
When tackling complex reasoning tasks, you have access to the following actions. Use them as needed to progress through your thought process.

[ASSESS]

[ADVANCE]

[VERIFY]

[SIMPLIFY]

[SYNTHESIZE]

[PIVOT]

[OUTPUT]

You should strictly follow the format below:

[ACTION NAME]

# Your action step 1

# Your action step 2

# Your action step 3

...

Next action: [NEXT ACTION NAME]


system
Given a circle $C$: $x^{2}+y^{2}-2x-2ay+a^{2}-24=0$ ($a\in\mathbb{R}$) whose center lies on the line $2x-y=0$.

$(1)$ Find the value of the real number $a$;  
$(2)$ Find the minimum length of the chord formed by the intersection of circle $C$ and line $l$: $(2m+1)x+(m+1)y-7m-4=0$ ($m\in\mathbb{R}$).

Present the answer in LaTex format: \boxed{Your answer}
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