+--------------------+----------------------+-------+-----------------+
| **Princeton Plasma |                      |       |                 |
| Physics            |                      |       |                 |
| Laboratory**       |                      |       |                 |
|                    |                      |       |                 |
| **NSTX             |                      |       |                 |
| Experimental       |                      |       |                 |
| Proposal**         |                      |       |                 |
+--------------------+----------------------+-------+-----------------+
| **Title: Divertor  |                      |       |                 |
| heat flux          |                      |       |                 |
| reduction and      |                      |       |                 |
| detachment in      |                      |       |                 |
| highly shaped      |                      |       |                 |
| plasmas**          |                      |       |                 |
+--------------------+----------------------+-------+-----------------+
| **OP-XP-708**      | > **Revision:**      | >     |                 |
|                    |                      |  Effe |                 |
|                    |                      | ctive |                 |
|                    |                      | >     |                 |
|                    |                      | Date: |                 |
|                    |                      | >     |                 |
|                    |                      | > *   |                 |
|                    |                      | (Ref. |                 |
|                    |                      | >     |                 |
|                    |                      | OP-AD |                 |
|                    |                      | -97)* |                 |
|                    |                      | >     |                 |
|                    |                      | >     |                 |
|                    |                      | Expir |                 |
|                    |                      | ation |                 |
|                    |                      | >     |                 |
|                    |                      | Date: |                 |
|                    |                      | >     |                 |
|                    |                      | > *(2 |                 |
|                    |                      | >     |                 |
|                    |                      |  yrs. |                 |
|                    |                      | > u   |                 |
|                    |                      | nless |                 |
|                    |                      | >     |                 |
|                    |                      |  othe |                 |
|                    |                      | rwise |                 |
|                    |                      | > st  |                 |
|                    |                      | ipula |                 |
|                    |                      | ted)* |                 |
+--------------------+----------------------+-------+-----------------+
| **PROPOSAL         |                      |       |                 |
| APPROVALS**        |                      |       |                 |
+--------------------+----------------------+-------+-----------------+
| **Author: V. A.    |                      |       | > Date          |
| Soukhanovskii**    |                      |       | > 02/08/2007    |
+--------------------+----------------------+-------+-----------------+
| **ATI -- ET Group  |                      |       | > Date          |
| Leader: V. A.      |                      |       |                 |
| Soukhanovskii (H.  |                      |       |                 |
| W. Kugel)**        |                      |       |                 |
+--------------------+----------------------+-------+-----------------+
| **RLM - Run        |                      |       | > Date          |
| Coordinator: D.    |                      |       |                 |
| Gates (M. G.       |                      |       |                 |
| Bell)**            |                      |       |                 |
+--------------------+----------------------+-------+-----------------+
| **Responsible      |                      |       |                 |
| Division:          |                      |       |                 |
| Experimental       |                      |       |                 |
| Research           |                      |       |                 |
| Operations**       |                      |       |                 |
+--------------------+----------------------+-------+-----------------+
| [**Chit Review     |                      |       |                 |
| Board**            |                      |       |                 |
| (designated by Run |                      |       |                 |
| Coordin            |                      |       |                 |
| ator)]{.underline} |                      |       |                 |
+--------------------+----------------------+-------+-----------------+
| **MINOR            |                      |       |                 |
| MODIFICATIONS**    |                      |       |                 |
| (Approved by       |                      |       |                 |
| Experimental       |                      |       |                 |
| Research           |                      |       |                 |
| Operations)        |                      |       |                 |
+--------------------+----------------------+-------+-----------------+
|                    |                      |       |                 |
+--------------------+----------------------+-------+-----------------+

NSTX EXPERIMENTAL PROPOSAL

Divertor heat flux reduction and detachment in highly shaped plasmas
OP-XP-708

# 1. Overview of planned experiment 

> The goal of this experiment is to determine conditions of the
> steady-state outer divertor target heat flux reduction and detachment
> in the NBI-heated H-mode plasma operational space in a higher-end
> elongation / triangularity LSN shape with κ=2.2−2.5 and δ=0.5-0.7,
> referred hereforth as the PF1A/PF1B shape. Two techniques will be used
> to achieve the outer target detachment: raising scrape-off layer
> density by means of D~2~ injections, and raising edge radiated power
> by injecting an extrinsic impurity (CD~4~ or N~2~). In the first part
> of the experiment deuterium will be injected in the lower divertor
> region. In the second part of the experiment deuterated methane or
> nitrogen will be injected in increased quantities to yield
> *P~rad~/P~in~* up to 0.5 to obtain the outer target detachment.
> Divertor measurements, such as the D~α~, D~β~, D~γ~ brightnesses, heat
> flux (from IR cameras), radiated power, divertor Langmuir probe
> *I~sat~* and neutral pressure will be measured and analyzed for signs
> of heat flux reduction, detachment, and an X-point MARFE formation.
> The goal is to determine the injected gas quantity necessary to
> establish radiative and/or detached (partially detached) divertor
> conditions, simultaneously retaining good core plasma quantities (MHD,
> confinement, impurity level).

