====== Cryogen usage ======

Approximate cryogen consumption and service frequency for CSO instruments.

^  Instrument  ^  Precool and \\ Initial  ^^  Subsequent ^^  Frequency  ^
^  :::  ^  LHe  ^  LN<sub>2</sub>  ^  LHe  ^  LN<sub>2</sub>  ^  :::  ^
| Bolocam   |  85  |   80  |   25  |   5  | daily  |
| Sharc II  |  60  |  110  |   15  |   10  | 2 days  |
| Zspec  |  160  |  360  |  40  |  50  | 2 days  |
| 230/460 GHz  |  13  | |  8  | | 4 days |  
| 345/650 GHz  |  13  | |  8  | | 7 days |
| Barney (345 GHz)     |  15  |  25  |  10  |  3  | daily  |
| 850 GHz   |  13  | |  8  | | 4 days |

  * Usage in liters.
  * When the Sharc II low temperature stage is not cycled, 15 l of LHe will last 6 days.
  * Zspec requires daily LN<sub>2</sub> service.
  * Additional LN<sub>2</sub> for receiver tuning, calibrations, etc.: 3–5 l  daily.
  * LHe supplied in 60 l or 100 l dewars, nominal contents in Hilo.
  * Because of depressurization and other losses, LHe dewars arrive at telescope with 80-85% of contents.
  * LHe availability on short notice may be difficult.
  * LN<sub>2</sub> supplied in 160 l or 180 l tanks.
  
  * This {{cryo-usage.xlsx|spreadsheet}} provides an //approximate// estimate of cryogen costs.
      * Change the number of observing nights (in red) for an approximate scaling. 
      * The estimate is reasonable for 3 < nights < 15. 
      * Costs are subject to change.
      * Final costs will depend on instrument and cryogen delivery schedules.
      * Assumes a Sharc II cycle every night.
      * The heterodyne instruments include 5 l /day of LN<sub>2</sub> for tuning and calibration.
      * The sidecab receivers are combined.
      * For the sidecab and 850 GHz receivers, 60 l LHe dewars are used.
      * For the other instruments, 100 l LHe dewars are used.
      * LHe dewar quantization is only approximate.
      * LHe boiloff from the delivery dewars is ignored.
      * For the LHe dewars, rental days = observing nights + 2.
      * Staggered deliveries of LHe are ignored.
===== Refererence information ======

  * [[http://literature.chart-ind.com/ProductDetail.aspx?Id=42|Chart/MVE Cryogenic Gases Data Book]] 
  * [[http://www.aspenycap.org/files/CryogenicGases.pdf|Chart/MVE Cryogenic Gases Data Book]] //(alternate source)//