# Presentation: 435603

## Planning for e-Beam Mapping 

- E. Fredrickson, A. Georgievski, M. Zarnstorff
*PPPL*
- V. Rudakov
*Kharkov*

** ****	****Program Advisory Committee Meeting 7**           July 13-14, 2004

*NCSX*

## Magnetic field mapping program

- Use field line tracing calculations to:	(ongoing)
- Create library of vacuum magnetic configurations.
- Identify configurations sensitive to field errors;
- non-axisymmetric errors (coil misalignment)
- axisymmetric errors (stray fields)
- Draft plan for field mapping studies 	(2005-6)
- Define goals for e-beam mapping
- Design e-beam mapping hardware.
- Define machine requirements for e-beam mapping studies.
- Construction of electron guns, detectors	(2006-7)
- Initial e-beam mapping experiments 	(FY 08)

## Biot-Savart approach used for Field line tracing calculations

- The calculations are performed by A. Georgievski in collaboration with V. Rudakov at Kharkov Laboratory.
- The baseline coil configuration is "c08r00".
- The ratios of the TF, PF and MC currents are varied to explore different configurations.
- c08r00 uses 8 independent power supplies; recently configurations with 6 independent supplies, available for first plasmas, have been investigated.

## Small increase in vertical field shifts island phase.
A resonant field null point is found at Bz = 10.06%.
Islands from MC and PF and  possibly TF induced the resonant error fields.
Could indicate a cancellation of out-of-phase error fields.

- 10.20%

- 10.06%

-   9.84%

- Small increase in vertical field shifts island phase.
- A resonant field null point is found at Bz = 10.06%.
- Islands from MC and PF and  possibly TF induced the resonant error fields.
- Could indicate a cancellation of out-of-phase error fields.

*An **** = 0.5 is most sensitive, but also has large 3/6 islands*

## Even with background 3/6 islands, 1/2 island visible in separatrix

- A <1 mm shift of a single modular coil is easily detectable in a Poincaré plot.
- Need many transits to map surfaces so close to separatrix; also need to launch e-beam close to separatrix.

- K = 1.118, Bz(1.4) = 9.84%,
- PF4 tilted around X direction by 1.

## The null configuration is very sensitive to poloidal field coil tilts

- Net tilt of ≈ 1 cm, gives 4 cm island.
- Assuming linear scaling of error field with tilt, and a minimum detectable island of ≈ 1 cm; minimum detectable tilt of PF6 is ≈ 1 mm.

- K =1.118, Bz(1.4)=10.06%.
- PF6 tilted around X direction with angle 6’.

## Individual toroidal field coil tilts introduce small error fields

- Perhaps TF coil mechanical alignment accuracy will be adequate.
- Orthogonality of TF and PF coils suggests mutual inductance measurement may be an attractive alternative for out-of-plane tilts.

- K =1.118, Bz(1.4)=10.06%.
- Tilt of TF coil = 12’.

## Null configuration is also very sensitive to average vertical field

- A change in the average vertical field of only a few Gauss is easily detectable (about the island null point).
- One implication is that near null point, power supply regulation is critical.
- 0.1% ripple, ≈ 2 cm fuzz at null point

- 9.84% < Bz < 10.2%, 10.06% at null point.

## Features of order 1 cm are detectable with luminescent probe

- Other issues include integration time, setup time, access and machine requirements.

- G.G. Lesnyakov, E D. Volkov, A.V. Georgievski,* et al., *
- Nucl. Fusion **32** (1992) 2157.

## e-beam mapping experiment issues to be resolved

- Machine requirements
- What field strength required/available?
- (pulse length, e-beam drift, permeability, p.s. regulation)
- What pulse length is needed/available?
- (integration time, field strength)
- E-beam mapping hardware issues
- What resolution is required?
- What is maximum acceptable opacity?
- What brightness can be achieved (integration time)?

## Plans for further work

- Upgrade mapping codes & complete grid-based code
- Accuracy of interpolation for fine-scale structure
- Still slow for coil alignment error calculations as new grid must be constructed each time.
- Finish studies of "6-supply" configurations
- Verify existence of useful configurations
- Explore methods to isolate sources of error fields (*e.g*., configurations with reduced coil sets).
- Draft plan for e-beam mapping studies (phases I & II).
- Set requirements for e-beam mapping hardware, access and machine capabilities.