等離子體物理學導論-(課堂PPT)

1、1,Introduction to Plasma Physics 等離子體物理學導論 主講: 陳 耀 第七講 山東大學威?？臻g天氣 物理與探測研究中心 2009.3 2009.6,2,2.3 曲率漂移,粒子被洛侖茲力約束在磁力線上, 導心沿著力線 平行運動; 若磁力線是彎曲的，則在導心坐標系中， 粒子將感受到慣性離心力，并產(chǎn)生曲率漂移。 慣性離心力可表示為,漂移速度：,曲率半徑,3,考慮勢場(無旋場) 或 無力場(電流與磁場平行)情況, 證明: 磁力線是彎曲的,則磁場必然是非均勻的.,4,小結(jié)：由磁場不均勻性造成的效應(yīng)： (1) 磁鏡效應(yīng) 由平行方向受到與梯度反向的作用力 (2) 梯度漂移 垂

2、直方向受力產(chǎn)生梯度漂移 (3) 曲率漂移 彎曲力線中, 粒子沿磁力線運動時，受離心力作用，產(chǎn)生曲率漂移 兩種漂移運動,通常同時存在: 漂移方向一致, 但大小與動能及電荷有關(guān) 產(chǎn)生電荷分離與電場,Q：給出具 Maxwell分布（溫度T）的等離子體粒子的兩種漂移速度！,5,2.4 緩變系統(tǒng)的絕熱不變量 (Adiabatic Invariants) （1）磁矩守恒（請驗證這一組等式?。?磁矩守恒迴旋軌道包圍的磁通是守恒的,在強場區(qū)，磁通/矩(角動量)守恒要求粒子 回旋軌道收縮和垂直動能增加,6,（2）縱向不變量 J (Longitudinal Invariant) 證明該縱向不變量. 該不變量在地磁

3、場中約束的粒子運動中有重要應(yīng)用. （3）第三絕熱不變量: 漂移面總磁通守恒：磁通不變量,7,在地磁場中的應(yīng)用： 在地磁場中，粒子的運動是三種不同時間尺度的 運動形式的疊加： 1. 迴旋運動磁矩守恒 2. 兩極間的磁鏡反射之往返運動 地磁場基本對稱時，粒子漂移一周 后將回到同一根磁力線上 3. 漂移時間尺度太長、系統(tǒng)不滿足緩變條件 因此地球磁場中漂移面所含磁通一般不守恒,回旋 往返 漂移,WEST,8,In 1990, the satellite Combined Release and Radiation Effects Satellite (CRRES) discovered a third

4、 radiation belt located between the inner and outer Van Allen belts. Also, around May 8, 1998, there were a series of large, solar disturbances that caused a new radiation belt to form in the so-called “slot region” between the inner and outer van Allen belts. The new belt eventually disappeared onc

5、e the solar activity subsided. Nuclear tests in space artificial radiation belts. Starfish Prime, damaged or destroyed as many as one third of the satellites in low earth orbit at the time (1962?).,Van Allen輻射帶的穩(wěn)定存在反映了縱向不變量的近似守恒, Inner and outer radiation belts: The outer belt: mainly electrons (0.1

6、10 MeV) (3 to 10Re) The inner belt: mainly protons (0.1 to 1.5 Re) 100 MeV & electrons (hundreds of kev). The relative drift between the ions and electrons produces the ring current in the geomagnetosphere. A gap between the inner and outer Van Allen belts, sometimes called safe zone or safe slot, i

7、s caused by the very low frequency (VLF) waves which scatter particles in pitch angle which results in the loss of particles to the atmosphere,9,During the development of so-called geomagnetic storms, charged particles are injected into the Van Allen belts from the outer magnetosphere, giving rise t

8、o a sharp increase in the ring current, and a corresponding decrease in the Earths equatorial magnetic field. The field decrease is measured by the so-called Dst index, which is based on hourly averages of the northward horizontal component of the terrestrial magnetic field. The above Figure shows t

9、he Dst index for the month of March 1989. The very marked reduction in the index, centred about March 13th, corresponds to one of the most severe geomagnetic storms experienced in recent decades. In fact, this particular storm was so severe that it tripped out the whole HydroQuebec electric distribu

10、tion system, plunging more than 6 million customers into darkness. Most of HydroQuebecs neighbouring systems in the United States came uncomfortably close to experiencing the same cascading power outage scenario. Note that a reduction in the Dst index by 600nT corresponds to a reduction in the terrestrial magnetic field at the equator.,10,2.5 不均勻電場的影響 假定電場具弱空間不均勻，將電場Taylor展開 至二階?。?運動主體仍為迴旋運動，疊加上電場漂移、 電場不均勻性導致的速度擾動,運動方程化為：,新的擾動力項,11,則總的電場力寫為：,相應(yīng)的漂移