Layout related issues

Location of PR2 tank

Is it possible to put the PR2 and SR2 vacuum chambers further away from the BS chamber ? The minimum separation is 2.7m (center-to-center). However, in order to improve the workability around the BS chamber, we want increase the separation.

MIF Diagram

Comparison Table

L_BS_PR2 is the separation between the center of BS chamber and the center of PR2 chamber. L_PRM_PR3 is the separation between PRM and PR3. The following table shows the the Folding parameters with different L_BS_PR2 and L_PRM_PR3. Case 1 is the default plan. Case 2 adds 2m to the BS-PR2 separation, and Case 3 adds 3m. Case 4 adds 3m to L_BS_PR2 and 1.5m to L_PRM_PR3.

Note that the arm cavity g-factor is assumed to be negative (1.5km-1.9km), which usually gives slightly smaller beam sizes on the PRM.

L_BS_PR2

L_PRM_PR3

Folding Angle

Lp1

Lp2

Lp3

PRM ROC

PRM Beam Size

PR2 ROC

PR2 Beam Size

PR3 ROC

PR3 Beam Size

Case 1

2.7m

2.7m

0.63deg

14.76m

12.07m

14.76m

310.42m

4.05mm

-3.13m

4.05mm

27.01m

35.43mm

Case 2

4.7m

2.7m

0.67deg

14.09m

11.40m

16.10m

295.3m

3.95mm

-2.88m

3.95mm

25.45m

35.46mm

Case 3

5.7m

2.7m

0.69deg

13.76m

11.06m

16.76m

287.75m

3.91mm

-2.75m

3.91mm

24.67m

35.48mm

Case 4

5.7m

4.2m

0.72deg

14.76m

10.57m

16.26m

304.45m

4.03mm

-2.72m

4.03mm

23.66m

35.46mm

Layout files

The optical layout files corresponding to the above cases.

Case 1 Case 2 Case 3 Case 4

iLCGT -> bLCGT PRCL/SRCL change due to the substrate change

Because the substrate material will be changed from Silica to Sapphire between iLCGT and bLCGT, the index of refraction change will induce the optical path length change of PRC and SRC. We can cancel this change by simply moving the ITMs. Probably we will do this. However, a question to be answered here is whether it is possible to cancel the change by changing the MC length and consequently changing the f1/f2 frequencies.

In short, the answer to the question is "Yes".

In general, it is not possible to satisfy the resonant condition of PRC and SRC at the same time, just by changing the MC length. Once the Lprc is given, the RF sideband frequencies are given as follows,

f1 = p*c/(4*Lprc)
f2 = q*c/(4*Lprc)

,where p, q are integral numbers and c is the speed of light.
Now, once the f1 frequency is given, the length of SRC is given in the following form:

Lsrc = n*c/(2*f1) -Lprc

,where n is an integer. The MC length is given as Lmc = 2*Lprc/a, a = GCD(p,q).
If Lprc is changed to Lprc2 = Lprc + dL, then a new f1 frequency f1d has to be chosen to still resonate it in the PRC. Since, f1d = p*c/(4*Lprc2), 1/f1d = 1/f1 + 4*dL/(p*c). Therefore, the new SRC length (Lsrc2) to resonate f1 in the SRC is:

Lsrc2 = n*c/(2*f1d) - Lprc2 = Lsrc + 2*n*dL/p -dL.

This means, if n = p, Lprc2 = Lsrc + dL, meaning that f1d automatically resonates in the SRC. This is not the case in general. However, if we chose n to make Lprc = Lsrc, then n = p is automatically satisfied. The current length parameters of LCGT falls into this category. Therefore, it is possible to cancel the optical distance change by the substrate change of ITMs just by changing the MC length.

LCGT/subgroup/ifo/MIF/LayoutRelated (last edited 2011-07-06 10:57:44 by YoichiAso)