KSTAR proposal 2011 FastIonConfTime by ki47AR



                                                                                                   MP No. _______

Subject: Measurement            of fast-ion confinement time in KSTAR
From: A. C. England, Y. S. Lee, W. C. Kim, Z. Y. Chen, J. W. Yoo, Y. S. Bae, S. G. Lee, J. M. Kwon,
         K. I. You, L. Terzolo, S. Sajjad, H. K. Na, H. L. Yang, J. G. Kwak, S. H. Jeong (KAERI),
         et al.

Group: Joint Experiment Team, NFRI

Original date of submission: March 4, 2011

Date: May 21, 2012

Approved by:                                                Date Approved:

1. Purpose of Experiments
Include immediate goal of the experiments, scientific importance and/or programmatic relevance. Refer to any relevant
program milestones.

By measuring the decay of the neutron rate after short-pulse “blip” deuterium Neutral Beam Injection
(NBI), we can compare the decay time with classical slowing-down theory, charge-exchange loss, and the
confinement time of the injected fast ions. This calculation requires the measured electron temperature and
density from Thomson scattering, and/or the electron temperature from ECE, and/or the electron
temperature from the soft x-ray diagnostic using argon gas puffing, Zeff measurements, as well as
information on the neutral density and calculations/estimations of the fast ion confinement time.

This experiment utilizes short NBI pulses or blips, which provide “test particles” that do not significantly
perturb the plasma. The program NUBEAM already is operable at NFRI and can be used as long as Te and
ne measurements exist. This program, which is designed for steady state operation, may be able to give
information about blip injection.

This measurement, which has been made at several other tokamaks and other devices [1-13], it can be used
to determine the diffusion of the injected fast ions and their containment properties after the full
complement of diagnostics is available. In conjunction with a neutron collimator, which is planned for the
future on KSTAR, it could be used to measure the fast ion diffusion coefficient as a function of radius and
any possible orbit losses from various magnetic configurations. The fast ion orbit loss is also a function of
the plasma current.

2. Background
Discuss Physics Basis of the proposed research. Prior results at Alcator or elsewhere, and any related work being carried
out separately.

For KSTAR, the neutron signal decay time, n-expt , is given by:

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     1           1                    1          1
                                           
  n exp t     s                   c          cx

                                                                               se         Einj  Ecrit
                                                                                             3/2   3/2

Here the classical time is given by                               s ( s)           ln(                  )
                                                                               3           En  Ecrit
                                                                                            3/2  3/2

              Einj is the beam injection energy,

              En is the energy at which the d(d,n)3He reaction rate, <ddv> has fallen one e-fold.
              For 80 keV deuterium injection into a cold plasma (Ti ~ 0), E n is about 55 keV.
              Fig 1 shows the SigmaV vs. deuteron energy for the neutron branch of the d-d cross section.

                                                                                                                100 keV
                                                                                      90 keV
                                                                                                80 keV

                                                                                  1/e of 100 keV v ~63 keV
                    sigmaV (mbm/s)

                                                                               1/e of 90 keV v, ~59 keV
                                                                           1/e of 80 keV v, ~55 keV

                                                            V for neutron branch of d-d cross section
                                                            from the NRL Plasma Formulary
                                                                  polynomial fit

                                           30          40   50        60        70         80     90      100      110
                                                                            Energy (keV)

              Fig 1. SigmaV vs. Deuteron Energy for the neutron branch of the d-d cross section.

              Ecrit is the critical energy when the electron Coulomb friction is equal to ion Coulomb friction.
              Ecrit is a function of the mass of the injected particle, Te, and Zeff . For deuterium ions in
              deuterium gas,                      Ecrit  18.66Zeff Te .


                                                                                                                         0.24 Te3/2 (keV )
               se ( s ) is the Spitzer slowing down time on electrons,  se (s) 
                                                                                                                           ne (1019 m3 )

              where the particle slowing down is a D+ ion.

For example, if c and cx are very long compared to s, and we assume Te = 1 keV, ne = 1.0 x 10 19 m-3, and
Zeff = 1, then s = 0.0409 s (40.9 ms) and we would expect n-expt ~ 18 ms.

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An alternative discussion about this process is found in [4] and uses calculations of the slowing down from
Sivrukhin [15] and an asymptotic expansion by Stix [16]. The results of the two calculations are reported to
be similar.

The fast ion confinement time, c, is in the NUBEAM code [17], which is available for use at KSTAR.
Later, when the experiment and the machine operation have matured, the difference between s and the
measured decay time,  n-expt,, will be explored to determine the orbit losses in KSTAR.

The charge-exchange time is given by cx = 1/ (no cx ) and is a function of the neutral density. This
quantity is also calculated in the NUBEAM code. For high-density high-temperature plasmas, the charge-
exchange time is expected to be very long and can be neglected in the equation. It may, however, be
important in the initial experiments when KSTAR is in the conditioning stages.

