<html><body><div style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000"><div>Hi Yingchao,<br></div><div><br data-mce-bogus="1"></div><div>It would appear that \tau_{ei} is an "energy-exchange" collision time, rather than the electron-ion collision time \tau_e. The relation between the two is:<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>\tau_e = \tau_{ei}*2*m_e/m_i<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>which explains the three-order discrepancy. That said, I agree that it should be the electron-ion collision time \tau_e rather than \tau_{ei} that is used in the magnetic resistivity calculation. (The \tau_{ei} should and does get used in the calculation of heat exchange.)</div><div><br data-mce-bogus="1"></div><div>Cheers,<br data-mce-bogus="1"></div><div>Greg.</div><div><br></div><hr id="zwchr" data-marker="__DIVIDER__"><div data-marker="__HEADERS__"><b>From: </b>"Yingchao Lu" <yingchao.lu@gmail.com><br><b>To: </b>"flash-users" <flash-users@flash.uchicago.edu><br><b>Sent: </b>Wednesday, 21 November, 2018 01:32:06<br><b>Subject: </b>[FLASH-USERS] Magnetic resistivity SpitzerHighZ<br></div><div><br></div><div data-marker="__QUOTED_TEXT__"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div>Hi FLASH users,</div><br><div>It seems the magnetic resistivity for Spitzer HighZ in FLASH is three orders of magnitude smaller than those found in the literature. </div><br><div><div>The code in source/physics/materialProperties/MagneticResistivity/MagneticResistivityMain/SpitzerHighZ/MagneticResistivity_fullState.F90 calculates the electron-ion equilibrium time</div><div>res_ieEquilTime(zbar, abar, tele, tion, nion, eqtime)</div><br><div>And the code in source/physics/materialProperties/MagneticResistivity/MagneticResistivityMain/SpitzerHighZ/res_ieEquilTime.F90 </div><div> eqtime = res_ieTimeCoef * &</div><div> 3.0 * res_boltz**1.5 / (8.0 * sqrt(2*PI) * res_qele**4) * &</div><div> (mion * tele + res_mele * tion)**1.5 / &</div><div> ( sqrt(mion*res_mele) * zbar**2 * nion * ll)</div><br><div>When Ti=Te, we can make some approximation, shown in the attached file. </div><br><div>There are several references for Spitzer magnetic resistivity and they are consistent with each other.</div><div><a href="http://people.hao.ucar.edu/judge/homepage/PHSX515/fall2012/Braginskii1965.pdf" target="_blank">http://people.hao.ucar.edu/judge/homepage/PHSX515/fall2012/Braginskii1965.pdf</a><br data-mce-bogus="1"></div><div><a href="https://www.cfa.harvard.edu/~namurphy/Lectures/Ay253_04_BeyondIdealMHD.pdf" target="_blank">https://www.cfa.harvard.edu/~namurphy/Lectures/Ay253_04_BeyondIdealMHD.pdf</a><br data-mce-bogus="1"></div></div><div>Physics Reports 417 (2005) 1–209<br></div><br><div>I think the (7) to (10) in the image should be correct. Could any one double check?</div><br><div>Thanks,</div><div>Yingchao</div><div><img src="cid:ii_joqfhny80" alt="Screen Shot 2018-11-20 at 5.26.52 PM.png" width="562" height="417"></div></div></div></div></div></div></div></div></div></div><br></div></div></body></html>