1. Absence of Impact Polarization in H
Michele Bianda
Istituto Ricerche Solari Locarno (IRSOL)
Switzerland
Collaborators:
A. Benz, D. Gisler, G. Küveler,
R. Ramelli, J.O. Stenflo

2. Outline Introduction to impact polarization Observations
Technical setup
Difficulties in observing polarization
Polarimeter: ZIMPOL

3. Impact polarization
Directed particle beam colliding with plasma  impact polarization
Created in flares?

4. Observations I Q/I M1.0 flare 2 August 2002 1051 UT
190 arc sec
140 arc sec I
Q/I
M1.0 flare
2 August 2002
1051 UT
No impact polarization observed
V/I

5. Observations I Q/I M3.9 flare 18 November 2003 0831 UT
190 arc sec
140 arc sec I
Q/I
M3.9 flare
18 November 2003
0831 UT
No impact polarization observed
V/I

6. Time evolution in flaring region

7. Observations of X17.1 flare, 28 Oct 2003
purple: slit position
green: TRACE 195 Å
yellow and blue: RHESSI

8. Observations of X17.1 flare, 28 Oct 2003

9. Observations of X17.1 flare, 28 Oct 2003

10. Difficulties observing polarization in visible light
Polarization measurement:
Combining intensity images with different polarization properties
Difference of images
“polarization”, if not recognized as instrumental effect.
Impact polarization:
fast evolving structure
high intensity gradients

11. Polarimeter techniques
Two beam technique:
+ simultaneous
− different optical paths
− different CCDs
One beam technique:
+ same path
+ same CCD
− not simultaneous ( seeing!) I1 I2 I1 I2 R

12. ZIMPOL concept (1)
Fast polarization modulation and on-chip demodulation
how? I1 0° I2
switched at 42 kHz
90°

13. ZIMPOL concept (2) Demodulation at 42 kHz
Same CCD pixel for different polarization states

15. Conclusions
Impact polarization not detected by ZIMPOL at IRSOL; more than 30 events were observed

16. Profiles from imaging observations