Figure 2 is taken from Fig. 4 of reference 7 from an experiment on JT-60U. Short pulses from a beam line
were injected into the plasma. The figure shows the neutron signal decay time with co- and counter-
injection as compared to classical slowing down theory, which is the solid line. Co-injection clearly
produced a longer decay time than counter-injection. Part of the difference was found to be due to orbit loss
effects and the remainder was thought to be due to loop voltage effects. Some counter injected ions are not
well contained. Since the KSTAR NBI-1 will be co-injected with a tangency radius of 1.486 m, it is
possible that this effect may be observed in KSTAR.

Fig. 2. Short pulse NBI in JT-60U with co- and counter-injection.

During the 2010 KSTAR 3rd campaign, four NBI beam-blips were made for shots 4299, 4300, 4302, and
4303 in Ohmic plasmas. The blip injection time was too long for a good measurement but a comparison to
the calculated time could be made on the basis of measurements of Te from the XICS diagnostic, nel from
the interferometer, and Zeff from the VB filterscopes. For the calculation, the measured density was
multiplied by 2 to approximate a parabolic density profile. Fig 3 shows the result that indicate a reasonable
agreement between the measurements and the calculations.

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                                                NBI Blip expt

                                                                  calculated 
     (msec)


                       measured 


                4298       4299     4300      4301       4302   4303     4304
                                           shot number

Fig 3. Measured and calculated decay times for 4 shots during the 2010 3 rd KSTAR campaign

3. Approach
Describe the methodology to be employed; explain the rationale for the choice of parameters, etc. Describe the analysis
techniques to be employed in interpreting the data, if applicable. If the approach is standard or otherwise self-evident, this
section may be absorbed into the Experimental Plan.

See the Experimental Plan.
The experiment can begin as soon as NBI injection is possible and electron temperature and density
measurements are available. It is mean to be performed under any conditions with NBI short pulses in the
KSTAR plasma 4th campaign. It can be employed in all conditions where a measurement of the fast-ion
confinement time will contribute to the understanding of the KSTAR plasma. As mentioned earlier,
however, it cannot be performed during the time that deuterium NBI is employed for plasma heating or
current drive. In particular, it should be useful for the runaway electron studies proposed by Dr. Z. Y. Chen.

4. Resources

4.1 Machine and Plasma Parameters
Give values or range for:

                    Toroidal Field: 1.5-3.5 T
                    Plasma Current: 0.1– 1.0 MA at flat top
                    Working Gas Species: D2
                    Density: 1x1019 ~ 7x1019 m-2 (line integrated density)
                    Boronization Requested (if yes, specify whether overnight or between-shot, how recently needed,
                    and any special conditions.): As required by the ongoing confinement/instability experiment

4.2 Auxiliary Systems

               Resonant Magnetic Perturbation (RMP) system may be an interesting system to test.

4.3 Diagnostics
List required diagnostics, and any special setup or configuration, e.g. non-standard digitization rate.

         1. Basic magnetics for plasma current (Rogowski coil), loop voltage (flux loops), and plasma
            position (magnetic probes)

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     2.    Density measurement (interferometer, Thomson scattering)
     3.    ECE
     4.    TV (CCD)
     5.    XICS
     6.    Zeff (filterscopes, Thomson scattering)
     7.    Fission Chamber (FC) and 3He neutron detectors, HXR detectors

5. Experimental Plan
Both sections must be filled in.

5.1 Run sequence Plan
Specify total number of runs required, and any special requirements, such as consecutive days, no Monday runs,
extended run period – 10 hours maximum – etc.

    Experimental Plan
      1) Plasma current scan. At a constant BT=3.0 T, measure the blip decay time for several values of
          the plasma current (e.g., 100 kA, 300 kA, 500kA, 700 kA, etc. to determine if there is fast -ion
          confinement improvement at high plasma current (~10 shots).
      2) Toroidal magnetic field scan. For a constant plasma current, e.g., Ip = 0.5 MA, measure the blip
          decay time for BT = 1.5 T to 3.5 T in 0.5 T steps (5 shots).
      3) ECCD scan. Measure the blip decay time with several values of ECCD current and compare to
          the no ECCD condition to determine if there is a degradation of fast -ion confinement time with
          ECCD current drive. (~ 5 shots)
      4) ICRH electron heating. Measure the blip decay time with ICRH under the conditions when
          ICRH electron heating is expected to determine if the ICRH causes degradation of the fast -ion
          confinement time. If neutron production increases during the ICRH this may make this
          measurement very difficult as the accelerated deuterons will influence the blip decay time. This
          is best done with an ICRH power scan. (several shots)
      5) Counter injection. With co- and counter- injection of the beam, measure the blip decay time to
          determine if orbit losses are present during counter injection. Several values of plasma current
          should be studied in each direction. (~10 shots)
      6) Disruptions. Measure the blip decay time during the disruption period to determine if there is a
          degradation of the fast –ion confinement time. ( many shots, see 5.2 below)
      7) RMP Scan. If RMP is used to eliminate ELMs, the blip decay time can be used to see if the fast
          ion time is reduced by the RMP (several shots, see 5.2 below)

LHCD scan. In 2012 and later, measure the blip decay time with LHCD to determine if there is a
degradation of fast-ion confinement time with LHCD. This should be done as a function of LHCD power
and magnetic field.

