MPa
> (2500 Torr) limits the flow rate to 4.6x10^21^ s^-1^ (\~ 65 Torr l /
> s) and the jet impact pressure to 30 kPa at the exit nozzle exit and
> to about 0.02 kPa at a distance of 10 cm from the nozzle exit. The
> corresponding plasma pressure at the separatrix is 0.01 -- 0.07 kPa
> (75 - 500 mTorr) suggesting that a higher SGI plenum and jet impact
> pressures are required for deeper penetration.

# 3. Experimental run plan

> The experiment is comprised of two parts which can be executed
> separately and on different dates. Part one addresses H-mode access
> and fueling optimization with high pressure SGI. The second part
> addresses the SGI fueling efficiency in the plasma start-up phase.

**3.1 H-mode access with SGI (up to 10 shots)**

1.  Obtain a reference H-mode discharge with HFS fueling (up to 3 shots)

-   Use 0.8 - 1.0 MA 2 NBI source LSN target plasma with HFS fueling

-   Template shots 122738, 122747 - HFS gas 1100 Torr, NBI sources A, B
    (start 60 ms, 80 ms)

2.  Replace the HFS injector gas with an SGI gas pulses and optimize (up
    to 12 shots)

-   Start with the following SGI setup: R=1.56 - 1.58 m, Plenum pressure
    5000 Torr

-   Start with HFS pressure of 500 Torr and reduce to 0 Torr in
    shot-increments (500, 300, 200, 100 Torr), adding a first SGI pulse
    of duration 50-200 ms at or around 100 ms

-   Adjust SGI timing to optimize H-mode access as necessary

-   Adjust SGI plenum pressure between 5000 Torr and 2500 Torr as
    necessary

3.  (Optional, time permitting) Use an SGI-fueled template shot but
    replace SGI with Injector 2 at similar pressure to compare fueling
    efficiency of a conventional gas injector with SGI.

4.  (Optional, time permitting) In one or two long H-mode shots, turn
    off SGI early in the flat-top (0.400-0.800 s) to see if density rate
    of rise changes.

**3.2 Use of SGI in discharge front-end (up to 5 shots)**

-   Use a suitable 1-2 source NBI LSN target plasma. Use LFS Injector \#
    1, 2 or 3 for initial density ramp-up (front-end) for a reference
    case. Replace the LFS injector with an identical or as similar as
    possible SGI pulse. Note the density ramp rate.

-   The SGI will be parked at R=1.56 - 1.58 m*.*

-   SGI setup: plenum pressure *P~0~*=2000-5000 Torr.

-   Adjust SGI pulse duration or pressure as needed

# 4. Required machine, NBI, RF, CHI and diagnostic capabilities

1.  SGI plenum pressure up to 5000 Torr

2.  Wall / impurity conditions to allow reliable H-mode access

Completed Physics Operations Request and Diagnostic Checklist are
attached.

# 5. Planned analysis

> We plan to use DEGAS 2, UEDGE and TRANSP for fueling efficiency and
> jet penetration analysis.

# 6. Planned publication of results

Results will be presented at the SOFE 2007 conference and / or published
in a refereed journal as appropriate.

PHYSICS OPERATIONS REQUEST

Title: H-mode fueling optimization using Supersonic Gas Injector -
Upgrade OP-XP-742

Machine conditions (specify ranges as appropriate)

> I~TF~ (kA): -53 kA Flattop start/stop (s): 0.180

I~P~ (MA): 0.80 Flattop start/stop (s): 0.800

Configuration:

> Outer gap (m): **0.08-0.09** Inner gap (m): **0.06-0.07**
>
> Elongation κ: **2.15** Triangularity δ: **0.7**
>
> Z position (m): **0.0**
>
> Gas Species: **D~2~** Injector(s): SGI, Injectors 2, HFS
>
> NBI - Species: **D** Sources: A, C Voltage (kV): 90 Duration (s): 0.8
> s

ICRF -- Power (MW): Phasing: Duration (s):

CHI:

![](media/image2.png){width="6.625in"
height="4.309722222222222in"}*Either:* List previous shot numbers for
setup: 122738

DIAGNOSTIC CHECKLIST

Title OP-XP-

  -------------------------------------------------------------------------------
  **Diagnostic**             **Need**   **Desire**   **Instructions**
  -------------------------- ---------- ------------ ----------------------------
  Bolometer -- tangential    **x**                   
  array                                              

  Bolometer -- divertor      **x**                   

  CHERS -- toroidal          **x**                   

  CHERS -- poloidal                                  

  Divertor fast camera                  **x**        

  Dust detector                                      

  EBW radiometers                                    

  Edge deposition monitors                           

  Edge pressure gauges       **x**                   

  Edge rotation diagnostic   **x**                   

  Fast ion D_alpha - FIDA                            

  Fast lost ion probes -                             
  IFLIP                                              

  Fast lost ion probes -                             
  SFLIP                                              

  Filterscopes               **x**                   

  FIReTIP                    **x**                   

  Gas puff imaging                      **x**        

  Hα camera - 1D             **x**                   

  High-k scattering                     **x**        

  Infrared cameras                      **x**        

  Interferometer - 1 mm                              

  Langmuir probes - divertor            **x**        

  Langmuir probes -- RF                 **x**        
  antenna                                            

  Magnetics -- Diamagnetism             **x**        

  Magnetics - Flux loops                **x**        

  Magnetics - Locked modes              **x**        

  Magnetics - Pickup coils              **x**        

  Magnetics - Rogowski coils            **x**        

  Magnetics - RWM sensors                            

  Mirnov coils -- high                               
  frequency                                          

  Mirnov coils -- poloidal              **x**        
  array                                              

  Mirnov coils -- toroidal              **x**        
  array                                              

  MSE                                   **x**        

  NPA -- ExB scanning                                

  NPA -- solid state                                 

  Neutron measurements                               

  Plasma TV                  **x**                   

  Reciprocating probe                                

  Reflectometer -- 65GHz                             

  Reflectometer --                                   
  correlation                                        

  Reflectometer -- FM/CW                             

  Reflectometer -- fixed f                           

  Reflectometer -- SOL                  **x**        

  RF edge probes                        **x**        

  Spectrometer -- SPRED      **x**                   

  Spectrometer -- VIPS       **x**                   

  SWIFT -- 2D flow                                   

  Thomson scattering         **x**                   

  Ultrasoft X-ray arrays                **x**        

  Ultrasoft X-ray arrays --             **x**        
  bicolor                                            

  Ultrasoft X-rays -- TG                **x**        
  spectr.                                            

  Visible bremsstrahlung                **x**        
  det.                                               

  X-ray crystal                                      
  spectrometer - H                                   

  X-ray crystal                                      
  spectrometer - V                                   

  X-ray fast pinhole camera                          
  -------------------------------------------------------------------------------