# Presentation: 485304

## Properties of D-T Plasmas Learned from TFTR

**for**** **
**Symposium on Recent Advances in **
**Plasma Physics**
**by**
**Richard J. Hawryluk**
**June 11, 2007**
**        **

## What are the Implications of the TFTR D-T Experiments for ITER?

**Transport and Turbulence**
**Isotope Effects**
**Stability**
**ICRF Heating**
**Alpha-particle Physics**
**Plasma-boundary Interface**

**I****p****(MA)****	****	****2.7**
**B****T****(T)****	****	****5.6**
**P****DT****(MW)****	****10.7**

**Notes:**
My talk today will be organized about the question how DT experiments differ from D.  The principal differences are: 
First, differences associated with isotope effects and I will treat differences in transport and in wave-particle interactions during ICRF heating.
Second, the production of alpha particles enables the study of alpha particle physics issues, including the observation of alpha heating.
Third,the technology associated with operation, maintenance and decommissioning.  I will only be able to briefly describe this important issue.  However, in many ways this was a watershed issue, demonstrating that the fusion community could safely conduct these experiments, use the fuel needed for a reactor and  deal with the issues of activation, contamination and waste disposal. 

## Lithium Wall Conditioning Techniques Dramatically Improved Performance in TFTR

- 	**n****i****(0)·T****i****(0)·********E**** increased by a factor of 20: **
** **
**	****L-mode:****	****0.48 x10****20**** m****-3****·keV·sec**
**	****Supershot:****	****9.9 x10****20**** m****-3****·keV·sec**** **
**      ****(with Lithium Wall Conditioning)**
**	****Core ion temperature highly sensitive to edge temperature as expected from ion-scale turbulence.**
**	****Graphite tiles were coated with lithium**
**	****-  *****Discovered that graphite retained   ***
***	******   ******tritium ==> major issue for ITER.***
***	******- Liquid lithium research motivated by***
***	******  ******TFTR results.***

**Notes:**
Mention that this innovation in plasma boundary control had a major impact on our understanding.  The dramatic increase in ion temperature in the core could be understood in terms of recent theoretical models in which the ion temperature and density gradients determine the onset of the instability - resulting in the profiles being in marginal stability. By reducing the edge density, the edge temperature increases enabling a reduction in the core transport from these models. 

## Global Ethermal Increased, I Decreasedin Core of DT Supershots Compared to D

** ****n****i****(0)********E****T****i****(0)**** ****increased by ~55% from D to DT**
**Some cases up to 80% increase**
**Enhanced confinement critical for fusion power production.**

******E****thermal ********<A>****0.89±0.1**
******i****tot**** ******** <A>****-1.8 ±0.2**

** ****S. Scott, M. Zarnstorff**

**Notes:**
The results on TFTR show some marked differences from those on JET, which will be important for both projecting the performance of future experiments as well as understanding the alpha heating experiments.  TFTR observed a significant increase in the ion temperature and a modest increase in the electron temperature and a correspondingly significant increase in the confinement time.  The triple product for the case shown increased by ~55% going from deuterium to DT and in some cases upto 80% increases where observed.  The thermal confinement increased only linearly with isotopic mass and the ion heat conductivity decreased substantially in the core by a factor of ~2 and had a strong adverse scaling with mass.

## ITG Model with Radial Electric Field Reproduced the Ion Temperature

**Maximum linear growth rate decreases with ion mass.**
**E****r**** shearing rate increases with T****i****.**
**Radial electric field shear  reproduces strong isotope effect in supershots.**

**D. Ernst**

**Notes:**
Need to decide whether to show both and how much to get into this topic.  If I use this will acknowledge Darin’s work.

