Corrections to the energy distribution of the NBI power PPF

1
Corrections to the energy distribution of the NBI
power PPF

• Background
• History of the problem
• Proposed changes
• Affected data

2
Background Beam Species Determination

• JET neutral beam is composed of full, half
  third energy particles
• Intensity of the Doppler shifted Balmer-a lines
  measured on NBTB
• Relative intensities proportional to fractional
  distribution in source via D-a, neutralisation
  and dissociation cross sections for D, D2, D3
• Source values parameterised in terms of
  extracted beam current
• Fitting algorithm used to obtain power fractions
  in neutral beam for PPF
• Source flux or density fractions?

3
History 1 - Hemsworth

• pre 2003 implicit assumption Doppler
  flux fractions
• 2003 JET-DN-C(85)8 (RS Hemsworth) rediscovered

i1,2,3 E, E/2, E/3 b beam g gas
defines number of radiating transitions per unit
length of beam
so DENSITY fractions given by
4
History 2 Error Further Compounded

• Doppler shifted Balmer alpha spectroscopy on JET
  neutral beams G J van Rooij (1994) copies this
  methodology when describing NBTB system
• Therefore NB Unit decided that PPF was incorrect
  because Doppler measurements from NBTB gave
  density fractions
• PPF re-written April 2003 for HC triode PINIs in
  deuterium only
• 2008 E Delabie (fz-Jülich) reports inconsistency
  between PPF and beam emission spectroscopy
  measurements (both into plasma and into gas)

5
History 3 - Investigation

• Thorough review of literature
• First principles derivation

Correct form of equation linking intensity to
beam components
so Doppler spectroscopy gives FLUX fractions from
ion source

• Confirmation that NBTB Doppler shifted BES also
  computes flux fractions

6
Check Intensity Ratios

• Calculate intensity ratios for different source
  flux fractions

• Calculate power ratios for different source flux
  fractions

7
Calculation of Power PPF

• Total neutral power calculated from measured data

• Full, half and third fractional flux components
  from theoretical calculation with 4x1019m-2 target

8
Changes to PPF

• Only HC Triode PINIs in D are affected
• Total power remains unchanged
• Increased power in half and third energy
• Decreased power in full energy