+--------------------+----------------------+-------+-----------------+
| **Princeton Plasma |                      |       |                 |
| Physics            |                      |       |                 |
| Laboratory**       |                      |       |                 |
|                    |                      |       |                 |
| **NSTX             |                      |       |                 |
| Experimental       |                      |       |                 |
| Proposal**         |                      |       |                 |
+--------------------+----------------------+-------+-----------------+
| **Title:           |                      |       |                 |
| Optimizing Current |                      |       |                 |
| Generation with    |                      |       |                 |
| Transient CHI**    |                      |       |                 |
+--------------------+----------------------+-------+-----------------+
| **OP-XP-725**      | > **Revision: 0**    | >     |                 |
|                    |                      |  Effe |                 |
|                    |                      | ctive |                 |
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|                    |                      | *4/13 |                 |
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|                    |                      | Expir |                 |
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|                    |                      | Date: |                 |
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|                    |                      | ipula |                 |
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+--------------------+----------------------+-------+-----------------+
| **PROPOSAL         |                      |       |                 |
| APPROVALS**        |                      |       |                 |
+--------------------+----------------------+-------+-----------------+
| **Responsible      |                      |       | > Date          |
| author: R. Raman** |                      |       |                 |
+--------------------+----------------------+-------+-----------------+
| **ATI -- ET Group  |                      |       | > Date          |
| Leader: R. Raman** |                      |       |                 |
+--------------------+----------------------+-------+-----------------+
| **RLM -- Run       |                      |       | > Date          |
| Coordinator: D.    |                      |       |                 |
| Gates**            |                      |       |                 |
+--------------------+----------------------+-------+-----------------+
| **Responsible      |                      |       |                 |
| Division:          |                      |       |                 |
| Experimental       |                      |       |                 |
| Research           |                      |       |                 |
| Operations**       |                      |       |                 |
+--------------------+----------------------+-------+-----------------+
| [**Chit Review     |                      |       |                 |
| Board**            |                      |       |                 |
| (designated by Run |                      |       |                 |
| Coordin            |                      |       |                 |
| ator)]{.underline} |                      |       |                 |
+--------------------+----------------------+-------+-----------------+
| **MINOR            |                      |       |                 |
| MODIFICATIONS**    |                      |       |                 |
| (Approved by       |                      |       |                 |
| Experimental       |                      |       |                 |
| Research           |                      |       |                 |
| Operations)        |                      |       |                 |
+--------------------+----------------------+-------+-----------------+
|                    |                      |       |                 |
+--------------------+----------------------+-------+-----------------+

NSTX EXPERIMENTAL PROPOSAL

Title: Optimizing Current Generation with Transient CHI OP-XP-725

Authors: R. Raman, B.A. Nelson, D. Mueller, M. Bell, T.R. Jarboe

# 1. Overview of planned experiment 

> Transient CHI discharges produced during XP606 will be optimized so as
> to reduce the extent of absorbing arcing and to increase the magnitude
> of the closed flux current.

# 2. Theoretical/ empirical justification

> Using the previously commissioned CHI-specific capacitor bank, and
> using gas and microwave injection from a region below the lower
> divertor plates, up to 160kA of closed flux current has been generated
> in NSTX. Compared to the lower current discharges produced during
> 2005, these higher current discharges had a large absorber arc current
> of about 25kA. By reducing the number of capacitors from nine to about
> 4, the absorber arc current magnitude can be reduced. After the end of
> 2006 operations the DC power supply used for charging the capacitor
> bank was replaced with a new higher power DC power supply. In addition
> the number of MOVs is being reduced from four to 2 banks to reduce the
> extent of MOV conduction current. Both these modifications should
> allow operation at voltages similar to or above that possible during
> the 2006 run, but with fewer number of capacitors. This modification
> should allow high current closed flux current generation, but with
> reduced absorber arcing. A new voltage monitoring system will be used
> to monitor voltage spikes. This information will be used for future
> increases to the capacitor bank charging voltage.
>
> This XP has minor modifications to the XP run in 2006 (XP 606), and
> covers only Part 1 of XP606. Please refer to XP606 for additional
> details.

# 3. Experimental run plan

**[3.1 Reproduce current persistence, reduce absorber arc current, and
diagnose to obtain missing data]{.underline}**

> Configure the CHI capacitor bank initially with five capacitors in
> parallel (C = 25mF). The capacitor bank will be triggered at t = 5ms
> throughout this experiment.
>
> Open line and ground switches in the OH circuit to prevent current
> from flowing in it.
>
> Use 5min HeGDC between shots to maintain constant wall conditions.
>
> Start with the gas timing and plenum pressure developed in shot
> 120879. Reload this shot. (Note: all PF coil currents are specified in
> the physics convention, *i.e.* positive current is counter-clockwise
> from above.). Extend the current flat-top duration in the following
> coils to +500ms (TF, PF5, PF3U, PF3L, PF1AU, PF1AL and PF2U).
>
> Program the CHI capacitor bank crowbar ignitron to fire at t = +8ms to
> rapidly reduce the CHI injector current.
>
> Start with a capacitor bank charging voltage of 1.6kV, and increase in
> steps of 100V up to 1.9kV, while monitoring the fast injector voltage
> signals for noise spike excursions.
>
> After current persistence is observed, readjust the PF3U/L coil
> current so as to position the plasma at z=0. Adjust the vertical field
> based on fast camera observations.
>
> Diagnose using (1) soft x-ray array, (b) bolometer array, (c) fast
> camera, (d) Thomson scattering and (e) spectroscopy.
>
> If the absorber arc current continues to be large (above few kA)
> reduce the number of capacitors to 4 and repeat the optimization
> procedure.