# 2. Theoretical/ empirical justification

> Previous divertor experiments in NSTX \[1, 2, 3\] with deuterium and
> neon puffing demonstrated that the outer divertor peak heat flux can
> be reduced by 50-80 % and simultaneously H-mode confinement can be
> maintained. These experiments have been conducted using the PF2L
> shape. The experiments revealed a strong dependence of the plasma
> performance and divertor heat flux reduction on a gas puffing
> location. When deuterium is puffed in the midplane or private flux
> region locations at rates 20-160 Torr l /s, radiative divertor
> conditions are apparently attained. When deuterium is puffed in the
> divertor at 200 - 450 Torr l /s, a partially detached divertor state
> can be achieved. Midplane neon injections apparently lead to the
> radiative mantle type heat exhaust since NSTX divertor temperature in
> the heat flux limited regime was too low for neon to radiate
> effectively. This experiment will study divertor heat reduction and
> detachment in high elongation/triangularity LSN shape (κ\<2.5 and
> δ\~0.7). This shape has shown great promise toward achieving CTF-like
> parameters (β~t~, β~n~, bootstrap and non-inductive current fraction)
> \[4\]. Because of large poloidal magnetic flux expansion, divertor
> peak heat flux is reduced in this shape by a factor 2-3 in comparison
> with the low triangularity/elongation shape. The Branch 5 and the
> LDGIS injectors will be used to puff deuterium in the lower divertor
> region in a steady-state fashion to further study the radiative and
> partially detached divertor regimes. Midplane CD~4~ or N~2~ injection
> will be used to increase divertor radiated power and to attempt the
> OSP detachment through divertor radiation simultaneously maintaining
> H-mode confinement.

# 3. Experimental run plan

# Part 1. Heat flux reduction and detachment in high elongation / triangularity (PF1A/PF1B) LSN plasmas with D~2~ injection (up to 25 shots)

I.  Setup an LSN HFS-fueled plasma with elongation κ = 2.2 − 2.5 and
    triangularity δ \< 0.75 (3 - 4 shots)

    -   Wall conditions should permit reproducible H-mode access.

    -   (Optional) Run a helium discharge to de-saturate walls if
        necessary

    -   Use 2 NBI sources at full energy (80 kV). Start with A, B and
        add C as needed

    -   HFS plenum pressure is 1200-1300 Torr

    -   Example shots: 120339 (0.7 A), 119622, 119645, 120640 (0.8 A)

    -   Greenwald density for *I~p~*=0.8 MA is n~G~ = 5.5 x 10^19^ m^-3^

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```
II. Perform a gas injection rate and location scan (up to 25 shots). Use
    Branch 5 injector and the PZV4/4a valve to inject gas in the outer
    SOL close to outer strike point. Use lower dome gas injection system
    (LDGIS) fast valves to inject high-rate gas pulses in the private
    flux region. Use LDGIS and PZV4/4a valve to inject gas in flow mode
    in the private flux region (Figures 1, 2).

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```
1.  Use Branch 5 gas injector (Bay K bottom, CHI gap) in flow mode at
    several plenum pressures to obtain injection rates 50 - 160 Torr l
    /s as shown in Table 1 (\~ 10 shots)

+----------+----------------+--------------------+--------------------+
| Number   | Flow rate in   | Injection time wrt | Gas pulse duration |
|          | PCS            | t0                 | (s)                |
|          |                |                    |                    |
|          | (Torr l /s)    | in PCS (s)         |                    |
+----------+----------------+--------------------+--------------------+
| 1        | 70             | 0.300              | 0.100              |
+----------+----------------+--------------------+--------------------+
| 2        | 80             | 0.300              | 0.100              |
+----------+----------------+--------------------+--------------------+
| 3        | 50-60          | 0.300              | 0.100              |
+----------+----------------+--------------------+--------------------+

> Table 1. Branch 5 gas injector parameter scan

-   Use valve PZV4/4a to control gas flow. Plenum fill pressure 2500
    Torr. Delay between valve waveform and gas appearance inside NSTX VV
    is 80-100 ms.

