GEM WAVE MODELLING CHALLENGE PRELIMINARY NOTES AGU AUTUMN MEETING SAN FRANCISCO 9 DECEMBER, 2013...

GEM WAVE MODELLING CHALLENGE

PRELIMINARY NOTES

AGU AUTUMN MEETINGSAN FRANCISCO9 DECEMBER, 2013David Nunn1

1. School of Electronics and Computer Science Southampton University, U.K.

GEM WAVE CHALLENGE

PROVISIONAL SIMULATION RESULTS

• Data: L=5; Ne=5.4/cc; Tperp= 62keV; T||=20keV Maximum linear growth rate at z=0 1146db/s• The code: 1D k||Bo ; Vlasov Hybrid Simulation• Narrow band code has bandwidth ~100Hz (variable). Centre of code internal bandpass filter matched to cg of actual spectrum.• It was shown in Katoh et al,2006 that frequency sweep due entirely to a spatial gradient of frequency in the generation region . i.e. an advective term. Omura and Nunn(2012),Nunn and Omura,2013 showed a mechanism for setting up this gradient thru the Jb(z,t) field• Narrow band code can allow linear spatial frequency variation by using matched filters• Broadband version of code has bandwidth ~1000Hz and can accommodate spatial frequency variation without matched filtering.• Vlasov code being low noise requires trigger signal. This may be a CW pulse (narrow band code), or broadband noise across simulation bandwidth (broadband code)

GEM WAVE CHALLENGE

General results

• Growth rates are high, emissions readily triggered. Usually risers with sweep rates ~3-8kHz/s, depending on triggering pulse, simulation bandwidth, simulation precision etc.

• Many runs self saturate in the region of 200pT, but some cases e.g. broadband code with hiss excitation require artificial saturation to prevent wave amplitudes reaching unreasonable values.

• The narrow band code may show a tendency to trigger fallers or downward hooks when the trigger pulse is strong and lengthy.

• The broadband code with CW wave excitation produces steep risers with a fairly broad spectrum ~200 Hz.

• Excitation by hiss in the broadband code gives a very swishy riser of bandwidth ~500Hz

F/T SPECTROGRAM OF CHORUS SIMULATION WITH BROADBAND

VLASOV VHS CODE; STEEP RISER ~ 8KHZ/SCW PULSE EXCITATION

BROADBAND VLASOV SIMULATION-PLOT OF WAVE AMPLITUDE PT IN Z,T PLANE FOR THE ENTIRE SIMULATION; NOTE

SPECTRAL STRUCTURE ANDGENERATION REGION EXTENDS UPSTREAM FROM EQUATOR

(HELLIWELL,67)

HISTORY IN Z.T PLANE OF CURRENT –JE IN PHASE WITH E FIELD

HISTORY IN Z.T PLANE OF CURRENT –JB IN PHASE WITH B FIELD

EXIT AMPLITUDE IN PT AT Z=+6000KMS FROM EQUATOR

QUASI-BROADBAND VLF VLASOV CODE – HISS EXCITATIONF/T SPECTROGRAM

NARROW BAND VLASOV CODE; SPECTROGRAM OF RISING CHORUS ELEMENT AT Z=+6000KM FROM EQUATOR

PLOT OF WAVE AMPLITUDE (PT) IN Z,T PLANE FOR SINGLE CHORUSELEMENT EVENT

PLOT OF RESONANT PARTICLE CURRENT COMPONENT PARALLEL TO WAVE E FIELD (JE) IN Z,T PLANE FOR CHORUS ELEMENT EVENT. THIS COMPONENT GIVES NON LINEAR GROWTH

PLOT OF RESONANT PARTICLE CURRENT COMPONENT PARALLEL TO WAVE B FIELD (JB) IN Z,T PLANE FOR CHORUS ELEMENT EVENT. THIS COMPONENT GIVES PHASE AND FREQUENCY SHIFTS IN THE WAVEFIELD

SPATIAL DFT OF SIMULATION BOX WAVEFIELD OF SLOW FALLERPRODUCED BY STRONG KEY DOWN EXCITATION PULSE 5PT; NARROW BAND VLASOV CODE

GEM WAVE CHALLENGE

Ongoing research…….

• Parallelise code with MPI relative to Vperp

• Long runs with higher precision, particularly in Vperp

• Investigate triggering at lower frequencies

• Investigate saturation problems

• Acknowledgements• These computations done on Kyoto University KUDPC Cray and• Southampton University IRIDIS3/4 systems.

SPATIAL DFT OF SIMULATION BOX WAVEFIELD OF SLOW FALLERPRODUCED BY STRONG KEY DOWN EXCITATION PULSE 5PT; NARROW BAND VLASOV CODE