**[3.2 Increase the magnitude of closed flux current by increasing the
injector flux and the toroidal flux.]{.underline}**

> Starting from the previous shot (TF=59kA), change the current in the
> TF coils to 65kA, in steps of 2kA to observe the effect on current
> multiplication at constant injector flux (if experimental condition
> allow, expand the range).
>
> Starting from the best case above (PF1B=6kA), change the current in
> the injector flux coils proportionally in steps of 10% (to increase
> the injector flux), up to a maximum of 10kA in the PF1B coil. If
> necessary, increase the capacitor bank voltage in steps of 100V, to
> the maximum allowable.
>
> For the case with the highest injector flux, readjust the current in
> the TF coil to maximize the closed flux fraction. To do this it may be
> necessary to go to higher voltage, so this part may need to be delayed
> until higher voltage capability is available.
>
> If current limits allow, repeat the optimization procedure at B~T~ =
> 0.6T.
>
> Repeat the best case from 3.1 or 3.2, several times (about 5) to check
> for reproducibility, while diagnosing with the usual set of
> diagnostics.
>
> If time permits, diagnose while applying HHFW pulse configured for
> plasma heating (about 10 shots).

**[3.3 Use Lithium wall conditioning capability to improve closed flux
generation]{.underline}**

> Based on the work conducted in the Li XPs and the methods developed
> there, select a suitable amount of Li to apply either between shots or
> once per several shots (for example like Ti gettering in HIT-II).
> Repeat the best discharges with Li wall conditioning to asses the
> impact of Li on these discharges. Note that it may not be necessary to
> do between shot HeGDC for several shots in a row (as on HIT-II)
> because unlike inductive operation there is no gas puffing during the
> CHI shot.
>
> In conducting this experiment it may be necessary to increase the
> amount of gas injected in the region below the lower divertor plates.

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

> **NOTE:** Do NOT conduct "hi-pot" tests of any of the NSTX vacuum
> vessel components above 2kV with either the CHI supply capacitors or
> the CHI snubber capacitors connected to NSTX, as these capacitors have
> a rating of only 2kV.
>
> **NOTE**: Ensure LDGIS interlocks are in the "green" state prior to
> conducting any "hi-pot" tests.
>
> **NOTE:** The trained personnel identified in the procedure for
> changing the capacitor bank configuration should be available during
> the initial phase of CHI operations when the capacitor bank size is
> being changed.
>
> The Phantom fast camera is required for this experiment.
>
> Good machine wall conditions are required (low water levels and
> preferably a very recent boronization of the vacuum vessel)

**Configuration**

1.  Connect the CHI capacitor to the CHI bus at the machine and connect
    the snubber capacitor and the MOV protection devices.

2.  Reduce the maximum voltage capability on the OH circuit to 4kV (from
    the normal 6kV).

3.  Configure PF1B for 2kV operation to drive current in the
    anti-clockwise direction as seen from above (normal for CHI). Change
    PF1B RIS and software limits to provide 10kA capability (from the
    present 5kA).

4.  Configure PF2L for 2kV operation, with coil current in the clockwise
    direction (opposite of normal operation).

5.  Configure PF4 to have the same polarity as PF5

6.  Enable the EC-PI klystron #2 to provide the divertor chamber
    preionization and disable klystron #1 connected to the midplane
    EC-PI launcher. Apply the EC-PI power from t = -3 to +8ms.

7.  Configure HHFW for 0-π phasing during heating, if required.

8.  Operate the NB sources at 40kV acceleration voltage if NBI is
    needed.

> **LDGIS system checks**

9.  Ensure LDGIS is in the "Puff" mode and has been tested prior to the
    experiment.

10. Ensure LDGIS gas pressure interlocks (PE107, PE104) are functional.

11. Set LDGIS operating line pressure to 100Psig helium.

12. Ensure 2000 Torr D~2~ filling gas pressure in LDGIS system

> **Pre-operational checklist**

13. Ensure MIG and Penning gauges are selected for operation.

14. Remove CHI jumpers.

15. Check TF interlock is set to 10kA.

16. Check for the appearance of ionization light on the fast camera
    during the EC-PI pulse to ensure correct triggering.

# 5. Planned analysis

> The magnetic analysis codes LRDFIT and EFIT will be used to analyze
> the plasma equilibrium. It is hoped to be able to use data from the
> MPTS and other kinetic diagnostics to supplement the magnetic data for
> the assessment of flux closure.

