[Solid_ec] calculation

[Xiaochao Zheng]

Hi Cunfeng: 

There is a slight difference here: When the curve is linear on the double-log scale, one could have: 
gain = a * (HV)^b, where a and b are constants. Looking at Chendi's data (see the spreadsheet file on the minutes), the value of b seems to be about 8.1, which is likely to be the number of stages for this PMT. In this case, the increase in the gain per dynode is linear with HV, and the total gain is HV raised to the power of number of stages, and thus Chendi's results are reasonable and is consistent with what we expect. 

At the meeting JP said what CHendi showed agrees with JP's experience. He said for the Hall A HRS detectors, when the HV is increased by fixed amount (such as 100V each time), the gain increase by a fixed scaling factor (for example, doubles every 100V). THis can be either explained using the single log scale function, or a power function as above. 

So I think the problem may be elsewhere: 
1) Can the PMT anode current saturate? 
2) Can the attenuator that Chendi used behave non-linearly? 
3) If we do a HV scan for the SDU3 module, is it possible to show the same (weird) behavior? Can the SDU group do such a scan to prove the method to be valid? (That we should get a fixed Npe for different HV values)? 

Thanks, 

Xiaochao 

> From: "cunfeng feng" <cunfeng.feng at cern.ch>
> To: "申忱迪" <15600915869 at 163.com>, "Xiaochao Zheng" <xiaochao at jlab.org>, "solid
> ec" <solid_ec at jlab.org>
> Sent: Thursday, September 7, 2017 10:56:18 PM
> Subject: Re: [Solid_ec] calculation

> Chendi,

> I agree with Xiaochao that the Gain-V relation is linearity under double-log
> axis as shown on the PMT specification sheet, not single-log axis. You should
> contact with the PMT company to explain why the Gain-V results is not linearity
> under double-log axis.

> Your PMT Gain raises much more, it should be the reason the NPE decrease.

> Cunfeng

> On 2017/9/7 22:26, 申忱迪 wrote:

>> hello

>> here is my calculation.

>> best regards

>> --
>> 申忱迪 Chen-di Shen
>> Department of Engineering Physics, Tsinghua University
>> 418, Liuqing Building, THU, Haidian District, Beijing, China, 100084
>> Tel：86- 15600915869 & 86-18101259887
>> email: shenchendi404 at 163.com

>> _______________________________________________
>> Solid_ec mailing list Solid_ec at jlab.org
>> https://mailman.jlab.org/mailman/listinfo/solid_ec
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