Why d_loss is rising

[magnificGH]

I have running gan_mnist.py, and generated the train_disc_cost.jpg. but Why d_loss is rising？I find the code is :disc_train_op = tf.train.AdamOptimizer(
learning_rate=2e-4,
beta1=0.5
).minimize(disc_cost, var_list=disc_params)
The code is minimize d_loss, so I don't understand result.