# 6. Planned publication of results

These results will be published at meetings and in journal articles.

PHYSICS OPERATIONS REQUEST

Title: Optimizing the Current generation with Transient CHI OP-XP-725

Machine conditions (specify ranges as appropriate)

> I~TF~ (kA): **-41 to -52** Flattop start/stop (s): **-0.02 / 0.7**

I~P~ (MA): **0.5** Flattop start/stop (s): **n/a**

Configuration: **CHI transitioning to CS limited**

> Outer gap (m): **N/A**, Inner gap (m): **N/A**
>
> Elongation κ: **N/A**, Triangularity δ: **N/A**
>
> Z position (m): **0**
>
> Gas Species: **D**, Injector: **LDGIS + LFS midplane**
>
> NBI- **40kV to 60kV D^0^ injection, 20ms pulse**

ICRF- **Up to 2MW in the heating phasing (0-π).**

CHI- **Capacitor bank operation, 2 -- 5 capacitors active**

Shot numbers for setup: **120870, Other useful shot numbers: 120888,
120890**

DIAGNOSTIC CHECKLIST

Transient CHI Startup OP-XP-725

+----------------------+----+-----+-----------------------------------+
| #### Diagnostic      | #  | ##  | #### Instructions                 |
|                      | ## | ##  |                                   |
|                      | #  | Des |                                   |
|                      | Ne | ire |                                   |
|                      | ed |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > Bolometer --       | >  |     | > \* Use when reproducible        |
| > tangential array   |  X |     | > conditions are achieved         |
+----------------------+----+-----+-----------------------------------+
| > Bolometer array -  |    | > X |                                   |
| > divertor           |    |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > CHERS              |    |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > Divertor fast      |    | > X |                                   |
| > camera             |    |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > Dust detector      |    |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > EBW radiometers    |    |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > Edge pressure      | >  |     |                                   |
| > gauges             |  X |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > Edge rotation      |    | > X | > \*                              |
| > spectroscopy       |    |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > Fast lost ion      |    |     |                                   |
| > probes - IFLIP     |    |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > Fast lost ion      |    |     |                                   |
| > probes - SFLIP     |    |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > Filterscopes       |    | > X |                                   |
+----------------------+----+-----+-----------------------------------+
| > FIReTIP            |    | > X | > \*                              |
+----------------------+----+-----+-----------------------------------+
| > Gas puff imaging   |    |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > H~alpha~ camera -  |    | > X | > \*                              |
| > 1D                 |    |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > Infrared cameras   |    | > X |                                   |
+----------------------+----+-----+-----------------------------------+
| > Interferometer - 1 |    |     |                                   |
| > mm                 |    |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > Langmuir probe     |    | > X |                                   |
| > array              |    |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > Magnetics --       | >  |     |                                   |
| > Diamagnetism       |  X |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > Magnetics - Flux   | >  |     |                                   |
| > loops              |  X |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > Magnetics - Locked |    |     |                                   |
| > modes              |    |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > Magnetics - Pickup | >  |     |                                   |
| > coils              |  X |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > Magnetics -        | >  |     |                                   |
| > Rogowski coils     |  X |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > Magnetics - RWM    |    |     |                                   |
| > sensors            |    |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > Mirnov coils --    | >  |     |                                   |
| > high frequency     |  X |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > Mirnov coils --    | >  |     |                                   |
| > poloidal array     |  X |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > Mirnov coils --    | >  |     |                                   |
| > toroidal array     |  X |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > MSE                |    | > X |                                   |
+----------------------+----+-----+-----------------------------------+
| > Neutral particle   |    |     |                                   |
| > analyzer           |    |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > Neutron            |    |     |                                   |
| > measurements       |    |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > Plasma TV          | >  |     |                                   |
|                      |  X |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > Reciprocating      |    | > X |                                   |
| > probe              |    |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > Reflectometer --   |    |     |                                   |
| > core               |    |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > Reflectometer -    |    |     |                                   |
| > SOL                |    |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > RF antenna camera  |    |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > RF antenna probe   |    |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > SPRED              |    | > X |                                   |
+----------------------+----+-----+-----------------------------------+
| > Thomson scattering |    | > X | > \*                              |
+----------------------+----+-----+-----------------------------------+
| > Ultrasoft X-ray    |    | > X | > \*                              |
| > arrays             |    |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > Ultrasoft X-ray    |    | > X | > \*                              |
| > arrays -- bicolor  |    |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > Visible            |    | > X | > \*                              |
| > bremsstrahlung     |    |     |                                   |
| > det.               |    |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > Visible            |    | > X |                                   |
| > spectrometer       |    |     |                                   |
| > (VIPS)             |    |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > X-ray crystal      |    |     |                                   |
| > spectrometer - H   |    |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > X-ray crystal      |    |     |                                   |
| > spectrometer - V   |    |     |                                   |
+----------------------+----+-----+-----------------------------------+
| > X-ray fast pinhole |    | > X | > \*                              |
| > camera             |    |     |                                   |
+----------------------+----+-----+-----------------------------------+