-   A flow rate value set in PCS corresponds to one half of the actual
    flow rate, since there are two piezoelectric valves PZV 4 and PZV4a
    mounted in parallel.

-   Adjust flow rate, timing, and duration of PZV4/4a gas pulse to
    optimize

2.  Use LDGIS fas valve injectors in series at several plenum pressures
    to obtain injection rates 50 - 600 Torr l /s as shown in Table 2 (\~
    10 shots). The LDGIS valves are: AV119 (Bay L), AV120 (Bay C), AV121
    (Bay I), AV122 (Bay F).

  ----------- ------------------- ------------------- -------------------
  Number      Plenum Pressure     Injection time wrt  Comment
              (Torr)              t0 (s)              

  1           400                 0.400               Gas pulses 40 ms
                                                      apart

  2           500                 0.400               Gas pulses 40 ms
                                                      apart

  3           600                 0.400               Gas pulses 40 ms
                                                      apart

  4           Optimal             0.400               Gas pulses 80 ms
                                                      apart

  5           Optimal             0.40                Gas pulses 20 ms
                                                      apart
  ----------- ------------------- ------------------- -------------------

> Table 2. LDGIS gas injector parameter scan

-   Adjust plenum pressure, timing, and time between gas pulses to
    optimize

-   Use LDGIS valves in the following order: AV120, AV122, AV119, AV121

2.  Use LDGIS injectors with PZV4/4a valves to inject gas in the private
    flux region in flow mode (up to 5 shots) as shown in Table 3.

+----------+----------------+--------------------+--------------------+
| Number   | Flow rate in   | Injection time wrt | Gas pulse duration |
|          | PCS            | t0                 | (s)                |
|          |                |                    |                    |
|          | (Torr l /s)    | in PCS (s)         |                    |
+----------+----------------+--------------------+--------------------+
| 1        | 40             | 0.300              | 0.100              |
+----------+----------------+--------------------+--------------------+
| 2        | 80             | 0.300              | 0.100              |
+----------+----------------+--------------------+--------------------+
| 3        | 30-60          | 0.300              | 0.100              |
+----------+----------------+--------------------+--------------------+

> Table 3. LDGIS gas injector parameter scan

4.  In one high density discharge, turn off NBI at the time when *n~e~*
    is high (\> 5 x 10^19^ m^-3^) to obtain high density low input power
    condition for 50 - 100 ms

5.  Use GPI diagnostic and edge reciprocating probe in 3-5 shots with
    divertor gas puffing to obtain edge turbulence data

6.  (Conditional) Use Supersonic gas injector (SGI) instead of divertor
    gas puffers to obtain radiative / detached divertor conditions

7.  Optional, time permitting: Use a target with 3 NBI sources at full
    energy (80 kV) and best gas injection scenario. Example shots:
    119622 (0.8 MA), 121120 (0.7 MA)

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```
III. **Optional \--** Heat flux reduction and detachment in high
     elongation / triangularity LSN plasmas with **CD~4~ or N~2~
     injection** (up to 10 shots, conditional, time-permitting)

     -   Perform CD~4~ injections in increasing quantities (from 1 to 20
         Torr l / s ) into intermediate density two NBI source shot
         from 1. Monitor radiated power (10 shots)

     -   Wall conditions should permit reproducible H-mode access

     -   Use Injector 3 for CD~4~ or N~2~. The gas pulse start time is
         0.30-0.35 s, pulse duration 0.05 -- 0.300 s

     -   Start with a impurity gas pulse at the rate of 1 Torr l / s,
         pulse duration 50 ms

     -   Increase impurity gas injection rate to 20 Torr l / s in steps
         of 1-2 Torr l / s, increase the pulse duration from 50 ms to
         200 ms, in accordance with plasma behavior and the flat-top
         length obtained (expect shortening due to increased plasma
         resistivity (*Z~eff~*) and higher ohmic flux consumption).
         Monitor plasma radiated power

     -   Conditional, time permitting - perform an impurity gas
         injection at established in 3 rates into a high density two NBI
         source shot from 1. Monitor radiated power

     -   A 10 liter bottle of CD~4~ has been reserved for this
         experiment. The quantity of methane in the bottle is 10 liter x
         (350 psi x 51.71 Torr/psi) = 181000 Torr l. A modification of
         gas handling setup may be developed to reduce the loss of
         methane to pipe and plenum pressure cycling and pumpout

     -   Run a standard fiducial as a last shot of the day to evaluate
         post-CD~4~ wall conditions

![](media/image1.png){width="3.3208333333333333in"
height="3.602777777777778in"}

Figure 1. Divertor strike point locations in reference to gas injector
locations, shot 117577. Gas willl be injected either from Branch 5
injector (CHI gap) or from LDGIS ports (shown by thin gray lines).