          Total: 15-30 shots, several day runs

5.2 Shot sequence plan
For each run day, give detailed specification for proposed shot sequence: number of shots at each condition, specific
parameters and auxiliary systems requirements, etc. Include contingency plans, if appropriate.

This will depend critically on the specific plan of the day. As an example, the following are shot sequence
plans for several of the above sequences:

    1) For a fixed BT = 3.0 T, scan Ip from 100 kA to 1 MA in 100 kA steps (~10 shots).
    2) For a fixed Ip= 500 kA, scan BT from 1.5 T to 3.5 T with 0.2 T steps (11 shots). This is the same
       sequence as specified by ZY Chen for density limit disruptions by gas puffing. Double blip
       injection would be (1) before the gas injection during the flat top and, if possible, (2) at the time of
       the disruption.

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     3) For stationary runaway discharges, scan the RMP current from 0 to 2 kA with 0.5 kA steps with
        n=1 or n=2 mode (16 shots). This is the same sequence as specified by Z. Y. Chen for suppression
        of runaway current by RMP. Double blip injection would be before and after RMP is applied.
     4) Control of disruptions by ECH in density limit disruptions. Application of on-axis ECH at 0.4
        MW, 0.6 MW, and 0.8 MW. This is the same sequence as specified by ZY Chen for control of
        disruptions by ECH. Double blip injection would be before and after ECH is applied.
     5) Control of disruptions by ECH in density limit disruptions. Application of off-axis ECH at 0.4
        MW, 0.6 MW, and 0.8 MW. This is the same sequence as specified by Z. Y. Chen for control of
        disruptions by ECH. Double blip injection would be before and after ECH is applied.
     6) Co- and counter-NBI. The plasma current will be reversed. A scan of the plasma current Ip from
        0.1 MA to ~1.0 MA with ~0.2 MA steps in both directions should be done. (10 shots for each

6. Anticipated Results
Discuss possible experimental outcomes and implications. Indicate if the program may be expected to lead to
publications, milestone completions, improved operating techniques, etc. Indicate if the experiments are intended to
contribute to a joint research effort, an ITER request, or an external database.

These results will be useful to determine the quality of the magnetic field and the presence of internal
magnetic field perturbations due to the various plasma conditions employed. If data can be obtained at the
time of the disruptions, it will add to the results of Z. Y. Chen. The results of the co- and counter- injection
can be compared with the results on JT-60U (see Figure 2 above). At least one publication is expected in
Nuclear Fusion or a similar journal.

7. References
Include references both to external and internal literature or communications which bear on this proposal. See Section 2.

     (1) L. A. Berry, A. C. England, J. F. Lyon, et al., Neutron Emission from ORMAK, Oak Ridge
          National Laboratory Report, ORNL-TM-5054, (1975) unpublished
     (2) J. D. Strachan, P. L. Colestock, S. L. Davis, et al, Nuclear Fusion, 21 (1981) 67-81
     (3) H. W. Hendel, A.C. England, D. L. Jasby, et al., Journal of Fusion Energy, 5 (1986) 231
     (4) W. W. Heidbrink, J. Kim, and R. J. Groebner, Nuclear Fusion, 28 (1988) 1897
     (5) W.W. Heidbrink, C.W. Barnes, G. W. Hammett, et al, Phys Fluids B 3 (1991) 3167-3170
     (6) M. Sasao, J. M. Adams, S. Conroy, et al. Plasma Phys. Control. Fusion. 36 (1994) 1-12
     (7) K. Tobita, K. Tani, T. Nishiani, et al., Nuclear Fusion, 34 (1994) 1097-1109
     (8) E. Ruskov, W.W. Heidbrink, and R.V. Budny, Nuclear Fusion, 35 (1995) 1099-1113
     (9) M. Isobe, K. Tobita, T. Nishitani, et al., Nuclear Fusion, 37 (1997) 437-444
     (10) M. Isobe, M. Sasao, S. Okamura, et al., J. Plasma Fusion Res, Series, 1 (1998) 366-369
     (11) W. W. Heidbrink, M. Miah, D. Darrow, et al. Nuclear Fusion, 43 (2003) 883-888
     (12) G. Fiksel, B. Hudson, D. J. DenHartog, et al. Phys. Rev. Lett. 95 (2005) 125001
     (13) M. Isobe, Y. Liu, J-W. Yang, Chin. Phys. Lett. 26 (2009) 105201
     (14) R. J. Goldston and P. H. Rutherford, Introduction to Plasma Physics, IOP Publishing (1997), p
     (15) D. V. Sivukhin, Reviews of Plasma Physics, Vol. 4, Consultants Bureau, New York (1966) 93,
          Eq. 8.1
     (16) T. H. Stix, Plasma Phys. 14 (1972) 367
     (17) NUBEAM code: http://w3.pppl.gov/ntcc/NUBEAM/

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