[Fix] CircularResistiveWall

Correct scale for the exact TransverseWakeFunction in CircularResistiveWall.
Thanks to Keon Hee Kim for providing the correction factor.

collective_effects/resistive_wall.py

@@ -46,9 +46,7 @@ class CircularResistiveWall(WakeField):
     
     Impedance from approximated formulas from Eq. (2.77) of Chao book [1].
     Wake function formulas from [2].
-    
-    !!! The exact formula for the transverse wake function is wrong !!!
-    
+        
     Parameters
     ----------
     time : array of float
@@ -163,6 +161,8 @@ class CircularResistiveWall(WakeField):
         using Eq. (25), or approxmiated expression Eq. (26), of [1]. The 
         approxmiated expression is valid if the time is large compared to the 
         characteristic time t0.
+        
+        Exact expression (Eq. (25) from [1]) is corrected by factor (c * t0).
 
         Parameters
         ----------
@@ -188,7 +188,7 @@ class CircularResistiveWall(WakeField):
         
         if exact==True:
             self.t0 = (2*self.rho*self.radius**2 / Z0)**(1/3) / c
-            factor = 8*Z0*c/(np.pi * self.radius**4) * self.length * -1
+            factor = -1 * (8 * Z0 * c**2 * self.t0) / (np.pi * self.radius**4) * self.length
             wt = np.zeros_like(time)
             
             for i, t in enumerate(time):