![](media/image2.png){width="5.403472222222222in" height="4.03125in"}

Figure 2. Lower dome and Branch 5 gas delivery systems schematic.

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

Physics Operations Request and Diagnostic Checklist are attached.

> Diagnostic capabilities: Tile Langmuir probes, IR cameras, main plasma
> and divertor bolometers, and the D~α~, D~γ~ cameras should be
> operational. Lower divertor Langmuir probe locations are (major radii,
> m): 0.2775, 0.4952, 0.7970, 0.9110, 1.0170.
>
> Branch 5 Injector in FLO mode must be tested prior to the execution of
> this experiment.

# 5. Planned analysis

> The following numerical tools will be used for data analysis: LRDFIT,
> UEDGE, ADAS, DEGAS 2, TRANSP, analytic two point divertor model.

# 6. Planned publication of results

Results will be presented at the upcoming EPS, APS meetings, and will be
published in a refereed journal as appropriate.

**References**

\[1\] V. A. Soukhanovskii, R. Maingi, R. Raman, R. E. Bell, C. Bush, R.
Kaita, H. W. Kugel, C. J. Lasnier, B. P. LeBlanc, J. E. Menard, S. F.
Paul , A. L. Roquemore, and the NSTX Team, "Divertor Heat Flux Reduction
and Detachment in NSTX", IAEA FEC 2006 (Chengdu, China 2006), to be
submitted to Nuc. Fusion, 2007

\[2\] V. A. Soukhanovskii, R. Maingi, R. Raman, R. E. Bell, C. Bush, R.
Kaita, H. W. Kugel, C. J. Lasnier, B. P. LeBlanc, J. Menard, S. F. Paul,
A. L. Roquemore, and the NSTX Research Team, \"Divertor heat flux
reduction and detachment experiments in NSTX\", *J. Nucl. Mater.,* to
appear, 2007.

\[3\] Soukhanovskii, VA; Johnson, DW; Kaita, R; Roquemore, AL,
\"Electron density measurements in the National Spherical Torus
Experiment detached divertor region using Stark broadening of deuterium
infrared Paschen emission lines\", *Rev. Sci. Instrum.,* **77,** 10F127,
(2006).

\[4\] J. E. Menard et. al., "Recent physics results from NSTX", IAEA FEC
2006 (Chengdu, China 2006), submitted to Nuc. Fusion, 2007

![](media/image3.png){width="6.748611111111111in"
height="4.7444444444444445in"}

Figure 3 Waveforms of example shot 120640 (0.8 A)

PHYSICS OPERATIONS REQUEST

Divertor heat flux reduction and detachment in highly shaped plasmas
OP-XP-708

Machine conditions (specify ranges as appropriate)

> I~TF~ (kA): **-53** Flattop start/stop (s): **-0.02/1.2**

I~P~ (MA): **0.7-0.8** Flattop start/stop (s): **0.12/0.9**

Configuration: **Lower Single Null**

> Outer gap (m): **0.10-0.13**, Inner gap (m): **0.05-0.0.08**
>
> Elongation κ: **2.2-2.3**, Triangularity δ: **0.72-0.74**
>
> Z position (m): **0.00**
>
> Gas Species: **D / He / CD4**,
>
> Gas Injector: **Midplane / Inner wall / Lower Dome/Branch 5**
>
> NBI - Species: **D**, Sources: **A/B/C**, Voltage (kV): **80**,
> Duration (s): **0.8-1.0**

ICRF -- Power (MW): **0**, Phasing: **Heating / CD**, Duration (s):
**\_\_\_\_\_**

CHI: **Off**

*Either:* List previous shot numbers for setup: **120640, 120339**

[Gas setup]{.underline}: CS Injector -- D~2~ at 1300 Torr, LDGIS - D~2~,
Injector 1 -- He, Injector 2 -- D~2~, Injector 3 - CD~4~,