Darin Ernst has developed an interesting and successful model to understand the isotope effect in TFTR.  In effect, the same mechanisms used to model transport barrier formation were applied here.  In particular, there is a competition between the linear growth rate with decreases with ion mass and the shearing rate which increases with ion temperature  On TFTR, the sharp density and ion temperature gradients contributed to a large component of the electric field which was not offset by toroidal rotation, since balanced injection was largely employed.  By including the radial electric field shear, he reproduced the strong isotope effect.  The implications of this work is that isotope effects depend strongly on operating regimes which have differences in pressure gradients, current profile or rotation effects.  However, more work is required to apply this type of a model to the various operating regimes and for different devices.

## Reversed-shear Plasmas can Transition to a 

**Reversed-shear Plasmas can Transition to a **
**Regime of Enhanced Confinement: ERS**

## Turbulent Fluctuations Suppressed When Flow Shearing Rate Exceeds Maximum Linear Growth Rate of Instabilities

## Isotope Effect on Confinement Varied Widely Depending on Operating Regime

**Diversity of scalings challenges theory and **
**gyro-Bohm scaling: <A>****-0.2**
**Recent ITER scaling for ELMy H-mode: ********E****thermal**** ******** <A>****+0.19**

**S. Scott, S. Sabbagh, C. K. Phillips**

**Notes:**
A large number of different operating regimes have been studied on both JET and TFTR.  JET has concentrated their studies on H-mode plasmas both Elm free as well as with Elms.  This is of particular relevance to ITER, since Elmy H-mode operation is their baseline operating scenario.  In Elm free discharges the confinement of DT discharges is slightly less than in D, whereas in Elmy it is slightly higher.  TFTR has studied isotope scaling in ohmic, ICRF L-mode, NBI L-mode, Supershot and reverse shear regimes.  With the exception of reverse shear discharges, a favorable scaling with hydrogenic mass was observed.  Today, I will focus on results from the JET Elmy H-mode studies and TFTR supershot studies.  The JET and TFTR DT experiments are significant since they are another test of our underlying understanding of transport and turbulence.  Theoretically, transport is  usually believed to be governed by turbulent process  determined by local plasma physics parameters  which would imply gyro-Bohm scaling and a weak adverse scaling with mass though a favorable scaling with device size.  However, the ITER physics database indicates a more favorable confinement scaling.

## Higher Neutral Beam Power Required for Enhanced Reverse Shear (ERS) Transition in D-T

**Challenge for theory: same or lower threshold expected**
**Was this a transport effect or a consequence of the beam deposition profile being different?**

**M. Bell, S. Scott, M. Zarnstorff**

## Implications of Transport Studies for ITER

**Burn control will require controlling the pressure and current profile in the presence of dominant alpha heating.**
**Are the required profiles consistent with the underlying transport rates?**
**Enhanced confinement at high density is key to optimizing performance.**
**Measure  turbulence in ITER low ************* regime and comprehensive profile and edge diagnostics.**
**Needed to apply the results to different configurations.**
**Need to develop predictive capability for ITER**
**Aggressive goal:  control transport locally??**

## Classical Alpha Particle Behavior was Confirmed for Normal Shear (Supershot) Discharges

**•****	****Alpha birth rate and profile agreed with modeling.**
**-****	****Neutron flux in good agreement with calculations based on plasma profile in normal shear discharges.**

**•****	****Escaping alpha flux at 90****o**** detector was consistent with classical first orbit losses**

**R. Budny, L. Johnson                                          S. Zweben, D. Darrow**

## Confined Alpha-particle Studies Relied on New Diagnostics Developed for D-T Experiments

**Confined alphas in the plasma core showed classical slowing down spectrum .**

**Alpha particles were well confined.**
**   ****0 ********D************ 0.03 m****2****/s**

**Rapid ash transported from the core to the edge in supershots. (CHERS)**
**  ****D****He****/********D**** ~ 1**

**R. Fisher, S. Medley, M. Petrov           R. Fonck, G. McKee, B. Stratton**

**E. Synakowski**

## Initial Evidence of Alpha-particle Heating

**•****	****Alpha heating ~15% of power through electron channel**
**•****	****Plasmas matched for dominant Te scaling in D only plasmas.**
**	****-****	****T****e****(0) ********E****0.5**
**	****-****	****account for the isotope ****	****	****effect on confinement**

