IMPORTANCE OF FAST MEASUREMENTS OF SOLAR WIND
PARAMETERS AT THE IP SHOCK FRONT
Moscow, February 6-10, 2012
Z. Němeček, J. Šafránková, L. Přech, O. Goncharov, A. Komárek
Charles University, Prague, Czech Republic
G. N. ZastenkerSpace Research Institute, RAS, Moscow, Russia
OOutline Brief description of the BMSW device
A new solution of plasma parameter determination – discussion of (dis)advantages
Examples of measurements
Comparison with measurements of another spacecraft
Importance of fast measurements
Conclusion
BMSW in course of time
• Solar wind parameters: density, velocity,
and temperature – with a time resolution of 1-0.03 s
• Engineering model - 2005
• Flight model – 2008
• Flight spare model – 2009
• Launch – July 18, 2011
B
BMSW in vacuum chamber
BMSW – engineering model
BMSW – flight model BMSW on the platform
BMSW - principles6 FCs and each FC is equipped with four grids: grounded grids cover the windows in both diaphragms; a positive control grid is placed between outer and inner diaphragms; and a suppressor grid lies between the inner diaphragm and a collector.
FC characteristics with homogeneous electric field
Influence of finite grid spacing
Influence of finite FC dimensions
The dependences of the normalized collector current on the spacing between wires
Configuration of the electric field in the space between two control grids
Safrankova et al. (2008)
Characteristics for different velocities Solar wind bulk energy of 1 keV
BMSW modes
BMSW can measure in two working modes:
• Sweeping mode – ion distribution between 100-3 000 eV; time resolution 0.5 or 1 s
• Adaptive mode – only 3 points on the distribution; time resolution 31 ms
BMSW – Block Scheme
Example of first measurements Aug 12, 2011
BMSW in the sweeping mode; speed of measurements – 0.031 s
- a full set of solar wind parameters – 1 s- 3 directed FCs show a change of the speed and density- 3 declined FCs show a change of the solar wind direction - Details of distributions – protons and alphas
Protons
Alphas
Data rate and data compression
A full time resolution – 0.031 s – can be transmitted only for rather limited time intervals, a compression algorithm is needed
- data from 3 direct FCs are averaged (12 points) in adaptive mode- steep slopes are transmitted with a full resolution and the rest of the sweep is averaged in sweeping mode - 12-point averages are transmitted from 3 declined FCs
Steps on the HV voltage are a result of compression algorithm
Comparison – BMSW, Wind, ACE
A first comparison of joint measurements of three solar wind spacecraft on August 14, 2011
Spectr-R, ACE, Wind
Spectr-R
Wind
ACE
Interplanetary shock September 9, 2011
Interplanetary shock on September 9, 2011 was observed by SOHO, Wind, ACE and also by Spektr-R
BMSW in sweeping mode and compressed data
Changes of the density and velocity direction
Comparison of BMSW and WindComparison of BMSW and WindSeptember 9, 2011 - cont
IP shock on September 9, 2011 –preliminary computed parameters with a time resolution of 1 s
Still 3 times better than earlier
Moscow time
Wind
BMSW
Is this overshoot real?
Why the fast measurements are needed?
Changes of the density and velocity direction as short as 0.3 s
? Active experiment in the solar wind?
Why the fast measurements are needed? IP shock is usually considered as a rectangular step
First measurements of the plasma parameters with 30 Hz time resolution
Oscillations of the flow direction with a period of about 0.3 s
Such oscillations could not be observed earlier, the best time resolution prior to BMSW was 3 s
Detailed analysis impossible due to lack of magnetic field measurements
Plasma waves connected with the IP shock front
A detail of observations
The flow angle can be determined with the full resolution but the resolution of plasma moments is 3 s only
The upstream oscillations are linearly polarized
On the other hand, a clear circular polarization was observed in the downstream region
Further analysis requires magnetic field data
Comparison with WIND magnetic field
WIND magnetic field, 92 ms time resolution
HF waves upstream
Two types of oscillations downstream
The upstream oscillations are circularly polarized
Downstream LF waves exhibit a circular polarization
Polarization of the HF part of downstream waves is not clear
Adaptive mode – compressed data
An example of processing of the adaptive working mode. Data compression not only decreases time resolution but it introduces artificial noise
Full time resolution without compression
- our data reveal the real fine structure of the solar wind flow
- a weak IP shock that cannot be resolved with 1-minute resolution
- frequency spectra of density, speed, and temperature are different
20 minutes
30 seconds
Comparison with standard data, the same time interval
Data distributionData distribution Web page of the device - under construction
Daily (6 hours) plots of FC currents - ready
Preliminary processed plasma moments with the time resolution of 30 s (density, velocity, and temperature) – under preparation
Detailed data from a short time interval – on the request
Future plansFuture plans
Finishing of the data processing software
Determination of temporal evolution of photocurrents
Gathering of interesting intervals with full time resolution
Investigation of fast disturbances Thank you
for your attention
Investigation of solar wind turbulence at kinetic scales
Preparation of a new generation of the BMSW device for future missions