# Presentation: 045242

## Based onBD/Cryo Internal Review Part IVOverview of the need for Liquid HydrogenCh. Darve

- Mucool Test Area
- Cryo-system Design

_**Objective for Muon Cooling Experiment (MuCool):**_
- Development of high intense muon source based on the phase rotation and muon cooling:
- High Intensity:1-2x1012muons/sec
- High Luminosity:Improve beam emittance
_**Principle of beam optic**_
_**Principle of ionization cooling**_

- Part IV – A look at the Windows and Absorber Vessel
- Overview of the need for Liquid Hydrogen

- 6-8 W/cm

- Bethe-Bloch

**Notes:**
First Slide

_**Why do we use LH**__**2**__** and Aluminum?**_
- Reference: Appendix by Robert Bernstein: “Failure-mode Metrology using Projected Target Videogrammetry”, by John A. Greenwood et al.,  Coordinate Measurement Systems Committee conference in Albuquerque - (08/2001)
- “The choice of absorber and window thickness is governed by a tradeoff between the energy loss and multiple Coulomb scattering in a material.  The beam is “cooled” by energy loss; both transverse and longitudinal momentum is lost to collisions with atomic electrons but the longitudinal momentum is restored by the RF acceleration between the absorbers.  Energy loss occurs when the muons in the beam electro magnetically interact with the electrons of the material and is governed by the Bethe-Bloch equation:
- Where *m* is the electron mass, *z* is the charge (in units of the electron charge) and *v* the velocity of the particle, v/c, ***** ** *is Avogadro’s number, *Z *and *A* are the atomic number and mass of the material, and  is the electromagnetic fine-structure constant.  The path length in the material, *x*, is measured in gm/cm2.  The quantity *I* is an effective ionization potential of magnitude *I = 10 Z* eV. The dependence of *dE/dx* on material is weak since *Z/A* is roughly 1/2 for all materials except hydrogen.  Numerically *dE/dx* is 1–1.5 MeV cm2 gm –1 and one multiplies by the density to find *dE/dx* in units of MeV/cm. The relevant point for this discussion is that *dE/dx* depends on *Z/A*”

- Part IV – A look at the Windows and Absorber Vessel
- Overview of the need for Liquid Hydrogen

**Notes:**
First Slide

- “Unfortunately as the beam traverses the material multiple Coulomb scattering increases the beam’s phase space.  Multiple Coulomb scattering represents the scattering of the incident particle on the atomic nuclei.  The root-mean-square angular deflection in a thickness of material *x* is given by the approximate formula
- where *X**o*, the “radiation length,” is given by
- and note the leading *Z**2** *dependence; hence as *Z* increases the scattering grows as *Z**2*.
- We then see
- and therefore the best choice is the lowest *Z* material, hydrogen.
- We would therefore expect the correct choice for window material would be Beryllium.  However Be is known to be highly toxic if inhaled, leading to Berylliosis, a disease of the lungs.  Proximity of a fragile Be window to a liquid hydrogen target is therefore too dangerous to consider and Aluminum is therefore the material of choice."

- Part IV – A look at the Windows and Absorber Vessel
- Overview of the need for Liquid Hydrogen

**Notes:**
First Slide

_**Main requirements for the cryo-system**__**:**_
- Density fluctuation in the LH2 should be smaller than +/- 2.5 %
- P=1.2 atm=17.6 psia=0.12 MPa
- Subcool temperature => 17 K

- Part IV – A look at the Windows and Absorber Vessel
- Overview of the need for Liquid Hydrogen

**1- Stay bellow boiling point**
**2- Temperature difference < 1 K**
**(using a large safety factor)**
**	****- in absorber volume**
**	****- in the cryo-system**

**Notes:**
First Slide

- Part IV – A look at the Windows and Absorber Vessel
- Overview of MuCool Test Area cryo-system - cryostat

**Notes:**
First Slide

- The **LH****2 ****pump** was designed and built by Caltech as a spare pump for the SAMPLE experiment
- 	(1⁄2 dia. of the pump used in E158)
_**Purpose**_:
-      To circulate LH2 in a close loop and provide force flow to remove the energy loss from the LH2 absorber, with T<1 K
**Max. available flow at 17 K, 1.2 atm = 450 g/s**
_**Reference**_:
- 	“E.J. Beise et al., A high power liquid hydrogen target for parity violation experiments, _Research instruments & methods in physics research_ (1996), 383-391”

- Part IV – A look at the Windows and Absorber Vessel
- Overview on the Absorber Pump flow method

**Notes:**
First Slide

- Part IV – A look at the Windows and Absorber Vessel
- Overview on the Absorber Pump flow method

**The LH****2**** pump is composed of:**
-  two impeller blades => to straighten the flow
-  three stators => to accelerate the flow
-  two cones => to reduce the impedance of the flow
**Materials: **
- Impellers: Aluminum 6061 T6
- Housing: 304

- A motor located at room temperature drive the pump:
-  typical Tevatron Wet Engine 2 HP motor will be used

**Notes:**
First Slide

_**What is the mass flow needed to cool the beam? **_
- Simulation of the flow by Wing Lau/ Charles H. Holding (Oxford) using Algor 2 D model
_**How to use the results?**_
- Determine velocity so that T<1K

- Part IV – A look at the Windows and Absorber Vessel
- Overview on the Absorber Pump flow method

**We determine the velocity, V, for the addoc temperature difference, ********T:**
**m (for given ********T, nozzle geometry and LH2 prop.)**
******P(for LH****2 ****cryoloop)**

- V

- T

**Notes:**
First Slide

_**We do need to understand the thermo-hydraulic behavior of the LH2 absorber**_
**Example: Case of the maximum available flow by the LH2 pump**
**In order to be functional the LH2 absorber would need to be optimized (goal: reduction of the pressure drop)**
- Proposed changed: If V=4 m/s then m=450 g/s

- Part IV – A look at the Windows and Absorber Vessel
- Overview on the Absorber Pump flow method

**LH2 abs:**
- Nozzle dia.= 0.43”
- 11 Supply nozzles
- 15 returns nozzles
**Piping in the magnet bore:**
- 20 cm long IPS 1” pipes
- 30 cm long IPS 2”pipe

**LH2 abs:**
- Nozzle dia.= 0.6”
- 8 Supply nozzles
- 12 returns nozzles
**Piping in the magnet bore:**
- 40 cm long IPS 1” pipes
- 10 cm long IPS 2”pipe

- Current geometry

- Requested geometry

**Notes:**
First Slide

- Part IV – A look at the Windows and Absorber Vessel
- LH2 Manifold absorber (by E. Black)

- Critical P

**Notes:**
First Slide

_**Status:**_
**We do need to study the optimal flow regime in collaboration with Oxford in order to design the cryo-system. **
**Need to study the: **
**Thermo-hydraulic behavior of LH2 absorber for which ********Tmax=1 K (and 3 K) which **
**Influence  of the beam distribution (volume-surface distribution)**
**Upgrades from the Algor model:**
**Geometry upgrade, temperature upgrade****	**
**Influence of the nozzle number to reduce the hot spot=>3D model**

- Part IV – A look at the Windows and Absorber Vessel
- Overview on the Absorber Pump flow method

**Notes:**
First Slide