The Hpht Cubic Press is the key equipment for synthesizing artificial diamonds. It can transformer carbon  into diamond scrystal under high temperature and high pressure conditions. The  six-anvil apparatus can apply pressure uniformly to the sample under high pressure, thus ensuring the stability of the synthesis process. The precise design of the anvils allows even distribution of pressure and control within the required range.

Controlling critical parameters such as temperature, pressure, and holding time is the key to ensuring stable diamond synthesis.

1. Temperature control: Multiple temperature sensors are set to monitor the temperatures at different positions of the sample and close-loop control is utilized to compare with the preset temperature curve, enabling uniform temperature rise of the sample during heating with the control error within ±1°C. 

2. Pressure control: The anvils are equipped with strain gauges to monitor real-time pressure changes. The control system compares the measured pressure with the preset curve and precisely controls the oil pressure to keep the pressure control error within ±0.5GPa.

3. Holding time control: A timer is set so that once the preset temperature and pressure are reached, the system activates the timer to precisely control the holding time with the error within ±10 seconds.

4. Automated control: All parameters vary following the preset curves, with the system automatically completing each stage of heating, holding, decompressing, etc., without manual intervention. 

5. Data recording: Critical parameters are recorded real-time throughout the process and compared to the preset curves, generating control reports. Alarms are triggered if deviations exceed limits.

6. Feedback and optimization: Based on results from multiple syntheses, parameter control can be further optimized by improving the preset curves to enhance process stability.

Through intelligent closed-loop control and fine monitoring of multiple parameters, the anvil apparatus enables high-precision control of critical parameters to make the entire synthesis process stable and controllable.

The quality of the synthesis cube is also an important step to ensure synthesis stability. The stability of the synthesis cube has a significant impact on the quality of artificial diamond , mainly in the following aspects:

1. Influences pressure uniformity: If the synthesis capsule is not stable enough, it can easily collapse or fracture under high pressure, resulting in uneven pressure distribution within the capsule and affecting the uniform synthesis of diamonds.

2. Influences temperature distribution: Poor thermal conductivity of the synthesis capsule can lead to temperature gradients inside, with insufficient synthetic conditions in some areas for forming complete diamond crystals.

3. Causes changes to the synthesis environment: Collapse of the synthesis capsule alters the relative positions between the sample and pressure medium, changing the pressure distribution between them, which is detrimental to stable synthesis.

4. Results in compressive deformation: Insufficient hardness of the synthesis capsule makes it prone to inelastic deformation under high pressure, failing to provide adequate supporting force and leading to compressive deformation of the sample.

5. Reduces synthesis efficiency: The instability of the synthesis capsule requires frequent replacement, not only wasting materials but also reducing the overall efficiency of synthesis.

6. Affects yield and quality: Poor stability of the synthesis capsule can lead to decreased yields and inconsistent quality.

By optimizing the design of the Hpht Cubic Press and carefully controlling the synthesis parameters, the process of artificial diamond synthesis can be made stable and controllable, improving the quality of synthetic diamonds. Overall, the precise design of the six-anvil press and the use of intelligent control systems are key to ensuring a stable synthesis process.