GEM WAVE MODELLING CHALLENGE PRELIMINARY NOTES AGU AUTUMN MEETING SAN FRANCISCO 9 DECEMBER, 2013 David Nunn 1 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 ~ 8 K H Z / S CW PULSE EXCITATION

B ROADBAND VLASOV SIMULATION - PLOT OF WAVE AMPLITUDE P T IN Z, T PLANE FOR THE ENTIRE SIMULATION ; NOTE SPECTRAL STRUCTURE AND GENERATION REGION EXTENDS UPSTREAM FROM EQUATOR (H ELLIWELL,67)

H ISTORY IN Z. T PLANE OF CURRENT –J E IN PHASE WITH E FIELD

H ISTORY IN Z. T PLANE OF CURRENT –J B IN PHASE WITH B FIELD

E XIT AMPLITUDE IN P T AT Z =+6000 KMS FROM EQUATOR

Q UASI -B ROADBAND VLF VLASOV CODE – HISS EXCITATION F / T SPECTROGRAM

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

PLOT OF WAVE AMPLITUDE ( P T) IN Z,T PLANE FOR SINGLE CHORUS ELEMENT EVENT

P LOT OF RESONANT PARTICLE CURRENT COMPONENT PARALLEL TO WAVE E FIELD (J E ) IN Z, T PLANE FOR CHORUS ELEMENT EVENT. T HIS COMPONENT GIVES NON LINEAR GROWTH

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

S PATIAL DFT OF SIMULATION BOX WAVEFIELD OF SLOW FALLER PRODUCED BY STRONG KEY DOWN EXCITATION PULSE 5 P T; 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.

S PATIAL DFT OF SIMULATION BOX WAVEFIELD OF SLOW FALLER PRODUCED BY STRONG KEY DOWN EXCITATION PULSE 5 P T; NARROW BAND VLASOV CODE