fix DCGun-Cornell tests

RegressionTests/DCGun-Cornell-1/DCGun-Cornell-1.in

@@ -29,6 +29,7 @@ no_fieldsolver:FIELDSOLVER,
 my_beam: BEAM,
 	PARTICLE=ELECTRON,
 	//pc = 10,          // momentum per particle in GeV/c
+	PC = P0,
 	NPART = 27,     //number of test particles simulated
 	BCURRENT = BCURRENT, // beam current in A
 	BFREQ = BFREQ * 1e-6;
@@ -47,4 +48,4 @@ RUN,	METHOD = "PARALLEL-T",
 	DISTRIBUTION = file_distribution;
 ENDTRACK;
 
-STOP;
+STOP;
\ No newline at end of file

RegressionTests/DCGun-Cornell-2/DCGun-Cornell-2.in

@@ -31,6 +31,7 @@ no_fieldsolver:FIELDSOLVER,
 my_beam: BEAM,
 	PARTICLE=ELECTRON,
 	//pc = 10,          // momentum per particle in GeV/c
+	PC = P0,
 	NPART = 27,     //number of test particles simulated
 	BCURRENT = BCURRENT, // beam current in A
 	BFREQ = BFREQ * 1e-6;
@@ -50,4 +51,4 @@ RUN,	METHOD = "PARALLEL-T",
 	DISTRIBUTION = file_distribution;
 ENDTRACK;
 
-STOP;
+STOP;
\ No newline at end of file