# Presentation: 648049

## Collective instability-induced fast ion losses in NSTX

- E. Fredrickson *for the NSTX Team*
**47****th**** APS – DPP Meeting**
- Oct 24-28, 2005
- Denver, Co.

***Culham Sci Ctr***
***U St. Andrews***
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**Notes:**
Use Helvetica
More introduction to rest of talk

## NSTX routinely operates with a large, super-Alfvénic, fast ion population

- Low field, moderate density, and 60 to 100 kV beam injection energy make NSTX an excellent platform for ITER-relevant fast ion-induced instability studies
- Large * implies easily measured fast ion losses/transport

**Notes:**
NSTX operates in ITER regime
Drop periods

## Fast Ion Modes dominate MHD spectrum

- Compressional and Global Alfvén Eigenmodes (CAE and GAE)
- Natural plasma resonance
- CAE parallel B, E is transverse
- GAE mixed transverse/parallel B
- Toroidal Alfvén Eigenmodes (TAE)
- Natural plasma resonance
- Strong drive pushes off-resonance
- Shear wave, lower frequency
- Energetic Particle Modes (EPM)
- Mode defined by fast ion parameters (fishbone)
- Frequency chirping common
- Include non-fishbones, n > 1

- Fast Ion Modes can be sorted into three categories:

- fci≈3MHz

**Notes:**
Dump sub bullets, put in conclusions, introduction
Neuts beam-target.  Invert order of bullet

## Fast ions heat plasma, drive current

- Transport/confinement affected by instabilities
- Beam (fast ion) driven current drive important NSTX
- ITER heated with super-Alfvénic fusion 's
- _Outline_
- Energetic Particle Modes (EPMs)
- Toroidal Alfvén Eigenmodes (TAE)
- High frequency modes (CAE/GAE)

## EPM induced losses pervasive

- In above example,  different EPMs closely spaced (in time) cause much different loss
- Mode structure plays big role in interaction with fast ions

- Neutrons primarily from beam-target; neutrons indicate nfast
- Losses weakly correlated with mode amplitude

**Notes:**
Expand 2nd figure to two chirps or less

## Frequency chirp of EPMs matches range of fast-ion bounce frequencies

- Precession frequency often low or negative due to low A, high 
- Many different mode-fast ion resonances are possible

**Notes:**
Beam Ion Energy

## Fast ions affected over all energies

- Strongest modulation is seen for lowest energies; below the "half" energy.
- Neutron drops of 10% suggest high energy ions also lost.
- Broad range of energy interaction consistent with bounce-resonances

- S. Medley, PPPL

**Notes:**
Ions affected over broad energy range Modulation is .  Dump

## EPMs core localized, kink-like 

- EPMs core localized, kink-like

- Seen in all operational regimes
- Example here is n=1, but higher n's are also common

- Reflectometer and SX cameras measure the internal structure
- No phase inversion; not an island

- Bursts last for about 1 msec

**Notes:**
Title: EPM highest amplitude in core
Drop first bullet

## EPMs localized to low shear

- Inverted SX emission profile and EFIT equilibrium, used to "invert" soft x-ray data.

- Simulate fast ion losses with mode amplitude/structure

- N. Crocker, S. Kubota, W. Peebles, UCLA

- D. Stutman, K. Tritz, JHU

**Notes:**
Localized to low shear.  Extent of mode localization
Not effective displacement  Label axis x-ray brightness

## EPM can evolve to a continuous mode

- Mode structure same as EPM bursts, but
- Amplitude larger than preceding EPMs.
- Decays fast after beams turn off
- Similar behavior seen for fishbones in conventional tokamaks.

