# Presentation: 669709

## e-Beam Mapping Plans (FY09)

- E. Fredrickson,
*For the NCSX Team*

** ****	****NCSX Research Forum**           Dec. 7, 2006

*NCSX*

- Auburn

## Goals of e-beam mapping studies

- NCSX will have a few weeks for preliminary e-beam mapping experiments in FY09.
- e-beam mapping goals:
- Verify coil assembly accuracy
- Measure error-field induced islands.
- Document control of vacuum field characteristics with coil currents
- Document good surfaces over wide range of configurations (*e.g.,* iota-scan)
- Verify correct rotational transform; for example, by locating rational surfaces (using islands)

##  Auburn will collaborate on  e-beam mapping campaign

- Auburn is also lending hardware:
- Movable electron gun, camera
- Help with detection apparatus
- Evaluating options for detection apparatus:
- Wire mesh
- Sparse, jogged mesh
- Fluorescent rod
- Additional issues under study
- Field value/pulse length (2 kG : > 30s, 1 kG : >2 min)
- Studies using e-beam energy dependence?
- Mutual inductances using symmetric differences

## Program to validate coil accuracy developed with field-line tracing

- Modular coils plus TF gives configuration sensitive to Modular coil displacements or tilts
- Configuration is insensitive to TF misalignments.
- The PF coils can be tested in pairs;
- The ratios of the TF, PF and MC currents are varied to explore different configurations.
- Insensitive to alignment errors for PF coils 1 - 3.
- PF coils may also be added singly

## Configurations sensitive to error-fields have intrinsic islands

- Separatrix of initial 3/6 island chain is "split" by 1/2 error field.
- Modular Coil #1 shifted by 3mm.
- Mapping near the separatrix requires many passes, high resolution.

- V. Rudakov, *Kharkov, *S. Georgievski

**Notes:**
04090403  (EII),  NCSX magnetic configuration. K =1.05, Bz(1.4)=6.26%,  Vst=1.5, V=1.5, to=0.422, tmax=0.529, Rst=1.045. Resonances 3/6, 9/17, 6/11. Without poloidal coils. PT, FW, r MC1 =+3mm.

## Configurations with single PF coil offer potential to isolate errors

*Configurations with single PF coil offer potential to isolate errors*

- PF6 lower and TF currents adjusted to give  = 0.5 surface.
- Intrinsic island separatrix is split, as in previous cases.

- PF6 tilted 0.2o ≈ 10mm
- 1mm displacement requires 1cm resolution

- S. Georgievski, *PPPL, *V. Rudakov, *Kharkov*

- ≈ 45 cm

- Peterson, et al., APS'06, Auburn CTH

**Notes:**
04062001
RIII, Variant IIb,  (c08r00),  K =1.11(1.10884), Bz(pf6)=10.06%(lower),  Bz=0% By=0.011%, Bo=1.7 T,  Vst=1.5,  V= 1.5, Rst=1.1,  o=0.483, max=0.517,  18TFC, PT.  PF6=12’. Lower PF6 tilted around X direction

## Vacuum configurations will be tested with  = 0.2 to  = 0.82

- Scans in shear will also be explored.
- Verification of transform is goal, as well as shape and good surfaces.
- Very flexible coil set gives large range of configurations.

- iota range
- 0.205-0.238

- iota range
- 0.68-0.80

- iota range
- 0.80-1.00

- S. Georgievski, *PPPL, *V. Rudakov, *Kharkov*

**Notes:**
Dv112401(c08r00),  NCSX magnetic configuration. K =0.7, Bz(1.4)=1%, Vst=0.5, Rst=1.21, to=0.205, tmax=0.238
Dv121702,  (c08r00),  NCSX magnetic configuration. K =1.2, Bz(1.4)=6.5%, Vst=0.5, to=0.68, tmax=0.8, Rst=1.08 . Resonance 3/4. One filamental case
Dv112602 (c08r00),  NCSX magnetic configuration. K =1.3, Bz(1.4)=0%, Vst=0.5, Rst=1.46, to=0.82, tmax=1

## Summary

- A plan is taking form for localizing possible sources of error fields to one of the three major coil sets (Modular coils, poloidal field coils, or toroidal field coils).
- A range of vacuum configurations will be mapped in FY09 to validate control of field topology.
- Auburn has offered to collaborate on field mapping, and to provide through loans some of the e-beam mapping hardware.

## Small increase/decrease (≈0.15%) in vertical field creates large islands.
Questionable whether control of fields will be good enough to exploit this configuration.

- 10.20%

- 10.06%

-   9.84%

*Small* increase/decrease (≈0.15%) in vertical field creates large islands.
- Questionable whether control of fields will be good enough to exploit this configuration.

*Configurations with small intrinsic islands exist, but... *

## 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’.

## "Bean" offers best access for scanning fluorescent rods

- Full coverage requires multiple probes.
- But rods can be relatively short, allowing fast scan times.
- Other cross-sections are being evaluated.