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In this tutorial
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1.1. CPO - Consistent Physical Object
A Consistent Physical Object (CPO), is a data structure that contains the relevant information on a Physical Entity, e.g. the plasma equilibrium, the core plasma profiles (densities, temperature etc.), distribution functions, etc.
What is important from the user's perspective is the way CPO data are stored. Each CPO structure can be accessed via UAL documentation at the ITM portal ITM Portal.
Accessing documentation structure is fairly easy. Open ITM Portal web page in browser and navigate to ISIP related documentation.
| ITM Portal page |
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After documentation is opened browse to: "Data structure" (it is located at the bottom of the picture)
| ITM Portal - ISIP related section |
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You should see web page similar to the content of picture below
| UAL documentation |
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After choosing "Browse" you will see the structure of the CPOs.
| CPOs within data structure |
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What you can see at the picture above is collection of CPOs. All CPOs are bound to the top level element. After you expand particular CPO you can browse it's details. In this case magdiag (Magnetic diagnostics) was expanded.
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Downloading structure If you plan to browse structure extensively, it is advised to download it to your local system. |
- know how to find CPO related documentation
- know how to browse through the tree structure
- know how to access CPO details
In this exercise you will browse documentation of CPO elements.
1. Log in into ITM Portal link
2. Browse to Documentation -> ISIP -> Data structure
3. Choose "Browse" from "Data structure 4.10b (Browse) (Download)"
4. Check few CPOs to get familiar with documentation
1.1 Structure of the CPO
In this section we will take a closer look at the data. After copying MDSPlus database files into your account's public area you can dump the data using cpodump script.
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cpodump 13 3 equilibrium |
1.1.1 Time independent CPOs vs. time dependent CPOs
In general a CPO can contain both time-dependent and time-independent information. Typically, information related to the tokamak hardware will not be time-dependent, while the value of plasma physical quantities will likely be time dependent. Therefore the fields of a CPO can be either time- dependent or time-independent. The CPO itself will be time-independent if it contains only time- independent fields. It will be time-dependent otherwise. Only few CPOs in the ITM database will be time-independent (e.g. topinfo, summary, vessel), while the others will describe physical phenomena which vary over time.
Time-dependent CPOs are treated as arrays of the elementary CPO structure, i.e. in Fortran: equilibrium( : ) is a pointer and equilibrium( i ) is an equilibrium structure corresponding to time index i. Since many physics code manipulate only one time slice at a time, special UAL functions exist to extract a single time slice of the CPO : these are the GET_SLICE and PUT_SLICE functions.
source: UAL User Guide
1.1.2 Time slice index
Each time slice is located at given index. When you are looking for a time slice, there are three possible ways of finding "correct" time slice.
- 1 : CLOSEST_SAMPLE
the returned CPO is the stored CPO whose time is closest to the passed time; - 2 : PREVIOUS_SAMPLE
the CPO whose time is just before the passed time is returned. - 3 : LINEAR INTERPOLATION
the values of the time-dependent return CPO fields are computed according to a linear interpolation between the corresponding values of the CPOs just before and after the passed time;
1.2. UAL - Universal Access Layer
In order to cope with multiple languages and maintaining at the same time a unique structure definition, the UAL architecture defines two layers. The top layer provides the external Application Programming Interface (API), and its code is automatically produced from the XML description of the ITM database structure. For each supported programming language, a high level layer is generated in the target language. The following sections will describe the language specific API, and they provide all the required information for simulation program developers.
The lower layer is implemented in C and provides unstructured data access to the underlying database. It defines an API which is used by all the high level layer implementations. Knowledge of this API (presented in a later section) is not necessary to end users, and is only required to the developers of new language specific high level implementations of the UAL as well as the developers of support tools for ITM management.
source: UAL User Guide