**G. Taylor, J. Strachan**

**T****e****(DT) - T****e****(D) (keV****)**

**   ****T****e****(R)  (keV)    **

**Notes:**
Experiments on JET and TFTR have begun the study of alpha-particle heating.  On TFTR, the alpha heating power was about 3% of the heating power, though about 15% of the power through the electron channel, enabling a measurement of electron heating.  On TFTR, the central electron temperature was observed to scale as the square root of the energy confinement time.  In these experiments, the sawteeth were stabilized and there was no detectable adverse MHD. Since the isotope effect was significant on TFTR, plasmas were matched with similar energy confinement time to account for the isotope effect on confinement.  A measurable increase in electron temperature was observed, in reasonable accord with expectations.

## MHD Activity can Cause Enhanced Transport of Alpha Particles

**Sawteeth caused a large radial redistribution of alpha particles **

**D. Darrow, S. Zweben****	****	****     R. Fonck, G. McKee, B. Stratton  **

**Notes:**
MHD activity cab affect the confinement of alpha particles.  Sawteeth were observed to radially redistribute the alpha particle profile for the intermediate energy alpha particles in the range of 150-600keV.  This may affect the heating dynamics in a burning plasma, though only transiently since the alpha slowing down time is short compared to the energy confinement time and the sawtooth period.

## Toroidal Alfvén Eigenmodes Can Cause Substantial Fast Ion Loss

**Energetic particles can drive Toroidal Alfvén Eigenmodes.**
**	****V******** ~ V****Alfvén **
**	****R****************> C**
**alignment of the eigenmodes with the alpha-particle pressure gradient**
**TAE modes observed in D plasmas driven by:**
**Beam ions**
**RF generated tail ions**

##  TAEs Driven by Neutral Beam or ICRF  Fast Ions Caused Substantial Fast Ion Losses

**In normal shear D-T discharges, TAE was stable.**

**E. Fredrickson, K. L. Wong, D. Darrow           R. White**

## Alpha-particle Physics Studies in Reversed Shear Discharges Resulted in New Discoveries.

**Alpha-driven TAE (subsequently identified as Cascade Modes) were observed.**

**TAEs redistributed deeply trapped alpha-particles**
**Further work required to benchmark models.**

**Stochastic ripple diffusion affected confinement of deeply trapped alpha particles**

**Neutron emission in D-T enhanced reverse shear discharges disagreed with TRANSP analysis in some shots by factors of 2-3**
**Source of discrepancy was not identified.**

**R. Nazikian, Z. Chang, G. Fu        S. Medley, M. Petrov, R. Fisher, M. Redi**

## Implications of Alpha-particle Physics Studies for ITER 

**Nonlinear consequences of alpha heating will be studied for the first time.**
**Comprehensive measurements of confined and lost alpha particles are critical.**
**Reliable operation enabling the exploration of new operating regimes and opportunities for discovery.**
**Scientific research is paced by diagnostic capabilities as well as operating regimes.**
**ITER needs to be flexible to adjust to scientific developments.**
**Nonlinear consequences of alpha-particle driven modes need to be put on a quantitative basis.**
**Interaction of ripple and alpha-particle driven modes needs to be addressed.**

## TFTR D-T Experiments Have Strongly Impacted Fusion Research

**•****	****Control of plasma edge**** critical for improved performance.**
**•****	****Identification of electrostatic ion turbulence**** in the core as responsible for ion plasma transport.**
**•****	****Discovery of role of shear reversal and flow shear in plasma stability.**
**•****	****First measurements of the confined alpha particles**** provided confidence in ITER.**
**•****	****First measurements of alpha driven energetic-particle modes**** have implications for ITER.**
***...******.Stability, plasma boundary, ICRF heating, Bootstrap Current for another day***