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. Zastenker Space Research Institute, RAS, Moscow, Russia

O Outline lBrief description of the BMSW device lA new solution of plasma parameter determination – discussion of (dis)advantages lExamples of measurements lComparison with measurements of another spacecraft lImportance of fast measurements lConclusion

BMSW in course of time Solar wind parameters: density, velocity, and temperature – with a time resolution of s Engineering model Flight model – 2008 Flight spare model – 2009 Launch – July 18, 2011 B BMSW in vacuum chamber BMSW – engineering model BMSW – flight modelBMSW on the platform

BMSW - principles 6 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 velocitiesSolar wind bulk energy of 1 keV

BMSW modes BMSW can measure in two working modes: Sweeping mode – ion distribution between eV; time resolution 0.5 or 1 s Adaptive mode – only 3 points on the distribution; time resolution 31 ms

BMSW – Block Scheme Current outputs Voltage outputs HV Mode switching HV

Example of first measurements Aug 12, 2011 BMSW in the sweeping mode; speed of measurements – 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 – 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 Wind Comparison of BMSW and Wind September 9, 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 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 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