Injector Bay B High Flow - D~2~ or He for GPI

DIAGNOSTIC CHECKLIST

Divertor heat flux reduction and detachment in highly shaped plasmas
OP-XP-708

+-------------------------------+-----+----+--------------------------+
| #### Diagnostic               | ### | #  | #### Instructions        |
|                               | # N | ## |                          |
|                               | eed | #  |                          |
|                               |     | De |                          |
|                               |     | si |                          |
|                               |     | re |                          |
+-------------------------------+-----+----+--------------------------+
| > Bolometer - tangential      | >  |    |                          |
| > array                       |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Bolometer array - divertor  | >  |    |                          |
+-------------------------------+-----+----+--------------------------+
| > CHERS                       | >  |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Divertor fast camera        | >  |    | > View the X-point       |
|                               |     |    | > region with Dα filter  |
+-------------------------------+-----+----+--------------------------+
| > Dust detector               |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > EBW radiometers             |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Edge deposition monitor     |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Edge pressure gauges        | >  |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Edge rotation spectroscopy  | >  |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Fast lost ion probes --     |     |    |                          |
| > IFLIP                       |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Fast lost ion probes --     |     |    |                          |
| > SFLIP                       |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Filtered 1D cameras         | >  |    | > CIII, Dα, Dγfilters   |
+-------------------------------+-----+----+--------------------------+
| > Filterscopes                | >  |    |                          |
+-------------------------------+-----+----+--------------------------+
| > FIReTIP                     | >  |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Gas puff imaging            | >  |    | > Measure turbulence     |
|                               |     |    | > during detachment      |
+-------------------------------+-----+----+--------------------------+
| > High-k scattering           |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Infrared cameras            | >  |    | > Divertor & CS          |
+-------------------------------+-----+----+--------------------------+
| > Interferometer -- 1 mm      |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Langmuir probes - PFC tiles | >  |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Langmuir probes - RF        |     |    |                          |
| > antenna                     |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Magnetics -- Diamagnetism   |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Magnetics -- Flux loops     | >  |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Magnetics -- Locked modes   |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Magnetics -- Pickup coils   | >  |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Magnetics - Rogowski coils  | >  |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Magnetics - RWM sensors     |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Mirnov coils -- high        |     |    |                          |
| > frequency                   |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Mirnov coils -- poloidal    |     |    |                          |
| > array                       |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Mirnov coils -- toroidal    |     |    |                          |
| > array                       |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > MSE                         |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Neutral particle analyzer   |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Neutron Rate (2 fission, 4  |     |    |                          |
| > scint)                      |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Neutron collimator          |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Plasma TV                   | >  |    | > Dα filter when         |
|                               |     |    | > requested, no filter   |
|                               |     |    | > otherwise              |
+-------------------------------+-----+----+--------------------------+
| > Reciprocating probe         | >  |    | > Operate on several     |
|                               |     |    | > shots when requested   |
+-------------------------------+-----+----+--------------------------+
| > Reflectometer - FM/CW       |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Reflectometer - fixed       |     |    |                          |
| > frequency homodyne          |     |    |                          |
| > quadrature                  |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Reflectometer - homodyne    |     |    |                          |
| > correlation                 |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Reflectometer - HHFW/SOL    |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > RF antenna camera           |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > RF antenna probe            |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Solid State NPA             |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > SPRED                       | >  |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Thomson scattering - 20     | >  |    |                          |
| > channel                     |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Thomson scattering - 30     | >  |    |                          |
| > channel                     |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Ultrasoft X-ray arrays      | >  |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Ultrasoft X-ray arrays - 2  |     | >  |                          |
| > color                       |     |   |                          |
+-------------------------------+-----+----+--------------------------+
| > Visible bremsstrahlung det. | >  |    |                          |
+-------------------------------+-----+----+--------------------------+
| > Visible spectrometers       | >  |    | > Chords: Bay C fibers   |
| > (VIPS)                      |     |    | > U-V; J-K; F-G-H        |
+-------------------------------+-----+----+--------------------------+
| > X-ray crystal               |     | >  |                          |
| > spectrometer - H            |     |   |                          |
+-------------------------------+-----+----+--------------------------+
| > X-ray crystal               |     | >  |                          |
| > spectrometer - V            |     |   |                          |
+-------------------------------+-----+----+--------------------------+
| > X-ray PIXCS (GEM) camera    |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > X-ray pinhole camera        |     |    |                          |
+-------------------------------+-----+----+--------------------------+
| > X-ray TG spectrometer       |     |    |                          |
+-------------------------------+-----+----+--------------------------+