**Notes:**
EPM may saturate
Same mode evolves from chirping to continuous

## Toroidal Alfvén EigenmodesFast Ion LossesMode StructureSimulations

## TAE-induced losses scale with amplitude

- TAE in absence of EPM are rare; modes work together
- No scaling with , up to         tor≈25%
- Similar to scaling seen on TFTR for ICRF and NBI induced TAE modes
- TFTR modes more core localized; similar losses, weaker Mirnov fluctuations

**Notes:**
Drop second bullet, TAE only is rare.  Check database, drop any shots with epm

## TAE typically chirp and burst

- Series of small chirps, multiple modes, then big burst with many more modes
- Neutron drops correlated with big bursts
- Sequence repeats
- Often EPM triggered by big bursts
- Often sequence of small bursts/chirps

## Single TAE amplitude is of the order n/n ≈ 1%

- Reflectometer shows "sea of TAE"

- Many modes suggest strongly non-linear problem
- Mirnov signal good measure relative mode amplitude

- Single TAE amplitude is of the order n/n ≈ 1%

- N. Crocker, S. Kubota, W. Peebles, UCLA

## TAE activity seen up to highest 

- Unlike MAST, where TAE activity is not present at highest 's*
- High beam voltage in NSTX means high , high density plasmas still have significant fast ion populations             (fast/beam ≈ 30%).

- *Gryaznevich,Sharapov, PPCF **46** (2004) S15-S29

**Notes:**
Unlike MAST, reference paper, 

## Chirping TAE simulated with M3D

- M3D Nonlinear hybrid simulations of beam-driven modes in NSTX shows a bursting n=2 TAE as the mode moves out radially

- G.Y. Fu et al., IAEA Fusion Energy conference. 2004

- G.Y. Fu, PPPL

**Notes:**
Simulation has good agreement with data

## Multiple TAE/EPM simulates "sea of Alfvén modes" expected in ITER

- EPM and TAE responsible for most fast ion loss events
- Distinction between TAE and EPM somewhat artificial
- Continuum of mode behavior from chirping/bursting EPMS to quasi-coherent TAE-like.

**Notes:**
Sub-bullet is title, title is sub-bullet
Define chirping

## Compressional and Global Alfvén Eigenmodes (CAE/GAE)CharacteristicsGAE "hole-clumps"(Angelfish)

## Modes identified by their polarization

- Polarization measured by orthogonal Mirnov coils

- TAE/EPM/MHD have transverse (shear) polarization
- GAE, a shear wave, also couples to the compressional polarization
- CAE have magnetic fluctuations aligned with pitch of magnetic field, compressional

**Notes:**
CAE/GAE observed high frequency
Distinguished by polarization, no fast ion loss associated with.

## GAE mode amplitude n/n ≈ 10–4

- GAE mode amplitude n/n ≈ 10–4

- Measurement made in low shear region where GAE expected to be localized
- Polarization measurement suggests GAE, not CAE

- Reflectometer spectrum shows same peaks as Mirnov coil

- S. Kubota, N. Crocker, W. Peebles, UCLA

**Notes:**
No GAE well.  GAE localization regions.  Switch bullets

## New observation: GAE "Hole-clump" behavior

- GAE bursts chirp both up and down during early NBI on NSTX.
- Red curve is single parameter fit to frequency evolution using Berk, Breizman, Petviashvili model of hole-clump pair creation*
- GAE drive through Doppler-shifted ion cyclotron resonance -
- Hole-clump-like behavior shows long correlation time for interaction of mode with fast ion population

- *H.L. Berk, B.N. Breizman, N.V. Petviashvili, Phys. Lett. A **234** (1997) 213.

## NSTX is well diagnosed testbed for fast ion instability studies

- NSTX fast ion loss events typically occur with multiple modes ("sea of TAE", as predicted for ITER)
- Lower frequency, strongly chirping (EPM) modes correlated with most fast ion loss events
- Fast ion losses from EPM/TAE are not serious in NSTX, but
- Next step is to document effect on heating profile and on beam driven currents
- Fast ion losses may be important for first-wall issues in next-step devices

**Notes:**
Biggest losses are from EPM, ITER

## Range of frequency chirp agrees well with fast ion "bump-on-tail"

- The red line indicates fast ions initially resonant (Doppler-shifted cyclotron) with the mode.
- For *k**||* fixed, the fast ions resonant at the minimum/maximum of frequency chirp are indicated by the blue lines.